U.S. patent application number 16/872759 was filed with the patent office on 2020-08-27 for deterministically controlled humidification system.
The applicant listed for this patent is Fisher & Paykel Healthcare Limited. Invention is credited to Dean Antony BARKER, Russel William BURGESS, Laith Adeeb HERMEZ, Robert Stuart KIRTON, Joel Michael LAWSON, Kevin Peter O'DONNELL.
Application Number | 20200269006 16/872759 |
Document ID | / |
Family ID | 1000004824590 |
Filed Date | 2020-08-27 |
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United States Patent
Application |
20200269006 |
Kind Code |
A1 |
BURGESS; Russel William ; et
al. |
August 27, 2020 |
DETERMINISTICALLY CONTROLLED HUMIDIFICATION SYSTEM
Abstract
A respiratory humidification system for providing humidification
to gases that pass through a gas passage way before being provided
to an airway of a patient is disclosed. The respiratory
humidification system may include a liquid flow controller
providing a controlled flow of liquid, a heating system including a
heating surface configured to be located in a gases passage way and
provide humidification to gases passing through the passage way,
wherein the heating system receives the controlled flow of liquid,
and one or more hardware processors providing deterministic control
of a humidity level of gases passing through the gas passage way by
instructing the liquid flow controller to adjust the controlled
flow of liquid received at the heating system.
Inventors: |
BURGESS; Russel William;
(Auckland, NZ) ; BARKER; Dean Antony; (Auckland,
NZ) ; HERMEZ; Laith Adeeb; (Auckland, NZ) ;
LAWSON; Joel Michael; (Pasadena, CA) ; KIRTON; Robert
Stuart; (Auckland, NZ) ; O'DONNELL; Kevin Peter;
(Auckland, NZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fisher & Paykel Healthcare Limited |
Auckland |
|
NZ |
|
|
Family ID: |
1000004824590 |
Appl. No.: |
16/872759 |
Filed: |
May 12, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15507692 |
Feb 28, 2017 |
10688272 |
|
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PCT/NZ2015/050128 |
Sep 3, 2015 |
|
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16872759 |
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62213534 |
Sep 2, 2015 |
|
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62045358 |
Sep 3, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M 2205/3331 20130101;
A61M 2205/3334 20130101; A61M 16/161 20140204; A61M 16/16 20130101;
A61M 16/147 20140204; A61M 16/109 20140204; A61M 39/24 20130101;
A61M 2205/7518 20130101; A61M 16/024 20170801; A61M 2205/3653
20130101; A61M 16/208 20130101; A61M 16/106 20140204; A61M
2016/0033 20130101; A61M 2205/3368 20130101 |
International
Class: |
A61M 16/16 20060101
A61M016/16; A61M 16/14 20060101 A61M016/14; A61M 16/10 20060101
A61M016/10; A61M 16/00 20060101 A61M016/00; A61M 39/24 20060101
A61M039/24 |
Claims
1. A respiratory humidification system for providing heated and
humidified respiratory gases to a patient, the respiratory
humidification system comprising: a liquid flow controller
providing a controlled flow of liquid; a heating system including a
heating surface configured to receive the controlled flow of liquid
and provide humidification to gases passing through the
humidification system; one or more temperature sensors measuring a
surface temperature of the heating surface; one or more hardware
processors providing deterministic control of a humidity level of
gases passing through the respiratory humidification system by
instructing the liquid flow controller to adjust the controlled
flow of liquid received at the heating system and instructing the
heating system to adjust the surface temperature of the heating
surface, wherein adjusting the surface temperature of the heating
surface provides control to produce a known evaporative area; and
one or more sensors configured to detect whether the heating
surface is wetted in at least one region.
2. The respiratory humidification system of claim 1, wherein the
one or more sensors are liquid sensors.
3. The respiratory humidification system of claim 1, wherein the
one or more sensors comprise at least two liquid sensors configured
to detect whether the heating surface is wetted at two or more
regions of the heating surface.
4. The respiratory humidification system of claim 1, wherein the
one or more sensors are located at, on, adjacent, or proximal the
heating surface.
5. The respiratory humidification system of claim 1, wherein the
liquid flow controller comprises a metering system.
6. The respiratory humidification system of claim 1, wherein the
liquid flow controller is a pump in an open loop configuration.
7. The respiratory humidification system of claim 1, wherein the
liquid flow controller is a pump or flow actuator in series with a
flow sensor in a closed loop configuration.
8. The respiratory humidification system of claim 2, further
comprising at least one temperature sensor forming part of the
heating system.
9. The respiratory humidification system of claim 8, wherein the at
least one temperature sensor is utilized to determine a proportion
of the heating surface that is saturated with a liquid.
10. The respiratory humidification system of claim 1, wherein the
one or more sensors are used to prevent overflow of liquid onto the
heating surface.
11. The respiratory humidification system of claim 1, wherein the
one or more sensors are used by the one or more hardware processors
to adjust the deterministic control of the humidity level of gases
passing through the respiratory system.
12. The respiratory humidification system of claim 1, wherein the
one or more sensors are used by the one or more hardware processors
to adjust the evaporative area of the heating surface.
13. The respiratory humidification system of claim 1, wherein the
one or more sensors are temperature sensors.
14. The respiratory humidification system of claim 13, wherein at
least one temperature sensor is utilized to determine a proportion
of the heating surface that is saturated with a liquid.
15. The respiratory humidification system of claim 1, wherein the
one or more sensors are resistive or capacitive sensors.
16. The respiratory humidification system of claim 1, wherein the
heating system comprises a printed circuit board (PCB) or etched
foil over-molded with a surface comprising micro-channels to form
the heating surface.
17. The respiratory humidification system of claim 16, wherein the
surface has micro-channels that extend in only a single
direction.
18. The respiratory humidification system of claim 16, wherein the
micro-channels include a first set of distribution channels
connected to a second set of main channels.
19. The respiratory humidification system of claim 18, wherein the
number of distribution channels is less than the number of main
channels.
20. The respiratory humidification system of claim 16, wherein the
micro-channels are distributed radially from a single point.
21. A respiratory humidification system for providing heated and
humidified respiratory gases to a patient, the respiratory
humidification system comprising: a liquid flow controller
providing a controlled flow of liquid; a heating system including a
heating surface configured to receive the controlled flow of liquid
and provide humidification to gases passing through the
humidification system; one or more temperature sensors measuring a
surface temperature of the heating surface; one or more hardware
processors providing deterministic control of a humidity level of
gases passing through the respiratory humidification system by
instructing the liquid flow controller to adjust the controlled
flow of liquid received at the heating system and instructing the
heating system to adjust the surface temperature of the heating
surface, wherein adjusting the surface temperature of the heating
surface provides control to produce a known evaporative area; and
one or more sensors configured to detect whether the heating
surface is wetted in at least one region, wherein the one or more
sensors comprise at least one temperature sensor, wherein the at
least one temperature sensor is utilized to determine a proportion
of the heating surface that is saturated with a liquid.
22. A respiratory humidification system for providing heated and
humidified respiratory gases to a patient, the respiratory
humidification system comprising: a liquid flow controller
providing a controlled flow of liquid; a heating system including a
heating surface configured to receive the controlled flow of liquid
and provide humidification to gases passing through the
humidification system; one or more temperature sensors measuring a
surface temperature of the heating surface; one or more hardware
processors providing deterministic control of a humidity level of
gases passing through the respiratory humidification system by
instructing the liquid flow controller to adjust the controlled
flow of liquid received at the heating system and instructing the
heating system to adjust the surface temperature of the heating
surface, wherein adjusting the surface temperature of the heating
surface provides control to produce a known evaporative area; one
or more sensors configured to detect whether the heating surface is
wetted in at least one region, wherein the one or more sensors
comprise at least two liquid sensors configured to detect whether
the heating surface is wetted at two or more regions of the heating
surface, wherein the one or more sensors are used by the one or
more hardware processors to adjust the evaporative area of the
heating surface; and at least one temperature sensor.
Description
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 15/507,692, filed Feb. 28, 2017, which is a
national phase of PCT Application No. PCT/NZ2015/050128, filed Sep.
3, 2015, which claims priority from U.S. Provisional Application
No. 62/045,358, filed Sep. 3, 2014, and U.S. Provisional
Application No. 62/213,534, filed Sep. 2, 2015, the contents of
each of which are incorporated by reference in its entirety. Any
and all applications for which a foreign or domestic priority claim
are identified in the Application Data Sheet filed with the present
application are hereby incorporated by reference under 37 CFR
1.57.
BACKGROUND
[0002] The present disclosure generally relates to humidified gases
therapy. More particularly, the present disclosure relates to
humidification systems for use in humidified gases therapy.
[0003] A patient dealing with respiratory illness, for example
chronic obstructive pulmonary disease (COPD), can have difficulty
engaging in effective respiration. This difficulty may be the
result of a variety of causes, including a breakdown of lung
tissue, dysfunctions of the small airways, excessive accumulation
of sputum, infection, genetic disorders, or cardiac insufficiency.
With some respiratory illnesses, it is useful to provide a therapy
that can improve the ventilation of the patient. In some
situations, the patient can be provided with a respiratory therapy
system that includes a gases source, an interface that may be used
to transmit gases to an airway of a patient, and a conduit
extending between the gases source and the interface. Gases
delivered to the airway of the patient from the gases source can
help to promote adequate ventilation. The gases source may include,
for example, a container of air and/or another gas suitable for
inspiration, e.g., oxygen or nitric oxide, a mechanical blower
capable of propelling gases through the conduit to the interface,
or some combination of both. The respiratory therapy system can
include a gases humidifier that can humidify and heat gases passing
through the respiratory therapy system to improve patient comfort
and/or improve the prognosis of the patient's respiratory illness.
The gases humidifier can include a water reservoir and a heating
element for heating the water in the reservoir. As the water heats
up, water vapor is formed that can join the stream of gases passing
through the gases humidifier.
[0004] Conventional gases humidifiers are useful in ameliorating
the discomfort of cold and dry gases therapies, but are typically
configured in such a way that all of the water in the reservoir, or
an excess of water, must be heated before the generation of vapor
rises to an acceptable level for providing adequately humidified
gases. In some cases it can take up to half an hour from turning
the humidifier on to begin generating sufficient water vapor.
Additionally, conventional gases humidifiers may not be able to
respond appropriately to changing input conditions, or may have an
impaired response in part due to the high thermal inertia of the
water in the reservoir.
SUMMARY
[0005] The present disclosure provides a water vaporization system
that does not require a reservoir of water, or an excess of water,
to be heated. Disclosed are embodiments which allow a desired
amount of water to be quickly vaporized, thus improving response
time to system or environmental changes and greatly reducing
warm-up periods.
[0006] According to a first aspect of the present disclosure, a
respiratory humidification system for providing humidification to
gases that pass through a gas passage way before being provided to
an airway of a patient, can include a liquid flow controller for
providing a controlled flow of liquid; a heating system including a
heating surface configured to be located in a gases passage way and
provide humidification to gases passing through the passage way,
wherein the heating system receives the controlled flow of liquid,
the heating system configured to maintain the heating surface at a
predetermined temperature of between approximately 30 degrees
Celsius (.degree. C.) and approximately 99.9.degree. C.; and one or
more hardware processors providing deterministic control of a
humidity level of gases passing through the gas passage way by
instructing the liquid flow controller to adjust the controlled
flow of liquid received at the heating system.
[0007] The heating system may be configured to maintain the heating
surface at a predetermined temperature of between approximately
35.degree. C. and approximately 90.degree. C., between
approximately 40.degree. C. and approximately 80.degree. C.,
between approximately 45.degree. C. and approximately 70.degree.
C., between approximately 45.degree. C. and approximately
60.degree. C., between approximately 50.degree. C. and
approximately 60.degree. C., or at a predetermined temperature at
approximately 50.degree. C.
[0008] The liquid may be water. The liquid flow controller may
include a metering system. The liquid flow controller may be a
pump. The pump may be a positive displacement pump. The positive
displacement pump may be a piezoelectric, diaphragm pump, or
peristaltic pump. The liquid flow controller may be a pressure
feed, such as a gravity feed, and a control valve. The liquid flow
controller may include a non-return valve configured to keep the
liquid flow controller primed and/or protect the system from
contamination. The liquid flow controller may be configured to use
a wicking or capillary action. The respiratory humidification
system may include a safety valve to prevent flow of liquids if the
liquid controller fails. The respiratory humidification system may
include a liquid reservoir. The respiratory humidification system
may include a flow restriction device positioned between the liquid
reservoir and the liquid flow controller and configured to prevent
gravity driven flow from influencing a delivered flow of liquid.
The flow restriction device may be an elastic protrusion that
restricts the flow path. The liquid flow controller may be a pump
in an open loop configuration. The liquid flow controller may be a
pump or flow actuator in series with a flow sensor in a closed loop
configuration. The liquid flow controller may provide a continuous
flow of water in the range of 0 mL/min to approximately 10 mL/min.
The liquid flow controller may provide a continuous flow of liquid
in the range of 0 mL/min to approximately 7 mL/min. The liquid flow
controller may provide a continuous flow of liquid in the range of
0 mL/min to approximately 5 mL/min. The liquid flow controller may
provide a continuous flow of liquid in the range of approximately
40 .mu.L/min to approximately 4 mL/min, or the range of
approximately 70 .mu.L/min to approximately 2.5 mL/min. The liquid
flow controller may provide a controlled flow of liquid with an
accuracy of approximately .+-.15% of a desired liquid flow rate, an
accuracy of approximately .+-.10% of a desired liquid flow rate, an
accuracy of approximately .+-.6.5% of a desired liquid flow rate,
or an accuracy of approximately .+-.5% of a desired liquid flow
rate.
[0009] The respiratory humidification system may include a flow
sensor. The flow sensor may be a thermal mass meter. The flow
sensor may be drip feed counter. The flow sensor may be a
differential pressure flow sensor.
[0010] The one or more hardware processors may provide
deterministic control of the humidity level based on a flow rate of
the gases. The one or more hardware processors may provide
deterministic control of the humidity level based on the
evaporation rate of water from the heating surface. The one or more
hardware processors may provide deterministic control of the
humidity level based on the temperature of the heating surface
wherein the temperature of the heating surface is maintained at a
constant temperature. The one or more hardware processors may
provide deterministic control of the humidity level based on the
temperature of the heating surface wherein the temperature of the
heater surface is controlled. The one or more hardware processors
may provide deterministic control of the humidity level based on
the absolute or barometric pressure of gases at the inlet. The one
or more hardware processors may provide deterministic control of
the humidity level based on the dew point temperature of the gases
at the inlet. The one or more hardware processors may provide
deterministic control of the humidity level based on enthalpy
provided by the heating surface. The one or more hardware
processors may provide deterministic control of the humidity level
based on the temperature of the gases prior to interaction with the
heating system. The one or more hardware processors may provide
deterministic control of the humidity level based on the relative
humidity of the gases prior to interaction with the heating system.
The one or more hardware processors may provide deterministic
control of the humidity level based on the effective heating area
of the heating surface. The one or more hardware processors may
provide deterministic control of the humidity level based on the
pressure of the gases. The one or more hardware processors may
provide deterministic control of the humidity level based on a
function of gas velocity. The one or more hardware processors may
provide deterministic control of the humidity level based on
temperature of the liquid in the controlled flow of liquid. The
respiratory humidification system may include a water temperature
sensor. The respiratory humidification system may include a gas
flow rate sensor. The respiratory humidification system may include
a gas flow rate sensor at an inlet of the gases passage way. The
respiratory humidification system may include a liquid flow rate
determined by a model. The respiratory humidification system may
include a gases flow rate determined by a model. The respiratory
humidification system may include an ambient pressure sensor. The
respiratory humidification system may include a pressure sensor
positioned at or near the heater surface. The respiratory
humidification system may include a heating surface temperature
sensor. The respiratory humidification system may include an
ambient dew point temperature sensor or ambient humidity sensor
positioned upstream of a humidification region. The respiratory
humidification system may include an ambient dew point temperature
sensor positioned upstream from a gases pre-heater. The respiratory
humidification system may include an ambient dew point temperature
sensor positioned downstream from a gases pre-heater. The
respiratory humidification system may include an ambient dew point
temperature sensor positioned downstream from a gases pre-heater
and a temperature sensor at a gases passage way inlet. The
respiratory humidification system may include at least one
temperature sensor forming part of the heating system. The at least
one temperature sensor may be utilized to determine a proportion of
the heater that is saturated with a liquid. The respiratory
humidification system may include a gases pre-heater. A temperature
of the gases at a gases passage way inlet may be controlled in an
open loop fashion via control of a power to the pre-heater. The
respiratory humidification system may include a liquid pre-heater.
The heating surface may include a wicking surface. Heat may be
supplied to the heating surface by a PCB with resistive traces or
tracking. Heat may be supplied to the heating surface by etched
foil or one or more flexible PCBs. Heat may be supplied by a
heating wire. Heat may be supplied by a PTC ceramic. Heat may be
supplied by a Peltier or thermoelectric device. The heating surface
may be over-molded and micro-channels may be included in the
over-mold configured to wick water onto the heater. A surface
temperature of the heating surface may be at least partially
determined by using a resistance or other characterization of the
heating system. The resistance may indicate an average heater
system temperature. In some configurations, the heating system is
arranged such that a higher density of heat is provided in a
specified region of the heater such that those regions have a
higher power density. The higher density of heat may be near an
outlet of a water supply. The higher density of heat may be
provided in a water pre-heating area. The respiratory
humidification system may include a temperature sensor at an outlet
of the gases passage way.
[0011] According to another aspect of the present disclosure, a
high efficiency respiratory humidification system for providing
heated and humidified respiratory gases to a patient is described.
The respiratory humidification system may include a respiratory gas
passage way having an inlet and an outlet, where gases flow from
the inlet to the outlet during operation; a pre-heater configured
to heat a gas flow; and a heating surface separate from the
pre-heater and located downstream from the pre-heater, the heating
surface including wicking features configured to wick a liquid
across a face of the heating surface, the heating surface further
configured to heat the liquid during and/or after wicking. The
respiratory humidification system may include a gas flow generator.
The pre-heater may be a gas heating element. The gas heating
element may be one of a PCB including resistive elements (e.g.,
traces or tracking), an etched foil film, a heating coil, or a PTC
element, among others. The respiratory humidification system may
include a temperature sensor positioned downstream from the
pre-heater. Power provided to the gas heating element may be
controlled according to a measurement obtained from the downstream
temperature sensor. The respiratory humidification system may
include a temperature sensor positioned upstream from the
pre-heater. Power provided to the gas heating element may be
controlled according to a gas flow rate and a measurement obtained
from the upstream temperature sensor. A characterization of the gas
heating element may be used as a temperature sensor. A desired
downstream temperature may be set according to an evaporation rate
of liquid from the heating surface. The desired downstream
temperature may be set in order to ensure substantially all
sensible heat is supplied to the gas flow by the pre-heater. The
desired downstream temperature may be set between 0.degree. C. and
approximately 5.degree. C. above an output dew point temperature.
The desired downstream temperature may be set to obtain a
predetermined output absolute humidity. The desired downstream
temperature may be set to obtain a given output absolute humidity.
The desired downstream temperature may be set to approximately
25.degree. C. to approximately 43.degree. C., or approximately
31.degree. C. to approximately 43.degree. C., or approximately
31.degree. C. to approximately 41.degree. C., or approximately
31.degree. C. to approximately 37.degree. C., or approximately
37.degree. C. The respiratory humidification system may include a
liquid flow generator. The respiratory humidification system may
include an apparatus for pre-heating the liquid flow. The apparatus
for pre-heating the liquid flow may be incorporated into the
heater-surface structure by increasing a number of resistive tracks
where the water is introduced. The apparatus for pre-heating the
liquid flow may be in a water supply line. The wicking features may
be one or more of an absorptive fabric or paper, micro-channels,
hydrophilic coated surface, capillary or contact wicks, or thin
porous media, among others. The wicking features may include a
coupling configured to distribute the liquid onto the heating
surface. The coupling may be a length of wicking media bonded or
brought into contact with the heating surface or wicking features.
The coupling may be a second surface forming an acute angle with
the wicking features. The coupling may be a cavity in contact with
the heating surface or wicking features. The coupling may be one or
more of a line source, a point source, a radial source, or multiple
line, point and radial sources, or any combination thereof. The
heating surface may be maintained at a temperature of between
approximately 30.degree. C. and approximately 99.9.degree. C.,
between approximately 35.degree. C. and approximately 90.degree.
C., between approximately 40.degree. C. and approximately
80.degree. C., between approximately 45.degree. C. and
approximately 70.degree. C., between approximately 45.degree. C.
and approximately 60.degree. C., between approximately 50.degree.
C. and approximately 60.degree. C., or at approximately 50.degree.
C. The wicking features may be mechanically configured to be
positioned within a liquid delivery tube. The respiratory
humidification system may be configured to be within, or as part
of, an inspiratory tube for delivering gas to a patient. The
respiratory humidification system may include a filter. The filter
may be in a liquid delivery line. The filter may be positioned
downstream from a pump. The filter may be positioned at an inlet to
the heating surface. The filter may be a biologic filter. The
respiratory humidification system may include a UV source for
sterility.
[0012] According to another aspect of the present disclosure, a
respiratory humidification system for providing heated and
humidified respiratory gases to a patient may include a liquid flow
controller providing a controlled flow of liquid; a heating system
including a heating surface configured to receive the controlled
flow of liquid and provide humidification to gases passing through
the humidification system; one or more temperature sensors
measuring a surface temperature of the heating surface; one or more
hardware processors providing deterministic control of a humidity
level of gases passing through the respiratory system by
instructing the liquid flow controller to adjust the controlled
flow of liquid received at the heating system and instructing the
heating system to adjust the surface temperature of the heating
surface, wherein adjusting the surface temperature of the heating
surface provides control to produce a known evaporative area; and
one or more liquid sensors configured to detect whether the heating
surface is wetted in at least one region. The one or more liquid
sensors may be at least two liquid sensors configured to detect
whether the heating surface is wetted at two or more regions of the
heating surface. The at least two liquid sensors may be two
temperature sensors. The one or more liquid sensors may be located
at, on, adjacent, or proximal the heating surface. The liquid may
be water.
