U.S. patent application number 15/087522 was filed with the patent office on 2016-10-06 for ventilator.
The applicant listed for this patent is Invent Medical Corporation. Invention is credited to Samuel M. Chang.
Application Number | 20160287824 15/087522 |
Document ID | / |
Family ID | 57015034 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160287824 |
Kind Code |
A1 |
Chang; Samuel M. |
October 6, 2016 |
Ventilator
Abstract
This invention provides ventilators that provide superior
air-oxygen mixing and gas delivery. The ventilators that supply a
gas mixture to the lungs of a subject. The gas mixture comprises a
first gas (e.g. oxygen) and a second gas (e.g. ambient air). The
ventilators comprise a first gas inlet, a second gas inlet, flow
modulator of the first gas, a flow modulator of the second gas, a
junction configured to mix the first gas and the second gas, a
patient interface configured to deliver the gas mixture to a
subject, a pressure sensor, a plurality of flow sensors comprising
at least a first flow sensor and a second flow sensor, and at least
one controller configured for obtaining data from the pressure
sensor and flow sensors and controlling the flow modulators to
provide a gas mixture having a target pressure and a target oxygen
content.
Inventors: |
Chang; Samuel M.; (Poway,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Invent Medical Corporation |
San Diego |
CA |
US |
|
|
Family ID: |
57015034 |
Appl. No.: |
15/087522 |
Filed: |
March 31, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62143026 |
Apr 3, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M 2202/0291 20130101;
A61M 2230/432 20130101; A61M 2230/04 20130101; A61M 2230/205
20130101; A61M 2202/0241 20130101; A61M 2205/50 20130101; A61M
2230/30 20130101; A61M 2230/30 20130101; A61M 2205/3355 20130101;
A61M 2016/0027 20130101; A61M 2230/005 20130101; A61M 2230/005
20130101; A61M 2230/005 20130101; A61M 2230/005 20130101; A61M
2230/005 20130101; A61M 2230/005 20130101; A61M 2230/005 20130101;
A61M 16/0051 20130101; A61M 16/026 20170801; A61M 16/12 20130101;
A61M 16/208 20130101; A61M 2230/04 20130101; A61M 2230/06 20130101;
A61M 16/0066 20130101; A61M 2230/205 20130101; A61M 16/1005
20140204; A61M 2230/50 20130101; A61M 2016/1025 20130101; A61M
2230/10 20130101; A61M 16/204 20140204; A61M 2016/0036 20130101;
A61M 2016/0039 20130101; A61M 2230/432 20130101; A61M 2202/0208
20130101; A61M 2230/06 20130101; A61M 16/202 20140204; A61M 16/1055
20130101; A61M 16/205 20140204; A61M 2230/10 20130101; A61M 2230/50
20130101; A61M 16/0057 20130101; A61M 2202/0266 20130101; A61M
2205/7518 20130101; A61M 2205/3331 20130101 |
International
Class: |
A61M 16/00 20060101
A61M016/00; A61M 16/12 20060101 A61M016/12; A61M 16/04 20060101
A61M016/04; A61M 16/20 20060101 A61M016/20; A61M 16/06 20060101
A61M016/06; A61M 16/10 20060101 A61M016/10; A61M 16/08 20060101
A61M016/08 |
Claims
1. A ventilator system comprising: an air inlet connected to a
first gas line; an oxygen inlet connected to a second gas line; an
air pump connected to a third gas line downstream of a junction of
the first gas line, the second gas line and the third gas line; an
oxygen control valve and an oxygen flow sensor both connected to
the second gas line upstream of the junction and downstream of the
oxygen inlet; a mixed gas flow sensor and a mixed gas pressure
sensor both connected to the third gas line downstream of the pump
and upstream of a patient interface; and a controller operably
connected to the air pump and the oxygen control valve, and further
configured to receive measurement signals from the oxygen flow
sensor, the mixed gas flow sensor and the mixed gas pressure
sensor.
2. The ventilator system of claim 1, wherein the controller is
configured to modulate a control signal for the oxygen control
valve based on measurement signals received from the oxygen flow
sensor and the mixed gas pressure sensor.
3. The ventilator system of claim 1, wherein the controller is
configured to modulate a control signal for the pump based on
measurement signals received from the oxygen flow sensor and the
mixed gas pressure sensor.
4. The ventilator system of claim 1, wherein the controller is
configured to modulate a control signal for the oxygen control
valve based on measurement signals received from the oxygen flow
sensor, the mixed gas pressure sensor and the mixed gas flow
sensor.
5. The ventilator system of claim 1, wherein the controller is
configured to modulate a control signal for the pump based on
measurement signals received from the oxygen flow sensor, the mixed
gas pressure sensor and the mixed gas flow sensor.
6. The ventilator system of claim 1, wherein an exhalation valve is
connected to the third gas line downstream of the pump and upstream
of the patient interface.
7. The ventilator system of claim 6, wherein the controller is
configured to modulate a control signal for the exhalation valve
based on measurement signals received from at least one of the
mixed gas pressure sensor and the mixed gas flow sensor.
8. The ventilator system of claim 7, wherein the controller is
configured to identify an inhalation phase and an exhalation phase
based on the measurement signals, and the controller is configured
to modulate a control signal for the exhalation valve so that it
closes the exhalation valve during an inhalation phase, and opens
the exhalation valve during an exhalation phase.
9. The ventilator system of claim 1, wherein the controller is
configured to receive a target pressure.
10. The ventilator system of claim 9, wherein the target pressure
is manually set by a user.
11. The ventilator system of claim 9, wherein the target pressure
is calculated based on a preset pressure and a pressure measured
from the mixed gas pressure sensor.
12. The ventilator system of claim 9, wherein the controller is
configured to calculate a pressure error based on a difference
between the target pressure and the pressure measured from the
mixed gas pressure sensor.
13. The ventilator system of claim 12, wherein the pressure error
is used to modulate a control signal of at least one of the pump
and the oxygen control valve.
14. The ventilator system of claim 1 further comprising: a bacteria
filter positioned in the third gas line downstream of the pump and
upstream of the patient interface.
15. The ventilator system of claim 1 further comprising: a pressure
regulator connected to the second gas line between the oxygen inlet
and the junction.
16. The ventilator system of claim 1 further comprising: a high
pressure oxygen source connected to the oxygen inlet.
17. The ventilator system of claim 1 further comprising: a low
pressure air source connected to the air inlet.
18. The ventilator system of claim 1, wherein the pump is a low
pressure variable speed blower.
19. The ventilator system of claim 1, wherein the pump is
configured to pressurize downstream gas to a pressure of no more
than 140 mbar.
20. The ventilator system of claim 1, wherein the pump is
configured to pressurize downstream gas to a pressure of no more
than 70 mbar.
21-69. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to ventilators.
BACKGROUND
[0002] A ventilator delivers a flow of gas such as air, which is
usually pressurized, to the airway of a patient to assist in or
substitute a patient's breathing. Ventilators can be configured to
operate cyclically, for example, by providing gas to the patient
during an inhalation phase and returned from the patient during a
subsequent exhalation phase. Some ventilators mix oxygen and air
for inspiration such that the patient receives a mixed gas with a
target oxygen content greater than ambient air.
[0003] Ventilators can be designed to be leak-free or to have
intentional leaks. In any design, accurate metering of gas and
air/oxygen mixing can be dramatically affected by an unintentional
leak. Most often, the exhalation valve on a leak-free ventilator is
provided on an exhalation limb of the ventilator at the patient
interface such that expiration gas exits through the exhalation
valve. This second limb adds to the bulk, weight, and production
cost of ventilators. Some single-limb ventilators vent the
expiration gas to atmosphere after it has traveled upstream in the
inspiration line as well as through the exhalation port proximal to
the patient. One of the shortcomings of these single-limb
ventilators is cross contamination of the ventilator as well as
high exhalation resistance.
[0004] In addition to being designed as leak-free, ventilators with
the most accurate mixing of air and oxygen and delivery of
pressurized gas to the patient have used a source of high pressure
oxygen source and a source of high pressure air. The high pressure
sources are either pressurized tanks or the high pressure lines of
a hospital via a compressor. These types of ventilators are
typically not mobilized for extended durations given the size of
the air tank that would be required for sustained ventilation.
[0005] Some ventilators circumvent the need for hospital line or
air tank air by providing a compressor or other air pump as the
source of pressurized air. Air pump ventilators that have been able
to produce satisfactory air/oxygen mixing and delivery requirements
use positive displacement pumps such as roots blowers, screw
compressors, piston compressors and scroll compressors, which are
typically configured to produce high pressure air. However, these
positive displacement pumps are typically noisy, causing discomfort
and disturbance to patients and support personnel.
[0006] One alternative approach has been to use low pressure
dynamic pumps. These pumps can operate with lower noise output but
have generally failed to provide high pressure and air-oxygen
mixing requirements. Some of these ventilators combine low flow
oxygen with low pressure air while others combine high pressure
oxygen with low pressure air. The ventilators that provide low flow
oxygen fail to meet the oxygen content for certain patients that
require high oxygen mixing. The ventilators that provide high
pressure oxygen and low pressure air often have failed to provide a
combination of pneumatic hardware and control algorithm that yield
satisfactory accuracy for real-time mixing.
[0007] Philips Respironics has produced one ventilator in its BiPAP
Vision line that has combined a high pressure oxygen source with a
low pressure centrifugal dynamic pump. While this ventilator can
produce a mixture having a satisfactory pressure, it has failed to
produce superior accuracy of air/oxygen mixing. Further, to achieve
pressure targets, this ventilator uses what Philips calls an
in-line flow restrictor and a pressure regulation valve, neither of
which is closed completely during inspiration or exhalation.
Philips does not teach an exhalation valve that is closed during
the inhalation phase. Additionally, Philips does not teach a
ventilator comprising a mixing chamber or a ventilator comprising a
pump downstream of an air/oxygen junction.
[0008] Rossen et al. (U.S. Pat. No. 5,823,186) describe a
respirator having an inspiration line fed by an air line having a
compressor and an oxygen line, wherein the oxygen line comprises a
metering unit and the air line comprises a flow sensor. Rossen et
al. do not teach a ventilator having any of the following features:
a dynamic pump, a proportional valve in the oxygen line, or a
single limb configuration with an exhalation valve and a check
valve upstream of the exhalation valve.
[0009] Hete et al. (US 20070044799) describe a gas delivery system
that generates a pressurized flow of breathable gas and includes a
primary gas delivery system and a supplemental gas delivery system.
The primary gas can be air. The supplemental gas can be oxygen. The
primary gas can be drawn in in by a pressure generator. Hete et al.
do not teach a ventilator having any of the following features: a
dynamic pump, a pressure sensor downstream of an oxygen/air
junction, a check valve downstream of a pump in an air line, or a
check valve upstream of an exhalation valve.
[0010] Von Blumenthal et al. (U.S. Pat. No. 8,047,205) describe a
gas mixing device for respirators. The gas-mixing device has a
storage tank into which compressed air and oxygen can be introduced
by dispensing valves and also has a blower which draws in gas from
the environment to the storage tank. Von Blumenthal et al. do not
teach a ventilator having any of the following features: a dynamic
pump, a flow sensor in an oxygen line, a flow sensor in an air
line, a pressure sensor downstream of the storage tank, a flow
sensor downstream of the storage tank, a proportional valve on an
air line or an oxygen line which feed a storage tank.
[0011] Richardson et al. (U.S. Pat. No. 6,279,574) describe a
ventilator having a reservoir that receives compressed air and
oxygen. Richardson et al. do not teach a ventilator having any of
the following features: a pump that conveys air to the reservoir, a
flow sensor downstream of the reservoir, a controller that
calculates flows of air and oxygen to obtain a target oxygen
content and pressure.
[0012] Ahmad (US 20120006326) describes a ventilator having a first
pathway and a second pathway that merge to provide a mixed gas.
Ahmad does not teach a ventilator having any of the following
features: a dynamic pump, a flow sensor downstream of the pump, a
check valve in an air line, or an exhalation valve in a mixed gas
line downstream of a pump.
[0013] What is need in the art is an economical pump-based
ventilator that can be coupled to a high pressure oxygen source and
produces oxygen-air mixing and volume- or pressure targeting with
superior accuracy.
SUMMARY OF THE INVENTION
[0014] This invention provides ventilators that supply a gas
mixture to the lungs of a subject. The gas mixture comprises a
first gas (e.g. oxygen) and a second gas (e.g. ambient air). The
ventilators comprise a first gas inlet, a second gas inlet, flow
modulator of the first gas, a flow modulator of the second gas,
feed lines that transmit respective gases from the first inlet and
the second inlet to a junction, a patient interface configured to
deliver the gas mixture to a subject, a pressure sensor, a
plurality of flow sensors comprising at least a first flow sensor
and a second flow sensor, and at least one controller configured
for obtaining data from the pressure sensor and the flow sensors
and controlling the flow modulators to provide a gas mixture having
a target pressure and a target oxygen content. The flow modulator
of the first gas is optionally a valve. The flow modulator of the
second gas is optionally a valve or a variable speed pump. In
general, gas flows from upstream components (e.g. gas inlets) to
downstream components (e.g. patient interface) during patient
inhalation. Optionally, the system is configured to allow gas to
flow from downstream components (e.g. patient interface) to
upstream components (e.g. exhalation valve) during patient
exhalation.
[0015] A ventilator of the invention optionally comprises: [0016]
a. an oxygen inlet; [0017] b. an air inlet; [0018] c. a junction
downstream of the oxygen inlet and the air inlet; [0019] d. a
patient interface downstream of the junction; [0020] e. a first
conduit configured to convey oxygen from the oxygen inlet to the
junction (`oxygen line`); [0021] f. a second conduit configured to
convey air from the air inlet to the junction (`air line`); [0022]
g. a third conduit configured to convey a gas mixture from the
junction to the patient (`mixed gas line`), wherein the gas mixture
comprises oxygen from the oxygen line and air from the air line;
[0023] h. a pump, wherein the pumped gas at least comprises the
air; [0024] i. an air flow modulator, wherein the air flow
modulator is configured to modulate at least the flow of air
through the air line, optionally wherein the pump is a variable
speed pump and the air flow modulator comprises the pump; [0025] j.
an oxygen flow modulator, wherein the oxygen flow modulator
comprises a first control valve comprised by the oxygen line
(`oxygen control valve`); [0026] k. a first flow sensor comprised
by the oxygen line (`oxygen flow sensor`); [0027] l. a second flow
sensor, wherein the second flow sensor is comprised by the air line
or the mixed gas line; and [0028] m. a controller configured to:
[0029] i. obtain feedback from the first flow sensor and the second
flow sensor; and [0030] ii. control the oxygen control valve and
the air flow modulator, e.g. to obtain a target oxygen content.