[0013] The liquid flow controller may be a metering system. The
liquid flow controller may include a pump. The pump may be a
positive displacement pump. The positive displacement pump may be a
piezoelectric diaphragm pump or peristaltic pump. The liquid flow
controller may be a pressure feed, such as gravity feed, and a
control valve. The liquid flow controller may include a non-return
valve configured to keep the liquid flow controller primed and/or
reduce the opportunity for flow reversal. The liquid flow
controller may be configured to use a wicking or capillary action.
The respiratory humidification system may include a safety valve to
prevent flow of liquids if the liquid controller fails. The
respiratory humidification system may include a liquid reservoir.
The respiratory humidification system may include a flow
restriction device positioned between the liquid reservoir and the
liquid flow controller and configured to prevent gravity driven
flow from influencing a delivered flow of liquid. The flow
restriction device may be an elastic protrusion that restricts the
flow path. The liquid flow controller may be a pump in an open loop
configuration. The liquid flow controller may be a pump or flow
actuator in series with a flow sensor in a closed loop
configuration. The pump may be piezoelectric pump. The flow sensor
may be a thermal mass meter. The liquid flow controller may provide
a continuous flow of water in the range of 0 mL/min to 10 mL/min.
The liquid flow controller may provide a continuous flow of water
in the range of 0 mL/min to 7 mL/min. The liquid flow controller
may provide a continuous flow of water in the range of 0 mL/min to
5 mL/min. The liquid flow controller may provide a continuous flow
of water in the range of 40 .mu.L/min to 4 mL/min, or the range of
70 .mu.L/min to 2.5 mL/min. The flow controller may provide a
controlled flow of liquid with an accuracy of approximately .+-.15%
of a desired liquid flow rate, an accuracy of approximately .+-.10%
of a desired liquid flow rate, an accuracy of approximately
.+-.6.5% of a desired liquid flow rate, or an accuracy of
approximately .+-.5% of a desired liquid flow rate.
[0014] The one or more hardware processors may provide
deterministic control of the humidity level based on a flow rate of
the gases. The one or more hardware processors may provide
deterministic control of the humidity level based on evaporation
rate of liquid from the heating surface. The one or more hardware
processors may provide deterministic control of the humidity level
based on the temperature of the heating surface wherein the
temperature of the heater surface is maintained at a constant
temperature. The one or more hardware processors may provide
deterministic control of the humidity level based on the
temperature of the heating surface wherein the temperature of the
heater surface is controlled. The one or more hardware processors
may provide deterministic control of the humidity level based on
the absolute or barometric pressure of gases at the inlet. The one
or more hardware processors may provide deterministic control of
the humidity level based on the dew point temperature of the gases
at an inlet. The one or more hardware processors may provide
deterministic control of the humidity level based on enthalpy
provided by the heating surface. The one or more hardware
processors may provide deterministic control of the humidity level
based on the temperature of the gases prior to interaction with the
heating system. The one or more hardware processors may provide
deterministic control of the humidity level based on the relative
humidity of the gases prior to interaction with the heating system.
The one or more hardware processors may provide deterministic
control of the humidity level based on the effective heating area
of the heating surface. The one or more hardware processors may
provide deterministic control of the humidity level based on the
pressure of the gases. The one or more hardware processors may
provide deterministic control of the humidity level based on a
function of gas velocity. The one or more hardware processors may
provide deterministic control of the humidity level based on a
temperature of the liquid in the controlled flow of liquid. The
respiratory humidification system may include a water temperature
sensor. The respiratory humidification system may include a gas
flow rate sensor. The respiratory humidification system may include
a gas flow rate sensor at an inlet of the gases passage way. The
respiratory humidification system may include a liquid flow rate
determined by a model. The respiratory humidification system may
include a gases flow rate determined by a model. The respiratory
humidification system may include an ambient pressure sensor. The
respiratory humidification system may include an ambient dew point
temperature sensor or ambient humidity sensor positioned upstream
of a humidification region. The respiratory humidification system
may include an ambient dew point temperature sensor positioned
upstream from a gases pre-heater. The respiratory humidification
system may include an ambient dew point temperature sensor
positioned downstream from a gases pre-heater. The respiratory
humidification system may include an ambient dew point temperature
sensor positioned downstream from a gases pre-heater and a
temperature sensor at a gases passage way inlet. The respiratory
humidification system may include at least one temperature sensor
forming part of the heating system. The at least one temperature
sensor may be utilized to determine a proportion of the heater that
is saturated with a liquid. The respiratory humidification system
may include a gases pre-heater. A temperature of the gases at a
gases passage way inlet may be controlled in an open loop fashion
via control of a power to the pre-heater. The respiratory
humidification system may include a liquid pre-heater. The one or
more liquid sensors may be used to prevent overflow of liquid onto
the heating surface. The one or more liquid sensors may be used by
the one or more hardware processors to adjust the deterministic
control of the humidity level of gases passing through the
respiratory system. The one or more liquid sensors may be used by
the one or more hardware processors to adjust the evaporative area
of the heating surface. The one or more liquid sensors may be
temperature sensors. The one or more liquid sensors may be
resistive or capacitive sensors.
[0015] According to another aspect of the present disclosure, a
heater plate for a respiratory humidification system includes a
printed circuit board (PCB) or etched foil over-molded with a
surface comprising micro-channels. The surface may have
micro-channels that extend in only a single direction. The
micro-channels may include a first set of distribution channels
connected to a second set of main channels. The number of
distribution channels may be less than the number of main channels.
The micro-channels may be distributed radially from a single point.
The heating system may be used with any of the respiratory
humidification systems described herein.
[0016] According to another aspect of the present disclosure, a
respiratory humidification system for providing humidification to
gases that pass through a gas passage way before being provided to
an airway of a patient, the respiratory humidification system
includes a liquid flow controller providing a controlled flow of
liquid; a heating system including a heating surface configured to
receive the controlled flow of liquid and provide humidification to
gases passing through the humidification system, wherein the
heating surface is configured to wick liquid across the surface
thereof; and a gas pre-heater arranged in the gas passage way
upstream of the heating system. The respiratory humidification
system may include a coupling configured to receive the controlled
flow of liquid from the liquid control and distribute the liquid
onto the heating surface. The respiratory humidification system may
be configured to be in-line with an inspiratory tube for delivering
gases to a patient. The respiratory humidification system may be
configured to be within an inspiratory tube for delivering gases to
a patient. The liquid may be water. The respiratory humidification
system may include a filter. The filter may be in a liquid delivery
line. The filter may be positioned downstream from a pump. The
filter may be positioned at an inlet to the heating surface. The
filter may be a biologic filter. The respiratory humidification
system may include a UV source for sterility.
[0017] The liquid flow controller may include a metering system.
The liquid flow controller may be a pump. The pump may be a
positive displacement pump. The positive displacement pump may be a
piezoelectric, diaphragm pump, or peristaltic pump. The liquid flow
controller may comprise a pressure feed, such as a gravity feed,
and a control valve. The liquid flow controller may include a
non-return valve configured to keep the liquid flow controller
primed. The liquid flow controller may be configured to use a
wicking or capillary action. The respiratory humidification system
may further include a safety valve to prevent flow of liquids if
the liquid controller fails. The respiratory humidification system
may further include a liquid reservoir. The respiratory
humidification system may further include a flow restriction device
positioned between the liquid reservoir and the liquid flow
controller and configured to prevent gravity driven flow from
influencing a delivered flow of liquid. The flow restriction device
may be an elastic protrusion that restricts the flow path. The
liquid flow controller may be a pump in an open loop configuration.
The liquid flow controller may be a pump or flow actuator in series
with a flow sensor in a closed loop configuration. The liquid flow
controller may provide a continuous flow of liquid in the range of
0 mL/min to approximately 10 mL/min. The liquid flow controller may
provide a continuous flow of liquid in the range of 0 mL/min to
approximately 7 mL/min. The liquid flow controller may provide a
continuous flow of liquid in the range of 0 mL/min to approximately
5 mL/min. The liquid flow controller may provide a continuous flow
of liquid in the range of 40 .mu.L/min to approximately 4 mL/min,
or in the range of approximately 70 .mu.L/min to approximately 2.5
mL/min. The liquid flow controller may provide a controlled flow of
liquid with an accuracy of approximately .+-.15% of a desired
liquid flow rate, an accuracy of approximately .+-.10% of a desired
liquid flow rate, an accuracy of approximately .+-.6.5% of a
desired liquid flow rate, or an accuracy of approximately .+-.5% of
a desired liquid flow rate.
[0018] The heating system may include a heater plate comprising a
printed circuit board (PCB) or etched foil over-molded with a
surface comprising micro-channels. The surface may have
micro-channels that extend in only a single direction. The
micro-channels may include a first set of distribution channels
connected to a second set of main channels. The number of
distribution channels may be less than the number of main channels.
The micro-channels may be distributed radially from a single point.
The coupling may be a fibrous, porous or sintered polymer. The
heating surface may be immersed in the gas flow. The heating
surface may include modular zones.
[0019] According to another aspect of the present disclosure, a
respiratory humidification system includes a liquid flow controller
providing a controlled flow of liquid; a heating system including a
heating surface configured to be located in a gases passage way and
provide humidification to gases passing through the passage way,
wherein the heating system receives the controlled flow of liquid,
the heating system configured to maintain the heating surface at a
predetermined temperature of between approximately 30.degree. C.
and approximately 99.9.degree. C.; and heating surface may be
configured to be maintained at a temperature of between
approximately 30.degree. C. and approximately 99.9.degree. C., and
wherein approximately 80%-99.9% of the power output of the system
is transferred into heat in the liquid. The heating surface maybe
configured to be maintained at a temperature of between
approximately 35.degree. C. and approximately 90.degree. C.,
between approximately 45.degree. C. and approximately 70.degree.
C., between approximately 45.degree. C. and approximately
60.degree. C., between approximately 50.degree. C. and
approximately 60.degree. C., or at a temperature of approximately
50.degree. C. In some configurations, approximately 85%-99.99% of
the power output of the system is transferred into heat in the
liquid, approximately 90%-99.99% of the power output of the system
is transferred into heat in the liquid, approximately 95%-99.99% of
the power output of the system is transferred into heat in the
liquid, or approximately 98% of the power output of the system is
transferred into heat in the liquid. The liquid may be water. The
respiratory humidification system may be configured as any of the
respiratory humidification systems described herein.
[0020] According to another aspect of the present disclosure, a
respiratory humidification system for providing humidification to
gases that pass through a gas passage way before being provided to
an airway of a patient includes an apparatus for heating a gas flow
and positioned upstream of a humidification region; a liquid flow
generator; and a heating system including a heating surface
configured to be located in a gases passage way and provide
humidification to gases passing through the passage way, wherein
the heating system is configured to maintain a heating surface at a
predetermined temperature of between approximately 30.degree. C.
and approximately 99.9.degree. C. The heating system may be
configured to maintain the heating surface at a predetermined
temperature of between approximately 35.degree. C. and
approximately 90.degree. C. The heating system may be configured to
maintain the heating surface at a predetermined temperature of
between approximately 40.degree. C. and approximately 80.degree. C.
The heating system may be configured to maintain the heating
surface at a predetermined temperature of between approximately
45.degree. C. and approximately 70.degree. C. The heating system
may be configured to maintain the heating surface at a
predetermined temperature of between approximately 45.degree. C.
and approximately 60.degree. C. The heating system may be
configured to maintain the heating surface at a predetermined
temperature of between approximately 50.degree. C. and
approximately 60.degree. C. The heating system may be configured to
maintain the heating surface at a predetermined temperature at
approximately 50.degree. C. The apparatus may be a pre-heater. The
pre-heater may include a gas heating element. The gas heating
element may be one of a PCB including resistive elements, an etched
foil film, a heating coil, or a PTC element, among others. The
respiratory humidification system may include a temperature sensor
positioned downstream from the pre-heater. Power provided to the
gas heating element may be controlled according to a measurement
obtained from the downstream temperature sensor. The respiratory
humidification system may include a temperature sensor positioned
upstream from the pre-heater. Power provided to the gas heating
element may be controlled according to an airflow rate and a
measurement obtained from the upstream temperature sensor. A
characterization of the gas heating element may be used as a
temperature sensor. A desired downstream temperature after the
pre-heater may be set according to an evaporation rate of the
heating surface. The desired downstream temperature may be set in
order to ensure substantially all sensible heat is supplied by the
pre-heater. The desired downstream temperature may be set between
0.degree. C. and approximately 5.degree. C. above an output
temperature. The desired downstream temperature may be set to
obtain a given output relative humidity. The desired downstream
temperature may be set to obtain a given output absolute humidity.
The desired downstream temperature may be set to approximately
25.degree. C. to approximately 43.degree. C., or approximately
31.degree. C. to approximately 43.degree. C., or approximately
31.degree. C. to approximately 41.degree. C., or approximately
31.degree. C. to approximately 37.degree. C., or approximately
37.degree. C. The respiratory humidification system may include an
apparatus for pre-heating the liquid flow. The apparatus for
pre-heating the liquid flow may be incorporated into the heating
structure by increasing a number of resistive heating tracks where
the liquid is introduced. The apparatus for pre-heating the liquid
flow may be in a liquid supply line.
[0021] According to another aspect of the present disclosure,
deterministic control, in a respiratory humidification system, of
humidity by control of water flow to a heating source is described.
Deterministic control of the humidity level may be based on a flow
rate of the gases. Deterministic control of the humidity level may
be based on evaporation rate of water from the heating surface.
Deterministic control of the humidity level may be based on the
temperature of the heating surface wherein the temperature of the
heater surface is maintained at a constant temperature.
Deterministic control of the humidity level may be based on the
temperature of the heating surface wherein the temperature of the
heater surface is controlled. Deterministic control of the humidity
level may be based on the absolute or barometric pressure of gases
at the inlet. Deterministic control of the humidity level may be
based on the dew point temperature of the gases at the inlet.
Deterministic control of the humidity level may be based on
enthalpy provided by the heating surface. Deterministic control of
the humidity level may be based on the temperature of the gases
prior to interaction with the heating system. Deterministic control
of the humidity level may be based on the relative humidity of the
gases prior to interaction with the heating system. Deterministic
control of the humidity level may be based on the effective heating
area of the heating surface. Deterministic control of the humidity
level may be based on the pressure of the gases. Deterministic
control of the humidity level may be based on a function of gas
velocity. Deterministic control of the humidity level may be based
on a temperature of the liquid in the controlled flow of liquid.
Deterministic control may be based on a combination of two or more
of the aforementioned inputs, and all combinations of the above
inputs are within the scope of this disclosure. Deterministic
control may be based on a combination of control of water flow to a
heating source and a flow rate of the gases. Deterministic control
may be based on a combination of control of water flow to a heating
source, a flow rate of the gases, and the dew point temperature of
the gases at the inlet. Deterministic control may be based on a
combination of control of water flow to a heating source, a flow
rate of the gases, and the absolute or barometric pressure of the
gases at the inlet. Deterministic control may be based on a
combination of control of water flow to a heating source, a flow
rate of the gases, the absolute or barometric pressure of the gases
at the inlet, and the dew point temperature of the gases at the
inlet. The respiratory humidification system may include a water
temperature sensor. The respiratory humidification system may
include a gas flow rate sensor. The respiratory humidification
system may include a gas flow rate sensor at an inlet of the gases
passage way. The respiratory humidification system may include a
liquid flow rate determined by a model. The respiratory
humidification system may include a gases flow rate determined by
model. The respiratory humidification system may include an ambient
pressure sensor. The respiratory humidification system may include
a pressure sensor positioned at or near the heater surface. The
respiratory humidification system may include a heating surface
temperature sensor. The respiratory humidification system may
include an ambient dew point temperature sensor or ambient humidity
sensor positioned upstream of a humidification region. The
respiratory humidification system may include an ambient dew point
temperature sensor positioned upstream from a gases pre-heater. The
respiratory humidification system may include an ambient dew point
temperature sensor positioned downstream from a gases pre-heater.
The respiratory humidification system may include an ambient dew
point temperature sensor positioned downstream from a gases
pre-heater and a temperature sensor at a gases passage way inlet.
The respiratory humidification system may include at least one
temperature sensor forming part of the heating system. The at least
one temperature sensor may be utilized to determine a proportion of
the heater surface area that is saturated (or covered) with a
liquid. The respiratory humidification system may include a gases
pre-heater. A temperature of the gases at a gases passage way inlet
may be controlled in an open loop fashion via control of a power to
the pre-heater. The respiratory humidification system may include a
liquid pre-heater. The heating surface may include a wicking
surface. Heat may be supplied to the heating surface by a PCB with
resistive traces or tracking. Heat may be supplied to the heating
surface by etched foil or flexible PCB s. Heat may supplied by a
heating wire. Heat may be supplied by a PTC ceramic. Heat may be
supplied by a Peltier or thermoelectric device. The heating surface
may be an over-mold including micro-channels in the over-mold
configured to conduct liquid, such as water. A surface temperature
of the heating surface may be at least partially determined by
using a resistance or other characterization of the heating system.
The resistance may indicate an average heater system temperature.
In some configurations, the heating system is arranged such that a
higher density of heat is provided in a specified region of the
heater such that those regions have a higher power density. The
higher density of heat may be near an outlet of a water supply. The
higher density of heat may be provided in a water pre-heating area.
The respiratory humidification system of may include a temperature
sensor at an outlet of the gases passage way.
[0022] According to another aspect of the present disclosure, a
respiratory humidification system is provided that provides in-line
humidification. In-line humidification allows humidification to
occur in the gas flow path, such that the humidification system may
be positioned within, partially within, or at the end of, an
inspiratory tube, for instance.
[0023] According to another aspect of the present disclosure, there
is provided a respiratory humidification system including a gases
channel through which gases may flow, the gases channel extending
between an inlet location and an outlet location, the gases channel
including a humidification location between the inlet and outlet
locations; a heating surface in fluid communication with the gases
channel, the heating surface configured to be maintained within a
temperature range; and a water flow controller configured to
control a flow of water to the heating surface; where in use, a
humidity level of the gases at the outlet location is
deterministically controlled by control of a water flow rate to the
heating surface.
[0024] The water flow controller can include a metering
arrangement. The metering arrangement can further include a pump.
The pump can be a positive displacement pump, such as, for example,
a piezoelectric diaphragm pump, a peristaltic pump, a micro-pump,
or a progressive cavity pump. The pump can also be a pressure feed
in series with a control valve. The pressure source may be gravity.
The respiratory humidification system may have a conduit in fluid
communication with the metering arrangement, the conduit configured
to carry water to the metering arrangement. The conduit can have a
non-return valve configured to keep the metering arrangement
primed. The conduit can also have a non-return valve configured to
keep the pump primed. The metering arrangement can include a
wicking structure that employs capillary action to controllably
meter the water to the wicking element and/or to the heating
surface. The conduit can also have a safety valve, such as a
pressure relief valve, in the conduit leading to the metering
arrangement. The respiratory humidification system can have a
reservoir configured to hold water. The respiratory humidification
system can also have a flow restriction device positioned between
the reservoir and the metering arrangement to prevent
gravity-driven flow from influencing the water flow path. The flow
restriction device can be an elastic protrusion that squeezes or
otherwise restricts the flow path. The water flow controller may be
a pump in an open-loop configuration. The water flow controller may
be a pump or a flow actuator in series with a flow sensor in a
closed-loop configuration. The water flow controller may provide a
continuous flow of water in the range of 0 mL/min to approximately
5 mL/min. The water flow controller may provide a continuous flow
of water in the range of 0 mL/min to approximately 7 mL/min. The
water flow controller may provide a continuous flow of water in the
range of 0 mL/min to approximately 5 mL/min. The water flow
controller may provide a continuous flow of water in the range of
approximately 40 .mu.L/min to approximately 4 mL/min, or in the
range of approximately 70 .mu.L/min to approximately 2.5 mL/min.
The water flow controller may provide a continuous flow of water in
the range of approximately 40 .mu.L/min to approximately 4 mL/min.
The water flow controller may provide a continuous flow of water in
the range of approximately 70 .mu.L/min to approximately 2.5
mL/min. The water flow controller may provide a flow rate of water
at an accuracy of approximately .+-.15%. The water flow controller
may provide a flow rate of water at an accuracy of approximately
.+-.10%. The water flow controller may provide a flow rate of water
at an accuracy of approximately .+-.6.5%. The water flow controller
may provide a flow rate of water at an accuracy of approximately
.+-.5%.
[0025] The heating surface may have a flow sensor. The flow sensor
may be a thermal mass meter. The flow sensor may be a drip feed
counter. The flow sensor may be a differential pressure flow
sensor.
[0026] Control of the water flow rate to the heating surface may be
based on a flow rate of the gases in the gases channel. Control of
the water flow rate to the heating surface may be based on an
evaporation rate of the water from the heating surface. Control of
the water flow rate to the heating surface may be based on a
temperature of the heating surface wherein the temperature of the
heating surface is maintained at a constant temperature. Control of
the water flow rate to the heating surface may be based on a
temperature of the heating surface wherein the temperature of the
heating surface is controlled. Control of the water flow rate to
the heating surface may be based on an absolute or barometric
pressure of the gases at or near the inlet location. Control of the
water flow rate to the heating surface may be based on a dew point
temperature of the gases at the inlet location. Control of the
water flow rate to the heating surface may be based on an enthalpy
provided by the heating surface. Control of the water flow rate to
the heating surface may be based on a power level provided by the
heating surface. Control of the water flow rate to the heating
surface may be based on a temperature of the gases at the inlet
location. The dew point temperature of the gases at the inlet
location may be derived by processing information provided by a
temperature sensor and a humidity sensor. Control of the water flow
rate to the heating surface may be based on the dew point
temperature of the gases at the inlet location. Control of the
water flow rate to the heating surface may be based on a relative
humidity level of the gases at the inlet location. Control of the
water flow rate to the heating surface may be based on an effective
heating area of the heating surface. Control of the water flow rate
to the heating surface may be based on a pressure level of the
gases in the gases channel. Control of the water flow rate to the
heating surface may be based on a velocity of the gases flowing in
the gases channel. Control of the water flow rate to the heating
surface may be based on a temperature of the water flow. The
respiratory humidification system may include a water temperature
sensor. The respiratory humidification system may include a gases
flow rate sensor. The respiratory humidification system may
determine the water flow rate based on a model. The respiratory
humidification system may determine the gases flow rate based on a
model. The respiratory humidification system may include an ambient
pressure sensor. The pressure sensor may be positioned at or near
the heater surface. The respiratory humidification system may
include a temperature sensor configured to measure a temperature of
the heating surface. The respiratory humidification system may
include an ambient dew point temperature sensor positioned within
the gases channel upstream of the humidification location. The
respiratory humidification system may include an ambient humidity
sensor positioned within the gases channel upstream of the
humidification location. The respiratory humidification system may
include a gases pre-heater. The gases pre-heater may be disposed
within the gases channel between the inlet and the humidification
locations. The ambient dew point sensor may be positioned within
the gases channel upstream of the gases pre-heater. The ambient
humidity sensor may be positioned within the gases channel upstream
of the gases pre-heater. The ambient dew point temperature sensor
may be positioned within the gases channel downstream of the gases
pre-heater. The ambient humidity sensor may be positioned within
the gases channel downstream of the gases pre-heater. The ambient
dew point temperature sensor may be positioned within the gases
channel downstream of the gases pre-heater in combination with a
temperature sensor positioned at the inlet location of the gases
channel. The respiratory humidification system may include at least
one temperature sensor configured to measure at least one
temperature of the heating surface. The at least one temperature
sensor may be configured to determine a proportion of the heating
surface that is saturated with water. The respiratory
humidification system may control a gases temperature at the inlet
location of the gases channel by controlling a power level to the
gases pre-heater in an open loop manner. The respiratory
humidification system may include a water pre-heater.
[0027] The heating surface can be configured to be maintained at a
temperature range. The temperature range may be between
approximately 30.degree. C. and approximately 99.9.degree. C. The
temperature range may be between approximately 35.degree. C. and
approximately 90.degree. C. The temperature range may be between
approximately 40.degree. C. and approximately 80.degree. C. The
temperature range may be between approximately 45.degree. C. and
approximately 70.degree. C. The temperature range may be between
approximately 45.degree. C. and approximately 60.degree. C. The
temperature range may be between approximately 50.degree. C. and
approximately 60.degree. C. The heating surface may be configured
to maintain a temperature of approximately 50.degree. C. The
heating surface may include a wicking surface. The heating surface
may include a heating element configured to provide heat to the
heating surface. The heating element may be a circuit board. The
circuit board may be a printed circuit board. The circuit board may
be a flexible circuit board. The flexible circuit board may be made
of polymer, the polymer may be silicone, polyester, or polyimide.
The circuit board may have a plurality of resistive tracks
(tracking or traces). The resistive tracks may be copper. The
heating element may be an etched foil. The heating element may be a
heating wire. The heating wire may be nichrome. The heating element
may be a positive thermal coefficient of resistance (PTC) ceramic.
The PTC ceramic may be barium titanate. The heating element may be
a thermoelectric device. The thermoelectric device may be a Peltier
device. The wicking surface may be provided by an over-molding on
the circuit board, the over-molding having micro-channels. The
heating surface temperature may be measured, at least in part, by
determining a resistance level or other characteristic of the
heating element. The resistance level of the heating element may be
used to indicate an average temperature of the heating surface. The
heating element may be arranged to deliver a higher power density
in a specified region of the heating element as compared to a power
density delivered to other regions of the heating element. The
specified higher density region of the heating element may be
located at an outlet of a water supply to the heating surface. The
specified higher density region of the heating element may be
located at a water pre-heating area on the heating surface. The
respiratory humidification system may include a temperature sensor
at the outlet location of the gases channel.
[0028] According to another aspect of the present disclosure, there
is provided a respiratory humidification system comprising a gases
channel through which gases may flow, the gases channel extending
between an inlet location and an outlet location, the gases channel
including a humidification location between the inlet and outlet
locations; a gases pre-heater disposed within the gases channel
between the inlet and the humidification locations; and a heating
surface in fluid communication with the gases channel at the
humidification location, the heating surface having a wicking
element configured to distribute water to the heating surface.
[0029] The respiratory humidification system may have a gases flow
generator adapted to propel, drive, or otherwise cause gases to
move in a general direction from the inlet location to the outlet
location of the gases channel. The gases pre-heater may include a
gases heating element. The gases heating element may be a printed
circuit board. The printed circuit board may have resistive
elements. The gases heating element may be an etched foil film. The
gases heating element may be a heating coil. The gases heating
element may be a PTC ceramic. The respiratory humidification system
may have a temperature sensor. The temperature sensor may be
positioned in the gases channel downstream of the gases pre-heater.
The temperature sensor may be positioned in the gases channel
upstream of the gases pre-heater. A characterization (e.g.,
resistance) of the gases heating element may be used to determine a
temperature of the gases. Control of a power level delivered to the
gases heating element may be based on information provided by the
temperature sensor positioned in the gases channel downstream of
the gases pre-heater. Control of the power level delivered to the
gases heating element may be based on information provided by a
gases flow sensor and by the temperature sensor positioned in the
gases channel upstream of the gases pre-heater. A desired
downstream temperature of the gases may be determined based on an
evaporation rate of the water from the heating surface. The desired
downstream temperature of the gases may be set to ensure that
substantially all sensible heat is supplied by the gases
pre-heater. The desired downstream temperature of the gases may be
set to obtain a desired relative humidity level of the gases at the
outlet location. The desired downstream temperature of the gases
may be set to be between 0.degree. C. and approximately 5.degree.
C. above desired temperature of the gases at the outlet location.
The desired downstream temperature of the gases may be set to be a
desired dew point temperature at the outlet location. The desired
downstream temperature of the gases may be set to approximately
25.degree. C. to approximately 43.degree. C., or approximately
31.degree. C. to approximately 43.degree. C., or approximately
31.degree. C. to approximately 41.degree. C., or approximately
31.degree. C. to approximately 37.degree. C., or approximately
37.degree. C. The heating surface may include a heating element
configured to provide heat to the heating surface. The heating
element may include a plurality of resistive tracks (tracking or
traces). The respiratory humidification system may include a water
flow generator configured to generate a flow of water to the
heating surface. The water flow generator may include a pump. The
pump may be a positive displacement pump. The positive displacement
pump may be a piezoelectric diaphragm pump, a peristaltic pump, a
micro-pump, or a progressive cavity pump. The respiratory
humidification system may include an apparatus for pre-heating the
water. The apparatus for pre-heating the water may be incorporated
into the heating element by increasing a density of resistive
tracks, and therefore the power density delivered to the heating
surface, at one or more areas of the heating element corresponding
to areas on the heating surface where the water is introduced. The
respiratory humidification system may include a water supply line
configured to deliver water to the heating surface. The apparatus
for pre-heating the water may be incorporated into the water supply
line.
[0030] The wicking element may include absorptive fabric. The
wicking element may include absorptive paper. The wicking element
may include micro-channels. The wicking element may include a
hydrophilic coated surface. The wicking element may include a
plurality of capillary/contact wicks. The wicking element may
include a thin, porous media, such as a fibrous, porous, or
sintered polymer. The wicking element may include a coupling, or be
coupled with a coupling, that performs some of the water
distribution to the heating surface. The coupling may be a length
of wicking media bonded to or otherwise brought into contact with
the wicking element or heating surface. The coupling may be a
porous polymer. The coupling may be a fabric. The coupling may be a
paper. The coupling may be a hydrophilic coated section. The
coupling may be a second surface forming an acute angle with the
wicking element. The second surface may be a glass plate. The
coupling may be a cavity in contact with the wicking element. The
coupling may be performed by a line source. The coupling may be
performed by multiple line sources. The coupling may be performed
by a point source. The coupling may be performed by multiple point
sources. The coupling may be performed by a radial source. The
coupling may be performed by multiple radial sources. The coupling
may be performed by a combination of line sources, point sources,
and/or radial sources. The heating surface may be adapted to
maintain a temperature of between approximately 30.degree. C. and
approximately 99.9.degree. C. The heating surface may be adapted to
maintain a temperature of between approximately 35.degree. C. and
approximately 90.degree. C. The heating surface may be adapted to
maintain a temperature of between approximately 40.degree. C. and
approximately 80.degree. C. The heating surface may be adapted to
maintain a temperature of between approximately 45.degree. C. and
approximately 70.degree. C. The heating surface may be adapted to
maintain a temperature of between approximately 45.degree. C. and
approximately 60.degree. C. The heating surface may be adapted to
maintain a temperature of between approximately 50.degree. C. and
approximately 60.degree. C. The heating surface may be adapted to
be maintained at a temperature of approximately 50.degree. C. The
respiratory humidification system may be mechanically configured
such that the wicking element, the heating surface, and the water
flow generator are positioned within, or incorporated as part of,
the gases channel. The respiratory humidification system may be
mechanically configured such that the water flow generator, the
coupling, the wicking element, and the heating surface are
positioned within, or incorporated as part of, the gases channel.
The respiratory humidification system may include a filter. The
filter may be in a water line. The filter may be positioned
downstream of the pump. The filter may be positioned at an inlet to
the heating surface. The filter may be a biologic filter. The
respiratory humidification system may include a plurality of
filters. The respiratory humidification system may include a first
filter in a water line between the reservoir and the water flow
generator and a second filter in a water line between the water
flow generator and the heating surface. The respiratory
humidification system may include an electromagnetic radiation
emitter for sterility. The electromagnetic radiation emitter may be
a UV light source. The UV light source may be a lamp or light
emitting diode (LED).
[0031] According to another aspect of the present disclosure, there
is provided a respiratory humidification system comprising a gases
channel through which gases may flow, the gases channel extending
between an inlet location and an outlet location, the gases channel
including a humidification location between the inlet and outlet
locations; a water flow metering system configured to meter water
at a water flow rate; a heating surface in fluid communication with
the gases channel at the humidification location, the heating
surface configured to receive the water provided by the water flow
metering system and to vaporize the received water; at least one
temperature sensor configured to measure a temperature of the
heating surface; two or more fluid sensors positioned at, on,
adjacent or proximal to two or more regions of the heating surface,
the two or more sensors configured to detect if the heating surface
is wetted in the two or more regions; a water flow controller
configured to control the water flow rate to the heating surface;
where in use, the respiratory humidification system
deterministically controls a humidity level of the gases at the
outlet location by controlling the water flow rate to the heating
surface.
[0032] The water flow metering system may include a pump. The pump
may be a positive displacement pump. The positive displacement pump
may be a piezoelectric diaphragm pump, a peristaltic pump, a
micro-pump, or a progressive cavity pump. The pump may be a
pressure feed, such as a gravity feed, in series with a control
valve. The respiratory humidification system may have a conduit in
fluid communication with the water flow metering system, the
conduit configured to carry water to the water flow metering
system. The conduit may have a non-return valve configured to keep
the water flow metering system primed. The conduit may have a
non-return valve configured to keep the pump primed. The water flow
metering system may include a wicking structure that employs
capillary action to controllably meter the water to a wicking
surface on the heating surface. The conduit may have a safety
valve, such as a pressure relief valve, in the conduit leading to
the water flow metering system. The respiratory humidification
system may have a reservoir configured to hold water. The
respiratory humidification system may have a flow restriction
device positioned between the reservoir and the water flow metering
system to prevent gravity-driven flow from influencing the water
flow path. The flow restriction device may be an elastic protrusion
that squeezes or otherwise restricts the flow path. The water flow
metering system may be a pump in an open-loop configuration. The
water flow metering system may be a pump or a flow actuator in
series with a flow sensor in a closed-loop configuration. The water
flow metering system may provide a continuous flow of water in the
range of 0 mL/min to approximately 5 mL/min. The water flow
metering system may provide a continuous flow of water in the range
of approximately 40 .mu.L/min to approximately 4 mL/min. The water
flow metering system may provide a continuous flow of water in the
range of approximately 70 .mu.L/min to approximately 2.5 mL/min.
The water flow metering system may provide a flow rate of water at
an accuracy of approximately .+-.15%. The water flow metering
system may provide a flow rate of water at an accuracy of
approximately .+-.10%. The water flow metering system may provide a
flow rate of water at an accuracy of approximately .+-.6.5%. The
water flow metering system may provide a flow rate of water at an
accuracy of approximately .+-.5%.
[0033] Control of the water flow rate to the heating surface may be
based on a flow rate of the gases in the gases channel. Control of
the water flow rate to the heating surface may be based on an
evaporation rate of the water from the heating surface. Control of
the water flow rate to the heating surface may be based on a
temperature of the heating surface wherein the temperature of the
heating surface is maintained at a constant temperature. Control of
the water flow rate to the heating surface may be based on a
temperature of the heating surface wherein the temperature of the
heating surface is controlled. Control of the water flow rate to
the heating surface may be based on an absolute or barometric
pressure of the gases at or near the inlet location. Control of the
water flow rate to the heating surface may be based on a dew point
temperature of the gases at the inlet location. Control of the
water flow rate to the heating surface may be based on an enthalpy
provided by the heating surface. Control of the water flow rate to
the heating surface may be based on a power level provided by the
heating surface. Control of the water flow rate to the heating
surface may be based on a temperature of the gases at the inlet
location. The dew point temperature of the gases at the inlet
location may be derived by processing information provided by a
temperature sensor and a humidity sensor. Control of the water flow
rate to the heating surface may be based on the dew point
temperature of the gases at the inlet location. Control of the
water flow rate to the heating surface may be based on a relative
humidity level of the gases at the inlet location. Control of the
water flow rate to the heating surface may be based on an effective
heating area of the heating surface. Control of the water flow rate
to the heating surface may be based on a pressure level of the
gases in the gases channel. Control of the water flow rate to the
heating surface may be based on a velocity of the gases flowing in
the gases channel. Control of the water flow rate to the heating
surface may be based on a temperature of the water flow.
[0034] The respiratory humidification system may include a water
temperature sensor. The respiratory humidification system may
include a gases flow rate sensor. The respiratory humidification
system may determine the water flow rate based on a model. The
respiratory humidification system may determine the gases flow rate
based on a model. The respiratory humidification system may include
an ambient pressure sensor. The pressure sensor may be positioned
at or near the heater surface. The respiratory humidification
system may include an ambient dew point temperature sensor
positioned within the gases channel upstream of the humidification
location. The respiratory humidification system may include an
ambient humidity sensor positioned within the gases channel
upstream of the humidification location. The respiratory
humidification system may include a gases pre-heater. The gases
pre-heater may be disposed within the gases channel between the
inlet and the humidification locations. The ambient dew point
temperature sensor may be positioned within the gases channel
upstream of the gases pre-heater. The ambient humidity sensor may
be positioned within the gases channel upstream of the gases
pre-heater. The ambient dew point temperature sensor may be
positioned within the gases channel downstream of the gases
pre-heater. The ambient humidity sensor may be positioned within
the gases channel downstream of the gases pre-heater. The ambient
dew point temperature sensor may be positioned within the gases
channel downstream of the gases pre-heater in combination with a
temperature sensor positioned at the inlet location of the gases
channel.
[0035] The at least one temperature sensor may be configured to
determine a proportion of the heating surface that is saturated
with water. The respiratory humidification system may control a
gases temperature at the inlet location of the gases channel by
controlling a power level to the gases pre-heater in an open loop
manner. The respiratory humidification system may include a water
pre-heater. The two or more fluid sensors may be used to prevent
overflow of liquid from the heating surface. Control of the water
flow rate to the heating surface may be based information provided
by the two or more fluid sensors. The two or more fluid sensors may
be used to control an evaporative area on the heating surface. The
two or more fluid sensors may be used exclusively to control the
evaporative area on the heating surface. The two or more fluid
sensors may be temperature sensors. The two or more fluid sensors
may be resistive or capacitive sensors.
[0036] According to another aspect of the present disclosure, there
is provided a heater plate for a respiratory humidification system,
the heater plate having a plurality of resistive tracks, the heater
plate being over-molded with a surface that includes
micro-channels. The heater plate may comprise a printed circuit
board (PCB). The heater plate may comprise an etched foil. The
micro-channels may include an arrangement of parallel channels
configured to direct water flow in one direction. The over-molded
surface may include a set of distribution channels connected to a
set of wicking channels, wherein there are fewer distribution
channels than there are wicking channels. The micro-channels may be
distributed radially from a single point.
[0037] According to another aspect of the present disclosure, there
is provided a respiratory therapy system comprising a gases channel
through which gases may flow, the gases channel extending between
an inlet location and an outlet location; a gases pre-heater
disposed within the gases channel; a humidification assembly
disposed within and in fluid communication with the gases channel,
the humidification assembly including: a heating surface in fluid
communication with the gases, the heating surface having a wicking
element configured to distribute water to the heating surface; a
coupling configured to distribute the water to the wicking element;
a water flow controller, in fluid communication with the coupling,
the water flow controller configured to meter the water to the
coupling, the water flow controller comprising a pump and a flow
sensor, the water flow controller configured to control a water
flow rate, wherein use, the wicking element distributes the metered
water to at least a portion of the heating surface, and the heating
surface causes the distributed water to be vaporized into the
gases. The heating surface may have heat provided to it by a
circuit board. The circuit board may be a printed circuit board.
The circuit board may have a plurality of resistive tracks. The
resistive tracks may be copper. The wicking surface may be provided
by an over-molding on the circuit board. The over-molding may have
micro-channels in it. The over-molding may be a thermoplastic
material. The heating surface may have modular zones. The heating
surface may have a first zone configured to pre-heat the water and
a second zone configured to vaporize the water.
[0038] The water flow controller can include a metering
arrangement. The metering arrangement can further include a pump.
The pump can be a positive displacement pump, such as, for example,
a piezoelectric diaphragm pump, a peristaltic pump, a micro-pump,
or a progressive cavity pump. The pump can also be a pressure feed,
such as a gravity feed, in series with a control valve. The
respiratory humidification system may have a conduit in fluid
communication with the metering arrangement, the conduit configured
to carry water to the metering arrangement. The conduit can have a
non-return valve configured to keep the metering arrangement
primed. The conduit can also have a non-return valve configured to
keep the pump primed. The metering arrangement can include a
wicking structure that employs capillary action to controllably
meter the water to the wicking element and/or to the heating
surface. The conduit can also have a safety valve, such as a
pressure relief valve, in the conduit leading to the metering
arrangement. The respiratory humidification system can have a
reservoir configured to hold water. The respiratory humidification
system can also have a flow restriction device positioned between
the reservoir and the metering arrangement to prevent
gravity-driven flow from influencing the water flow path. The flow
restriction device can be an elastic protrusion that squeezes or
otherwise restricts the flow path. The water flow controller may be
a pump in an open-loop configuration. The water flow controller may
be a pump or a flow actuator in series with a flow sensor in a
closed-loop configuration. The water flow controller may provide a
continuous flow of water in the range of 0 mL/min to approximately
5 mL/min. The water flow controller may provide a continuous flow
of water in the range of approximately 40 .mu.L/min to
approximately 4 mL/min. The water flow controller may provide a
continuous flow of water in the range of approximately 70 .mu.L/min
to approximately 2.5 mL/min. The water flow controller may provide
a flow rate of water at an accuracy of approximately .+-.15%. The
water flow controller may provide a flow rate of water at an
accuracy of approximately .+-.10%. The water flow controller may
provide a flow rate of water at an accuracy of approximately
.+-.6.5%. The water flow controller may provide a flow rate of
water at an accuracy of approximately .+-.5%.
[0039] The heating surface can be configured to be maintained at a
temperature range. The temperature range may be between
approximately 30.degree. C. and approximately 99.9.degree. C. The
temperature range may be between approximately 35.degree. C. and
approximately 90.degree. C. The temperature range may be between
approximately 40.degree. C. and approximately 80.degree. C. The
temperature range may be between approximately 45.degree. C. and
approximately 70.degree. C. The temperature range may be between
approximately 45.degree. C. and approximately 60.degree. C. The
temperature range may be between approximately 50.degree. C. and
approximately 60.degree. C. The heating surface may be configured
to maintain a temperature of approximately 50.degree. C. The
heating surface may include a wicking surface. The heating surface
may include a heating element configured to provide heat to the
heating surface. The heating element may be a circuit board. The
circuit board may be a printed circuit board. The circuit board may
be a flexible circuit board. The flexible circuit board may be made
of polymer. The polymer may be silicone, polyester, or polyimide.
The circuit board may have a plurality of resistive tracks. The
resistive tracks may be copper. The heating element may be an
etched foil. The heating element may be a heating wire. The heating
wire may be nichrome. The heating element may be a positive thermal
coefficient of resistance (PTC) ceramic. The PTC ceramic may be
barium titanate. The heating element may be a thermoelectric
device. The thermoelectric device may be a Peltier device. The
wicking surface may be provided by an over-molding on the circuit
board, the over-molding having micro-channels. The heating surface
temperature may be measured, at least in part, by determining a
resistance level or other characteristic of the heating element.
The resistance level of the heating element may be used to indicate
an average temperature of the heating surface. The heating element
may be arranged to deliver a higher power density in a specified
region of the heating element as compared to a power density
delivered to other regions of the heating element. The specified
higher density region of the heating element may be located at an
outlet of a water supply to the heating surface. The specified
higher density region of the heating element may be located at a
water pre-heating area on the heating surface. The respiratory
humidification system may include a temperature sensor at the
outlet location of the gases channel.
[0040] The respiratory humidification system may have a gases flow
generator adapted to propel, drive, or otherwise cause gases to
move in a general direction from the inlet location to the outlet
location of the gases channel. The gases pre-heater may include a
gases heating element. The gases heating element may be a printed
circuit board. The printed circuit board may have resistive
elements. The gases heating element may be an etched foil film. The
gases heating element may be a heating coil. The gases heating
element may be a PTC ceramic. The respiratory humidification system
may have a temperature sensor. The temperature sensor may be
positioned in the gases channel downstream of the gases pre-heater.