[0031] Optionally, the ventilator comprises a first pressure sensor
comprised by the mixed gas line and the controller is configured to
obtain feedback from the first pressure sensor and control the air
flow modulator and optionally the oxygen control valve, e.g. to
obtain a target pressure.
[0032] In a first aspect of the invention, the pump is a variable
speed pump (e.g. variable speed blower) controlled by the
controller and comprised by the air line. Optionally, the second
flow sensor is comprised by the air line (`air flow sensor`), e.g.
downstream of the pump. Optionally, the ventilator further
comprises an exhalation valve, wherein the exhalation valve is
downstream of the pump (e.g. upstream of the junction) and is
controlled by the controller, and wherein the ventilator further
comprises a first check valve downstream of the pump and upstream
of the exhalation valve. Optionally, the air flow sensor is
downstream of the exhalation valve.
[0033] In a second aspect of the invention, the pump is a variable
speed pump (e.g. blower) controlled by the controller and comprised
by the mixed gas line. Optionally, the ventilator further comprises
a check valve comprised by the air line (`air line check valve`).
Optionally, the second flow sensor is comprised by the mixed gas
line (`mixed gas flow sensor`), e.g. downstream of the variable
speed pump. Optionally the oxygen control valve is a proportional
valve such as a proportional solenoid valve.
[0034] In a third aspect of the invention, the junction comprises a
mixing chamber and a second control valve, wherein the second
control valve is a proportional valve comprised by the mixed gas
line downstream of the mixing chamber (`mixed gas control valve`),
wherein the mixed gas control valve is controlled by the
controller. Optionally, the second flow sensor is a flow sensor
comprised by the air line (`air flow sensor`). Optionally, the
mixing chamber is a fixed volume chamber. Optionally, the mixing
chamber (e.g. fixed volume chamber) comprises a volume of at least
about 300 ml, e.g. about 300 ml to about 5000 ml. Optionally, the
mixing chamber comprises a pressure sensor. Optionally, the
controller is configured to pressurize the mixing chamber to a
pressure of about 10 mbar to about 30 mbar above the target
pressure. Optionally, the mixing chamber comprises an oxygen
sensor. Optionally, the mixed gas line comprises a flow sensor, a
pressure sensor, or both. Optionally, the ventilator comprises an
exhalation valve downstream of the mixing chamber and upstream of
the patient interface (e.g. wherein the exhalation valve is
controlled by the controller) and the ventilator further comprises
a check valve is downstream of the mixing chamber and upstream of
the exhalation valve. Optionally, the controller is configured to
control the flow of at least one of air through the air line and
oxygen through the oxygen line. Optionally, the oxygen line
comprises a check valve (e.g. downstream of the oxygen control
valve) and the air line comprises a check valve (e.g. downstream of
the pump). Optionally, the pump is a variable speed pump or the
ventilator comprises a third control valve, wherein the third
control valve is comprised by the air line and is downstream of the
pump (e.g. a constant speed pump).
[0035] The present invention contemplates ventilators according to
any aspect of the invention. For example, the invention
contemplates a ventilator according to the first aspect or,
alternatively, according to the second aspect. A ventilator
according to the third aspect of the invention can optionally be
provided, e.g. in conjunction with, or as an alternative to, the
first aspect of the invention or the second aspect of the
invention.
[0036] In any aspect of the invention, the pump is optionally a
blower such as a pump comprising an impeller (`fan blower`). For
example, the pump can be a fan blower, wherein the fan blower is a
small pump and/or a low pressure pump.
[0037] In any aspect of the invention, the ventilator comprises at
least one conduit through which gas flows downstream during an
inhalation phase and upstream during an exhalation phase
(`bidirectional conduit`). Optionally, the bidirectional conduit
comprises an exhalation valve wherein the exhalation valve is
downstream of the pump, upstream of the patient interface, and
controlled by the controller, and optionally, the ventilator
further comprises a check valve downstream of the pump and upstream
of the exhalation valve. Optionally, the exhalation valve is
upstream of the second flow sensor. Optionally, the exhalation
valve is a control valve, wherein the controller is configured to
open the exhalation valve during an exhalation phase and close the
valve during an inhalation phase.
[0038] In any aspect of the invention, the mixed gas line
optionally comprises a pressure sensor.
[0039] In any aspect of the invention, the oxygen line optionally
comprises a pressure regulator, wherein the pressure regulator is
upstream of the oxygen control valve.
[0040] In any aspect of the invention, the oxygen flow sensor is
optionally downstream of the oxygen control valve.
[0041] In any aspect of the invention, the patient interface
optionally comprises a mask, a mouth piece, a nasal prong, or a
patient tube such as a tracheal tube (e.g. an endotracheal tube or
a tracheostomy tube).
[0042] In any aspect of the invention, the controller is optionally
configured to use one or more feedback control loops. For example,
the controller is optionally configured to use a cascaded feedback
control loop comprising an outer feedback loop and one or more
inner feedback loops, wherein the command of the outer feedback
loop is used to provide a target of the one or more inner feedback
loops.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 depicts a ventilator of the invention
[0044] FIG. 2 depicts a ventilator of the invention.
[0045] FIG. 3 depicts a ventilator of the invention.
[0046] FIG. 4 depicts a ventilator of the invention.
[0047] FIG. 5 depicts a pressure feedback control loop used by
controller useful in a ventilator of the invention.
[0048] FIG. 6A depicts an air flow feedback control loop used by an
air flow controller useful in the present invention.
[0049] FIG. 6B depicts an oxygen flow feedback control loop used by
an oxygen flow controller useful in the present invention.
[0050] FIG. 7 depicts a feedback control loop used by a controller
useful in the present invention.
[0051] FIG. 8 depicts a feedback control loop used by a controller
useful in the present invention.
[0052] FIG. 9 depicts a feedback control loop used by a controller
useful in the present invention.
[0053] FIG. 10 depicts a feedback control loop used by a controller
useful in the present invention.
[0054] FIG. 11 depicts a feedback control loop used by a controller
useful in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0055] As used here, the following definitions and abbreviations
apply.
[0056] "Examplary" (or "e.g." or "by example") means a non-limiting
example.
Controller
[0057] A ventilator of the present invention comprises a controller
configured for receiving data (`feedback`) from sensors and
controlling flow modulators to produce a gas mixture exhibiting one
or more parameter targets. The parameter targets of the gas mixture
at least a target oxygen content (e.g. FiO.sub.2). Optionally, the
parameter targets of the gas mixture comprise a target pressure, a
target volume, a target flow or a combination thereof.
[0058] In general, a controller can be configured to control (i.e.
send data or analog signals to and/or receive data or analog
signals from) output devices and input devices (collectively
referred to as `I/O devices`) or another controller of the
ventilator. Output devices can include, e.g. flow modulators and a
user interface (`UI`). Input device devices can include, e.g.
sensors and a UI.
[0059] Any controller is useful in the present invention.
Optionally, the controller comprises a microcontroller such as a
microprocessor or an analog controller. A controller of the present
invention can optionally comprise or be connected to one at least
one non-volatile memory device having a compilation of executable
instructions (`module`) configured for causing at least one
processor to control I/O devices.
[0060] The controller can optionally be a single controller
connected to and configured to control the I/O devices or, or
alternatively, can comprise a collection of interacting controllers
in communication with each other or with a common controller.
Optionally, the controller comprises, as interacting controllers, a
gas mixture controller, an air flow controller, and an oxygen flow
controller. For example, the controller can comprise a plurality of
interacting controllers that are independent hardware (e.g.
microprocessors) in communication with each other, independent
modules that which reference each other, or subroutines of a single
module.
[0061] Optionally, a controller is configured to provide a command.
The command can comprise, e.g. a digital command or an analog
command. A digital command (e.g. a command comprising a parameter
target a target flow, a target volume or a target pressure) can
optionally be a command provided (e.g. input in) to an algorithm or
another controller that produces one or more commands or outputs
based on the digital command. An analog command (e.g. a command
comprising a voltage provided to a flow modulator) can optionally
be an analog signal provided to one or more flow modulators. As
used herein, commands are sometimes referenced by the gas parameter
they are configured to target and that is optionally measured as
feedback for the controller to correct the command. For example, a
pressure feedback loop can be a feedback loop configured to produce
a target pressure (e.g. a constant pressure setpoint), e.g. by
commanding a flow modulator (e.g. as depicted in FIG. 8). As
another example, a pressure feedback loop can be a feedback loop
configured to produce a target pressure by commanding a target flow
(e.g. as depicted in FIG. 5). As another example, a flow feedback
loop can be a feedback loop configured to produce a target flow,
e.g. by commanding a flow modulator (e.g. as depicted in FIG. 6A
and FIG. 6A).
[0062] Optionally, the controller is configured to use a feedback
control loop. A feedback control loop can be, e.g., any series of
steps comprising at least one step of command by the controller
that is configured to produce (e.g. directly or indirectly) a gas
exhibiting a parameter target and further comprises at least one
step of providing feedback of the output to the controller, wherein
the feedback is used by the controller to correct the command, e.g.
to more accurately achieve the parameter target in a subsequent
step of command. Examples of feedback control loops useful in the
invention are depicted in FIG. 5 through FIG. 8, FIG. 10, and FIG.
11.
[0063] Optionally, a controller configured to use a feedback
control loop is configured to receive a parameter target (e.g.
target pressure profile or single target pressure), for example
from a user of the ventilator, and provide a setpoint based on the
parameter target. For example, the parameter target optionally
comprises a parameter profile comprising one or more parameter
targets (e.g. pressure targets). Each of the one or more parameter
targets can be provided as a setpoint. For example, the parameter
target optionally comprises a pressure profile having a constant
pressure and the setpoint provided by the controller is the
constant pressure. As another example, the parameter target
optionally comprises a pressure profile having a specific pressure
shape (e.g. pressure vs time curve) having a desired rise time and
the setpoint is a point in the pressure shape. As another example,
the parameter target can be a target flow (e.g. target flow profile
or flow vs time curve) and the controller can provide one or more
flow setpoints. Accordingly, setpoints provided by the controller
can change or can remain constant, and can be compared to feedback
received from one or more sensors to correct a command (e.g. a
command provided to a flow modulator or a command provided to
another controller).
[0064] Optionally, the controller is configured to use a cascaded
feedback control loop. Optionally, the cascaded feedback control
loop comprises an outer feedback control loop and one or more inner
feedback control loops that are within the outer loop. Optionally,
the one or more inner feedback control loops comprise a plurality
of parallel feedback loops, e.g. as depicted in FIG. 7. For each
feedback loop, the controller is optionally configured to provide
(e.g. obtain or calculate) a parameter target, provide a command
that, when carried out, achieves the parameter target (e.g. an
analog signal calibrated to achieve the parameter target using a
flow modulator or a digital signal comprising a flow target that,
when achieved, achieves the parameter target), obtain the actual
value of the gas parameter from a sensor as feedback of the
command, compare the actual value to the target to produce a
command error (e.g. the difference between the target and the
actual value), and modify a subsequent command based on the command
error in real time. Optionally, the cascaded feedback loop
comprises a pressure feedback loop as an outer loop, an air flow
feedback loop as a first inner loop, and an oxygen flow feedback
loop as a second inner loop (e.g. as depicted in FIG. 7).
Optionally, the pressure loop is configured to achieve a pressure
target by commanding a target gas mixture flow, wherein an
algorithm is used to provide a target oxygen flow and a target air
flow based on the target gas mixture flow and a target oxygen
content, and wherein the air flow loop is configured to modulate
air flow to achieve the target air flow by commanding an air flow
modulator, and wherein the oxygen flow loop is configured to
modulate oxygen flow and achieve the target oxygen flow by
commanding an oxygen flow modulator. The pressure loop can, e.g.
command a target flow of a gas mixture that achieve a target
pressure, wherein an algorithm splits the command into a target air
flow and a target oxygen flow based on an target oxygen content,
e.g. as depicted in FIG. 5. Target air flow is optionally achieved
by a controller configured to a use an air flow feedback loop, as
depicted in FIG. 6A. Target oxygen flow is optionally achieved by a
controller configured to a use an oxygen flow feedback loop, as
depicted in FIG. 6B.
[0065] Gas Mixture Controller
[0066] A controller useful in the present invention can comprise a
gas mixture controller configured to provide a command that
produces a gas mixture exhibiting at least one parameter target
(e.g. one or more of target pressure, target volume, target flow,
and target oxygen content). The command can produce the gas mixture
directly, e.g. by commanding a flow modulator, or indirectly, e.g.
by commanding a target flow of one or more flow controller, that in
turn produces the gas mixture. The gas mixture can be, e.g. a mixed
gas delivered to a patient interface or a mixing chamber gas.
Accordingly, the gas mixture controller can be, e.g. a mixed gas
controller or a mixing chamber controller.
[0067] Optionally, the controller is configured to provide (e.g.
obtain from a user) a target gas mixture pressure and a target gas
mixture oxygen content and determine a target gas mixture flow that
achieves the target pressure and determine a target air flow and a
target oxygen flow that collectively achieves the target gas
mixture flow and the target gas mixture oxygen content.
[0068] Optionally, the gas mixture controller comprises a gas
mixture module configured to: [0069] a. obtain a target pressure;
[0070] b. obtain a target oxygen content; [0071] c. determine a
mixed gas flow command based on the target pressure and the oxygen
content command, wherein the mixed gas flow command comprises a
target air flow and a target oxygen flow command; [0072] d. control
an air flow modulator based on the target air flow; and [0073] e.
control an oxygen flow modulator based on the target oxygen
flow.
[0074] Optionally, the step of controlling an air flow modulator
comprises sending the target air flow to an air flow controller.
Optionally, the step of controlling an oxygen flow modulator
comprises sending the target oxygen flow to an oxygen flow
controller. As used herein, the term `sending`, as used in
reference to sending of a command from a first controller to a
second controller (e.g. an independent second hardware component, a
second module of the same controller, or a second subroutine of the
same module) includes sending the command from the first controller
to the second controller wherein the first and second controllers
are separate hardware components, or the first controller making
the command available for retrieval by a second controller, e.g.
wherein the first and second controllers are modules or subroutines
on a single hardware component and the second controller references
the command produced by the first controller.
[0075] Optionally, the gas mixture module is further configured to
perform the following steps following control of the air and oxygen
flow modulators: [0076] a. obtain a pressure reading from a
pressure sensor of the gas mixture (`pressure feedback`); [0077] b.
compare the pressure feedback to the target pressure; [0078] c.
determine a pressure error based on the comparison of the pressure
feedback and the target pressure; [0079] d. based on the pressure
error, correct the mixed gas flow command; and [0080] e. repeat
steps a.-d. a plurality of times (e.g. continuously).
[0081] Air Flow Controller
[0082] A controller useful in the present invention can comprise an
air flow controller configured for controlling an air flow
modulator.
[0083] Optionally, the air flow controller comprises an air flow
module configured to: [0084] a. obtain a target air flow (e.g. from
a gas mixture controller); [0085] b. provide an air flow command
based on the target air flow (e.g. a command that is calibrated to
achieve the target air flow); [0086] c. command the air flow
modulator with the air flow command; [0087] d. determine the actual
air flow in the air flow line (`air flow feedback`), e.g. by
obtaining an air flow reading from an air flow sensor or by
calculating actual air flow based on (e.g. as the difference
between) actual gas mixture flow and actual oxygen flow; [0088] e.
compare the air flow feedback to the target air flow; [0089] f.
determine an air flow error based on the comparison of the air flow
feedback and the target air flow; [0090] g. based on the air flow
error, correct the air flow command; and [0091] h. repeat steps
c.-g. a plurality of times (e.g. continuously).
[0092] Oxygen Flow Controller Embodiment FIG. 1
[0093] A controller useful in the present invention can comprise an
oxygen flow controller configured for controlling an oxygen flow
modulator.
[0094] Optionally, the oxygen flow controller comprises an oxygen
flow module configured to: [0095] a. obtain a target oxygen flow
(e.g. from a gas mixture controller); [0096] b. provide an oxygen
flow command based on the target oxygen flow (e.g. a command that
is calibrated to achieve the target air flow); [0097] c. command
the oxygen flow modulator with the oxygen flow command; [0098] d.
determine the actual oxygen flow in the oxygen flow line (`oxygen
flow feedback`), e.g. by obtaining an oxygen flow reading from an
oxygen flow sensor or by calculating actual oxygen flow based on
(e.g. as the difference between) actual gas mixture flow and actual
air flow; [0099] e. compare the oxygen flow feedback to the target
oxygen flow; [0100] f. determine an oxygen flow error based on the
comparison of the oxygen flow feedback and the target oxygen flow;
[0101] g. based on the oxygen flow error, correct the oxygen flow
command; and [0102] h. repeat steps c.-g. a plurality of times
(e.g. continuously).
[0103] Target Parameters
[0104] A controller useful in the present invention can be
configured to control an air flow modulator and an oxygen flow
modulator to produce a gas mixture exhibiting a plurality of
parameter targets. The gas mixture can be, e.g., a mixed gas that
flows from a junction fed by an air line and an oxygen line or, as
another example, the gas mixture can be a mixing chamber gas fed by
an air line and an oxygen line. One or more steps of controlling a
modulator or another controller to produce a gas exhibiting a
parameter target is also referred to herein as `achieving` the
parameter targets. Parameters that are targeted (e.g. oxygen
content, pressure, flow, or volume) are also referred to herein as
`target parameters`. The target (e.g. target value, target profile,
or target shape) of such a target parameter is also referred to
herein as a `parameter target`. According to the present invention,
the plurality of gas mixture parameter targets comprises a target
oxygen content and at least one of a target pressure, a target
flow, and a target volume.
[0105] Optionally, to achieve a gas mixture parameter target (e.g.
target pressure or target flow), the controller determines a
parameter target (e.g. target flow) for each of the feed lines. For
example, the controller can be configured to determine a target
oxygen flow (i.e. target flow of gas through the oxygen line) and a
target air flow (i.e. target flow of air through the air line) that
produce a gas mixture exhibiting a target oxygen content and at
least one of a target pressure, a target flow, and a target
volume.
[0106] Optionally, the gas mixture is a mixing chamber gas fed by
an air line and an oxygen line. In such an embodiment, the target
parameters of the mixing chamber gas can optionally comprise oxygen
content and pressure. Further, in this embodiment, the controller
is optionally configured to achieve a parameter target (e.g. target
pressure, target flow, or target volume) of a mixed gas that
delivers gas from the mixing chamber to a patient interface, e.g.
by modulating a mixed gas control valve.
[0107] According to the present invention, a controller can achieve
a parameter target by controlling one or more flow modulators.
Optionally, the controller is configured to achieve a parameter
target by using the parameter target as a feedback control loop
target (`setpoint`). For example, the parameter target can comprise
a target flow, wherein the controller provides the flow target as a
setpoint for controlling a flow modulator. Additionally or
alternatively, a controller can optionally be configured to achieve
a target of a first parameter by calculating a target for a second
parameter, wherein the first parameter is a function of the second
parameter. For example, the parameter target can comprises a target
pressure, wherein the controller is configured to calculate a
target flow as a setpoint, wherein pressure is a function of flow,
such that achieving the target flow achieves the target pressure
(e.g. upon correction of the target flow). As another example, the
parameter target can comprise a total flow such as the target flow
of a mixed gas line or sum of target flows of an air line and an
oxygen line that feed a mixing chamber, and the controller is
configured to calculate the target flow setpoints for a plurality
of feed lines (e.g. an oxygen line and an air line), wherein the
total flow is the sum of the feed line flows. As another example,
the parameter target can comprise a target pressure (e.g. of a
mixing chamber gas), and the controller is configured to calculate
the target tidal volume setpoints and/or the total volume delivered
through a plurality of feed lines. For each parameter setpoint of a
feedback control loop, the controller can optionally be configured
to receive feedback from a sensor of the respective parameter for
comparison with the setpoint.
[0108] A parameter target (e.g. target mixed gas parameter) such as
target pressure, target volume, or target flow, can optionally be a
parameter target value or a parameter target profile. A parameter
target profile can include e.g. a parameter target shape, a target
change in parameter value, a target rate of change, a target
pattern of parameter values, or a parameter target function. For
example, a target pressure profile can comprise a target pressure
shape having an adjustable rise time setting and/or a gradual
pressure profile (e.g. for patient safety or comfort). Optionally,
the controller is configured to provide a plurality of alternative
pressure shapes (e.g. as choices to a user), e.g. pressure shapes
having different rise times such as a first rise time (e.g. fast
rise time), a second rise time (e.g. medium rise time), and a third
rise time (e.g. slow rise time).
[0109] Optionally, the target oxygen content is a target value
(e.g. a constant value).
[0110] Optionally, the one or more target parameters include any
of: tidal volume, rate, breath time or period, inhalation time or
period, exhalation time or period, inhalation volume, peak flow,
flow rate, respiration flow curve shape, respiration pressure curve
shape. Other useful target parameters are known in the art.
[0111] The parameter targets can be fixed or can fluctuate over
time. For example, the controller can be configured to provide a
breathing regimen in which the one or more parameters of the mixed
gas (e.g. pressure) fluctuate over time. Optionally, the breathing
regimen comprises a pattern of fluctuations in one or more
parameters (e.g. pressure). For example, the breathing regimen can
comprise a plurality of phases that alternate, such as an
inhalation phase and an exhalation phase. As used herein, the term
`maximum target` (e.g. `maximum target pressure`) refers to the
maximum value of a target profile. The term `instant`, when used
with respect to a parameter target means the current value of the
parameter, e.g. the instant pressure of the mixed gas line is the
actual current pressure of the mixed gas line and the instant
target pressure is the target value for the instant pressure.
[0112] Optionally, the ventilator comprises a mixing chamber, and
the controller is configured to provide a mixed gas having a target
pressure and a mixing chamber gas having a target pressure, wherein
the mixed gas is delivered to a patient, and wherein the target
pressure of the mixing chamber is greater than the target pressure
of the mixed gas. Optionally, the controller is configured to
calculate the target pressure of the mixing chamber gas based on
the target pressure of the mixed gas. For example, the controller
can comprise an equation that references the target pressure of the
mixed gas as an independent variable and the target pressure of the
mixing chamber gas as a dependent variable. Optionally, the
equation defines a difference (e.g. a set overage) or a ratio
between the mixing chamber gas target pressure and the mixed gas
target pressure. Optionally, the mixed gas target pressure is a
target pressure profile, and the mixing chamber gas target pressure
is based on the instantaneous pressure value or the maximum
pressure value of the target pressure profile. For example, the
mixing chamber target pressure can be a set overage of or a ratio
of the instantaneous pressure value or the maximum pressure value
of the target pressure profile.
[0113] Parameter targets of a gas mixture (e.g. the mixed gas) can
be inputted by a user or can be determined (e.g. calculated) based
on another parameter target (e.g. which is inputted by a user). For
example, a ventilator can optionally be configured to receive an
input (e.g. user input) comprising a target pressure and optionally
a target volume and/or a target flow. Additionally or
alternatively, a ventilator can comprise a flow target controller
configured to determine a target flow based on parameter target
such as a target pressure or a target volume. Optionally, a target
flow determined based on a target volume, wherein the target flow
is adjusted based on a real time measurement of volume error.
[0114] Other Parameters
[0115] Optionally, controller output is dependent on one or more
input parameters, e.g. input parameters detected by a sensor. Such
parameters can be used, e.g. as triggers for steps of control of
flow modulator or steps of controlling an alarm.
[0116] Input parameters optionally include physiologic
parameters.
[0117] The physiological parameters may include one or more of
blood pressure, heart rate, pulse oximetry, blood gas level, ECG,
EEG, body temperature, (end-tidal) carbon dioxide concentration,
parameters indicating pending cardiac conditions, cardiac output,
snoring detection, and sedation index.
[0118] Ventilation Modes
[0119] The ventilator controller of the invention can be configured
to provide any mode of ventilation.
[0120] Optionally, the ventilator mode comprises a breathing
profile and/or a breath cycle. Optionally, the breathing profile
comprises an inhalation phase and an exhalation phase.
[0121] Optionally, the inhalation phase is patient-triggered or
machine-triggered. A patient-trigged inhalation is a spontaneous
breath initiated by the subject, wherein the trigger is provided by
the patient (e.g. patient breathing effort) and, for example, the
controller receives feedback from a sensor that responds to patient
breathing effort (e.g. a sensor that detects a change in flow or
pressure in ventilator indicative of patient breathing effort). A
machine-trigged inhalation is a mandatory breath initiated by the
controller, e.g. triggered by the elapsed time following the
initiation of previous inhalation and/or exhalation phase.
[0122] Optionally, the controller is configured to provide a breath
cycle. A breath cycle optionally comprises one or more triggers of
cycle events, e.g. inhalation, exhalation, inhalation initiation,
inhalation termination, exhalation initiation, and/or exhalation
termination. Optionally, the breath cycle comprises an inhalation
trigger. Optionally, breath cycle comprises an inhalation
initiation trigger, e.g. that includes one or more instructions
containing at least one event that initiates an inhalation phase.
Optionally, the breath cycle comprises an inhalation termination
trigger, e.g. that includes one or more instructions containing at
least one event that terminates an inhalation phase.
[0123] Optionally, the breath cycle contains an inhalation
termination trigger. Optionally, the inhalation termination trigger
comprises a target pressure (e.g. mixed gas pressure), target
inhalation tidal volume (e.g. mixed gas tidal volume), a target
time (e.g. duration of elapsed time following the start of an
inhalation phase), or a target flow (e.g. flow rate of mixed
gas).
[0124] Optionally, the controller is configured for using different
cycles and/or triggers for a plurality of breaths. For example, an
inhalation phase of a first breath can be terminated based on a
target pressure and an inhalation phase of a second breath can be
terminated based on a target volume. Optionally, the controller is
configured for terminating an inhalation phase based on a target
volume, wherein the target volume is adjusted between at least two
breaths. For example, the controller can be configured to set a
first target volume and adjust the target volume in subsequent
breaths upon one or more parameters being met or unmet (e.g.
adjusting the target volume to obtain a target pressure).
[0125] Optionally, the controller is configured for receiving (e.g.
from a user) a trigger definition such as a cycle setpoint, e.g.
that triggers one or more events in a breath cycle such as
termination of inhalation. Optionally, the controller is configured
for receiving an inhalation termination cycle setpoint of a first
parameter (e.g. pressure) and an inhalation termination cycle
setpoint of a second parameter (e.g. volume) which are used
independently or in concert to trigger termination of an inhalation
phase of one or more breaths.
[0126] Optionally, the controller is configured for providing a
mandatory breath, or a spontaneous breath. A mandatory breath can
comprises an inhalation phase in which the controller controls the
timing, tidal volume or both. A spontaneous breath can be, e.g. an
inhalation phase in which the timing and/or the tidal volume is
controlled by the patient.
[0127] Optionally, the controller is configured to provide any of
the following modes of ventilation: mandatory ventilation,
spontaneous ventilation, intermittent mandatory ventilation
(`IMV`), synchronized intermittent mandatory ventilation (`SIMV`),
continuous mandatory ventilation (`CMV`), continuous positive
airway pressure (`CPAP`), pressure support ventilation (`PSV`), and
continuous spontaneous ventilation (`CSV`).