The temperature sensor may be positioned in the gases channel
upstream of the gases pre-heater. A characterization (e.g.,
resistance) of the gases heating element may be used to determine a
temperature of the gases. Control of a power level delivered to the
gases heating element may be based on information provided by the
temperature sensor positioned in the gases channel downstream of
the gases pre-heater. Control of the power level delivered to the
gases heating element may be based on information provided by a
gases flow sensor and by the temperature sensor positioned in the
gases channel upstream of the gases pre-heater. A desired
downstream temperature of the gases may be determined based on an
evaporation rate of the water from the heating surface. The desired
downstream temperature of the gases may be set to ensure that all
sensible heat is supplied by the gases pre-heater. The desired
downstream temperature of the gases may be set to obtain a desired
relative humidity level of the gases at the outlet location. The
desired downstream temperature of the gases may be set to be
between 0.degree. C. and approximately 5.degree. C. above a desired
temperature of the gases at the outlet location. The desired
downstream temperature of the gases may be set to be a desired dew
point temperature at the outlet location. The desired downstream
temperature of the gases may be set to approximately 25.degree. C.
to approximately 43.degree. C., or approximately 31.degree. C. to
approximately 43.degree. C., or approximately 31.degree. C. to
approximately 41.degree. C., or approximately 31.degree. C. to
approximately 37.degree. C., or approximately 37.degree. C.
[0041] The respiratory humidification system may include a filter.
The filter may be in a water line. The filter may be positioned
downstream of the pump. The filter may be positioned at an inlet to
the heating surface. The filter may be a biologic filter. The
respiratory humidification system may include a plurality of
filters. The respiratory humidification system may include a first
filter in a water line between the reservoir and the water flow
generator and a second filter in a water line between the water
flow generator and the heating surface. The respiratory
humidification system may include an electromagnetic radiation
emitter for sterility. The electromagnetic radiation emitter may be
a UV light source. The UV light source may be a lamp or an LED.
[0042] According to another aspect of the present disclosure, there
is provided a respiratory humidification system configured to
evaporate water, the respiratory humidification system configured
to output power, wherein the output power is transferred into heat
in the water. The respiratory humidification system may be
configured such that between approximately 80% and approximately
99.9% of the power output is transferred into heat in the water.
The respiratory humidification system may be configured such that
between approximately 85% and approximately 99.9% of the power
output is transferred into heat in the water. The respiratory
humidification system may be configured such that between
approximately 90% and approximately 99.9% of the power output is
transferred into heat in the water. The respiratory humidification
system may be configured such that approximately 98% of the power
output is transferred into heat in the water. The heating surface
may be adapted to maintain a temperature of between approximately
30.degree. C. and approximately 99.9.degree. C. The heating surface
may be adapted to maintain a temperature of between approximately
35.degree. C. and approximately 90.degree. C. The heating surface
may be adapted to maintain a temperature of between approximately
40.degree. C. and approximately 80.degree. C. The heating surface
may be adapted to maintain a temperature of between approximately
45.degree. C. and approximately 70.degree. C. The heating surface
may be adapted to maintain a temperature of between approximately
45.degree. C. and approximately 60.degree. C. The heating surface
may be adapted to maintain a temperature of between approximately
50.degree. C. and approximately 60.degree. C. The heating surface
may be adapted to maintain a temperature of approximately
50.degree. C.
[0043] According to another aspect of the present disclosure, there
is provided a respiratory humidification system comprising a gases
channel through which gases may flow, the gases channel extending
between an inlet location and an outlet location, the gases channel
including a humidification location between the inlet and outlet
locations; a gases pre-heater disposed within the gases channel
between the inlet and the humidification locations; a heating
surface in fluid communication with the gases channel at the
humidification location; a water flow generator, in fluid
communication with the heating surface, the water flow generator
configured to meter water to the heating surface.
[0044] The heating surface may be adapted to maintain a temperature
of between approximately 30.degree. C. and approximately
99.9.degree. C. The heating surface may be configured to maintain a
temperature of between approximately 35.degree. C. and
approximately 90.degree. C. The heating surface may be configured
to maintain a temperature of between approximately 40.degree. C.
and approximately 80.degree. C. The heating surface may be
configured to maintain a temperature of between approximately
45.degree. C. and approximately 70.degree. C. The heating surface
may be configured to maintain a temperature of between
approximately 45.degree. C. and approximately 60.degree. C. The
heating surface may be configured to maintain a temperature of
between approximately 50.degree. C. and approximately 60.degree. C.
The heating surface may be adapted to maintain a temperature of
approximately 50.degree. C.
[0045] The respiratory humidification system may have a gases flow
generator adapted to propel, drive, or otherwise cause gases to
move in a general direction from the inlet location to the outlet
location of the gases channel. The gases pre-heater may include a
gases heating element. The gases heating element may be a printed
circuit board. The printed circuit board may have resistive
elements. The gases heating element may be an etched foil film. The
gases heating element may be a heating coil. The gases heating
element may be a PTC ceramic. The respiratory humidification system
may have a temperature sensor. The temperature sensor may be
positioned in the gases channel downstream of the gases pre-heater.
The temperature sensor may be positioned in the gases channel
upstream of the gases pre-heater. A characterization (e.g.,
resistance) of the gases heating element may be used to determine a
temperature of the gases. Control of a power level delivered to the
gases heating element may be based on information provided by the
temperature sensor positioned in the gases channel downstream of
the gases pre-heater. Control of the power level delivered to the
gases heating element may be based on information provided by a
gases flow sensor and by the temperature sensor positioned in the
gases channel upstream of the gases pre-heater. A desired
downstream temperature of the gases may be determined based on an
evaporation rate of the water from the heating surface. The desired
downstream temperature of the gases may be set to ensure that all
sensible heat is supplied by the gases pre-heater. The desired
downstream temperature of the gases may be set to obtain a desired
relative humidity level of the gases at the outlet location. The
desired downstream temperature of the gases may be set to be
between 0.degree. C. and approximately 5.degree. C. above a desired
temperature of the gases at the outlet location. The desired
downstream temperature of the gases may be set to be a desired dew
point temperature at the outlet location. The desired downstream
temperature of the gases may be set to approximately 25.degree. C.
to 43.degree. C., or approximately 31.degree. C. to 43.degree. C.,
or approximately 31.degree. C. to 41.degree. C., or approximately
31.degree. C. to 37.degree. C., or approximately 37.degree. C. The
heating surface may include a heating element configured to provide
heat to the heating surface. The heating element may include a
plurality of resistive tracks.
[0046] The water flow generator may include a pump. The pump may be
a positive displacement pump. The positive displacement pump may be
a piezoelectric diaphragm pump, a peristaltic pump, a micro-pump,
or a progressive cavity pump. The respiratory humidification system
may include an apparatus for pre-heating the water. The apparatus
for pre-heating the water may be incorporated into the heating
element by increasing a density of resistive tracks (traces or
tracking), and therefore the power density delivered to the heating
surface, at one or more areas of the heating element corresponding
to areas on the heating surface where the water is introduced. The
respiratory humidification system may include a water supply line
configured to deliver water to the heating surface. The apparatus
for pre-heating the water may be incorporated into the water supply
line.
[0047] According to another aspect of the present disclosure, there
is provided a respiratory humidification system comprising a gases
channel through which gases may flow, the gases channel extending
between an inlet location and an outlet location; a heating surface
in fluid communication with the gases channel; and a water flow
controller configured to control a water flow rate of water
delivered to the heating surface; wherein in use, a humidity level
of the gases at the outlet location is deterministically controlled
by controlling the water flow rate. The respiratory humidification
system may include a water flow sensor. Control of the water flow
rate may be based on a flow rate of the gases in the gases channel.
Control of the water flow rate may be based on an evaporation rate
of the water from the heating surface. Control of the water flow
rate may be based on a temperature of the heating surface wherein
the temperature of the heating surface is maintained at a constant
temperature. Control of the water flow rate may be based on a
temperature of the heating surface wherein the temperature of the
heating surface is controlled. Control of the water flow rate may
be based on an absolute or barometric pressure of the gases at or
near the inlet location. Control of the water flow rate may be
based on a dew point temperature of the gases at the inlet
location. The dew point temperature of the gases at the inlet
location may be derived by processing information provided by a
temperature sensor and a humidity sensor. Control of the water flow
rate may be based on an enthalpy provided by the heating surface.
Control of the water flow rate may be based on a power level
provided by the heating surface. Control of the water flow rate may
be based on a temperature of the gases at the inlet location.
Control of the water flow rate may be based on a relative humidity
level of the gases at the inlet location. Control of the water flow
rate may be based on an effective heating area of the heating
surface. Control of the water flow rate may be based on a pressure
level of the gases in the gases channel. Control of the water flow
rate may be based on a velocity of the gases flowing in the gases
channel. Control of the water flow rate may be based on a
temperature of the water flow. The respiratory humidification
system may include a water temperature sensor. The respiratory
humidification system may include a gases flow rate sensor. The
respiratory humidification system may determine the water flow rate
based on a model. The respiratory humidification system may
determine the gases flow rate based on a model. The respiratory
humidification system may include a pressure sensor. The
respiratory humidification system may include an ambient pressure
sensor. The pressure sensor may be positioned at or near the heater
surface. The respiratory humidification system may include a
temperature sensor configured to measure a temperature of the
heating surface. The respiratory humidification system may include
an ambient dew point temperature sensor positioned within the gases
channel upstream of the humidification location. The respiratory
humidification system may include an ambient humidity sensor
positioned within the gases channel upstream of the humidification
location. The respiratory humidification system may include a gases
pre-heater. The gases pre-heater may be disposed within the gases
channel near the inlet location. The ambient dew point temperature
sensor may be positioned within the gases channel upstream of the
gases pre-heater. The ambient humidity sensor may be positioned
within the gases channel upstream of the gases pre-heater. The
ambient dew point temperature sensor may be positioned within the
gases channel downstream of the gases pre-heater. The ambient
humidity sensor may be positioned within the gases channel
downstream of the gases pre-heater. The ambient dew point
temperature sensor may be positioned within the gases channel
downstream of the gases pre-heater in combination with a
temperature sensor positioned at the inlet location of the gases
channel. The respiratory humidification system may include at least
one temperature sensor configured to measure at least one
temperature of the heating surface. The at least one temperature
sensor may be configured to determine a proportion of the heating
surface that is saturated with water. The respiratory
humidification system may control a gases temperature at or near
the inlet location of the gases channel by controlling a power
level to the gases pre-heater in an open loop manner. The
respiratory humidification system may include a water
pre-heater.
[0048] According to another aspect of the present disclosure, there
is provided a humidification system positioned within an
inspiratory tube of a respiratory therapy system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] Various embodiments of the present disclosure will now be
described, by way of illustrative example only, with reference to
the accompanying drawings. In the drawings, similar elements have
like reference numerals.
[0050] FIGS. 1A-1E are schematic diagrams of various embodiments of
respiratory therapy systems.
[0051] FIG. 2A is a functional block diagram of an overall control
system in accordance with an embodiment of the present
disclosure.
[0052] FIG. 2B is a functional block diagram of an inlet and
pre-heating control sub-system in accordance with an embodiment of
the present disclosure.
[0053] FIG. 2C is a functional block diagram of a water flow
control sub-system in accordance with an embodiment of the present
disclosure.
[0054] FIG. 2D is a functional block diagram of a heated surface
control sub-system in accordance with an embodiment of the present
disclosure.
[0055] FIG. 2E is a functional block diagram of overall controller
in accordance with an embodiment of the present disclosure.
[0056] FIG. 3A is a schematic perspective view of an example
integrated humidification system in accordance with one embodiment
of the present disclosure.
[0057] FIG. 3B is a schematic vertical cross-section view showing
an air flow of the humidification system of FIG. 3A.
[0058] FIG. 3C is a schematic vertical cross-section view showing a
water flow of the humidification system of FIG. 3A.
[0059] FIG. 3D is a schematic horizontal cross-section view of the
humidification system of FIG. 3A.
[0060] FIGS. 3E-3F show the humidification system 300 installed for
use with a flow generation system.
[0061] FIG. 4A is a schematic perspective view of a printed circuit
board heating element in accordance with an embodiment of the
present disclosure.
[0062] FIG. 4B is a schematic top view of a printed circuit board
heating element in accordance with an embodiment of the present
disclosure.
[0063] FIG. 4C is a partial schematic top view of a printed circuit
board heating element in accordance with an embodiment of the
present disclosure.
[0064] FIG. 4D illustrates a top schematic view of two embodiments
of an etched foil heating element in accordance with an embodiment
of the present disclosure.
[0065] FIG. 4E illustrates an embodiment of an etched foil heating
element in a rolled configuration.
[0066] FIG. 5A is a schematic diagram illustrating a
grid-structured micro-channel water distribution pattern in
accordance with an embodiment of the present disclosure.
[0067] FIG. 5B is a schematic diagram illustrating a radial
micro-channel water distribution pattern in accordance with an
embodiment of the present disclosure.
[0068] FIG. 6A is a schematic perspective axially sectioned view of
a portion respiratory humidification system including an example of
a coupling in accordance with an embodiment of the present
disclosure.
[0069] FIG. 6B is a schematic perspective sectioned side view of
the respiratory humidification system of FIG. 6A including the
example coupling.
[0070] FIG. 6C is a schematic side view of the humidification
system of FIG. 6A including the example coupling.
[0071] FIG. 6D is a schematic perspective assembled axial view of
the humidification system of FIG. 6A.
[0072] FIG. 7 is a schematic perspective diagram of a distribution
tube coupling wrapped over an edge of a heating surface in
accordance with an embodiment of the present disclosure.
[0073] FIG. 8 is a schematic diagram of a porous media coupling in
accordance with an embodiment of the present disclosure.
[0074] FIG. 9A is a schematic perspective view of a radial coupling
in accordance with an embodiment of the present disclosure.
[0075] FIG. 9B is a schematic perspective sectional view of the
radial coupling of FIG. 9A.
[0076] FIG. 10A is a schematic perspective view of a sandwich
coupling in accordance with an embodiment of the present
disclosure.
[0077] FIG. 10B is a schematic perspective sectioned view of the
sandwich coupling of FIG. 10A.
[0078] FIG. 10C is a schematic sectioned view of the sandwich
coupling of FIG. 10A attached to a humidification housing in
accordance with an embodiment of the present disclosure.
[0079] FIG. 10D is a schematic sectioned view of the sandwich
coupling of FIG. 10A attached to a humidification housing that
includes a printed circuit board heating element, in accordance
with an embodiment of the present disclosure.
[0080] FIG. 11A is a plot of a dew point temperature accuracy of a
respiratory humidification system in accordance with an embodiment
of the present disclosure.
[0081] FIG. 11B is a plot of a dew point temperature error across
air flow rate of a respiratory humidification system in accordance
with an embodiment of the present disclosure.
[0082] FIG. 12A is a schematic perspective view of an alternative
embodiment of a humidification system in accordance with an
embodiment of the present disclosure.
[0083] FIG. 12B is a schematic cross-section view of the
humidification system of FIG. 12A.
[0084] FIG. 12C is a schematic cross-section view showing the top
layer of the humidification system of FIG. 12A.
[0085] FIG. 12D is a schematic cross-section view showing the
bottom layer of the humidification system of FIG. 12A.
[0086] FIG. 13 is a schematic view of an inline humidification
system in accordance with one an embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0087] The following description is merely illustrative in nature
and is in no way intended to limit the disclosure, its application,
or uses. For purposes of clarity, the same reference numbers will
be used in the drawings to identify similar elements. However, for
the sake of convenience, certain features present or annotated with
reference numerals in some figures of the present disclosure are
not shown or annotated with reference numerals in other figures of
the present disclosure. Unless the context clearly requires
otherwise, these omissions should not be interpreted to mean that
features omitted from the drawings of one figure could not be
equally incorporated or implemented in the configurations of the
disclosed methods, apparatus and systems related to or embodied in
other figures. Conversely, unless the context clearly requires
otherwise, it should not be assumed that the presence of certain
features in some figures of the present disclosure means that the
disclosed methods, apparatus and systems related to or embodied in
such figures must necessarily include these features.
[0088] Certain features, aspects, and advantages of the present
disclosure include the realization of an on-demand humidifier,
where the requisite amount of water (or other humidification fluid)
is metered onto a heated surface, evaporated and mixed with a
pre-heated gases source to produce a desired humidity level, in an
open-loop and deterministic configuration. Advantageously, by
employing the disclosed humidification control systems, devices,
and methods, allocated water can be deposited onto a heating
element that is in fluid communication with a gases channel on an
as-needed basis as opposed to heating an entire fluid supply at
once, or heating an otherwise excess volume of liquid, such as a
chamber of liquid. Illustratively, by measuring an inlet gases flow
rate, an inlet gases dew point temperature, and/or a gases channel
pressure level, a fluid flow rate of liquid to a heating surface
may be determined and controlled to achieve a desired output
humidity and temperature level (or outlet dew point temperature) of
gases to be delivered to the patient.
[0089] With reference to FIG. 1A, a non-limiting exemplary
configuration of a respiratory therapy system 100 is shown. In the
illustrated configuration, the respiratory therapy system 100
includes a flow generator 120. The flow generator 120 can have, for
example, a blower 121 adapted to propel gases through the
respiratory therapy system 100. The gases propelled using the
blower 121 may, for example, include air received from the
environment outside of the respiratory therapy system 100 (for
example, `ambient air` or `ambient gases`) and/or gases from a
gases container in communication with the respiratory therapy
system 100 (see for example gases reservoir 137 in FIG. 1E). Gases
from the flow generator 120 are directed to and/or through a
respiratory humidification system 101 adapted to add moisture to
the gases. The respiratory humidification system 101 includes a
gases channel 102 (which may also be referred to herein as "a
breathing tube," or "an inspiratory tube") adapted to receive gases
from the flow generator 120 and/or another gases source and channel
the gases to an outlet, such as a patient interface 122. As
indicated using the {right arrow over (UD)} (or
Upstream-Downstream) vector at the top of FIG. 1A, in use, gases
may generally move from the flow generator 120 to the respiratory
humidification system 101 (for example, through the gases channel
102), and from the respiratory humidification system 101 to the
outlet or patient interface 122 (for example, through the gases
channel 102) in a downstream direction.
[0090] With further reference to the non-limiting exemplary
configuration shown in FIG. 1A, the respiratory humidification
system 101 includes a fluid reservoir 106 which in use houses a
fluid. "Fluid" in this context may refer to liquids or fluent
solids suitable for humidifying respiratory gases and may include,
for example, water. The fluid may be a water with additives that
are more volatile than water. The fluid reservoir 106 is fluidly or
otherwise physically linked to a metering arrangement (also
referred to as a liquid flow controller or water flow controller
herein) 110. The metering arrangement 110 is configured to meter
fluid from the fluid reservoir 106 to a humidification housing 115
located in the gases channel 102 or outside of, but in pneumatic
communication with, the gases channel 102. The metering arrangement
110 can further include a pump. The pump can be a positive
displacement pump, such as, for example, a piezoelectric diaphragm
pump, a peristaltic pump, a micro-pump, or a progressive cavity
pump. The pump can also be a pressure feed, such as a gravity feed
in series with a control valve (for example, as shown in FIG. 1D
and described below). The metering arrangement can include a
wicking structure that employs capillary action to controllably
meter the water to the wicking element and/or to the heating
surface.
[0091] The metering arrangement 110 can be controlled by a water
flow controller. The water flow controller may be a pump in an
open-loop configuration. The water flow controller may be a pump or
a flow actuator in series with a flow sensor in a closed-loop
configuration. In some configurations, a water flow controller
configured as a pump in an open-loop configuration is preferred
because it is simpler and only requires one part (the pump).
However, a pump in an open-loop configuration may not be able to
deliver water accurately, but may still be useful under conditions
where accuracy is not essential. Therefore, in other
configurations, a pump or a flow actuator in series with a flow
sensor in a closed-loop configuration can be used where greater
accuracy is desired. In this configuration, the selection of the
pump may be less important as it does not have to be accurate, and
a dedicated flow sensor is used to control accuracy. Another
advantage to a pump or a flow actuator in series with a flow sensor
in a closed-loop configuration is that it provides two independent
indications of flow (the pump setting and the sensed flow) which
adds a layer of safety to the system (for example, the pump and
sensor can be compared against each other to verify they are
operating correctly).
[0092] The water flow controller may provide a continuous flow of
water in the range of 0 mL/min to approximately 10 mL/min. The
water flow controller may provide a continuous flow of water in the
range of 0 mL/min to approximately 7 mL/min. The water flow
controller may provide a continuous flow of water in the range of 0
mL/min to approximately 5 mL/min. The water flow controller may
provide a continuous flow of water in the range of approximately 40
.mu.L/min to approximately 4 mL/min. The water flow controller may
provide a continuous flow of water in the range of approximately 70
.mu.L/min to approximately 2.5 mL/min. The water flow controller
may provide a flow rate of water at an accuracy of approximately
.+-.15%. The water flow controller may provide a flow rate of water
at an accuracy of approximately .+-.10%. The water flow controller
may provide a flow rate of water at an accuracy of approximately
.+-.6.5%. The water flow controller may provide a flow rate of
water at an accuracy of approximately .+-.5%.
[0093] The water flow controller, including metering system 110,
may be configured to ensure that the surface of the heating element
114 is entirely wetted (saturated). A fully wetted surface may
allow for improved deterministic control of the humidity. The
wetted surface also means that humidity can be increased more
quickly as water travels more quickly over a wet surface than it
does over a dry surface.
[0094] Any positive displacement pump may be used in the water
controller or metering arrangement 110. Positive displacement pumps
work by displacing a fixed volume of water and generally yield good
accuracy. Any of a variety of positive displacement pumps are
suitable, for example, peristaltic, diaphragm, vane, plunger, etc.,
and a majority of these can be scaled to work at the flow rates
contemplated herein. However, piezoelectric micro-pumps (miniature
diaphragm pumps using piezoelectric elements as the actuators) and
peristaltic pumps (which use rollers to squeeze water through a
tube at a constant rate) may be particularly advantageous as many
are already commercially available at sizes, prices, operating
ranges and powers, etc., that are suitable for the systems
described herein. Additionally, a pressure feed, such as a gravity
feed, in series with a control valve (see FIG. 1D) and/or
wicking/capillary action may be used in place of a pump. In some
configurations, an electro/magneto-hydrodynamic pump may be
used.
[0095] When the water flow controller includes a flow sensor, in
some configurations, the flow sensor may be a thermal mass meter.
These sensors work by heating the liquid and measuring either the
power required to do so (for example, a heated flow bead) or the
temperature gradient introduced, or some variation on this.