[0128] Optionally, the controller is configured to provide any of
the following modes of ventilation: Spontaneous, Spontenaous Timed,
and Timed. Optionally, any of such ventilation modes is a leak
mode.
[0129] Optionally, the controller is configured to provide any of
the following modes of ventilation: Volume Control Ventilation,
Pressure Control Ventilation, Pressure Regulated Volume Control,
Volume Support, Proportional Assist Ventilation, and Volume Assured
Pressure Support.
[0130] Optionally, the controller is configured to provide a flow
pattern selected from constant flow (e.g. square wave flow),
ascending ramp flow, sine wave flow, descending ramp flow, and
decaying exponential flow.
Oxygen
[0131] According to the present invention a ventilator comprises an
oxygen inlet for receiving pressurized oxygen. The oxygen inlet can
optionally be connected to any oxygen source containing oxygen at a
concentration substantially greater than that of the air source.
Optionally, the oxygen source comprises pure or substantially pure
oxygen.
[0132] Optionally, the oxygen source is a pressurized tank or an
oxygen pipeline (e.g. a hospital's high-pressure oxygen gas
network).
[0133] Optionally, the oxygen source comprises a pressure regulator
or the ventilator comprises a pressure regulator downstream of the
oxygen inlet. The optional pressure regulator can be, e.g. any
reducing valve configured to provide gas at a set pressure. The
pressure regulator can optionally be a manual valve, a control
valve, or a fixed orifice (i.e. not modulatable).
Air
[0134] According to the present invention a ventilator comprises an
air inlet. The air inlet can be connected to any air source.
Optionally, the air source is ambient air. For example the air
inlet is optionally a port through which ambient air is drawn by
the air pump.
[0135] Optionally, the ventilator comprises an air filter
downstream of the air inlet. Optionally, the air filter is upstream
of the junction. Optionally, the air filter is upstream of the air
pump.
Gas Pump
[0136] A ventilator of the present invention comprises a gas pump
downstream of the air inlet. The pump can be any gas pump.
Optionally, the speed of the gas pump is controlled by a controller
of the ventilator (`variable speed pump`).
[0137] Optionally, the pump is a positive displacement pump or a
dynamic pump. Positive displacement pumps convey gas by displacing
the gas. Dynamic pumps convey gas by transferring energy to the gas
from a moving object (e.g. an impeller) to create gas velocity.
Examples of useful positive displacement pumps include rotary
positive displacement pumps and reciprocating positive displacement
pumps. Examples of useful dynamic pumps include fan blowers such as
centrifugal flow pumps.
[0138] Optionally, the pump is a positive flow pump. Optionally,
the positive flow pump is a rotary pump selected from a lobe pump
(e.g. roots blower), a screw pump, a liquid ring pump, a scroll
pump, and a vane pump. Optionally, the positive flow pump is a
reciprocating pump selected from a diaphragm pump, a double acting
pump, and a single acting pump.
[0139] Optionally, the pump is a dynamic pump comprising an
impeller (`fan blower`). The fan blower can comprise, e.g. an axial
flow impeller or a radial flow impeller. Optionally, the fan blower
is a centrifugal pump. Dynamic pumps such as centrifugal pumps have
advantages such as providing reduced production cost ventilators,
reduced noise, and reduced power consumption compared to positive
displacement pumps commonly used in ventilators that provide high
pressure air. However, the prior art has generally failed to
produce accurate air-oxygen mixing of low pressure air with high
pressure oxygen and has typically instead used high pressure
positive displacement pumps or, in the case of the Philips
Respironics BiPAP Vision, used a complex combination of many
components (e.g. an in-line flow restrictor and a pressure
regulation valve) and complex algorithms that are difficult to
carry out. Accordingly, through insight of the inventor, it is
quite remarkable that low pressure ventilators of the present
invention can achieve accurate air-oxygen mixing using dynamic
pumps with a high pressure oxygen source.
[0140] Optionally, the pump is a low pressure pump, e.g. a low
pressure dynamic pump. Such a low pressure pump can be any pump
configured to pressurize downstream gas to a pressure of no more
than 140 mbar (e.g. no more than 110 mbar or no more than 70 mbar).
For example, the design of the pump itself can be configured or
rated for providing no more than a maximum pressure (e.g. 140 mbar)
or the ventilator controller can be configured to control the pump
speed such that the pump produces no more than a maximum pressure
(e.g. 140 mbar). Surprisingly, through insight of the inventor,
embodiments of the present invention are believed to achieve
accurate air-oxygen mixing of low pressure air even with high
pressure oxygen (e.g. oxygen from an oxygen tank or hospital oxygen
line). This is a remarkable improvement over prior art
configurations.
[0141] Optionally, the dynamic pump is configured for conveying gas
at about 100 liters per minute (`lpm`) or greater, e.g. at least
about 150 lpm.
[0142] Optionally, the pump is a small dynamic pump. A small
dynamic pump can be, e.g. a dynamic pump having an impellar
diameter of less than about 20 cm, e.g. less than about 18 cm, less
than about 14 cm, less than about 10 cm, about 4 cm to about 9 cm,
or about 4 cm to about 10 cm. Optionally, the small dynamic pump is
a pump configured for conveying gas at no more than 200 lpm.
Optionally, the small dynamic pump is a pump configure to produce a
gas pressure of no more than about 110 millibar (`mbar), e.g. no
more than about 80 mbar or no more than about 60 millibar. Such
small dynamic pumps can provide advantages such as, e.g. increased
efficiency, and/or reduced size to provide a more compact
ventilator while producing accurate flow rates in ventilators of
the the present invention. Optionally, a small pump comprises a
noise reduction mechanism such as noise insulating enclosure. These
advantages can be compounded with accurate air/oxygen mixing and
pressure targeting using ventilator configurations taught
herein.
Conduits
[0143] A ventilator of the invention comprises a plurality of
conduits that transport gas from the inlets to the patient
interface. The ventilator comprises at least a first conduit that
conveys gas from the oxygen inlet to a junction (`oxygen line`), a
second conduit that conveys gas from the air inlet to the junction
(`air line`), and a third conduit that conveys gas from the
junction to the patient interface (`mixed gas line`).
Oxygen/Air Mixing
[0144] A ventilator of the present invention comprises a junction
downstream of the air inlet and oxygen inlets. The junction is
configured for receiving air from the air line, receiving oxygen
from the oxygen line, and outputting a mixed gas to the mixed gas
line.
[0145] The junction can comprise, e.g. a direct mixing junction or
a mixing chamber.
[0146] Direct Mixing
[0147] A ventilator of the present invention can optionally
comprise a direct mixing junction. A direct mixing junction can
optionally be any junction which experiences the same pressure as
the gas flowing through the patient interface, i.e. does not
comprise a reservoir having an over pressure relative to the mixed
gas line. Optionally, the direct junction is a passive junction
such as a T-junction. Optionally, the direct junction is fixed
volume junction. Optionally, the direct junction comprises no
moving parts.
[0148] Mixing Chamber
[0149] A ventilator of the present invention can optionally
comprise a mixing chamber. According to the present invention, a
mixing chamber is any chamber that is pressurized greater than that
of the mixed gas line (i.e. the target pressure of the inspiration
gas). In this embodiment, the ventilator comprises a control valve
(e.g. proportional valve) downstream of the mixing chamber (`mixed
gas control valve`), wherein the mixed gas control valve is
controlled by the controller.
[0150] Optionally, the mixing chamber comprises a fixed volume
reservoir (e.g. a pressurized gas tank). Unlike a piston or bellows
mixing chamber or other variable volume mixing chamber, the volume
of a fixed volume reservoir does not change as it is filled.
Instead, the mixing chamber is pressurized as it is filled.
[0151] Optionally, the mixing chamber is a passive reservoir. A
passive reservoir is a reservoir that has no luminal moving parts
that act to draw in or homogenize gas.
[0152] Optionally, the mixing chamber (e.g. fixed volume and/or
passive mixing chamber) comprises a volume of at least about 300
ml, e.g. a volume of about 300 ml to about 5000 ml. Optionally, the
volume of the mixing chamber (e.g. fixed volume and/or passive
mixing chamber) is about 1000 ml to about 3000 ml, e.g. about 1500
ml to about 2500 ml. Such a mixing chamber is useful, e.g. for
human subjects. Optionally, the volume of the mixing chamber (e.g.
fixed volume and/or passive mixing chamber) is about 300 ml to
about 1000 ml. Such a mixing chamber is useful, e.g. for subjects
having lung capacities substantially less than adult humans (e.g.
infants, children, or veterinary subjects).
[0153] Optionally, the mixing chamber comprises a pressure
sensor.
[0154] Optionally, the controller is configured to pressurize the
mixing chamber to a pressure (e.g. instant pressure) greater than
that of the mixed gas line (e.g. greater than the instant target
pressure or the maximum target pressure of the mixed gas line).
Optionally, the controller is configured to pressurize the mixing
chamber to a pressure (e.g. instant pressure) at least about 5 mbar
(e.g. at least about 10 mbar) greater than that of the mixed gas
line (e.g. greater than the instant target pressure or the maximum
target pressure of the mixed gas line). Optionally, the controller
is configured to pressurize the mixing chamber to a pressure (e.g.
instant pressure) about 1 mbar to about 30 mbar (e.g. 5 mbar to
about 20 mbar or about 10 mbar to about 20 mbar) greater than that
of the mixed gas line (e.g. greater than the instant target
pressure or the maximum target pressure of the mixed gas line).
Optionally, the controller is configured to pressurize the mixing
chamber to a pressure of about 10 mbar greater than the instant
pressure of the mixed gas line or greater than the maximum pressure
experienced by the mixed gas line. For example, the controller can
be configured to pressurize the mixing chamber to a pressure that
is about 10 mbar greater than the instant target pressure of the
mixed gas or above the maximum target pressure of the mixed
gas.
[0155] Optionally, the controller is configured to pressurize the
mixing chamber to a pressure of less than about 150 mbar, e.g. less
than about 100 mbar. Optionally, the controller is configured to
limit the pressure of the mixing chamber at all times to less than
about 150 mbar. Such a configuration provides enhances safety for
the patient and reduces the burden on a pump.
[0156] Optionally, the mixing chamber comprises an oxygen
sensor.
[0157] Optionally, each of the air line and the oxygen line that
feed the mixing chamber optionally comprise a flow sensor, i.e. an
air flow sensor and an oxygen flow sensor, respectively.
Optionally, the controller is configured to control the flow of at
least one of air through the air line and oxygen through the oxygen
line.
[0158] Optionally, the mixed gas line fed by the mixing chamber
comprises a mixed gas flow sensor, a pressure sensor, or both.
[0159] Optionally, the ventilator comprises an exhalation valve
downstream of the mixing chamber and upstream of the patient
interface (e.g. upstream of the mixed gas control valve), wherein
the exhalation valve is controlled by the controller; and
optionally the ventilator further comprises a check valve
downstream of the mixing chamber and upstream of the exhalation
valve.
[0160] Optionally, the oxygen line that feeds the mixing chamber
comprises a check valve (e.g. downstream of the oxygen control
valve) and/or the air line that feeds the mixing chamber comprises
a check valve (e.g. downstream of the pump). Such check valves can
be configured to prevent escape of gas from the mixing chamber to
the upstream (e.g. upon pressurization of the mixing chamber).
[0161] Optionally, the pump that conveys air to the mixing chamber
is a variable speed pump or the air line comprises a control valve
downstream of the pump (e.g. a constant speed pump).
[0162] Through insight of the inventor, a ventilator comprising a
mixing chamber as taught herein, can deliver flow/volume and
pressure to the patient with high accuracy with uniform oxygen
mixing throughout the breath delivery.
[0163] Another optional advantage of a ventilator comprising a
mixing chamber as taught herein, is that a modular ventilator
configuration, e.g. with a disconnectable oxygen line, can be
easily designed and implemented and optionally facilitates
burden-free servicing.
Sensors
[0164] A ventilator of the present invention comprises a plurality
of sensors from which the controller receives feedback. Such
feedback can optionally be used in the control of flow modulators.
The ventilator optionally comprises at least one pressure sensor
comprised by the mixed gas line (`mixed gas pressure sensor`), at
least a first flow sensor and a second flow sensor. The first and
second flow sensors are respectively comprised by two lines
selected from an air line, an oxygen line, and a line that
transmits a gas mixture of both oxygen from the oxygen line and air
from the air line. For example, the first flow sensor can be a flow
sensor comprised by the oxygen line (`oxygen flow sensor) and the
second flow sensor can be a flow sensor comprised by the air line
(`air flow sensor`) or a flow sensor comprised by the mixed gas
line (`mixed gas flow sensor`).
[0165] Optionally, the ventilator comprises at least three flow
sensors--an oxygen flow sensor, an air flow sensor, and mixed gas
flow sensor.
[0166] Optionally, the ventilator comprises a mixing chamber and at
least two pressure sensors--a first pressure sensor comprised by
the mixed gas line and a second pressure sensor comprised by the
mixing chamber.
[0167] Optionally, the ventilator comprises a sensor of oxygen
content (`oxygen sensor`). For example, the ventilator optionally
comprises a mixing chamber comprising an oxygen sensor.
[0168] Sensors useful in the present invention optionally produce a
signal (e.g. digital or analog signal) that can be interpreted by
the controller to determine the state or value of sensed
parameter.
[0169] Sensors comprised by a component of the intention (e.g.
conduit) can optionally be placed directly in the component or
placed in a bleed line that takes a sample from the component.
[0170] Pressure Sensors
[0171] Pressure sensors useful in the present invention include any
device (e.g. a single device or a collection of devices) capable of
producing a signal indicative of the gas pressure and providing the
signal to the controller. For example the pressure sensor can be a
transducer that converts pressure into an electrical signal (e.g. a
strain-gage base transducer).
[0172] Optionally, the mixed gas line comprises a pressure sensor.
Such a pressure sensor can be used, e.g. to inform the controller
of the pressure of the mixed gas that will be delivered to the
patient.
[0173] Optionally, the ventilator comprises a mixing chamber and
the mixing chamber comprises a pressure sensor. Such a pressure
sensor can be used, e.g. to inform the controller of the mixing
chamber pressure. Optionally, the mixed gas line comprises a
proportional valve and the controller compares the actual mixing
chamber pressure to a target mixed gas pressure to determine the
level of modulation of the proportional valve to achieve the target
mixed gas pressure in a mixed gas that is delivered to the
patient.
[0174] A useful pressure sensor is, for example, a differential
pressure sensor.
[0175] Oxygen Sensor
[0176] A ventilator of the invention optionally comprises an oxygen
sensor. Oxygen sensors useful in the present invention include any
device capable of producing a signal indicative of the oxygen
content of a gas and providing the signal to the controller. For
example, the oxygen sensor can produce a signal that converts the
concentration of oxygen into an electrical signal, e.g. from which
the controller can determine the percentage or fraction of oxygen
(`FiO.sub.2`).
[0177] Optionally, the ventilator comprises an oxygen sensor
comprised by the mixed gas line or the junction. Such an oxygen
sensor can be used, e.g. to inform the controller of the oxygen
content of the gas mixture that will be delivered to the
patient.
[0178] Optionally, the invention contemplates embodiments that
compare the oxygen content of the gas mixture to the target gas
mixture oxygen content and modulate the oxygen modulator and/or the
air modulator to modulate the oxygen content of the mixed gas.
While oxygen sensors can optionally be comprised by ventilators of
the present invention, certain embodiments taught herein comprise a
controller that use flow sensors to provide feedback to oxygen and
air modulators and thus can control oxygen content independent of
direct measurement of oxygen content for feedback control.
Accordingly, even in embodiments wherein an oxygen sensor is
comprised by the ventilator, the oxygen sensor can optionally be
configured for monitoring purposes (e.g. for display to a user or
to trigger an alarm) such that feedback control of oxygen and air
modulators and can continue in the event of oxygen sensor
malfunction. Additionally or alternatively, the oxygen sensor can
be configured as a secondary feedback mechanism in the event that
one of the flow sensors malfunction such that the controller uses
the oxygen sensor for feedback control of the oxygen and air
modulators instead of the malfunctioned flow sensor. Through
insight of the inventor, such configurations provide a superior
safety feature that ensures accurate delivery of a desired
air-oxygen mix.
[0179] Optionally, the oxygen sensor is an O.sub.2 cell.
[0180] Optionally, the ventilator is configured such that the
oxygen sensor can be removed and/or installed from the exterior of
the ventilator or oxygen line thereof. Additionally or
alternatively, the ventilator is optionally configured such that
the oxygen sensor can be removed and/or installed without
substantially disassembling or opening the oxygen line. For
example, the ventilator or oxygen line thereof can be provided with
a port (e.g. a tapped hole in a sidewall of the line) which accepts
an oxygen sensor, wherein the port is accessible from the outside
the ventilator or oxygen line thereof
[0181] Flow Sensors
[0182] A ventilator of the invention comprises a plurality of flow
sensors. Flow sensors useful in the present invention include any
device capable of producing a signal indicative of the flow of a
gas and providing the signal to the controller. For example, a flow
sensor can comprise a pneumotach, a variable orifice transducer, a
mass flow sensor or any flow transducer that produces a signal,
e.g. from which the controller can determine the flow rate or
instantaneous volume delivered through a conduit.
[0183] Optionally, a ventilator has a flow sensor comprised any of
the oxygen line, the air line, and the mixed gas line.
[0184] Optionally, the ventilator comprises a flow sensor comprised
by the mixed gas line. Optionally, such a flow sensor is used to
provide feedback for a controller, wherein the controller is
configured for a volume- or flow-targeted mode of delivery.
Additionally or alternatively, such a flow sensor is optionally
used by a controller for measurement of tidal volume, leak (e.g.
estimated or calculated leak), flow for breath trigger, or flow for
cycling between inhalation and exhalation phases.
[0185] Optionally, the oxygen line comprises a flow sensor.
Optionally, the flow sensor is downstream of an oxygen control
valve. Such placement of the flow sensor downstream of the control
valve can, e.g. prevent damage the oxygen flow sensor under fault
conditions.
Valves
[0186] A ventilator of the invention comprises a plurality of
valves.
[0187] Valves useful of the present invention include valves
configured for modulation by the controller (`control valves`) and
valves that are modulated by another means (`non-control valves`).
Useful non-control valves include manual valves and non-adjustable
valves.
[0188] Optionally, any valve taught herein can be configured as a
control valve. Alternatively, the ventilator comprises a plurality
of control valves and at least one non-control valve (e.g. a
non-control check valve).
[0189] Useful control valves include on-off valves and proportional
valves.
[0190] Control Valves
[0191] Useful control valves include any valve that can be
modulated by the controller.
[0192] Examples of useful control valves include on-off valves and
proportional valves.
[0193] Optionally, a valve used in the invention is a fail-safe
valve. Fail-safe valves are valves that automatically assume a
resting state upon removal of an actuating signal. For example, a
fail-safe valve can be a normally closed valve having a resting
state in the closed position and which opens upon receiving an open
signal from the controller or can be a normally open valve having a
resting state in the open position and which closes upon receiving
a close signal from the controller.
[0194] Ventilators of the present invention comprise at least a
first control valve comprised by the oxygen line (`oxygen control
valve`).
[0195] Optionally, the ventilator comprises an exhalation valve as
a control valve.
[0196] Optionally, one or more of the air line and the mixed gas
line comprise a control valve.
[0197] Optionally, the oxygen control valve is a proportional valve
or an on-off valve.
[0198] Optionally, the oxygen control valve is a solenoid, e.g. a
proportional solenoid or an on-off solenoid (e.g. a rapid an-off
solenoid controlled via pulse width modulation).
[0199] Oxygen Control Valve
[0200] A ventilator of the present invention can comprise an oxygen
control valve. The oxygen control valve can be any control valve
comprised by the oxygen line upstream of the junction that can be
controlled to modulate the flow of oxygen from the oxygen inlet to
the junction. By controlling the oxygen control valve, the
controller can modulate parameters of the mixed gas such as the
oxygen content and/or pressure.
[0201] Optionally, the oxygen control valve is a proportional
valve. Alternatively, the oxygen control valve can optionally be an
on-off valve, e.g. in embodiments wherein the junction comprises a
mixing chamber.
[0202] Air Control Valve
[0203] Optionally, a ventilator of the present invention comprises
an air control valve. The air control valve can be any control
valve comprised by the air line upstream of the junction that can
be controlled to modulate the flow of air from the air inlet to the
junction. By controlling the air control valve, the controller can
modulate parameters of the mixed gas such as the oxygen content
and/or pressure.
[0204] Optionally, the air control valve is a proportional valve.
Alternatively, the air control valve can optionally be an on-off
valve (e.g. controlled via pulse width modulation), e.g. when the
junction comprises a mixing chamber.
[0205] Mixed Gas Control Valve
[0206] Optionally, a ventilator of the present invention comprises
a mixed gas control valve, e.g. in embodiments wherein the junction
comprises a mixing chamber. The mixed gas control valve can be any
control valve comprised by the mixed gas line downstream of the
junction that can be controlled to modulate the flow of mixed gas
from the junction to the patient. By controlling the mixed gas
control valve, the controller can modulate parameters of the mixed
gas such as the pressure or flow.
[0207] Optionally, the mixed gas control valve is a proportional
valve (e.g. proportional solenoid).
[0208] Exhalation Valve
[0209] Optionally, a ventilator of the invention comprises an
exhalation valve as a control valve. An exhalation valve can
optionally be any valve which is opened during an exhalation phase
and relatively closed (e.g. completely closed or partly closed)
during an inhalation phase.
[0210] Optionally, the exhalation valve is an on-off valve.
[0211] Optionally, the exhalation valve is a proportional valve
(e.g. proportional solenoid or proportional scissor valve). Such a
configuration can be used, for example, to add functionality to the
ventilator during exhalation and/or inspiration. For example, the
proportional exhalation valve can be used to control the amount of
back pressure (i.e. through valve orifice size) during exhalation
or toggle pressure during inspiration. Optionally, the ventilator
comprising such an exhalation valve is configured to provide Airway
Pressure Release Ventilation (`APRV`)
[0212] Optionally, the exhalation valve is a normally open valve
which is closed by the controller during an inhalation phase. In
this configuration, patients can breathe freely from room air in
case of power failure or machine failure. Alternatively, the
exhalation valve can be a normally closed valve which is opened by
the controller during an exhalation valve. Alternatively, the
exhalation valve can receive an open signal from the controller
during the exhalation phase and receive a close signal from the
controller during the inhalation phase.
[0213] In embodiments comprising an exhalation valve, the
ventilator optionally comprises a valve upstream of the exhalation
valve that prevents gas from flowing upstream (`exhalation
isolator`) to one or more components such as a blower or a mixing
chamber. The exhalation isolator can be a control valve or
non-control valve. As an illustrative example, the exhalation
isolator can comprise a check valve upstream of the exhalation
valve. As another example, the exhalation isolator can be a control
valve that is closed during an exhalation phase. A check a valve is
used as an illustrative example of an exhalation isolator. However,
for each of said examples, the invention also provides an
alternative embodiment comprising any exhalation isolator.
[0214] Optionally, the ventilator comprises the exhalation valve
upstream of a flow sensor. In this configuration, the controller
can measure the exhaled gas, e.g. in a single limb patient circuit
configuration using a flow sensor that is configured to measure
both inhaled gas and the exhaled gas. The measurement of exhaled
gas can be used by the controller, e.g. to perform any of the
following: measure exhalation flow, determine exhalation tidal
volume, determine duration of exhalation phase, and determine the
cycle time to switch from an exhalation phase to an inhalation
phase.
[0215] Optionally, the exhalation valve and the exhalation isolator
can be independent valves that collectively achieve the desired
function, e.g. an exhalation valve and check valve positioned next
to each other or separated by other components such as conduits and
valves). Alternatively, the exhalation valve and the exhalation
isolator can optionally be subcomponents of a single valve, for
example, a three way valve with an exhaust port.
[0216] Optionally the ventilator comprises a valve having
exhalation valve and exhalation isolator functions. For example, a
three way valve can be provided which has an inlet port which
receives an inlet flow of gas from upstream, an outlet port which
outflows gas downstream towards the patient, and an exhaust port
configured for exhausting downstream air. Such a three-way valve
can optionally be a normally closed valve which, when unactuated,
blocks inlet flow and connects the outlet port to the exhaust port,
and which, when actuated by the controller, connects the inlet port
to the outlet port and blocks the exhaust port. Alternatively, such
a three-way valve can optionally be a normally closed valve which,
when unactuated, passes inlet flow from the inlet port to the
outlet port and blocks the exhaust port, and which, when actuated
by the controller, blocks the inlet flow and connects the outlet
port to the exhaust port.
[0217] Among the other advantages taught herein, a ventilator
having an exhalation valve and isolation valve, e.g. in a single
limb ventilator, can isolate the patient interface, reducing the
chances of cross-contamination of upstream components during
exhalation.
[0218] One advantage of an exhalation valve as taught herein is
that it can optionally be configure to prevent potential cross
contamination of the components. This allows, e.g. the ventilator
to be used by one or more additional patients after a first patient
has used the ventilator. While a bacteria filter is optionally
provided, e.g. upstream of a patient interface, the exhalation
valve can configured to protect upstream components from
cross-contamination in embodiments that do not comprise a bacteria
filter. For example, while a ventilator of the invention can be
manufactured that has a connector at the furthest downstream end of
the mixed gas line configured for connection to patient interface
and optionally connected to a bacteria filter between the connector
and the patient interface. While the manufacture may optionally
recommend the use of a bacteria filter at the ventilator outlet,
this is not always practiced by users a cost-effective and simple
solution would eliminate concerns from clinicians, equipment
providers/dealers, care givers and patients as well. Through
insight of the inventor, employing an exhalation valve optionally
configured as taught herein, a potentially very serious issue of
cross-contamination can be eliminated at minimal cost and burden to
users.
[0219] Check Valves
[0220] A ventilator of the invention optionally comprises one or
more check valves that prevent the transmission of gas from
downstream to upstream.
[0221] Optionally, the ventilator comprises at least one check
valve upstream of an exhalation valve and downstream of a
blower.
[0222] Optionally, the ventilator comprises at least one check
valve upstream of an exhalation valve and downstream of a mixing
chamber.
[0223] Optionally, the ventilator comprises at least one check
valve upstream of a mixing chamber and downstream of the
blower.
[0224] Optionally, the ventilator comprises at least one check
valve upstream of a mixing chamber and downstream of an air
inlet.
[0225] Optionally, the ventilator comprises at least one check
valve upstream of a mixing chamber and downstream of an oxygen
inlet.
[0226] Optionally, the ventilator comprises at least one check
valve upstream of the junction and downstream of the air inlet.
[0227] Optionally, the ventilator comprises at least one check
valve upstream of the blower and downstream of the air inlet.
[0228] Pressure Regulator
[0229] Optionally, a ventilator of the invention comprises a
pressure regulator downstream of the oxygen inlet, e.g. upstream of
the oxygen control valve. The pressure regulator can be, e.g. any
reducing valve configured to provide gas at a set pressure. The
pressure regulator can optionally be a manual valve, a control
valve, or a fixed valve (i.e. not modulatable).
[0230] Proportional Valves
[0231] A ventilator of the invention comprises at least one
proportional valve. According to the present invention, a
proportional valve is any valve that can be modulated by the
controller to assume a first position, a second position, and a
plurality of positions intermediate of the first and second
positions. Optionally, the first position is fully open.
Optionally, the second position is fully closed. Optionally, the
plurality of intermediate positions vary from each other by less
than 10% (e.g. less than 5%, less than 1%, less than 0.5%, or are
continuously variable) which respect to orifice or flow rate.
[0232] Optionally, a proportional valve is a continuously variable
valve (e.g. with an infinite number of intermediate positions) or a
discrete position valve (e.g. with a discrete number of
intermediate positions).
[0233] Optionally, the proportional valve is a continuously
variable valve having less than 3% of center overlap.