Alternatively, the flow sensor may be replaced or supplemented with
a drip feed (for example, counting drops as is a common method of
measuring flow in an IV drip); differential pressure sensors that
measure the pressure drop across a restriction to calculate flow;
and/or positive displacement sensors that use the same principle as
the positive displacement pump to sense flow. By way of
non-limiting example, a suitable pump is the mp6 micro pump
available from Bartels Mikrotechnik. An example liquid flow sensor
is the LG16 available from Sinsiron, the data sheet of which is
available at
http://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokume-
nte/LiquidFlow/Sensirion_Liquid_Flow_LG16_Datasheet_V3.pdf and
incorporated herein by reference.
[0096] The fluid reservoir 106 is connected to the metering
arrangement 110 via a first fluid conduit 108. The first conduit
108 can have a non-return valve configured to keep the metering
arrangement primed. The first conduit 108 can also have a
non-return valve configured to keep the pump primed. The first
conduit 108 can also have a safety valve, such as a pressure relief
valve, in the conduit leading to the metering arrangement to
prevent flow of liquid in case of pump or water controller failure.
The respiratory humidification system 101 can also have a flow
restriction device positioned between the reservoir 106 and the
metering arrangement 110 to prevent gravity-driven flow from
influencing the water flow path. The flow restriction device can be
an elastic protrusion that squeezes or otherwise restricts the flow
path. The metering arrangement 110 meters fluid to the
humidification housing 115 through a second fluid conduit 112. In
particular, the metered fluid can enter the humidification housing
115 through inlets 116 to the humidification housing 115.
[0097] A heating device 114 may be present in, at, or near the
humidification housing 115. The heating device 114 can have a
wicking element configured to distribute the metered fluid to the
heating device 114. In some configurations, the wicking element is
configured to wick the metered fluid evenly across the surface of
the heating device 114. The heating device 114 may be configured to
vaporize the metered fluid such that it becomes entrained in the
gases flow in use by the respiratory therapy system 100. The
heating device 114 can be configured to be maintain a heating
surface at a temperature range. The temperature range may be
between approximately 30.degree. C. and approximately 99.9.degree.
C. The temperature range may be between approximately 35.degree. C.
and approximately 90.degree. C. The temperature range may be
between approximately 40.degree. C. and approximately 80.degree. C.
The temperature range may be between approximately 45.degree. C.
and approximately 70.degree. C. The temperature range may be
between approximately 45.degree. C. and approximately 60.degree. C.
The temperature range may be between approximately 50.degree. C.
and approximately 60.degree. C. The heating surface may be
configured to maintain a temperature of approximately 50.degree. C.
"Approximately" should be understood herein to be within an
acceptable tolerance of the specified degree such as, for example,
.+-.3.degree. C. The heating surface may include a wicking surface.
The heating surface may include a heating element configured to
provide heat to the heating surface. The heating element may be a
circuit board. The circuit board may be a printed circuit board
(for example, as shown and described in reference to FIGS. 4A-4C
below). The circuit board may be a flexible circuit board. The
flexible circuit board may be made of aluminum-polyimide. The
circuit board may have a plurality of resistive tracks. The
resistive tracks may be copper. The heating element may be an
etched foil (for example, as shown and described in reference to
FIGS. 4D-4E below). The heating element may be a heating wire. The
heating wire may be nichrome. The heating element may be a positive
thermal coefficient of resistance (PTC) ceramic. The PTC ceramic
may be barium titanate. The heating element may be a thermoelectric
device. The thermoelectric device may be a Peltier device. The
wicking surface may be provided by an over-molding on the circuit
board, the over-molding having micro-channels. The heating surface
temperature may be measured, at least in part, by determining a
resistance level or other characteristic of the heating element.
The resistance level of the heating element may be used to indicate
an average temperature of the heating surface. The heating element
may be arranged to deliver a higher power density in a specified
region of the heating element as compared to a power density
delivered to other regions of the heating element (for example, as
explained in reference to FIG. 4C). The specified higher density
region of the heating element may be located at an outlet of a
water supply to the heating surface. The specified higher density
region of the heating element may be located at a water pre-heating
area on the heating surface.
[0098] A component of the respiratory therapy system 100 or of the
respiratory humidification system 101 can include a controller 118
that can control the operation of components of the respiratory
therapy system 100 or of the respiratory humidification system 101,
including but not limited to the flow generator 120, the metering
arrangement 110, and/or the heating device 114.
[0099] The metering arrangement 110 may be configured to meter or
allocate fluid to the humidification housing 115 and/or to the
heating device 114 at metering rates that raise the moisture
content of gases passing through the gases channel 102 such that
the gases reach a predetermined, calculated, or estimated humidity
level representing a level of gases humidification needed or
desired by a patient using the respiratory humidification system
101 while taking care to reduce or eliminate the likelihood of
undue moisture accumulation in the gases channel 102. To implement
this, in one example, the controller 118 can control the metering
rate of the metering arrangement 110 based on (a) a measured flow
rate of gases passing through the gases channel 102, (b) a measured
moisture value corresponding to the humidity of gases upstream of
the humidification housing 115, (c) a measured pressure level
corresponding to the pressure level in the gases channel 102, or
(d) a combination thereof. The controller 118 can control the
metering rate of the metering arrangement 110 based on a
combination of one or more of measured inputs (a)-(c), such as
based on (a) measure flow rate of gases passing through the gases
channel 102 and (b) a measured moisture value corresponding to the
humidity of gases upstream of the humidification housing 115, or
(a) a measured flow rate of gases passing through the gases channel
102 and (c) a measured pressure level corresponding to the pressure
level in the gases channel 102.
[0100] In some configurations, the metering rate of the metering
arrangement 110 may be directly calculated by the controller 118.
Illustratively, by way of non-limiting example, if the flow rate of
gases passing through the flow channel 102 is determined to be 20
L/min, and the desired output humidity of gases exiting the
respiratory humidification system 101 is determined to be 44 mg/L
then, if one were to assume that the humidity of gases entering the
system was zero (that is, if the gases were completely dry), 0.88
g/min of fluid (20 L/min*0.044 g/L) would need to be added to the
gases in the gases channel 102. A correction factor may then be
calculated corresponding to the (assumed, estimated, calculated or
measured) humidity of the gases entering the respiratory
humidification system 101. Accordingly, particularly if the fluid
can be vaporized rapidly, the metering rate of the metering
arrangement 110 may be set to 0.88 g/min, adjusted by the
correction factor derived from the assumed, estimated, calculated,
or measured humidity of gases upstream of the humidification
housing 115 or of ambient gases present outside of the respiratory
therapy system 100.
[0101] The desired output humidity (for example, relative humidity
(RH)=100% or absolute humidity (AH)=44 mg/L) and/or desired output
temperature (for example, 37.degree. C. or 98.6.degree. F.) of
gases may be input by a user of the respiratory humidification
device 101 through, for example, a user interface 105 located on a
housing 103 of the respiratory therapy system 100 or using a remote
control module. The user interface 105 can include, for example,
one or more buttons, knobs, dials, keyboards, switches, levers,
touch screens, speakers, displays, and/or other input or output
modules so that a user might use to view data and/or input commands
to control components of the respiratory therapy system 100 or of
the respiratory humidification system 101.
[0102] The respiratory therapy system 100 or the respiratory
humidification system 101 may include deterministic or open loop
control. Various control systems will be described in greater
detail in reference to FIGS. 2A-2E below. In general, deterministic
control may allow for on-demand humidification achieved by
controlling certain input variables, for example, by controlling
water flow to the heating surface. In some configurations, control
of the water flow rate to the heating surface may be based on a
flow rate of the gases in the gases channel. Control of the water
flow rate to the heating surface may be based on an evaporation
rate of the water from the heating surface. Control of the water
flow rate to the heating surface may be based on a temperature of
the heating surface wherein the temperature of the heating surface
is maintained at a constant temperature. Control of the water flow
rate to the heating surface may be based on a temperature of the
heating surface wherein the temperature of the heating surface is
controlled. Control of the water flow rate to the heating surface
may be based on an absolute or barometric pressure of the gases at
or near the inlet location. Control of the water flow rate to the
heating surface may be based on a dew point temperature of the
gases at the inlet location. Control of the water flow rate to the
heating surface may be based on an enthalpy provided by the heating
surface. Control of the water flow rate to the heating surface may
be based on a power level provided by the heating surface. Control
of the water flow rate to the heating surface may be based on a
temperature of the gases at the inlet location. The dew point
temperature of the gases at the inlet location may be derived by
processing information provided by a temperature sensor and a
humidity sensor. Control of the water flow rate to the heating
surface may be based on the dew point temperature of the gases at
the inlet location. Control of the water flow rate to the heating
surface may be based on a relative humidity level of the gases at
the inlet location. Control of the water flow rate to the heating
surface may be based on an effective heating area of the heating
surface. Control of the water flow rate to the heating surface may
be based on a pressure level of the gases in the gases channel.
Control of the water flow rate to the heating surface may be based
on a velocity of the gases flowing in the gases channel. Control of
the water flow rate to the heating surface may be based on a
temperature of the water flow. As shown and described in reference
to FIG. 1E below, the respiratory therapy system 100 and/or the
components thereof (including the respiratory humidification system
101) may include a number of sensors to measure these
variables.
[0103] The illustrated configuration should not be taken to be
limiting and many other configurations for the respiratory therapy
system 100 and the components thereof (including the respiratory
humidification system 101) are contemplated. Additional details for
configurations of components of the respiratory therapy system 100
are described below.
[0104] The first and second fluid conduits 108, 112 may be
configured to communicate fluids to various components of the
respiratory humidification system 101. As illustrated in FIG. 1A,
the first fluid conduit 108 may be configured to fluidly
communicate fluid from the fluid reservoir 106 to the metering
arrangement 110, and the second fluid conduit 112 may be configured
to fluidly communicate fluid from the metering arrangement 110 to
the humidification housing 115. In some configurations, the first
and/or second fluid conduits 108, 112 are optional. For example, if
the fluid reservoir 106 is in direct fluid communication with the
metering arrangement 110, the first fluid conduit 108 need not be
present. Likewise, if the metering arrangement 110 is in direct
fluid communication with the humidification region 115, the second
fluid conduit 112 need not be present.
[0105] As illustrated in FIG. 1E, the first and/or second fluid
conduits 108, 112 may additionally comprise one or more filters 128
configured to remove contaminants, impurities, or other undesired
materials from the fluid passing from the fluid reservoir 106. The
filters 128 can include any structure configured to do such,
including permeable or semipermeable membranes positioned in the
fluid flow paths of the first and/or second conduits 108, 112
and/or configured for use in microfiltration, ultrafiltration, or
reverse osmosis. The presence of one or more filters 128 in the
first and/or second conduits 108, 112 may help to assure a user of
the respiratory humidification system 101 that the quality of fluid
introduced into the humidification housing 115 is at an acceptable
level. If one or more of the filters 128 has been used for too long
a period of time, the filters 128 and/or the first and/or second
conduits 108, 112 may be replaced. The age of the filters 128 may
be indicated to a user through, for example, a chemical color
change indicator located in or on the first and/or second conduits
108, 112 or the filters 128 may change in color over time due to
prolonged exposure to gases and/or fluids. The filter 218 may serve
as a preliminary distributor of the humidification liquid.
[0106] As described above, the metering arrangement 110 can serve
to meter fluids from the fluid reservoir 106 to the humidification
housing 115. The metering arrangement 110 can include, for example,
a fluid displacement pump that may actively transfer fluid from the
fluid reservoir 106 to the humidification housing 115 along, for
example, the first and/or second conduits 108, 112. In certain
embodiments, the metering arrangement 110 may run in reverse or act
to withdraw fluid from the humidification housing 115. The fluid
displacement pump can include, for example, a positive displacement
pump, such as a piezoelectric diaphragm pump, a peristaltic pump, a
micro-pump, or a progressive cavity pump.
[0107] As shown in FIG. 1B, the system can be embodied as an
in-line humidifier. In this embodiment, the humidification system
101 can be an add on to a respiratory circuit for use with any flow
generation system or it can be a stand-alone humidifier using
ambient air and relying on normal patient respiration to generate a
flow of gases.
[0108] As demonstrated in FIG. 1C, in some configurations, the
heating device 114 may be positioned outside of the gas channel
102. For example, the heating device 114 may be present in a
separate compartment 124. The compartment 124 may be physically
linked to the gas channel 102 but may be fluidly isolated from the
gas channel 102. The compartment 124 may be fluidly isolated from
the gas channel 102 through the use of a semipermeable membrane 126
positioned between the compartment 124 and the gas channel 102. In
some configurations, the semipermeable membrane 126 may not allow
fluid to pass through but may allow vaporized fluids to pass
through (and thereby allow vaporized fluids to join gases passing
through the gas channel 102). Examples of suitable materials for
use with the semipermeable membrane include perfluorinated polymers
or polymers with fine pores and include materials such as those
used in the tubing described in commonly-owned U.S. Pat. No.
6,769,431, filed May 8, 2001 and titled "Expiratory Limit for a
Breathing Circuit," and U.S. patent application Ser. No.
13/517,925, filed Dec. 22, 2010 and titled "Components for Medical
Circuits," both of which are incorporated by reference herein in
their entirety. In use, fluid may be metered through the outlet 116
to the compartment 124, vaporized using the heating device 114
(which may additionally be positioned in the compartment 124), and
forced through the semipermeable membrane 126 to join the
downstream-moving gases passing through the gas channel 102.
Fluidly isolating the outlet 116 from the gas channel 102 may, for
example, reduce the likelihood of liquid water being present in the
gas channel 102.
[0109] It should be understood that the metering arrangement 110
need not necessarily include a pump and may simply include a
structure configured to allocate fluid to the humidification
housing 115 in predetermined, desired, or regulated amounts. For
example, and as demonstrated in FIG. 1D, the fluid reservoir 106
may be suspended vertically above the gases channel 102 and/or
humidification housing 115. The fluid reservoir 106 may be in
communication with an electromechanical valve 150 that may, in
response to signals generated by the controller 118, partially or
fully open or close to control the passage of fluid from the fluid
reservoir 106 to the humidification housing 115 through the second
fluid conduit 112.
[0110] In some configurations, the second fluid conduit 112 may not
be present and the fluid reservoir 106 may cooperate with the
electromechanical valve 150 to transfer fluids directly to the
humidification region 115 (and/or to a location at or near the
heating device 114). Fluid flow sensors such as, but not limited
to, Micro-Electrical-Mechanical Systems or MEMS sensors, may be
used to determine the fluid flow through the electromechanical
valve 150 or second fluid conduit 112. Signals from the fluid flow
sensor or values derived therefrom may be used to, for example,
control the operation of the electromechanical valve 150 via
closed-loop control. Although in FIG. 1D the fluid reservoir 106 is
shown as being vertically above the gases channel 102, in some
configurations, the fluid reservoir 106 may be at the same level as
the gases channel 102 or lower than the gases channel 102. Other
forces may act upon the fluid reservoir 106 to meter fluid in
combination with the electromechanical valve 150. For example, the
respiratory humidification system 101 may be configured such that
fluids are propelled from the reservoir 106 using the force of
gases passing through the respiratory therapy system 100 and/or the
respiratory humidification system 101. In some configurations, the
gases may act on the fluid in the fluid reservoir 106 directly. In
some configurations, the fluid reservoir 106 may be pressurized by
fluid filled pouches (filled by, for example, gases from the flow
generator 120 or from a separate gases source) that force fluid
from the fluid reservoir 106. The pressure exerted by the pouches
may be controlled using a biasing force generated by, for example,
a spring or other mechanical arrangement.
[0111] In some embodiments, the heating device 114 may be
configured to transfer heat to fluids that are metered on to or
near the heating device 114 to encourage fluid vaporization and
entrainment into the gases flow passing through the gases channel
102. The particular form of the heating device 114 is not limited
and many varieties of heating devices may be envisioned for use
with the respiratory humidification system 101. In some
configurations, the heating device 114 may include a heating plate
or element that may resistively heat upon the application of
electrical energy. The resistive heating plate may be constructed
from an electrically conductive metallic material but may also be
made from conductive plastics.
[0112] The controller 118 can include a microprocessor or some
other architecture configured to direct the operation of
controllable components of the systems 100, 101. In some
configurations, one controller 118 may control the operation of
every controllable component of the respiratory therapy system 100
and/or respiratory humidification system 101, including but not
limited to the metering arrangement 110, the heating device 114,
and/or the flow generator 120. The controller 118 may be physically
present in, on, or near a component of the respiratory therapy
system 100, including but not limited to the flow generator 120,
the respiratory humidification system 101, the housing 103, and/or
the gas channel 102. In some configurations, the controller 118 may
be physically separate from the respiratory therapy system 100. For
example, the controller 118 could be located on a remote computer,
tablet, mobile phone, smartwatch, or another device, and the
controller 118 may remotely direct the operation of the
controllable components of the respiratory therapy system 100. In
some configurations, multiple controllers may be used to control
the controllable components of the respiratory therapy system 100
and/or respiratory humidification system 101. The multiple
controllers may each be directed to exclusive control of one or
more controllable components of one or both of the systems 100,
101. In some configurations, the control of one or more
controllable components of one or both of the systems 100, 101 may
be handled by multiple controllers. The multiple controllers may be
configured to communicate with one another.
[0113] To control the metering rate of the metering arrangement 110
through the controller 118 in accordance with the functions
described above or elsewhere in this specification (for example, by
using measured flow values, moisture values, and/or pressure
values; see, for example, the description of FIGS. 2A-2E below),
the assumed, estimated, calculated or measured signals and values
can be determined. In some configurations, the signals and/or
values can be determined as described below.
[0114] A predetermined value may be selected to represent the flow
rate of gases passing through the gases channel 102. By way of
non-limiting example, the flow rate of gases passing through the
gases channel 102 may be assumed to be 40 L/min.
[0115] A gases flow rate value, corresponding to the flow rate of
gases passing through the gases channel 102, may be estimated or
approximated through a variety of means. In some cases, the flow
generator 120 includes a mechanical blower 121. The motor speed,
motor torque, and/or motor current of a motor of the blower 121 may
be determined using a motor sensing module 130 (for example, as
illustrated in FIG. 1E) including, for example, one or more
relevant transducers. One or more of the signals output by the
motor sensing module 130, or values derived therefrom, may be
inputs into a lookup table or equation, either of which in turn may
return an estimated or approximated gases flow rate value based on,
for example, an experimentally-determined set of inputs and
outputs.
[0116] Flow signals representative of the flow rate of gases
passing through the gases channel 102 may be generated by a gases
flow sensor 134 (see FIG. 1E) positioned in the gases channel 102.
A signal generated by the gases flow sensor 134 may be processed
and converted to a gases flow rate value.
[0117] A predetermined value may be selected to represent the
relative or absolute humidity of gases upstream of the
humidification housing 115. Illustratively, by way of non-limiting
example, the relative humidity of gases upstream of the
humidification housing 115 may be assumed to be 50%, or the
absolute humidity of gases upstream of the humidification housing
115 may be assumed to be 15 mg/L.
[0118] If the temperature and relative humidity of gases passing
through the gases channel 102 can be sensed or otherwise estimated
or determined, the dew point temperature of the gases may be
derived using, for example, the Clausius-Clapeyron equation. The
relative humidity value may be converted into an absolute humidity
value if the temperature and pressure of the gases upstream of the
humidification housing 115 can be sensed or otherwise estimated or
determined.
[0119] A moisture signal representative of the relative or absolute
humidity of the gases upstream of the humidification housing 115,
or of ambient gases outside of the respiratory therapy system 100
may be generated by a humidity sensor 136 (for example, as
illustrated in FIG. 1E) positioned upstream of the humidification
housing 115 or outside of the respiratory therapy system 100. A
signal generated by the humidity sensor 136 may be processed and
converted to a moisture value.
[0120] Various sensor modules may also be positioned in the gases
channel 102 downstream of the humidification housing 115. As
demonstrated in FIG. 1E, the sensor modules may include, for
example, a flow sensor 138, a humidity sensor 140 (for example,
including absolute and/or relative humidity sensors), a temperature
sensor 141, and/or a pressure sensor 142. One or more of these
sensors may be used by the controller 118 to facilitate control of
components of the respiratory therapy system 100 and/or respiratory
humidification system 101, including control of the operation of
the gases flow generator 120 (including, for example, a motor speed
of a blower 121), of the heat output of the heating device 114, of
the metering rate of the metering arrangement 110, and/or of some
other component.
[0121] Also, as demonstrated in FIG. 1E, a gas concentration sensor
135 may be positioned in the gases channel 102. The gas
concentration sensor 135 may be configured to sense the
concentration of one or more gases in the gases stream. The gas
concentration sensor 135 can include an ultrasonic sensor adapted
to sense, for example, oxygen. The gas sensed may include, for
example, oxygen, nitric oxide, carbon dioxide, and/or heliox
introduced to the gases channel 102 from a gases reservoir 137
through a gases concentration adjustment valve 139. The gas
concentration sensor 135 may use a gas concentration signal
generated by the gas concentration sensor 135 to control the gas
concentration adjustment valve 139 (for example, via closed-loop
control) based on a predetermined desired gas concentration (for
example, entered by a user through the user interface 105).
[0122] In some configurations, and as demonstrated in FIG. 1E, a
fluid sensor 117 may be in communication with the humidification
housing 115 and/or the heating device 114 as a safety measure to
help avoid burning the patient with overheated gases.
Illustratively, the fluid sensor 117 may be configured to generate
a signal upon detection of the presence of fluid in the
humidification housing 115 and/or in or on the heating device 114.
The controller 118 may use the signal emitted by the fluid sensor
117 to control the operation of the metering arrangement 110 and/or
the operation of the heating device 114. For example, the metering
rate of the metering arrangement 110 and/or the heat output of the
heating device 114 may be set to a function of the signal generated
by the fluid sensor 117. The metering rate of the metering
arrangement 110 may be increased if the signal does not indicate
the presence of fluids in or near the humidification housing 115,
or on a modular area of the heating device, since the heating
devices is intended to be covered with a film of humidification
fluid. Likewise, the heat output of the heating device 114 may be
reduced or set to zero if the signal does not indicate the presence
of fluids in or near the humidification housing 115, or on a
modular area of the heating device, so as to avoid heating the
gases to an unsafe temperature. The fluid sensor 117 may be thus
used to aid in the control of the metering arrangement 110 and/or
the heating device 114 if it is determined that fluids are not
present in the humidification region 115 and/or on the heating
surface of heating device 114 when they would otherwise be expected
to be present in such locations (for example, if the metering
arrangement 110 is attempting to meter fluids at a positive rate).