Alternatively, the proportional valve is optionally a continuously
variable valve is any variable valve having a center overlap of at
least 3%.
[0234] Optionally, the proportional valve is a solenoid valve or a
stepper valve.
[0235] Optionally, the proportional valve is a solenoid valve such
as a stroke-controlled solenoid or a force-controlled solenoid.
[0236] Optionally, the proportional valve comprises a servo
motor.
[0237] Optionally, the proportional valve is a plunger valve or a
butterfly valve.
Patient Interface
[0238] A ventilator of the present invention can optionally
comprise a patient interface or can be configured for connection to
a patient interface (e.g. the ventilator comprises a tube coupler
downstream of the junction). Useful patient interfaces include any
component configured to deliver the mixed gas to the lungs of a
subject.
[0239] Optionally, the patient interface comprises a mask, a mouth
piece, a nasal prong, or a tube.
[0240] Optionally, the patient interface comprises a tube, e.g. a
tube that is inserted into the patient. Optionally, the tube
comprises a tracheal tube, e.g. an endotracheal tube, a
tracheostomy tube, or a tracheal button.
[0241] While the invention is frequently illustrated herein as a
ventilator comprising a patient interface and an optional bacteria
filter, the invention also provides, for each of said embodiments,
an alternative embodiment that comprises a connector on the mixed
gas line (e.g. at the outlet or most downstream end), e.g. rather
than comprising a patient interface or optional bacteria filter.
The connector can be configured, e.g. for connection to a patient
interface (or a gas conduit) and optionally a bacteria filter. Such
a configuration allows the user to obtain a ventilator of the
invention and independently obtain a patient interface, e.g. a
generic patient interface of his choice from any manufacturer.
Modular Ventilator
[0242] A ventilator of the present invention can optionally be
configured such that the oxygen line can be disconnected from the
ventilator, e.g. at the junction. In such a configuration, two
independent systems can be provided. For example, a first system
can be provided having an air line, a mixed gas line, and a
junction comprising a connector configured for coupling to an
oxygen line such that the junction mixes oxygen and air when the
oxygen line is connected. A second system can be provided having an
oxygen line configured for connection to the junction. Controlled
components of the oxygen line (e.g. an oxygen valve and oxygen
sensor) can be configured for coupling (e.g. via a data link) to
the first controller for control thereby or, alternatively, the
second system can comprise a second controller configured for
coupling (e.g. via data a link) to the first controller.
[0243] Among other advantages, such a ventilator allows patients
who do not require additional oxygen to use or purchase a
ventilator having only the air system, reducing the cost of the
devices. If and when oxygen mixing is needed, the oxygen system can
be added to the existing system, enabling the ventilator to be
upgraded without purchasing a replacement ventilator. Accordingly,
the oxygen system can be implemented internally or installed as an
external add-on module, thus allowing various options of
devices.
Other Gases
[0244] While the invention has been illustrated by using air and
oxygen as gas sources, the invention contemplates ventilators
configured to mix any gases. For example, the invention
contemplates a ventilator configured to use a first gas and a
second gas in place of the air and the oxygen, respectively.
Accordingly, it is to be understood that, in such embodiments, the
components of the respective feed lines, which are often referred
to herein as `air` components or `oxygen` components (e.g. air flow
sensor, oxygen flow sensor, oxygen control valve, etc.) can instead
be referred to `first gas` components or `second gas` components,
respectively (e.g. first gas flow sensor, second gas flow sensor,
second gas control valve, etc. The first gas and second gas can
optionally each be selected from air, oxygen, a noble gas (e.g.
xenon), an anesthetic, nitrogen, or a gas mixture comprising any of
said gases and one or more additional gases. Optionally, the first
gas is air (e.g. ambient air) and the second gas is any gas, e.g.
an auxiliary gas (e.g. pressurized gas) such as oxygen, a noble gas
(e.g. xenon), an anesthetic, or nitrogen. Additionally, a
ventilator of the invention can be configured to mix three or more
gasses (e.g. a third gas in addition to the first and the second
gases).
EXAMPLES
Example 1
Ventilator
[0245] One embodiment of the invention provides a ventilator having
a pump upstream of an air/oxygen junction. An example of such a
ventilator is depicted in FIG. 1
[0246] The ventilator comprises an oxygen inlet 1, an air inlet 2,
a junction 3 downstream of the inlets 1,2 and a patient interface 4
downstream of the junction 3. Oxygen is conveyed through oxygen
line 35, which is a gas conduit, from the oxygen inlet 1 to the
junction 3. Air is conveyed through air line 36, which is a gas
conduit, from the air inlet 2 to the junction 3. Air and oxygen are
mixed at the junction 3 to form a mixed gas which is conveyed from
the junction 3 to the patient interface by mixed gas line 37, which
is a gas conduit. The junction can be, e.g. a passive junction such
as a T-junction.
[0247] The oxygen line 35 comprises an oxygen control valve 9,
which is a proportional valve such as a proportional solenoid. The
oxygen control valve 9 is positioned downstream of the oxygen inlet
1 and upstream of the junction 3 to modulate the flow of oxygen
from the oxygen inlet 1 to the junction 3. The oxygen line 35 also
comprises an oxygen flow sensor 10, e.g. downstream of the oxygen
control valve 9, which measures the flow of gas through the oxygen
line 35. Optionally, the ventilator comprises a pressure regulator
14, e.g. if the oxygen inlet 1 is connected to an unregulated
source of oxygen.
[0248] The air line 36 comprises a pump 8 downstream of the air
inlet 2 and upstream junction 3, which pumps gas from the air inlet
2 to the junction 3. The pump 8 is optionally a variable speed pump
such as a variable speed blower (e.g. a fan blower) that can be
modulated by a controller to control the flow of air from the air
inlet 2 to the junction 3. As an alternative to a variable speed
pump, the ventilator can comprise a control valve (not shown)
downstream of the pump and upstream of the junction which is
modulated by a controller to control the air flow. The air line 36
also comprises a flow sensor, such as air flow sensor 11 which
measures the flow of gas through the air line 36.
[0249] The mixed gas line 37 comprises a pressure sensor, such as
mixed gas pressure sensor 12, which measures the pressure of the
mixed gas in the mixed gas line 37. Optionally, the mixed gas line
comprises an air filter such as bacteria filter 13 which filters
mixed gas before reaching the patient interface 4.
[0250] Optionally, the ventilator comprises a valve, such as
exhalation valve 15, which opens to exhaust gas from the ventilator
during an exhalation phase and is closed during an inhalation
phase. The exhalation valve 15 can be comprised by, e.g. the air
line 36 downstream of the pump 8. Upstream of the exhalation valve
15, e.g. downstream of the pump 8, the air line optionally
comprises a check valve 16. Such a check valve can be used, e.g. to
prevent exhalation gas from the patient from backflowing through
cross-contaminating the pump 8 or other upstream components. The
exhalation valve 15 can optionally be a normally-open valve (e.g.
solenoid) to allow free breathing by the patient in case of
ventilator malfunction.
[0251] The ventilator further comprises a controller 18 which
modulates the oxygen control valve 9 and the pump 8 to control
parameters of the mixed gas such as oxygen content and pressure.
The controller is configured to obtain feedback from the oxygen
flow sensor 10, the air flow sensor 11, and the pressure sensor 12
to correct its modulation of the oxygen control valve 9 and the
pump 8 and accurately impart the desired parameters of the mixed
gas. Optionally, the controller is configured to modulate an
exhalation valve 15 such that the exhalation valve 15 is open
during an exhalation phase and is relatively closed during an
inhalation phase.
Example 2
Ventilator with Pump Downstream of Junction
[0252] One embodiment of the invention provides a ventilator having
a pump downstream of an air/oxygen junction. An example of such a
ventilator is depicted in FIG. 2.
[0253] The ventilator comprises an oxygen inlet 1, an air inlet 2,
a junction 3 downstream of the inlets 1,2 and a patient interface 4
downstream of the junction 3. Oxygen is conveyed through oxygen
line 5, which is a gas conduit, from the oxygen inlet 1 to the
junction 3. Air is conveyed through air line 6, which is a gas
conduit, from the air inlet 2 to the junction 3. Air and oxygen are
mixed at the junction 3 to form a mixed gas which is conveyed from
the junction 3 to the patient interface by mixed gas line 7, which
is a gas conduit. The junction can be, e.g. a passive junction such
as a T-junction.
[0254] The mixed gas line 7 comprises a pump 8 downstream of the
junction 3, which pumps mixed gas from the junction 3 to the
patient interface 4. The pump 8 is a variable speed pump such as a
variable speed blower (e.g. a fan blower) that can be modulated by
a controller to control the flow of air from the air inlet to the
junction. The mixed gas line 7 also comprises a flow sensor, such
as mixed gas flow sensor 17, which measures the flow of gas in
mixed gas line 7. The mixed gas line 7 also comprises a pressure
sensor, such as mixed gas pressure sensor 12, which measures the
pressure of the mixed gas in the mixed gas line 7. The pressure
sensor 12 is downstream of the pump 8. Optionally, the mixed gas
flow sensor 17 is downstream of the pump 8. Optionally, the mixed
gas line comprises an air filter such as bacteria filter 13 which
filters mixed gas before reaching the patient interface 4.
[0255] The oxygen line 5 comprises an oxygen control valve 9, which
is a proportional valve such as a proportional solenoid. The oxygen
control valve 9 is positioned downstream of the oxygen inlet 1 and
upstream of the junction 3 to modulate the flow of oxygen from the
oxygen inlet 1 to the junction 3. The oxygen line 5 also comprises
an oxygen flow sensor 10, e.g. downstream of the oxygen valve 9
which measures the flow of gas through the oxygen line 5.
Optionally, the ventilator comprises a pressure regulator 14, e.g.
if the oxygen inlet 1 is connected to an unregulated source of
oxygen.
[0256] The air line 6 optionally comprises a check valve 18
downstream of the air inlet 2 and upstream of the junction 3. The
check valve 18 can be used, e.g. to prevent escape of oxygen from
the oxygen line 5.
[0257] Optionally, the ventilator comprises a valve, such as
exhalation valve 15, which opens to exhaust gas from the ventilator
during an exhalation phase and is closed during an inhalation
phase. The exhalation valve 15 can be comprised by, e.g. the mixed
gas line 7 downstream of the pump 8. Upstream of the exhalation
valve 15, e.g. downstream of the pump 8, the mixed gas line 7
optionally comprises a check valve 16. Such a check valve can be
used, e.g. to prevent exhalation gas from the patient from
backflowing through and cross-contaminating pump 8. The exhalation
valve 15 can optionally be a normally-open valve (e.g. solenoid) to
allow free breathing by the patient in case of ventilator
malfunction.
[0258] The ventilator further comprises a controller 24 which
modulates the oxygen control valve 9 and the pump 8 to control
parameters of the mixed gas such as oxygen content and pressure.
The controller is configured to obtain feedback from the oxygen
flow sensor 10, the mixed gas flow sensor 17, and the pressure
sensor 12 to correct its modulation of the oxygen control valve 9
and the pump 8 and accurately achieve the parameters targets of the
mixed gas. Optionally, the controller is configured to modulate an
exhalation valve 15 such that the exhalation valve 15 is open
during an exhalation phase and is closed during an inhalation
phase.
[0259] Through insight of the inventor, such a ventilator having a
pump downstream of the junction and, e.g. a controller as taught
herein (e.g. any taught in Example 4 through Example 6), provides
one or more of the following advantages. It can provide a simple
control mechanism. For example, the pump can control both
flow/volume and pressure delivered to the patients while the oxygen
valve can function to maintain a set oxygen content and function as
a secondary control flow/volume and pressure delivered.
Additionally, oxygen mixing can be more uniform. Additionally, this
embodiment may also yield more accurate flow/volume and pressure
delivery as the pump can be used as the primary control mechanism
for actual flow/volume and/or pressure delivery to the patient.
Such an unexpected property provides an additional surprising
advantage in the event mixing becomes off (e.g. if the oxygen valve
is not perfectly in sync with a mixing algorithm) because the
flow/volume and pressure delivery will be still accurate because
the pump can ensures the accurate flow and/or pressure
delivery.
Example 3
Ventilator with a Mixing Chamber
[0260] One embodiment of the invention provides a ventilator having
a junction comprising a mixing chamber downstream of an oxygen
inlet and an air inlet and having a pump upstream of the mixing
chamber. An example of such a ventilator is depicted in FIG. 3.
[0261] The ventilator comprises an oxygen inlet 1, an air inlet 2,
an air/oxygen junction comprising a mixing chamber 19 downstream of
the inlets 1,2 and a patient interface 4 downstream of the mixing
chamber 19. Oxygen is conveyed through oxygen line 45, which is a
gas conduit, from the oxygen inlet 1 to the mixing chamber 19. Air
is conveyed through air line 46, which is a gas conduit, from the
air inlet 2 to the mixing chamber 19. Air and oxygen are mixed in
the mixing chamber to form a mixed gas which is conveyed from the
mixing chamber 19 to the patient interface 4 by mixed gas line 47,
which is a gas conduit. Alternatively, air and oxygen can be mixed
upstream of the mixing chamber (not shown).
[0262] The oxygen line 45 comprises an oxygen control valve 9,
which is a proportional valve such as a proportional solenoid. The
oxygen control valve 9 is positioned downstream of the oxygen inlet
1 and upstream of the mixing chamber 19 to modulate the flow of
oxygen from the oxygen inlet 1 to the mixing chamber. The oxygen
line 45 also comprises an oxygen flow sensor 10, e.g. downstream of
the oxygen control valve 9, which measures the flow of gas through
the oxygen line 45. Optionally, the ventilator comprises a pressure
regulator 14, e.g. if the oxygen inlet 1 is connected to an
unregulated source of oxygen.