In some configurations, the respiratory therapy system 100 or a
component thereof (including the respiratory humidification system
101) may be configured to generate an alarm or convey a message to
a user (for example, through the user interface 105) upon such a
determination to let the user know that the situation should be
corrected (for example, by refilling the fluid reservoir 106).
[0123] While, in some configurations, a humidification system may
include separate sensors to measure the surface temperature and
other sensors to measure whether the surface is wetted (e.g. fluid
sensors 117, preferably at/near the edge of the heating element
114, which could be temperature sensors but also any other
water-detectors such as a resistive or capacitive sensor), in other
configurations, it is possible to use a control algorithm to set
the surface temperature so as to achieve a desired evaporative
(wetted) area. The algorithm may be based on the system
measurements (gas flow rate, water flow rate, etc., as described
below) and a model (e.g. Dalton's law of evaporation). The fluid
sensors 117 may therefore serve as a safety mechanism to prevent
overfill and as a means of correcting/adjusting the algorithm (by
providing a calibration point where the surface is known to be
saturated). The system may therefore be configured to provide a
modular arrangement, such that a single zone, or selected zones,
could be wet, and that single zone, or those selected zones, could
be powered. Again, this modular system could be controlled using a
control algorithm based on system measurements. Separate sensors
may be used to measure the surface temperature and other sensors to
measure whether the surface is wetted. The fluid sensors 117 may be
used in closed feedback control to control the metering of the
water to the selected zone or zones, or, alternatively, the control
algorithm may use a model to control the metering of the water to
the selected zone or zones, such that the fluid sensors 117 may
serve as a safety mechanism to prevent overfill and as a means of
correcting/adjusting the algorithm (by providing a calibration
point where the surface is known to be saturated).
[0124] In some configurations, the fluid sensor 117 may include a
capacitive fluid sensor. If a heating surface of heating device 114
is present, the capacitive fluid sensor may, for example, include a
pair of conductive sense electrodes positioned on opposing sides of
the heating surface. If the conductive sense electrodes are
connected in a circuit and a voltage is applied, the capacitance of
the circuit will vary depending on the presence or absence of
water. The capacitance of the circuit may be measured using, for
example, a standard AC measuring circuit. Many other sensing
systems, including ultrasonic or optical level sensing systems, may
also be used to determine the presence of fluid.
[0125] Various sensor modules may be utilized by the controller 118
to control various components of the respiratory therapy system 100
and/or the respiratory humidification system 101. The sensor
modules can include one or more sensors for detecting various
characteristics of gases in the gases channel 102 or elsewhere in,
around, or near the respiratory therapy system 100 (including in or
near the gases inlet 123, the gases outlet 127, the patient
interface 122, or at, upstream and/or downstream of the
humidification housing 115), including pressure, gases flow rate,
temperature, absolute humidity, relative humidity, enthalpy, gas
composition, oxygen concentration, carbon dioxide concentration,
ambient temperature, and/or ambient humidity. One or more of these
sensors and/or sensor modules may be used, for example, to
facilitate the control of the flow generator 120 (including control
of the pressure and/or flow rate of gases propelled downstream by
the flow generator 120), control of the heat output of the heating
device 114 (including control of the temperature of the heating
device), and/or control of the metering rate of the metering
arrangement 110 (including control of power and/or current applied
to the metering arrangement 110).
[0126] In some configurations, respiratory activity of a patient
using the respiratory therapy system 100 and/or respiratory
humidification system 101 may be determined, estimated or
calculated using one or more of the sensors or sensing modules
described above or elsewhere in this disclosure. The controller 118
may control various components of the respiratory therapy system
100 and/or the respiratory humidification system 101 such that the
components operate based on a determined respiratory activity or
respiratory state. Illustratively, by way of non-limiting example,
the heating device 114 may be configured to only be energized or to
only vaporize substantial amounts of fluid when the patient is
determined to be inspiring. The metering arrangement 110 may be
configured to only meter fluids when the patient is determined to
be inspiring. The flow generator 120 may be configured to only
generate a flow or to increase the flow generated when the patient
is determined to be inspiring.
[0127] Additionally, the components may be controlled such that
they act in a synchronized manner with the determined instantaneous
respiratory activity or respiratory state of the patient, rather
than being limited to binary states of operation. For example, the
heating device 114 may be configured to, at the start of
inspiration, have a relatively low heat output, increase in heat
output towards a maximum at the peak of inspiration, and then
decrease in heat output towards the end of inspiration. The
metering arrangement 110 may meter a relatively small quantity of
fluid at the start of inspiration, progressively increase the
metering rate towards a maximum at the peak of inspiration, and
then decrease in rate towards the end of inspiration. The flow
generator 120 may be configured to generate or propel gases at a
relatively low flow rate at the start of inspiration, progressively
increase the flow rate of gases towards a maximum at the peak of
inspiration, and then decrease in flow rate towards the end of
inspiration. Other components of one or both of the systems 100,
101 may be controlled similarly.
[0128] In some configurations, the flow generator 120 may, for
example, include a source or container of compressed gas (for
example, air, oxygen, etc.). If a container is used, the container
may include a valve that can be adjusted to control the flow of
gases leaving the container. In some configurations, the flow
generator 120 may use such a source of compressed gases and/or
another gases source in lieu of the blower 121. In some
configurations, the flow generator 120 may use such a source of
compressed gases and/or another gases source together with the
blower 121. The blower 121 can include a motorized blower or a
bellows arrangement or some other structure adapted to generate a
gases flow. In some configurations, the flow generator 120 may draw
in atmospheric gases through the gases inlet 123. In some
configurations, the flow generator 120 may be adapted to both draw
in atmospheric gases through the gases inlet 123 and accept other
gases (for example, oxygen, nitric oxide, carbon dioxide, etc.)
through the same gas inlet 123 or through a different gas inlet
(not shown). In some configurations and as demonstrated in FIG. 1B,
the flow generator 120 may not be present and the respiratory
therapy system 100 may be configured such that only unpressurized
ambient air is humidified and channeled to the outlet/patient
interface 122.
[0129] In some configurations and as demonstrated in FIG. 1E, the
respiratory therapy system 100 and/or respiratory humidification
system 101 may comprise an electromagnetic radiation emitter 151
(positioned in, for example, the gas channel 102). The emitter 151
may comprise an ultraviolet light source (e.g., UV LED), a
microwave emitter, or some other radiation emitter configured to
sterilize the gas flow path. Means for sterilizing the passage
through which gases pass through the respiratory therapy system 100
and/or respiratory humidification system 101 can reduce concerns of
patient infection through the introduction of undesired
pathogens.
[0130] In some configurations and as demonstrated in FIG. 1E, the
respiratory therapy system 100 and/or the respiratory
humidification system 101 can include a gases heating region 132.
The gases heating region 132 can pre-heat gases passing through the
gases channel 102 before the gases reach the humidification housing
115. If the gases are pre-heated before they are humidified, the
efficiency of the humidification may be improved. The gases heating
region 132 can include, for example, one or more resistive heating
wires present in, on, around, or near the inner and/or outer walls
of the gases channel 102. The gases heating region 132 may be
controlled by and in electrical communication with the controller
118, which may control the heat output of the gas heating region
132 using sensor signals in a manner, for example, similar to the
control of the heat output of the heating device 114 as described
elsewhere in this disclosure. The controller 118 can control the
temperature and/or the heat output of the gases heating region 132
such that gases arrive at the gases outlet 127, the patient
interface 122, or at the patient at a temperature of between
approximately 31.degree. C. to approximately 43.degree. C. In some
cases, if the gases heating region 132 is distal from the gases
outlet 127 or the patient interface 122, the gases heating region
132 may heat the gases to a temperature higher than between
approximately 37.degree. C. to approximately 43.degree. C. such
that the gases arrive at the gases outlet 127, the patient
interface 122, or the patient at the desired temperature (due to
temperature loss as the gases pass along, for example, the gases
channel 102). To find the correct temperature, the temperature loss
of gases passing through the respiratory therapy system 100 may be
theoretically or experimentally modeled. Gases in the range of
approximately 25.degree. C. to approximately 43.degree. C., or
approximately 31.degree. C. to approximately 43.degree. C., or
approximately 31.degree. C. to approximately 41.degree. C., or
approximately 31.degree. C. to approximately 37.degree. C. are
generally considered to be comfortable for patient use.
[0131] The gases heating region 132 may include a gases pre-heater
which may include a gases heating element. The gases heating
element may be a printed circuit board. The printed circuit board
may have resistive elements. The gases heating element may be an
etched foil film (see for example, FIGS. 4D and 4E). The gases
heating element may be a heating coil. The gases heating element
may be a PTC ceramic. The respiratory humidification system 100 may
have a temperature sensor. The temperature sensor may be positioned
in the gases channel downstream of the gases pre-heater. A
temperature sensor may be positioned in the gases channel upstream
of the gases pre-heater, either instead of or in addition to the
temperature sensor positioned downstream of the gases pre-heater. A
characterization of the gases heating element may be used to
determine a temperature of the gases. Control of a power level
delivered to the gases heating element may be based on information
provided by a temperature sensor positioned in the gases channel
downstream of the gases pre-heater. Control of the power level
delivered to the gases heating element may be based on information
provided by a gases flow sensor and by a temperature sensor
positioned in the gases channel upstream of the gases pre-heater. A
desired downstream temperature of the gases may be determined based
on an evaporation rate of the water from the heating surface. The
desired downstream temperature of the gases may be set to ensure
that substantially all sensible heat is supplied by the gases
pre-heater. The desired downstream temperature of the gases may be
set to obtain a desired relative humidity level of the gases at the
outlet location. The desired downstream temperature of the gases
may be set to be between 0.degree. C. and approximately 5.degree.
C. above a desired temperature of the gases at the outlet location.
The desired downstream temperature of the gases may be set to be a
desired dew point temperature at the outlet location. The desired
downstream temperature may be set to approximately 25.degree. C. to
approximately 43.degree. C., or approximately 31.degree. C. to
approximately 43.degree. C., or approximately 31.degree. C. to
approximately 41.degree. C., or approximately 31.degree. C. to
approximately 37.degree. C., or approximately 37.degree. C. The
heating surface may include a heating element configured to provide
heat to the heating surface. The heating element may include a
plurality of resistive tracks. The heating element may be a printed
circuit board. The printed circuit board may have resistive
elements. The gases heating element may be an etched foil film (see
for example, FIGS. 4D and 4E).
[0132] FIGS. 2A-2E are functional block diagrams illustrating
various control features of the present disclosure. In some
configurations, the control features described herein allow for
deterministic, or open-loop control of the humidification system.
That is, it is possible to calculate a required flow rate of water
to achieve a certain humidity and dose that amount of water onto a
heater. The heater may evaporate the water dosed thereon to obtain
the desired dew point temperature. Deterministic control, may
preclude the need (that is present in many conventional
humidification system) to measure the outgoing humidity or some
other indirect variable, and then feed this back through a
closed-loop controller to achieve a specific dew point temperature.
In some configurations, the control features described herein allow
for a humidification system that evaporates only the right of
amount of water, or other humidification liquid, at the correct
time to accurately produce the correct humidity. The control
features described herein may be combined or otherwise modified to
be included into any of the respiratory humidification systems
described herein. In some configurations, deterministic control of
the humidity by controlling the water flow to the heater surface
together can allow for heating the heater surface at a relatively
low temperature heater.
[0133] For deterministic control, the water flow rate to be dosed
onto the surface to produce a desired dew point temperature may be
calculated from the equations below.
[0134] Symbols used in the following equations can be understood
with reference to Table 1, which also provides the associated units
for each variable. Additionally, a symbol appended with
subscript(s) b indicates component a at the location b. The
subscripts a, i, s, and o refer to ambient, inlet, surface
(heater-plate), and outlet respectively; the subscripts w, wv, and
air refer to the water, water vapor, and dry air respectively.
Thus, for example, Q.sub.air,i indicates the mass flow rate of air
at the inlet. It should be noted that equations 1-6 are written at
steady state (or, equivalently, under the assumption that all the
variables respond instantaneously).
TABLE-US-00001 TABLE 1 NOMENCLATURE Symbol Meaning Symbol Meaning
Symbol Meaning T Temperature (.degree. C.) p Pressure (Pa) T.sub.d
Dew-point temperature (.degree. C.) Q Mass flow rate h.sub.s
Specific humidity M Molecular weight (kg s.sup.-1) (kg kg.sup.-1)
(g mol.sup.-1) P Power (W) c.sub.p Specific heat .PHI. Relative
humidity capacity (J kg.sup.-1 K.sup.-1) (dimensionless) l Latent
heat of .rho. Density (kg m.sup.-3) m Mass (kg) vaporization (J
kg.sup.-1)
[0135] For deterministic control, the water flow rate to be dosed
onto the surface to produce a desired dew point may be calculated
from the following equations:
h s ( T d , p ) = M wv M air p sat ( T d ) p - p sat ( T d ) Eq . 1
Q air , i = Q i 1 1 + h s ( T d , i , p ) Eq . 2 Q w = Q air , 1 [
h s ( T d , o , p ) - h s ( T d , i p ) ] Eq . 3 ##EQU00001##
[0136] Where h.sub.s is the specific humidity. The evaporation rate
of water from the surface is modelled by the equation:
Q.sub.w=kAf(v)[p.sub.sat(T.sub.s)-.PHI.p.sub.sat(T.sub.di)] Eq.
4
[0137] Where A is the area of the surface, k is a constant to be
determined for any particular surface, and f(v) is an empirically
determined function of gas velocity. The powers required for
evaporation, P.sub.l, and for heating the water, P.sub.w, are given
by:
P.sub.l=l(T.sub.s)Q.sub.w Eq. 5
P.sub.w=c.sub.p,wQ.sub.w(T.sub.s-T.sub.a) Eq. 6
The powers required to air, and the water vapor, P.sub.wv, are
given by:
P.sub.air=c.sub.p,airQ.sub.air,i(T.sub.o-T.sub.i) Eq. 7
P.sub.wv=c.sub.p,wv[Q.sub.w(T.sub.o-T.sub.a)+(Q.sub.in-Q.sub.air,i)(T.su-
b.o-T.sub.i)] Eq. 8
[0138] Equations 1-3 represent the general idea of deterministic or
open loop control of the system: the required amount of water to
achieve a certain dew-point temperature. In the representation
given, provided measurements of Q.sub.air,i, Q.sub.w, T.sub.d,i,
and p, the dew point temperature at the output, T.sub.d,o, can be
fully determined.
[0139] It is possible to make substitutions or rearrangements so
that different inputs or outputs are used (e.g., absolute or
relative humidity at the outlet, or volumetric flow at the inlet or
a different location, etc.). It is possible to avoid making
measurements of some of the input variables. T.sub.d,i and p could
be completely unmeasured if appropriate assumptions could be made
(e.g., a known altitude to compute p) or if the error introduced
were acceptable (e.g., if T.sub.d,i T.sub.d,o, its effect is small.
It may not be possible to proceed without measurements of
Q.sub.air,i or Q.sub.w since they are dominant factors. It is
possible that some of the measurements are not made directly. For
example, it is not necessary to measure T.sub.d,i directly, instead
a sensor measurement of T.sub.i and .PHI..sub.i (RH at inlet), can
be used to compute T.sub.d,i. The same can be said of the other
variables.
[0140] Equations 1-6 assume that the pressure is constant
throughout the system, although it is possible to revise the
equations to avoid this assumption. Although the pressure can vary
significantly through the entire system (e.g., the pressure drop
across the cannula), the pressure in the vicinity of the
evaporation surface and sensors is usually very close to constant,
rendering such corrections unnecessary, in some configurations.
[0141] Equation 4 can be used to compute the area and temperature
requirements for the evaporative surface and to model the system
for control response. It is based on Dalton's law of evaporation,
and unlike the previous equations it is semi-empirical. Therefore,
other equations could be used that are not completely equivalent.
Specifically equation 4 can be used to compute T.sub.s for a given
A, or vice versa, both for design and control of the system, or to
compute an independent check on Q.sub.w. In general, equation 4
implies that the temperature of the incoming gas does not
significantly impact the evaporation rate. However, there are two
mechanisms by which it does, which can be important in some
situations. First, the incoming temperature changes the relative
humidity, .PHI.. This may be significant if T.sub.d,o is close to
T.sub.s. The second, and more important mechanism, is in the
exchange of heat. If T.sub.i<T.sub.d,o, the water vapor must
heat the air, and if there is not enough sensible heat in the water
vapor to increase the gas temperature above T.sub.d,o, some of it
must condense to release latent heat. This can be a major
complication when considering the net evaporation rate; although
the surface can easily drive the evaporation, the cool air rapidly
condenses the vapor. This may be avoided by increasing the surface
temperature. This problem is further exacerbated by the nature of
the evaporation. The water cannot be immediately evaporated into
the entire gas, as a boundary layer exists near surface, so the
water must evaporate into this and then diffuse across gas (in
laminar flow) or be mixed (in turbulent flow). The vapor in the
boundary layer can be saturated at the surface temperature,
inhibiting further evaporation, so one of the main limiting factors
is not the evaporation rate at the surface, but the rate at which
the vapor is diffused or advected from the boundary layer. Thus the
heat exchange between the vapor and air occurs at a boundary and
the vapor must be hotter to prevent condensation (since the bulk of
the latent heat is not accessible). These effects interfere both
with the physical ability of the system to evaporate the water and
the validity of the evaporative model.
[0142] Equations 5 and 6 are used to compute the power requirements
and to model the system for control response. These equations make
the assumption of 100% efficiency, which cannot be exactly true,
but testing has indicated that the systems disclosed herein are
very efficient. In a system where this is not true, appropriate
corrections would have to be made, at the expense of accuracy and
simplicity. Equations 5 and 6 can be used to compute an independent
check on the power inputs (e.g., to limit enthalpy). They could
also be used for control, for example, for open loop control or as
a corrective feedback.
[0143] Although these equations have been used directly with
acceptable results, implementing a robust and stable system may
require further consideration as equations 1-6 are only accurate at
steady state. For example, considering the water flow rate: a
finite volume of water must reside on the evaporative surface,
therefore, the evaporation rate of water does not immediately equal
the flow rate of water, since this hidden "buffer variable" can
cause a temporary difference.
[0144] Considering the finite water film thickness as an
instructive example, if the mass of water on the surface is
m.sub.w=A.rho..sub.wt.sub.w, where t.sub.w is the water thickness
(assumed constant), then to a first approximation (assuming that
the heater-plate only supplies power for evaporation):
.rho. w t w dA dt = Q w - kAf ( v ) [ p sat ( T s ) - .phi. p sat (
T d , i ) ] Eq . 9 1 c p , s m s dT s dt = P s - .rho. w kAf ( v )
[ p sat ( T s ) - .phi. p sat ( T d , i ) ] Eq . 10
##EQU00002##
[0145] Equation 9 is obtained by considering the difference in
water arriving at the surface as compared with that which is
evaporating, and equation 10 is obtained, similarly, by considering
the power delivered to the surface less that consumed by
evaporation. Thus, the surface temperature and evaporative area are
coupled in a time-varying and non-linear fashion, and a simplistic
controller that relies only on the principles of equations 1-3
directly will produce the desired humidity only if and when the
above system stabilizes. This highlights the important possibility
of instability, even though they are only first order systems when
considered individually, when combined, they could oscillate or be
unstable.
[0146] Given, that for water, .rho..sub.w=1000 kg m.sup.-3 and
l=2.26 MJ kg.sup.-1, if it is assumed (based on reasonable figures
obtained by testing a prototype system) k=1 .mu.L min.sup.-1
cm.sup.-2 kPa.sup.-1, t.sub.w=10 .mu.m, Q.sub.w=0.9 mL min.sup.-1,
=15.degree. C., .PHI.=75%, f(v)=1, m.sub.s=0.025, c.sub.p,z=400 J
kg.sup.-1 K.sup.-1, and P.sub.s=34 W operating at the point A=30
cm.sup.-2 and T.sub.s=70.degree. C., then it is possible to
linearize p.sub.sat(T.sub.s) to 1353T.sub.s-63.28, from which the
system can be represented as:
dA dt = f ( A , T s ) = 90 - A [ 0.1353 T s - 6.456 ] Eq . 11 dT s
dt = g ( A , T s ) = 340 - A [ 0.5097 T s - 24.32 ] Eq . 12
##EQU00003##
The Jacobian of the system is then:
J = [ f A ( A , T s ) f T s ( A , T s ) g A ( A , T s ) g T s ( A ,
T s ) ] = [ 6.456 - 0.1353 T s - 0.1343 A 24.32 - 0.5097 T s -
0.5097 A ] Eq . 13 ##EQU00004##
[0147] Or, at the operating point:
J 0 = [ - 3.015 - 4.059 - 11.36 - 15.29 ] Eq . 14 ##EQU00005##
[0148] The eigenvalues of J.sub.0 are -18.3 and 0.0006, indicating
that the system is unstable. The reason for this instability is
that the system is driven at constant power--any mismatch will
result in an excess or deficit of water, completely saturating or
drying the surface respectively. By introducing a proportional
feedback on the power term, the expression for the surface
temperature becomes:
dT s dt = g ( A , T s ) = 340 - .alpha. ( T s - T 0 ) - A [ 0.5097
T s - 24.32 ] Eq . 15 ##EQU00006## Then:
J = [ - 3.015 - 4.059 - 11.36 - .alpha. - 15.29 ] Eq . 16
##EQU00007##
[0149] The characteristic polynomial is then
.lamda..sup.2+.lamda.(.alpha.+18.31)+3.015(.alpha.+15.29)-46.11=0,
leading to the eigenvalues:
.lamda. = - ( .alpha. + 18.31 ) .+-. .alpha. 2 + 24.56 .alpha. +
335.3 2 Eq . 17 ##EQU00008##
[0150] From which it can be shown that for .lamda.<0
(stability), .alpha.>0.0033. So even a small amount of feedback
will stabilize the system, at least at this operating point.
[0151] Since the area is difficult to measure directly it is worth
examining whether this is an observable state. Since the system is
non-linear this is difficult to assess, but the equation for
T.sub.s can be re-expressed as:
1 c p , s m s d T s dt = P s - .rho. w ( Q w - .rho. w , t w dA dt
) Eq . 18 ##EQU00009##
[0152] Then rearrange to obtain:
.rho. w t w dA dt = Q w + .rho. w [ 1 c p , s m s dT s dt - P s ]
Eq . 19 ##EQU00010##
[0153] This, informally, indicates that the area is an observable
state, with the other measurements all being known, instead of
attempting to sense the area at some limit, the equation can be
integrated over time to compute A continuously. Of course, it may
still be desirable to design the system with the ability to sense
when the surface is saturated, but such a model allows us to
control the area smoothly, rather than bouncing off a hard
limit.
[0154] A number of factors limit the control response time. The
first fundamental limit is the dynamics of the evaporation surface
during a transient. This is important largely for enthalpic
considerations, and also when implementing breath-by-breath
humidity control.
[0155] If the surface temperature is held constant, the evaporative
area may be changed to control humidity. It can grow actively (by
pumping water) but only shrink passively (by evaporation), thus
limiting the downwards response to the time it takes to evaporate
the "reservoir" of water. For example, if the air flow rate is
dropped from 20 L min.sup.-1 to 10 L min.sup.-1, the initial
evaporation rate will be 0.7 mL min.sup.-1 for nominal conditions
(37.degree. C. dew-point temperature, etc.). If the area is
initially 20 cm.sup.2, and drops to 10 cm.sup.2 (to maintain the
dew-point temperature), and water film is 10 .mu.m thick, 0.1 mL of
extra water must be evaporated to shrink the area. Even if the pump
switches off, it will take a minimum of 8.6 s to shrink (0.1 mL at
0.7 mL min.sup.-1) minimum because as the area shrinks the
evaporation rate drops off too, and if the pump switches on during
that time it will slow the response further.
[0156] If the evaporative area is held constant, the surface
temperature must change, and the limitation is again passive
cooling. A 40 cm.sup.2 plate with a 10 .mu.m film holds 0.4 g of
water; the latent power required for evaporation at 10 L min.sup.-1
could be about 13 W, and 33.5 J is required lower water temperature
by 20.degree. C., corresponding to 2.6 s, assuming, similar to the
former scenario, that the heater-plate switches off during this
time and ignoring the fact that the evaporation rate will decrease
as the surface cools.
[0157] 10 .mu.m can be a difficult water thickness to achieve, even
with the micro-channels; for a wicking paper or fabric a more
reasonable figure would be in the range of 0.1 mm or more,
resulting in proportionately longer response times.
[0158] In some configurations, designing a breath-by-breath type
humidifier requires a thin film of water; otherwise the surface
temperature must be traded off against response time (a higher
surface temperature to yield a small evaporation area). In the
extreme, such a trade-off results in a very hot surface
(>100.degree. C.) which boils the water off and introduces
issues of patient safety and materials compatibility.
[0159] Another factor that influences the response time is the
thermal mass and resistance of the heater-plate. The thermal mass
of the heater-plate contributes in the same way as the water,
requiring time to cool passively by evaporation. An increased
thermal resistance means a higher heater element temperature, which
exacerbates the effect of thermal mass (by requiring larger
temperature changes).
[0160] Equations 1-3 compute the water flow rate assuming all of
the water evaporates. In some configurations, the goal of the
control system is to ensure that it all does evaporate, to improve
the transient response, and to control other aspects of the system.
In some configurations, this may require as many independent inputs
as there are independent outputs, otherwise the system will not be
controllable. In the most basic scenario, in which it is only
desired to control the humidity at the outlet, in which case one
relevant control input, such as water flow rate, would suffice.
However, if it is also desired to control the temperature at the
outlet, another control input is required--for example, this could
be the power delivered to the heater-plate. However, if it is
desired to keep the heater-plate temperature within certain bounds,
this would require another control input. The additional input
could be to add a secondary heater to pre-heat the incoming
air.
[0161] In some configurations, the concept of pre-heating the air
may be important. Although a goal of the system is to determine the
humidity at the outlet, being able to determine the temperature is
also desired to prevent condensation. As explained above, the power
delivered to the heater-plate would allow us to do this, but using
heat from the evaporation surface convolves the two problems
(evaporating water and heating air). Pre-heating the air separates
these two problems and leads to several advantages, including:
[0162] Easier control: since the latent heat and sensible heat are
added independently, they can be controlled almost independently. A
combined control system would be more complex and less robust.
[0163] Improved evaporation: as explained above with reference to
the evaporation equation, evaporating water into a warmed gas
(i.e., T.sub.i>T.sub.d,o) is easier to do and model than
evaporating into a cool gas (i.e., T.sub.i<T.sub.d,o).
[0164] Lower surface temperatures: following on from the improved
evaporation, a warmed gas allows lower surface temperatures, and
the surface temperature/area can be controlled independently.
[0165] Power: with the air being pre-heated, the burden on the
heater-plate will be reduced, which yields the knock-on effects of
requiring less temperature to drive the heating and better
efficiency since the temperature is lower.
[0166] Enthalpy/safety: the bulk of the enthalpy in the system is
supplied as latent heat in the water vapor, with the heat being
added separately it is easier to ensure that the enthalpy is kept
within limits while still being able to ensure that the gas at the
exit is not saturated (to prevent condensation). In a system
without preheating, the only way to limit the enthalpy is to limit
the total power, without any direct control over whether this
reduces the sensible rather than latent heat (and thus resulting in
condensation).
[0167] In a similar vein, the system may also comprise pre-heating
the water flow. This could be done by either heating the water
source, heating the water feed line, or having a special zone on
the heater-plate (e.g., the water wicks over the water pre-heater
before reaching the evaporative region, or the initial region has a
higher power density).
[0168] In some configurations, pre-heating the gas allows the
latent heat and sensible heat to be provided to the system
separately. The sensible heat may be provided by the pre-heater,
while the latent heat may be provided by the water vapor. The
result is that the heater plate may be kept at a lower temperature,
which has advantages, such as patient safety. More specifically,
safety is enhanced by lower temperatures as overshoots in delivered
enthalpy are reduced, for example, a surface at 37.degree. C. will
not generate vapor at a dew point temperature of greater than
37.degree. C., and hence no harm will ever come to the patient by
way of burns.
[0169] One ancillary result of separating out the latent and
sensible heats is that it becomes desirable to keep the heated
portion of the evaporative surface saturated--if an unheated
portion of the heating surface is exposed it will contribute to
heating the air, which again convolutes the control task. For that
reason it may be desirable to include a method of sensing when the
water has reached the end of the surface, either by a physical
means (temperature drop, shorting a conductor, capacitance), or the
models formerly presented. This is also useful as a safety
mechanism to prevent the system from flooding.
[0170] FIG. 2A illustrates an overall control topology of the
respiratory humidification system 101 which illustrates in
simplistic form a basic control principle in which a known amount
of air plus a known amount of water results in a known humidity. By
controlling the water and temperature it is possible to effectively
control the evaporative rate of the water from the heating surface
into the gas. In some configurations, it is not necessary to
measure the evaporation flow rate as it is merely a function of
other input variables. For example, it is possible to set the flow
rate of water based on the desired evaporation rate. In some
configurations, it is possible to calculate the evaporation that is
actually occurring based on the surface temperature and power as a
check. In the illustrated control topology, water is input into a
liquid flow conditioner and routed to a heater-plate controller.
Air and/or gas are received at an inlet for conditioning and
testing before being routed to a heater-plate controller. The
heater plate-controller computes the dew point temperature
T.sub.d,o, from the known (for example, determined either directly
or indirectly through sensors) parameters of the incoming water and
air and/or gas.
[0171] The inlet conditioning and testing represented in FIG. 2A
can include an inlet sub-system at or near the gases supply
location including one or more inlet sensors configured to measure
inlet gases ambient humidity, inlet gases flow, inlet gases
temperature, and a pressure level of the gases channel. An inlet
gases heater may also be provided at or near the gases supply
location to pre-heat the gases to a desired (predetermined)
temperature as they enter and pass through the gases channel such
that the gases arrive at the humidification location at a desired
temperature. By separately pre-heating the gases, the energy
delivered to the heating element in the humidification region can
be used to vaporize the humidification fluid, thereby separating
the functions of heating the gases (by supplying sensible heat from
the gases pre-heater) and humidifying the gases (by providing
latent heat from the heating element) in the gases channel.
Advantageously, such a separation of functions permits the heating
element to be operated at lower power levels corresponding to lower
temperature levels which results in safer and more efficient
operation of the respiratory humidification system. Moreover, the
temperature of the heated gases can be altered quickly, such that
the system becomes more responsive to changes than a system which
heats an entire fluid reservoir, or a significant volume in excess
to that required.
[0172] The liquid flow controller represented in FIG. 2A can
include a humidification fluid flow control sub-system that
monitors and controls the rate at which fluid is metered to the
humidification region and, more specifically, to the heating
element. A fluid flow sensor measures the flow of the
humidification fluid and provides the measurement to a fluid flow
controller. The controller compares the measured fluid flow rate
with the desired fluid flow rate (which may be predefined,
estimated, or deterministically derived), and adjusts the power
level to the metering arrangement accordingly. In some embodiments,
the humidification fluid is pre-heated before being delivered to
the heating element for vaporization to reduce the amount of latent
heat required by the heating element to vaporize the humidification
fluid. Various modes of pre-heating the humidification fluid can be
used, including heating the fluid reservoir, heating the fluid feed
line, or having a special fluid pre-heating zone on the heating
element before reaching an evaporation region. In accordance with
certain embodiments, a check valve is disposed within the fluid
feed line prior to the metering arrangement to prevent back-flow of
the humidification fluid. In some embodiments, a safety valve is
disposed within the fluid feed line prior to the metering
arrangement to release pressure in the line due to pump failure,
along with other possible causes.
[0173] The heater-plate controller represented in FIG. 2A can
include a heated surface sub-system that monitors and controls the
temperature of the heating element. A heating surface includes an
area over which humidification fluid is distributed and vaporized
by heat energy provided by the heating surface. A wicking element
is provided over at least a portion of the heating surface. The
wicking element is configured to receive and distribute a layer of
the humidification fluid, the layer having a thickness, over the
one or more portions of the heating surface that delivers the heat
to vaporize the fluid. The wicking element can include paper,
fabric, micro fiber, or microstructures, including microfluidic
channels. The heating surface can include a heating plate, a
resistive heating plate, or a circuit board having resistive
tracks, to name a few. In some embodiments, the heating surface is
a circuit board that is over-molded with a thermoplastic material.
In some embodiments, multiple heating surfaces, or zones, may be
used. Each heating surface may be maintained at the same or at
different temperature levels. A heating surface temperature sensor
is in thermal contact with the heating surface and in communication
with a heating surface temperature controller. A surface heater,
also in communication with the surface temperature controller, is
configured to control the temperature of the heating surface, or
multiple heating surfaces or zones, depending on the configuration
of the heating surface.
[0174] FIGS. 2B-2D illustrate configurations of various control
sub-systems that operate together with the configuration of an
overall controller of FIG. 2E to deterministically control
humidification systems as described herein.
[0175] FIG. 2B is a functional block diagram of an inlet and
pre-heating control sub-system in accordance with an embodiment of
the present disclosure. The pre-heater is not required, but may be
included in some configurations. The inlet sensors can be replaced
with equivalent measurements or appropriate assumptions and/or
calculations as explained above. In some configurations, T.sub.i
could also be controlled in an open loop fashion using the power
equations. In some configurations, the ambient humidity T.sub.d,i
can be sensed anywhere prior to humidification, although prior to
the pre-heater is preferable. If placed after the pre-heater it
could be merged with the inlet sensor T.sub.i.
[0176] The inlet and pre-heating control sub-system of FIG. 2B can
measure the air and/or gas coming into the system using inlet
sensors (for example, those sensors described above in reference to
FIG. 1E) to determine the ambient humidity T.sub.d,i, the incoming
gas flow rate, Q.sub.i, and the incoming gas pressure, P. As
described above, the gas can then be heated with a pre-heater,
although this is not necessary in all embodiments. An inlet
temperature sensor downstream of the pre-heater measures the
temperature, T.sub.i, of the heated gas and provides the
measurement to the pre-heat controller. The pre-heat controller may
compare T.sub.i with a calculated temperature, T.sub.i,set,
determined by the overall controller of FIG. 2E below and send
signals to the pre-heater to adjust the temperature
accordingly.
[0177] FIG. 2C is a functional block diagram of a water flow
control sub-system in accordance with an embodiment of the present
disclosure. In some configurations, the flow sensor and feedback
(the liquid flow controller) can be omitted if a sufficiently well
characterized and stable pump is used. The sub-system may also
include a water pre-heater, as described elsewhere herein. A check
valve may also be used prior to the pump to prevent back-flow of
water. A safety valve may also be used prior to the pump if the
pump is prone to failure. The system could also comprise a passive
water meter and a flow sensor, for example, a pressure feed, such
as a gravity feed, and a proportional valve instead of the
pump.
[0178] In the configuration of FIG. 2C, water enters a water pump
from a water source. The water pump may pump the water into the
system. The water pump may be any of the pumps described above. A
water flow sensor is positioned downstream from the pump and
measures the flow rate of the water, Q.sub.w, which is output to a
liquid flow controller. The liquid flow controller provides a
feedback loop whereby the water pump is adjusted based on a
comparison of Q.sub.w, and a calculated water flow rate,
Q.sub.w,set. The calculated water flow rate, Q.sub.w,set is
determined by the overall system controller of FIG. 2E as described
below.
[0179] FIG. 2D is a functional block diagram of a heated surface
control sub-system in accordance with an embodiment of the present
disclosure. Although only one surface is shown, multiple surfaces
could be used. There could be multiple surface heating zones and
multiple temperature sensors. In some configuration there are two
heating zones and temperature sensors. An outlet temperature sensor
could also be included to assist in control. The surface
temperature sensor could be replaced or supplemented by using the
resistance or other characterization of the surface heater. For
example, in the current implementation the resistance of the copper
tracking indicates the average heater temperature. In some
configurations, it may be preferred that the surface temperature
sensor give as close as possible measurement of the true surface
temperature, which would benefit the evaporation models described
above.
[0180] In the illustrated configuration of FIG. 2D, water flow and
gas flow, for example, the outputs of the subsystems of FIGS. 2B
and 2C, are routed over a surface. The surface may be a heating
source as described throughout this application. The surface
includes one or more surface temperature sensors which provide
measurements of the surface temperature, T.sub.s, to a surface
temperature controller. The surface temperature controller provides
a feedback and control mechanism whereby a surface heater, in
thermal communication with the surface is adjusted. The surface
temperature controller may compare T.sub.s to a calculated surface
temperature, T.sub.s,set. The calculated surface temperature,
T.sub.s,set is determined by the overall system controller of FIG.
2E below.
[0181] FIG. 2E is a functional block diagram of overall controller
in accordance with an embodiment of the present disclosure. FIG. 2E
shows an example of an overall controller that ties the above three
controllers of FIGS. 2B-2D together. As shown in FIG. 2E, in some
configurations, there is no closed loop feedback on the outlet
dew-point temperature, as the figure indicates that the control is
simply an open-loop set-point based on the inputs. The input
variables are split into two groups to signify that one group,
T.sub.d,i, Q.sub.i, p, and T.sub.d,o,set, is fundamental to the
controller, while the other group can be omitted in simpler
controllers. In the most basic controller, the three output
variables may be set according to the fundamental system equations,
in other words, Q.sub.w,set can be determined by equations 1-3,
T.sub.i,set can be set to the desired output to the desired gas
inlet temperature, and T.sub.s,set can be determined by equation 4.
In some configurations, P.sub.air, P.sub.s, and any other extra
variables are not used or only used as system checks.
[0182] FIG. 3A is a schematic perspective view of an example
integrated humidification system 300 in accordance with one
embodiment of the present disclosure. FIG. 3B is a schematic
vertical cross-section view showing an air flow of the
humidification system 300. FIG. 3C is a schematic vertical
cross-section view showing a water flow of the humidification
system 300. FIG. 3D is a schematic horizontal cross-section view of
the humidification system 300. In some configurations, the
humidification system 300 can be a stand-alone humidifier using
ambient air and relying on normal patient respiration to generate a
flow of gases. In some configurations, the humidification system
300 can be an add on to a respiratory circuit for use with any flow
generation system, for instance with a ventilator. FIGS. 3E-3F show
the humidification system 300 installed for use with a flow
generation system in an integrated system.
[0183] As shown in FIG. 3A, the humidification system 300 includes
a housing 303, a gases inlet 331, a gases outlet 333. The gases
inlet 331 is configured to receive gases into the humidification
system 300. In some configurations, the gases inlet 331 is adapted
to connect with a gases inlet tube, flow generation system, or
other gases sources. The gases outlet 333 is configured to deliver
humidified gases out of the humidification system 300 and to a
patient. In some configurations, the gases outlet 333 is adapted to
connect to a gases outlet tube, for example, a respiratory tube
connected to a patient interface (for example, a cannula). The
humidification system 300 also includes, one or more water inlets
308 configured to allow water received from a water flow controller
into the humidification system 300. In some embodiments, the
humidification system 300 includes an inlet and an outlet for
water. In some embodiments, the humidification system 300 only
includes inlets, as all water input into the system is evaporated
to humidify the gas. The humidification system 300 also includes an
electrical connector 351 for supplying power to the system and for
communicating with various components thereof. The humidification
system may also serve to provide power to the heated breathing tube
and in-built sensors, such that the design acts as a conduit for
downstream system components that require power or
communications.
[0184] FIG. 3B is a schematic vertical cross-section view showing
an air flow of the humidification housing of FIG. 3A. As shown in
FIG. 3B the housing 303 defines a gases flow path 338. In this
configuration, the gases enter the humidification system 300 at the
gases inlet 331 and are directed downward by an interior wall 337.
An opening 338 at the bottom of the interior wall 337 allows the
gases to pass to the other side of the interior wall 337 where the
gases are directed upwards and out of the humidification system 300
at the gases outlet 333. The housing 303 may include internal
baffles 305. Along the flow path 335 the gases are humidified by
vaporized water evaporating off of the heating element 314. The
heating element 314 can be partially seen through the gases inlet
331 in FIG. 3A and a cross-sectional view of the heating element
314 is visible in FIGS. 3C and 3D. An example configuration of the
heating element 314 is described as heating element 400 in
reference to FIGS. 4A-4C below.
[0185] FIG. 3C is a schematic vertical cross-section view showing a
water flow of the humidification housing of FIG. 3A. In the
illustrated configuration, water entering at the inlets 308 is
distributed through channels 318 so as to contact the heating
element 314. In the illustrated configuration, the channels 318 are
partially located within the interior wall 337.
[0186] FIG. 3D is a schematic horizontal cross-section view of the
humidification housing of FIG. 3A. As shown in FIG. 3D, the heating
element 314 divides the housing 303 in a first direction and the
internal wall 337 divides the housing 303 in a second direction,
orthogonal to the first direction. Thus, the heating element 314 is
immersed in the flow path. In some configurations this is preferred
as it to effectively doubles the surface area, provides a dramatic
increase in power efficiency, makes the surface temperature reading
more accurate, and allows the housing 303 to be kept relatively
cool (and therefore, safe). In the embodiment of FIG. 3D, baffles
305 are included in the air flow path.
[0187] FIGS. 3E-3F show the humidification system 300 installed for
use with an embodiment of flow generation system 390. The flow
generation system 390 can include a gases inlet 391 for connecting
to an external gases source and a gases outlet 393 that can be
adapted to connect to the gases inlet 331 of the humidification
system 300. In the illustrated configuration, the flow generation
system 390 includes a plurality of input controls 395. In some
configurations, the flow generation system 390 can be an Airvo
available from Fisher & Paykel Healthcare of Auckland, NZ.
[0188] FIG. 4A is a schematic perspective view of a heating element
400 in accordance with an embodiment of the present disclosure.
FIG. 4B is a schematic top view of the heating element 400. FIG. 4C
is a partial schematic top view of the heating element 400. In some
configurations, the printed circuit board heating element 400 may
be used as the heating device 314 of the humidification system 300
described above in reference to FIGS. 3A-3F, or as any other
heating device described herein (for example, the heating device
114 of FIGS. 1A-1E).
[0189] The heating element 400 may include a printed circuit board
401 for providing heating. The printed circuit board 401 may have a
plurality of resistive tracks 411. The resistive tracks 411 may be
copper. An outer surface of the heating element 400 may include a
wicking surface. The wicking surface may be provided by an
over-molding on the printed circuit board 401. The over-molding may
have micro-channels in it (the micro-channels are described in
greater detail below). The over-molding may be a thermoplastic
material. The heating element 400 may have modular zones. For
example, in the illustrated embodiment, the resistive tracks 411
are divided into three modular zones, 403, 405A, 405B. In some
configurations, the modular zones 405A and 405B are connected in
series. In some configurations, the heating element 400 may have a
first zone configured to pre-heat the water and a second zone
configured to vaporize the water as will be described in reference
to FIG. 4C. A single zone could be wet, and that single zone could
be powered. This gives flexibility in the Controller.
Alternatively, the entire heater surface can be powered, and the
entire heater surface can be kept wet rather than operating the
isolated zones.
[0190] As shown in FIG. 4B, the heating element 400 may include
electrical contacts 457 (for either power transfer or
communication) that can used to power additional components of a
respiratory humidification system. For example, electrical contacts
457 may provide power to a heated breathing tube (HBT). As another
example, the electrical contacts 457 may be used to power or
communicate with additional sensors (e.g., temperature sensors,
pressure sensors, or other sensors as described herein).
[0191] The micro-channels may provide a wicking surface. The
wicking surface may work synergistically with the pre-heating of
the gas to allow the heating surface to be maintained at a
relatively low temperature. This is because lower temperatures
require larger surface areas to generate the requisite vapor flux,
and larger areas require more efficient mechanisms for spreading
the liquid so as to recruit more of the heated surface for
evaporation.
[0192] In some configurations, micro-channels may be small scale
(for example, micro-scale) grooves formed on a surface. The surface
may be either flat or curved. In some configurations, the
micro-channels may be highly ordered. In some configurations, the
micro-channels are arranged in a pattern (see, for example, FIG.