[0263] The air line 46 comprises a pump 8 downstream of the air
inlet 2 and upstream mixing chamber 19, which pumps mixed gas from
the air inlet 2 to the mixing chamber 19. The pump 8 is optionally
a variable speed pump such as a variable speed blower (e.g. a fan
blower) that can be modulated by a controller to control the flow
of air from the air inlet 2 to the mixing chamber 19. As an
alternative to a variable speed pump, the ventilator can comprise
air line 56 comprising, as an air flow modulator, a control valve
28 downstream of a constant speed pump 27 and upstream of the
mixing chamber 19, as depicted in FIG. 4, wherein the control valve
28 is modulated by a controller 26 to control the air flow. The air
line 46 also comprises a flow sensor, such as air flow sensor 11
which measures the flow of gas through the air line 46.
[0264] The mixed gas line 47 comprises a pressure sensor, such as
mixed gas pressure sensor 12, which measures the pressure of the
mixed gas in the mixed gas line 47. The mixed gas line 47 further
comprises a control valve such as mixed gas control valve 30, which
can be a proportional valve, that is controlled by the controller
to modulate the flow of mixed gas from the mixing chamber 19 to the
patient. Optionally, the mixed gas line comprises an air filter
such as bacteria filter 13 which filters air before reaching the
patient interface 4.
[0265] The mixing chamber 19 comprises a pressure sensor 21 which
provides pressure feedback to the controller 25 and, optionally
comprises an oxygen sensor 20, which measures the oxygen
concentration in the mixing chamber and provides oxygen
concentration feedback to the controller 25. The mixing chamber 19
is filled with gas from the oxygen line 45 and the air line 46 to
provide a mixing chamber gas having an oxygen content equal to that
of the target oxygen content of the mixed gas and having a pressure
substantially greater than that of the mixed gas (e.g. about 10
mbar greater). Mixing chamber 19 provides a pressurized reservoir
with no moving parts in its lumen and has a fixed physical volume
such that gas is released, as needed, to the mixed gas line 47 by
the mixed gas valve 30. Optionally, the physical volume and
pressure of the mixing chamber is configured to provide at least a
tidal volume, i.e. the volume of one breath, for the patient.
[0266] Optionally, the ventilator comprises a valve, such as
exhalation valve 15, which opens to exhaust gas from the ventilator
during an exhalation phase and is closed during an inhalation
phase. The exhalation valve 15 is comprised by the mixed gas line
47 downstream of the mixing chamber 19 and upstream of the patient
interface 4. Upstream of the exhalation valve 15 and downstream of
the mixing chamber 19, the mixed gas line optionally comprises a
check valve 16. Such a check valve can be used, e.g. to prevent
exhalation gas from the patient from backflowing through and
cross-contaminating the mixing chamber The exhalation valve 15 can
optionally be a normally-open valve (e.g. solenoid) to allow free
breathing by the patient in case of ventilator malfunction.
[0267] The ventilator further comprises a controller 25 or 26 which
is configured to pressurize the mixing chamber 19 at a level
substantially greater (e.g. about 10 mbar greater) than the mixed
gas line 47. Specifically, controller 25 modulates the oxygen
control valve 9 and the air flow modulator (e.g. pump 8 or valve
28) to control parameters of the mixing chamber gas such as oxygen
content and mixing chamber pressure. The controller is configured
to obtain feedback from the oxygen flow sensor 10, the air flow
sensor 11, the pressure sensor 21, and optionally, the oxygen
sensor 20, to correct its modulation of the oxygen control valve 9
and the pump 8 and accurately impart the desired parameters of the
mixing chamber gas. The controller 25 is further configured to
modulate the mixed gas control valve 30 to control the pressure,
volume, and/or flow rate of mixed gas that flows from the mixing
chamber 19 to the patient and optionally obtain feedback from a
mixed gas pressure sensor 12 and/or mixed gas flow sensor 17 to
correct its modulation of the mixed gas control valve 30 and
accurately achieve the pressure target, flow target, or volume
target. Optionally, the controller is configured to modulate an
exhalation valve 15 such that the exhalation valve 15 is open
during an exhalation phase and is closed during an inhalation
phase.
[0268] Through insight of the inventor, a ventilator comprising a
mixing chamber as taught herein, can deliver flow/volume and
pressure to the patient with high accuracy with uniform oxygen
mixing throughout the breath delivery.
[0269] Another optional advantage of a ventilator comprising a
mixing chamber as taught herein, is that a modular ventilator
configuration, e.g. with a disconnectable oxygen line, can be
easily designed and implemented and optionally facilitates
burden-free servicing.
Example 4
Ventilator Controller with Cascaded Feedback Control Loop Having an
Outer Loop and Inner Loops
[0270] One embodiment of the invention provides a ventilator having
as feed lines an oxygen line and an air line that join to provide a
gas mixture to a junction, wherein gas flow through each feed line
to the junction can be controlled using a respective flow modulator
e.g. as detailed in any of Example 1 through Example 3. In this
embodiment, the parameters of the gas mixture at or downstream of
the junction depend on the flow through each feed line that feeds
the junction. Specifically, the pressure and flow rate of the gas
are functions of the total (i.e. collective) flow through the feed
lines and the oxygen content of gas mixture is a function of the
ratio or relative flow through the feed lines.
[0271] The ventilator comprises a controller that controls the
oxygen flow modulator and the air flow modulator to produce a gas
mixture having a set of parameter targets. The oxygen flow
modulator is, for example, a proportional valve comprised by the
oxygen line. The air flow modulator is, for example, a variable
speed pump comprised by the air line or downstream of the
air/oxygen junction, or a proportional valve comprised by the air
line.
[0272] The set of parameter targets comprises a target oxygen
content of the gas mixture and one or more of a target pressure of
the gas mixture, a target flow rate (`flow`) of the gas mixture,
and a target volume (e.g. target tidal volume) of the gas mixture.
The controller provides setpoints based on the parameter targets.
For example, the parameter target can be a constant target (e.g. a
constant pressure) and the controller provides the target as a
setpoint. As another example, the parameter target can be a target
shape (e.g. pressure shape) having a plurality of discrete or
relative parameter values and the controller provides a plurality
of setpoints, for example, wherein the plurality of parameter
values are time-dependent setpoints and the controller continuously
updates a setpoint corresponding to the target value at the instant
time.
[0273] The controller calculates a target flow of a gas that flows
through one or more feed lines based on the parameter targets of
the gas mixture such that the flow targets of the feedline gases
impart the parameter targets of the gas mixture (e.g. oxygen
content and at least one of pressure and flow). At least two of the
oxygen feed line, the air feed line, and a line downstream of the
junction (e.g. mixed gas feed line) comprise a respective flow
sensor that sends feedback of the actual flow through the
respective line to the controller. The controller can be configured
to use a first equation that relates the flow through each line to
each other. For example, the total flow downstream of the junction
(i.e. gas mixture flow) is equal to the sum of the flows through
the oxygen line and the air line. As another example, the flow
through one of the feed lines is equal to the difference between
the flow of the other feed line and the total flow downstream of
the junction. The controller can also be configured to use a second
equation that relates the oxygen content of the gas mixture to the
respective oxygen content and respective flows of the oxygen line
and the air line.
[0274] To impart a target pressure of the gas mixture, the
controller is configured to calculate a flow target (e.g. mass
flow) of the gas mixture using third equation that estimates the
relationship of flow to pressure. The relationship of pressure and
flow (or cumulative flow, i.e. volume delivered) is affected by
certain variables. For example, in embodiments wherein the gas
mixture is delivered to a mixing chamber, the container size of the
mixing chamber affects the relationship of flow and pressure. In
embodiments wherein the gas mixture is delivered directly to a
patient, compliance of the patient system (e.g. lung and tube
compliance) has a dramatic effect on the relationship of flow and
pressure.
[0275] The target gas mixture flow is a command of the first
feedback loop. The controller is configured to use a first feedback
loop that corrects the target gas mixture flow using feedback
received from a pressure sensor. Based on the calculated target gas
mixture flow, the controller commands (i.e. calculates in this
example) respective flow targets for the air line and the oxygen
line using one or more equations that relate the gas mixture flow
and oxygen content to respective flows and oxygen contents of the
oxygen line and the air line, e.g. as detailed above.
[0276] The controller is configured to use a second feedback loop
for control of the air flow modulator to impart the calculated air
flow target. The controller is configured to use a third feedback
loop for control of the oxygen flow modulator to impart the
calculated oxygen flow. For each feedback loop, the controller
corrects its command to the respective flow modulator after
comparing the calculated target flow to actual flow. The actual
flow is derived from feedback received from one or more flow
sensors. For example, the actual flow value of the line can be
obtained directly from a flow sensor comprised by the line, or it
can be calculated using feedback from flow sensors of other lines,
wherein flow of the gas mixture is the sum of the oxygen flow and
the air flow.
[0277] Accordingly, this example demonstrates a cascaded feedback
control loop that comprises the first feedback control loop as an
outer loop and each of the second and third feedback loops as inner
loops. Specifically, flow values are commanded by the first
feedback loop to achieve a target gas mixture pressure, and the
second and third feedback loops use the commanded target flow
values as setpoints and achieve the setpoints by commanding
respective flow modulators.
[0278] The cascaded feedback loop configuration taught in this
example is useful in embodiments of the present invention, e.g. the
ventilators detailed in any of Example 1, Example 2, or Example 3.
For example, in embodiments that deliver gases from air and oxygen
feed lines to a patient interface (e.g. without an intermediate
mixing chamber that is pressurized to an overpressure), the
controller can be used to control the delivery of gases to the
patient interface. As another example, in embodiments that have a
mixing chamber downstream of air and oxygen feed lines, the
controller can be used to control the delivery of gases to the
mixing chamber.
[0279] Through insight of the inventor, ventilators of the
invention can use this feedback loop configuration to provide a
superior ventilator having precise control of pressure and
air/oxygen mixing.
Example 5
Ventilator Controller Feedback Control Loops
[0280] FIG. 5, FIG. 6A, FIG. 6B, and FIG. 7 depict examples of
useful feedback loops which can be used by the controller to obtain
a target pressure and a target oxygen content. Each of these
feedback loops are useful in embodiments of the present invention,
e.g. the ventilators detailed in any of Example 1, Example 2, or
Example 3. For example, in embodiments that deliver gases from air
and oxygen feed lines to a patient interface (e.g. without an
intermediate mixing chamber that is pressurized to an
overpressure), the feedback loops can be used to control the
delivery of gases to the patient interface. As another example, in
embodiments that have a mixing chamber downstream of air and oxygen
feed lines, the feedback loops can be used to control the delivery
of gases to the mixing chamber. In the figures, gas flow is
depicted by solid lines and data flow and controller commands are
depicted by dashed lines.
[0281] FIG. 5 depicts a pressure feedback loop that commands a flow
target of a gas mixture to achieve a target pressure (e.g. in a
patient interface or a mixing chamber), and splits the command into
a target air flow and a target oxygen flow based on a target oxygen
content. Target air flow is optionally controlled by a controller
configured to a use an air flow feedback loop, as depicted in FIG.
6A. Target oxygen flow is optionally controlled by a controller
configured to a use an oxygen flow feedback loop, as depicted in
FIG. 6B.
[0282] The ventilator is optionally configured to use a cascaded
feedback loop, wherein the cascaded feedback loop comprises a
pressure loop as an outer loop that calculates flows that, when
imparted by flow modulators, produce a gas mixture with a desired
pressure setpoint, and wherein the cascaded feedback loop further
comprises inner loops that command respective flow modulators that
impart the calculated flows, e.g. as detailed in Example 4.
Optionally, the ventilator comprises a controller configured to use
a feedback loop that contains an outer loop and two parallel inner
loops, each within the outer loop, e.g. as depicted in FIG. 7. In
FIG. 7, the outer loop is a pressure feedback loop. A first inner
loop is an air flow feedback loop that commands an air flow
modulator. A second inner loop is an oxygen flow feedback loop that
commands an oxygen flow modulator. For each feedback loop, the
controller provides at least one setpoint based on a target for a
gas parameter, provides a command configured (e.g. calibrated) to
produce the setpoint, obtains the actual value of the gas parameter
from a sensor as feedback from the command, compares the actual
value to the setpoint to produce a command error (i.e., the
difference between the setpoint and the actual value), and modifies
a subsequent command based on the command error in real time. As
the setpoint for a feedback loop can often be the target itself
(e.g. as opposed to a setpoint calculated based on the target), the
term "target" is sometimes used herein when referring to the
setpoint of a feedback loop; however, it is to be understood that a
setpoint can alternatively be a setpoint provided (e.g. calculated)
based on the target rather than the target itself.
[0283] The pressure feedback loop (e.g. the pressure loop of FIG. 5
or FIG. 7) is configured to impart the target pressure (e.g. in a
"patient system" as shown, or in any alternative system component
such as a mixing chamber) by commanding (e.g. calculating) a target
flow of the gas mixture. An algorithm is used to provide a target
oxygen flow and a target air flow based on the mixed gas flow
target and the target oxygen content. The air flow loop is
configured to achieve the target air flow by commanding the air
flow modulator. The oxygen flow loop is configured to achieve the
target oxygen flow by commanding the oxygen flow modulator.
[0284] As depicted in the feedback loop of FIG. 5 and FIG. 7, the
controller can be configured to perform the following steps:
[0285] A. A target pressure (e.g., a constant pressure value, or
one of various pressure shapes such as adjustable rise time
setting) is obtained. For example, if the target pressure is the
target pressure of the mixed gas that's delivered to the patient,
the target pressure can be set by user input (e.g. by a clinician).
As another example, if the target pressure is the target pressure
of an optional mixing chamber, the target pressure of the mixing
chamber can be calculated based on a target pressure of the mixed
gas, e.g. a defined overpressure of the maximum target pressure of
the mixed gas. The controller can then provide a pressure setpoint
based on the target pressure (e.g. wherein the setpoint is a point
in a target pressure shape or wherein the setpoint is the constant
pressure of a target pressure comprising constant pressure).
[0286] B. Summing junction of pressure target and pressure
feedback. A comparison is made between the pressure target and the
pressure feedback, i.e. actual pressure measured via a pressure
sensor in the circuit.
[0287] C. A pressure error is calculated from the comparison of the
pressure target and the pressure feedback. Specifically, the
pressure error is the difference between the pressure target and
the pressure feedback.