5A, showing one example of a grid structured pattern, and FIG. 5B,
showing one example of a radial pattern; these examples are
non-limiting and other patterns are possible). In some
configurations, the purpose of the micro-channels is to spread a
liquid across a surface thereby increasing its surface area for a
given volume. In some configurations, the micro-channels have a
substantially uniform cross-sectional profile along their length.
For example, the micro-channels may have a circular or
semi-circular, elliptic or semi-elliptic, rectangular, triangular
(V-shaped), or trapezoidal cross-sections. In some configurations,
the micro-channels may include rounded edges and/or corners. In
some configurations, the micro-channels may have a variable
cross-sectional profile that changes over the length of the
micro-channel. For example, a micro-channel can become deeper
and/or wider along its length. The micro-channels may be "open"
micro-channels, which include at least one side open to the
environment. For example, a micro-channel may be a V-shaped groove
formed into a surface, and liquid in or on the micro-channel may be
open to the environment at at least the open side of the V. Such
micro-channels may facilitate evaporation of the liquid as the open
side of the micro-channel provides a place for the evaporated
liquid to go. For example, an open side of an open micro-channel
may open into a gas passageway. Liquid on or in the micro-channel
may evaporate, and the evaporated liquid may be entrained in the
gases flowing through the gas passage way. In some configurations,
the micro-channels may have a depth (which can also be considered a
height) that ranges from between 1-1000 .mu.m. In some
configurations, the depth of a micro-channel is between 20-200
.mu.m. In some configurations, the width of a micro-channel can be
between 1-1000 .mu.m. In some configurations, the width of a
micro-channel is between 20-200 .mu.m. In some configurations, the
tilt of the side walls of a micro-channel can range from 0-45
degrees. As used herein, the tilt of the sidewalls is measured
between the wall and vertical (in other words, between the wall and
an axis extending normal to the surface in which the micro-channel
is formed). That is, a wall tilt of 0 degrees represents a totally
vertical wall. For example, if the side walls of a micro-channel
include a 0 degree wall tilt, the micro-channel may be
substantially square shaped, and the top of the square may be open.
As another example, if the side walls of a micro-groove include a
45 degree wall tilt, the micro-channel may be substantially
V-shaped if the tilted side wall directly intersect, or
substantially trapezoidally shaped if the side walls intersect a
horizontal flat bottom surface of the micro-channel, and the top of
the micro-channel may be open. In some configurations, the tilt of
the side walls of a micro-channel can range from 5-20 degrees. The
micro-channels can spread the liquid by wicking (capillary action)
or, in some situations, by gravitational flow of the liquid through
the channels. In some configurations, the micro-channels may be
defined by protrusions extending above a surface, where the
micro-channel is formed by the space between the protrusions.
[0193] In some configurations, the heating element 400 includes one
or more sensors for measuring the temperature of the surface of the
heating element 400. The one or more sensors may be thermistors
421. In some configurations, the heating surface temperature may be
calculated at least in part, by determining a resistance level or
other characteristic of the heating element 400. The resistance
level of the heating element may be used to indicate an average
temperature of the heating surface. The heating element may be
arranged to deliver a higher power density in a specified region of
the heating element as compared to a power density delivered to
other regions of the heating element. The specified higher density
region of the heating element may be located at an outlet of a
water supply to the heating surface. The specified higher density
region of the heating element may be located at a water pre-heating
area on the heating surface. The respiratory humidification system
may include a temperature sensor at the outlet location of the
gases channel, which may act as a safety check.
[0194] The resistive tracks 411 and/or sensors, for example, the
thermistors 421 may be electrically connected to electrical
contacts 452 positioned on a contact region 451 of the printed
circuit board 401. The contact region 451 can be positioned so as
to mate with the electrical connector 351 of the humidification
system 300.
[0195] In some configurations, the heating element 400 is
configured to provide some "pre-heating" to the water. This can be
accomplished, in some configurations, simply by increasing the
track (and therefore power) density at the area(s) where the water
is introduced. This zone would have the power density increased by
the extra amount required to heat the water within a small area.
For example, as shown in FIG. 4C, if water is introduced to the
heating element 400 at location 408 and the surface of the heating
element is configured to wick the water across the heating element
400 in the direction of the arrows, the heating element 400 can
include a greater density of resistive tracking 411 at locations at
and around location 418 (in other words, near location 408 where
the water is introduced) and a lower density of resistive tracking
411 at locations around location 428 (in other words, distanced
from location 418).
[0196] The power required for latent and sensible heating are,
approximately, P.sub.L=L{dot over (m)} and P.sub.s=c.sub.p{dot over
(m)}(T.sub.s-T.sub.w) (where L is the latent heat of vaporization,
c.sub.p is the specific heat capacity of water, {dot over (m)} is
the water flow rate, T.sub.s is the surface temperature, and
T.sub.w is the water temperature). The ratio of sensible to latent
heat is then
P S P L = c p m . ( T s - T w ) L m . = c p ( T s - T w ) L .
##EQU00011##
Because the water flow rate cancels out, this is constant enough
for us to design a zone of power density some fixed ratio higher
than the rest of the plate and achieve the desired effect. This is
not always precise because T.sub.s-T.sub.w can change by a
significant amount, but, in some configurations, there is no need
for it to be overly precise.
[0197] Pre-heating of the water is generally a less of important
aspect of the system than pre-heating the air, because it is a
smaller component of the total heat required (about half compared
to the air) and has less impact on the evaporation and little
impact on the outgoing gas conditions. Still, in some
configurations the heating the water consumes up to 9% of the power
in the system, so it is not insignificant. Without pre-heating, the
impact this has is that there will be a temperature gradient across
the surface as the water heats, which reduces the evaporation rate
in those areas and makes the evaporation models more complex.
[0198] Another option for providing pre-heating for the water is to
include a heater in the water supply line (i.e., between the
pump/flow sensor and coupling to the surface), this could be a PTC
(positive temperature coefficient) element, or a heating coil, or
any other heater, in thermal contact with the water flow, which
heats the water to the same temperature as the surface of the
heating element 400.
[0199] While the heating element 400 has been described above in
reference to heating water, a similar heating element 400 may also
be used to heat gas, for example, as a gas pre-heater.
[0200] FIG. 4D illustrate a top schematic view of two alternative
embodiments of heating element 400A, 400B in accordance with an
embodiment of the present disclosure. The heating elements 400A,
400B may include an etched foil film 401A, 401B. The etched foil
film 401A, 401B may include a plurality of resistive tracking 411A,
411B. The heating elements 400A, 400B may each also include
electrical connections 451A, 451B.
[0201] FIG. 4E illustrates an embodiment of the heating element
400A in a rolled configuration.
[0202] In some configurations, a humidification system includes
various components, for example, a distribution and/or wicking
system, to deliver the humidification fluid to the heating element.
In some configurations, it is preferred to deliver water to the
heating element surface across the entire surface, in other words,
to saturate it. It is important to realize that the
distribution/wicking system needs to be able to sustain a flow
rate. In some configurations, it is not enough to have water
distribution over the surface, if that distributor cannot wick the
water fast enough to keep the heating element saturated. In some
configurations it is preferred to sustain a liquid flow rate of up
to 5 mL min.sup.-1.
[0203] A distribution and/or wicking system may include two parts:
the wicking surface, which distributes the water across the
surface, and the coupling, which connects the water supply to the
surface at one or more points. The coupling can also do some of the
water distribution (e.g., by coupling the water over a region or
line rather than at a point). The technologies that can be used for
both coupling and wicking include, but are not limited to:
fabrics/papers (for example, Kimberly-Clark Hydroknit);
micro-channels; hydrophilic coatings (for example, Lotus Leaf
Coatings HydroPhil); capillary/contact wicks (custom designs)
and/or porous polymers (for example, Porex fibres)
[0204] The requirements for the coupling depend heavily on the
nature of the surface. If the surface is isotropic (wicks the same
in all directions) then the coupling only needs to couple the water
to the surface at a single point. If the surface is anisotropic
(depends on direction) some additional features will be required to
account for this, i.e., it will need to actually direct the water
over some region to ensure that the wicking is even. It also
depends on the hydrophobicity of the surface--a hydrophilic surface
readily absorbs the water so the coupling only needs to bring the
water into loose contact with the surface, but a hydrophobic
surface requires a coupling which needs to "force" the water
against the surface to prevent it from merely "rolling" off, or
provide an intermediate mechanism with a greater affinity to the
humidification fluid, at the interface with the surface.
[0205] For example, the fabric of the wicking surface may be very
close to isotropic and essentially hydrophilic so that a point
source is sufficient. Bringing a tube that delivers the liquid into
contact with the surface may be sufficient to generate flow (up to
a certain surface size and depending on orientation). In some
configurations, and on some substrates such as silicone, the
wicking surface comprises micro-channels that may only wick in the
direction of the channels, and that possess poor hydrophilicity.
When using surfaces that wick in one direction and/or are not very
hydrophilic it may be beneficial to have a distributor that holds
the water in place until it is drawn away by the micro-channels,
and that also may direct it along the other (e.g., perpendicular)
direction.
[0206] In some configurations, a wicking surface can be a
micro-channeled surface, which can include parallel channels in
only one direction; a small set of distribution channels connected
to a larger number of main channels; and/or channels distributed
radially from a single point, among other possible configurations.
A wicking surface may also be an absorptive fabric or paper, a
super-hydrophilic coated surface, or, a thin porous media.
[0207] In some configurations, a coupling can be a length of
wicking media bonded to the surface, which could include a porous
or fibrous polymer; a fabric/paper, and/or a hydrophilic section. A
coupling could also be a second surface forming an acute angle with
the wicking surface, which draws the water by capillary action,
which could include a flat slide, such as a glass slide, against
the surface, at low angle, or alternatively a circular bar against
the surface, forming a low contact angle at the point of contact. A
wicking surface could also include a cavity in contact with the
surface, which could include a flat face with a water-supplied
cavity facing directly, and pressed against, the surface a C-shaped
tube connected along an edge of the surface. In some
configurations, any of these coupling methods can be a line source
(useful if the surface is anisotropic, e.g., the micro-channels, in
which case it is perpendicular to the surface's main wicking
direction; for example, a thin section of porous polymer laid
across the channels); a point source (useful if the surface is
isotropic or contains built-in water distribution); a radial
source; or multiple line/point/radial sources (which may be useful
if there are two separate wicking surfaces (e.g., sides of the
heater plate) or the wicking speed of the surface is insufficient
to saturate the surface from a single source).
[0208] Specific examples of wicking surfaces and/or couplings will
now be described by way of example and not limitation.
[0209] FIG. 5A is a schematic diagram illustrating a
grid-structured micro-channel water distribution pattern 500a in
accordance with an embodiment of the present disclosure. The
distribution patter 500a includes a water input area 501a, first
micro-channels 502a, and second micro-channels 503a. The first
micro-channels 502a can serve as distribution channels which
distribute the water to the second micro-channels 503a. The second
micro-channels 503a distribute the water across the surface. The
grid-structured micro-channel water distribution pattern 500a can
be applied to the surface of the heating element 400. The
grid-structured micro-channel water distribution patter 500a is one
example of a wicking element as described herein. In some
configurations, the first micro-channels 502a move the water in a
first direction and the second micro-channels 503a move the water
in a second direction orthogonal to the first direction. However,
the grid-structured micro-channel water distribution pattern 500a
can be modified to include first micro-channels 502a oriented at
other positions relative the second micro-channels 503a. In some
configurations, the grid-structured micro-channel water
distribution pattern 500a includes only first micro-channels 502a
or only second micro-channels 503a. In general, grid-structured
micro-channel water distribution pattern 500a is a system where the
micro-channels distribute the water: the water is supplied to
several distribution channels, which splits off onto many channels
that wick across the bulk of the surface.
[0210] FIG. 5B illustrates a radial micro-channel water
distribution pattern 500b in accordance with an embodiment of the
present disclosure. FIG. 5B is a still image taken from a video
showing the radial micro-channels wicking a fluorescent dye. The
fluorescent dye was dropped onto the center point 501b and wicked
outwards by the channels. The radial micro-channel water
distribution pattern 500b includes micro-channels that spread
radially from a center point 501b where the water is introduced. In
some configurations, to keep the channel density the same the
micro-channels may split as they radiate from the center point
501b. The radial micro-channel water distribution pattern 500b may
also include circumferentially extending micro-channels.
[0211] FIG. 6A is a schematic perspective axially sectioned view of
a respiratory humidification system 600 including a glass slide
coupling 631 in accordance with an embodiment of the present
disclosure. FIG. 6B is a schematic perspective sectioned side view
of the respiratory humidification system 600 of FIG. 6A. FIG. 6C is
a schematic side view of the respiratory humidification system 600
of FIG. 6A. FIG. 6D is a schematic perspective assembled axial view
of the respiratory humidification system 600 of FIG. 6A. The glass
slide coupling 631 may be considered a contact-angle/capillary line
distributor.
[0212] In the illustrated embodiment, the respiratory
humidification system 600 includes a gas inlet 601 and a gas outlet
603 with a gas flow channel 605 extending there between. As gases
move from the inlet 601 to the outlet 603 they are humidified in
the flow channel 605. The respiratory humidification system 600
also includes a micro pump 621 adapted to supply water from a water
source into the system. The water is delivered from the micro pump
621 into the flow channel 605 via water pipe inlet 621. The
respiratory humidification system further includes a glass slide
coupling 631, which is held at an acute angle 625 (see FIG. 6C)
against the surface 633 of the heating element 614. The surface 633
includes micro-channels extending in the direction of the arrows
and perpendicular to the glass slide 631. The water supply tube 623
is placed at the intersection of the glass slide coupling 631 and
surface 633. Because of the acute angle 625 (see FIG. 6C) between
the glass slide coupling 631 and surface 633, the water is wicked
along the intersection, and then wicked across the surface 633 by
the micro-channels. Notably, the couple 600 only exposes the heater
element 614 on one side; however, in some configurations the design
could be modified to expose the heater element 614 on both sides.
The respiratory humidification system 600 may also include a
honey-comb gas diffuser 645 in the gas flow path 605.
[0213] FIG. 7 is a schematic perspective diagram of a distribution
tube coupling 700 wrapped over an edge of a heating element 714 in
accordance with an embodiment of the present disclosure. This
drawing shows a tube 701 being used as a coupling or distributor.
The tube 701 clips over the heating element 714, and then water is
pumped into the tube 701. As the tube 714 fills, water is drawn
across the heating element 714. Notably, the tube coupling 700 can
distribute water onto both the top surface 714a and the bottom
surface 714b of a heating element 714.
[0214] FIG. 8 is a schematic diagram of a porous media coupling 800
in accordance with an embodiment of the present disclosure. The
coupling 800 is shown as a hashed strip extending along the surface
of a heating element 814. The coupling may be, for instance, a
piece of fabric. The water is dosed onto the fabric to allow the
water to be distributed along the .mu.-channels. In some
configurations, the coupling 800 may be a thin, porous media, such
as a porous or sintered polymer.
[0215] FIG. 9A is a schematic perspective view of a radial coupling
900 in accordance with an embodiment of the present disclosure.
FIG. 9B is a schematic perspective sectional view of the radial
coupling 900 of FIG. 9A. The radial coupling 900 may be considered
a cavity/face coupling. In general, the coupling 900 pushes water
against the surface of a heating element. In some configurations,
the coupling 900 is configured to work with surfaces that are
sufficiently hydrophilic or absorptive. In some configurations, the
coupling 900 is adapted so that, when there are multiple outlets,
the outlets are balanced, e.g., that the water doesn't simply favor
one path and flow entirely in that direction.
[0216] The coupling 900 receives a supply of water at an inlet 901
and supplies it radially at the center of a heating element and to
both sides. As shown in FIG. 9B, water flows down from the inlet
901 through a series of channels 903 to the heating element (not
shown). The coupling 900 can include multiple outlets 905. In some
configurations, the coupling 900 also delivers water through a
central channel 907 that extends through a hole in the heating
element to a similar system on the other side. In FIG. 9B arrows
are added to illustrate the flow of water.
[0217] FIG. 10A is a schematic perspective view of a sandwich
coupling 1000 in accordance with an embodiment of the present
disclosure. FIG. 10B is a schematic perspective sectioned view of
the sandwich coupling 1000 of FIG. 10A. The coupling 1000 includes
a body 1001 with one or more protruding sections 1003. A water
outlet 1005 may be positioned on one of or each inward facing
surface of the protruding sections 1003. As shown in FIG. 10B, the
coupling 1000 includes a water inlet 1011 and internal channels
that deliver water to the water outlet 1005. Arrows have been added
to FIG. 10B to show the flow of water. A heating element (as shown
in FIGS. 10C and 10D) may be positioned between the protruding
sections 1003 and receive water from the outlets 1005.
[0218] FIG. 10C is a schematic sectioned view of the sandwich
coupling 1000 of FIG. 10A attached to a humidification housing 303
in accordance with an embodiment of the present disclosure. FIG.
10D is a schematic sectioned view of the sandwich coupling 1000 of
FIG. 10A attached to a humidification housing 303 that includes a
printed circuit board heating element 400, in accordance with an
embodiment of the present disclosure. The housing 303 may be
similar to the housing 303 of the humidification system 300
described in reference to FIGS. 3A-3D and the heating element 400
may be similar to the heating element 400 described in reference to
FIGS. 4A-4C.
[0219] Embodiments of humidification systems as described herein
have been tested and yield satisfactory results in terms of
attainable dew-point temperature and control accuracy. For example,
a dew point temperature, T.sub.d=37.degree. C. can be achieved for
gas flows up to approximately 45 L min.sup.-1 and at sea-level,
dropping to approximately T.sub.d=35.degree. C. at a flow of 60 L
min.sup.-1. This is consistent with the maximum power attainable
with the specific PCB design utilized.
[0220] FIGS. 11A and 11B show the accuracy performance of a
respiratory humidification system in accordance with an embodiment
of the present disclosure. The system was operated under open-loop
control mode as described above across a range of flows and
dew-points, with the dew-point temperature being measured
independently at the outlet, and the dew-point temperature
predicted by the system being calculated by inverting Eq. 3:
T d , o = h s - 1 ( Q w Q air , i + h s ( T d , i p ) , p ) Eq . 20
##EQU00012##
[0221] FIG. 11A is a plot of a dew point temperature accuracy of
the tested respiratory humidification and shows the measured dew
point temperature plotted against the predicted dew point
temperature. Two points where the heater-plate saturated due to
under-power are not visible on the plot, but can be ignored since
this condition is detectable. Most of the points are within
.+-.2.degree. C. of measured dew-point temperature. FIG. 11B is a
plot of a dew point temperature error across gas flow rate of the
tested respiratory humidification system.
[0222] FIG. 12A is a schematic perspective view of an alternative
embodiment of a humidification system 1200 in accordance with an
embodiment of the present disclosure. FIG. 12B is a schematic
cross-section view of the humidification system 1200 of FIG. 12A.
As shown in FIG. 12B, the humidification system 1200 includes a top
layer and a bottom layer. FIG. 12C is a schematic cross-section
view showing the top layer of the humidification system 1200 of
FIG. 12A. FIG. 12D is a schematic cross-section view showing the
bottom layer 1200 of the humidification system of FIG. 12A.
[0223] The humidification system 1200 includes a gas inlet 1201 and
a gas outlet 1202. The humidification system can include a blower
1231 configured to move gas from the gas inlet 1201 to the gas
outlet 1202. The inlet 1201 and the outlet 1202 may be connected by
a channel. A flow sensing device 1251 and a gas sensing device 1281
may be located within the channel. The humidification system 1200
includes power/communication connectors 1203.
[0224] The humidification system 1200 can include a heater surface
cavity 1211 configured to receive a heating element as described
elsewhere herein. The heating surface cavity also includes a water
dosing section 1261 which may be configured with a coupling to
apply water to the heating element. The water dosing section 1261
may be in fluid communication with a liquid flow module 1241, a
water inlet 1242, a check valve 1243, and micro pump 1244. The
humidification system 1200 may also include an electronics cavity
1271 accessible via a port 1272.
[0225] FIG. 13 is a schematic view of an inline humidification
system in accordance with one an embodiment of the present
disclosure. The inline humidification system of FIG. 13 includes a
pre-heater and a heater (the heater represented by the heated
surface) in a gas passageway between an inlet and an outlet. A
heater controller is connected to both the pre-heater and the
heater. The pre-heater heats the gas before the gas reaches the
heater. The heater is also connected to a water controller which
dispenses water onto the heater surface. The amount of water
applied by the water controller and the amount of heat applied by
the heater controller may be deterministically controlled according
to the principles described herein to vaporize the water and
humidify the gas. The outlet of the system may be connected to a
heated breathing tube (HBT), i.e. an inspiratory or delivery tube.
The necessary power and sensing systems for the HBT may be provided
integrally by the humidification system, or provided separately or
externally. The advantages of including the humidification system
as part of the delivery tube is simplicity, reduction in cost, and
quality control by ensuring that it is replaced as necessary.
[0226] The foregoing description details certain embodiments of the
systems, devices, and methods disclosed herein. It will be
appreciated, however, that no matter how detailed the foregoing
appears in text, the systems, devices, and methods may be practiced
in many ways. As is also stated above, it should be noted that the
use of particular terminology when describing certain features or
aspects of the invention should not be taken to imply that the
terminology is being re-defined herein to be restricted to
including any specific characteristics of the features or aspects
of the technology with which that terminology is associated.
"Approximately," or similar terms used herein, should be understood
to mean within an acceptable tolerance of the specified item, for
example, in reference to .degree. C., approximately can mean within
an acceptable tolerance, such as, for example, within .+-.3.degree.
C.
[0227] It will be appreciated by those skilled in the art that
various modifications and changes may be made without departing
from the scope of the described technology. Such modifications and
changes are intended to fall within the scope of the embodiments.
It will also be appreciated by those of skill in the art that parts
included in one embodiment are interchangeable with other
embodiments; one or more parts from a depicted embodiment may be
included with other depicted embodiments in any combination. For
example, any of the various components described herein and/or
depicted in the Figures may be combined, interchanged or excluded
from other embodiments.
* * * * *
References