[0288] D. The pressure error becomes the input to the gas mixture
flow target controller (e.g. mixed gas controller or mixing chamber
gas controller) which corrects the pressure command, i.e. modifies
the previous pressure command, based on the pressure error. The
pressure command is a command configured to produce the target
pressure. The gas mixture flow target controller (labeled "flow
target controller") produces a gas mixture flow target as the
pressure command, e.g. wherein the gas mixture flow target is the
flow target value of a mixed gas comprising oxygen from the oxygen
line and air from the air line which reaches the patient or, if a
mixing chamber is provided, the gas mixture flow target is the
target total flow of oxygen and air fed to a mixing chamber. The
control cycle can be, e.g. 1-5 msec depending on the performance
requirements. The feedback control mechanism can be, e.g.
proportional, integral, derivative, PI, PID, feedforward, or a
modified form thereof.
[0289] E. The pressure command (i.e. mixed gas mixture flow target)
is input into the FiO.sub.2 algorithm.
[0290] F. The FiO.sub.2 (Fraction of Inspired Oxygen) algorithm
calculates a target air flow and a target oxygen flow based on the
gas mixture flow target and the target oxygen content. The target
oxygen content is obtained, e.g. from user input of a FiO.sub.2
setting. Specifically, the gas mixture flow target is split into a
target air flow and a target oxygen flow based on the target oxygen
content.
[0291] G. The air flow target is input to the air flow
controller
[0292] H. The air flow controller commands the air flow modulator
to achieve the target air flow. The air flow modulator is, for
example, a variable speed pump (e.g. a dynamic pump) in the air
line or mixed gas line or a proportional valve in the air line
downstream of a pump (e.g. dynamic pump). The air flow controller
can, for example, meter air flow from a flow sensor (e.g. measured
directly in the air line or calculated as the difference between
the flow of the gas mixture and the flow of oxygen) and obtain the
actual air flow as feedback for comparison with the target air flow
to produce an air flow error and correct the air flow command. The
feedback control mechanism can be, e.g., proportional, integral,
derivative, PI, PID, feedforward, or a modified form thereof.
[0293] I. The oxygen flow target is input to the oxygen flow
controller
[0294] J. The oxygen flow controller commands the oxygen flow
modulator to achieve the oxygen flow target. The oxygen flow
modulator is, for example, a proportional valve in the oxygen line.
The oxygen flow controller meters, for example, oxygen flow from a
flow sensor in the oxygen line and obtains the actual oxygen flow
as feedback for comparison with the target oxygen flow to produce
an oxygen flow error and correct the oxygen flow command. The
feedback control mechanism can be, e.g., proportional, integral,
derivative, PI, PID, feedforward, or a modified form thereof.
[0295] K. Air flow output--Air flows from the air flow modulator
downstream to the junction.
[0296] L. Oxygen flow output--Oxygen flows from the oxygen flow
modulator downstream to the junction.
[0297] M. Summing junction of air flow and oxygen flow outputs. The
oxygen flow output merges with the air flow output to form a gas
mixture.
[0298] N. Gas mixture. The gas mixture output, i.e., a mixture
comprising the air flow output plus oxygen flow output, is
provided. The gas mixture can be, e.g. mixed gas for delivery to
the patient or can be a gas mixture delivered to a mixing chamber.
The pressure of the gas mixture is function of at least the flow of
the gas mixture, specifically the volume delivered which is an
integration of flow, noting that the relationship of pressure v.s.
flow or volume delivered can depend on physical volume or
compliance of the target space to which the gas mixture is
delivered (e.g. patient system or mixing chamber). For example, in
an embodiment wherein the gas mixture is fed to a mixing chamber or
directly to a patient, the pressure of the gas mixture can depend,
at least in part, on the volume of the mixing chamber or the
patient system, respectively. When the gas mixture is the mixed gas
delivered to the patient (e.g. rather than to an intermediate
mixing chamber), the pressure is affected by compliance of the
patient system (e.g. static and/or dynamic compliance) such as
patient-lung compliance and tubing compliance. The patient system
can comprise the patient and the patient interface and includes,
for example, a patient circuit, inline humidifier, inline bacteria
filter, mask and any optional component inline with the patient
tubing. These features can introduce additional compliance which
can be corrected by feedback control of the pressure.
[0299] O. The pressure sensor measures the actual pressure of the
gas mixture and provides feedback to the gas mixture controller.
Optionally, the gas mixture is the mixed gas provided to the
patient and the pressure sensor is located, e.g., either in the
patient circuit or upstream in the ventilator. Alternatively, the
gas mixture is optionally the mixing chamber gas and the pressure
sensor is comprised by the mixing chamber.
[0300] P. Pressure feedback--The actual pressure of the gas mixture
measured by the pressure sensor is obtained by the controller for
comparison with the target pressure in the summing junction, as
detailed in step B, and the feedback loop is continuously repeated
in real time.
[0301] FIG. 6A depicts a feedback control loop that can optionally
be used by an air flow controller, e.g. the air flow controller of
step H in the feedback loop detailed in the example above. As
depicted in FIG. 6A, the feedback control loop comprises the
following steps:
[0302] G. The air flow target is provided.
[0303] H1. Summing junction of air flow target and air flow
feedback. A comparison is made between the air flow target and the
air flow feedback, e.g. the actual air flow measured in the air
line or calculated based on the difference between measured oxygen
flow and measured gas mixture flow.
[0304] H2. An air flow error is calculated from the comparison of
the air flow target and the air flow feedback. Specifically, the
air flow error is the difference between the air flow target and
the air flow feedback.
[0305] H3. The air flow error becomes the input to the air flow
controller which corrects the air flow command, i.e. modifies the
previous air flow command, based on the air flow error. The
feedback control mechanism can be, e.g. proportional, integral,
derivative, PI, PID, feedforward, or a modified form thereof.
[0306] H4. The air flow command is provided to the air flow
modulator. The air flow command is, for example, a signal such as a
voltage provided to the air flow modulator.
[0307] H5. The air flow modulator receives the air flow command and
assumes a position (e.g. pump speed or valve position), e.g. that
is dependent on the signal level of the command. The air flow
modulator is, for example, a variable speed pump (e.g. variable
speed dynamic pump) in the air line or downstream of the air/oxygen
junction or a proportional valve in the air line downstream of a
pump (e.g. fixed speed dynamic pump).
[0308] K. Air flow output--Air flows downstream from the air flow
modulator
[0309] H6. The air flow sensor, provided in the air line, measures
the actual air flow. As an alternative to using an air flow sensor,
an air flow calculator can be used to calculate the air flow
feedback, e.g. as the difference between measured oxygen flow and
measured gas mixture flow.
[0310] H7. The actual air flow (e.g. measured by the air flow
sensor) is provided to the controller as air flow feedback for
comparison with the target air flow in the summing junction, as
detailed in step H1, and the feedback loop is continuously repeated
in real time.
[0311] FIG. 6B depicts a feedback control loop that can optionally
be used by an oxygen flow controller, e.g. the oxygen flow
controller of step J in the feedback loop detailed in the example
above.
[0312] G. The oxygen flow target is provided
[0313] J1. Summing junction of oxygen flow target and oxygen flow
feedback. A comparison is made between the oxygen flow target and
the oxygen flow feedback, i.e. the actual oxygen flow measured in
the oxygen line or calculated based on the difference between
measured air flow and measured gas mixture flow.
[0314] J2. An oxygen flow error is calculated from the comparison
of the oxygen flow target and the oxygen flow feedback.
Specifically, the oxygen flow error is the difference between the
oxygen flow target and the oxygen flow feedback.
[0315] J3. The oxygen flow error becomes the input to the oxygen
flow controller which corrects the oxygen flow command, i.e.
modifies the previous oxygen flow command, based on the oxygen flow
error. The feedback control mechanism can be, e.g. proportional,
integral, derivative, PI, PID, feedforward, or a modified form
thereof.
[0316] J4. The oxygen flow command is provided to the oxygen flow
modulator. The oxygen flow command is, for example, a signal such
as a voltage provided to the oxygen flow modulator.
[0317] J5. The oxygen flow modulator receives the oxygen flow
command and assumes a position (e.g. valve position), e.g. that is
dependent on the signal level of the command. The oxygen flow
modulator is, for example, a proportional valve in the oxygen line
downstream of the oxygen inlet.
[0318] L. Oxygen flow output--Oxygen flows downstream from the
oxygen flow modulator
[0319] J6. The oxygen flow sensor, provided in the oxygen line,
measures the actual oxygen flow. As an alternative to using an
oxygen flow sensor, an oxygen flow calculator can be used to
calculate the oxygen flow feedback, e.g. as the difference between
measured air flow and measured gas mixture flow.
[0320] J7. The actual oxygen flow (e.g. measured by the oxygen flow
sensor) is provided to the controller as oxygen flow feedback for
comparison with the target oxygen flow in the summing junction, as
detailed in step J1, and the feedback loop is continuously repeated
in real time.
[0321] Through insight of the inventor, ventilators of the
invention can use the feedback loops of this example to provide a
superior ventilator having precise control of pressure and
air/oxygen mixing.
Example 6
Ventilator Controller Feedback Control Loops
[0322] This example details a controller configured to use one or
more feedback loops for delivering mixed gas to a patient with
other forms of targeting such as volume targeting or flow
targeting.
[0323] FIG. 9, FIG. 6A, FIG. 6B, and FIG. 10 depict examples of
useful feedback loops which can be used by the controller to obtain
a target volume or flow and a target oxygen content. Each of these
feedback loops are useful in embodiments of the present invention,
e.g. the ventilators detailed in in Example 1 or Example 2
[0324] FIG. 9 depicts a volume or flow controller that commands a
flow target of a gas mixture to achieve a target flow in a patient
interface and splits the command into a target air flow and a
target oxygen flow based on a target oxygen content. The flow
target is, for example, calculated based on a volume target (e.g.
determined by a user inputted waveform such as sine wave or
descending ramp or by a real time volume measurement and
calculation of real time volume error). Target air flow is
optionally controlled by a controller configured to a use an air
flow feedback loop, as depicted in FIG. 6A. Target oxygen flow is
optionally controlled by a controller configured to a use an oxygen
flow feedback loop, as depicted in FIG. 6B.
[0325] Optionally, the ventilator comprises a controller configured
to use parallel inner loops, each having a setpoint (labeled "air
flow target" and "O.sub.2 flow target", respectively) determined by
a controller such as a controller which utilizes an a FiO.sub.2
algorithm, e.g. as depicted in FIG. 10. A first loop is an air flow
feedback loop that commands an air flow modulator. A second loop is
an oxygen flow feedback loop that commands an oxygen flow
modulator. The mixed gas controller provides the air flow target
and oxygen flow target which are used as setpoints (i.e. targets)
by the air flow controller and oxygen flow controller,
respectively. For each feedback loop, the controller provides a
flow, provides a command configured (e.g. calibrated) to achieve
the target flow, obtains or calculates the actual value of the flow
from a sensor as feedback from the command, compares the actual
flow value to the target flow to produce a command error (i.e., the
difference between the target and the actual value), and modifies a
subsequent command based on the command error in real time.
[0326] An algorithm is used to provide a target oxygen flow and a
target air flow based on the mixed gas flow target and the target
oxygen content. The air flow loop is configured to achieve the
target air flow by commanding the air flow modulator. The oxygen
flow loop is configured to achieve the target oxygen flow by
commanding the oxygen flow modulator.
[0327] As depicted in the control diagrams of FIG. 9 and FIG. 10,
the controller can be configured to perform the following
steps:
[0328] An input (e.g. user input) such as target volume, as shown,
or flow target, is obtained by the mixed gas controller.
[0329] D2. If a volume target was provided as the input, a mixed
gas flow target is provided based on the input. For example, the
mixed gas controller can comprise a functional component (labeled
"flow target controller") that determines (e.g. calculates) a flow
target based on the volume target shape or real time measured
volume error.
[0330] E. the mixed gas flow target is input into the FiO.sub.2
algorithm.
[0331] F. The FiO.sub.2 (Fraction of Inspired Oxygen) algorithm
calculates a target air flow and a target oxygen flow based on the
gas mixture flow target and the target oxygen content. The target
oxygen content is obtained, e.g. from user input of a FiO.sub.2
setting. Specifically, the gas mixture flow target is split into an
air flow target and an oxygen flow target based on the target
oxygen content.
[0332] G. The air flow target is input to the air flow
controller
[0333] H. The air flow controller commands the air flow modulator
to achieve the target air flow. The air flow modulator is, for
example, a variable speed pump (e.g. a dynamic pump) in the air
line or a mixed gas line or a proportional valve in the air line
downstream of a pump (e.g. dynamic pump). The air flow controller
can, for example, meter air flow from a flow sensor (e.g. measured
directly in the air line or calculated as the difference between
the flow of the gas mixture and the flow of oxygen) and obtain the
actual air flow as feedback for comparison with the target air flow
to produce an air flow error and correct the air flow command. The
feedback control mechanism can be, e.g., proportional, integral,
derivative, PI, PID, feedforward, or a modified form thereof.
[0334] I. The oxygen flow target is input to the oxygen flow
controller
[0335] J. The oxygen flow controller commands the oxygen flow
modulator to achieve the oxygen flow target. The oxygen flow
modulator is, for example, a proportional valve in the oxygen line.
The oxygen flow controller meters, for example, oxygen flow from a
flow sensor in the oxygen line and obtains the actual oxygen flow
as feedback for comparison with the target oxygen flow to produce
an oxygen flow error and correct the oxygen flow command. The
feedback control mechanism can be, e.g., proportional, integral,
derivative, PI, PID, feedforward, or a modified form thereof.
[0336] K. Air flow output--Air flows from the air flow modulator
downstream to the junction.
[0337] L. Oxygen flow output--Oxygen flows from the oxygen flow
modulator downstream to the junction.
[0338] M. Summing junction of air flow and oxygen flow outputs. The
oxygen flow output merges with the air flow output to form the
mixed gas.
[0339] N. Gas mixture. The gas mixture output, i.e., the mixed gas
comprising the air flow output plus oxygen flow output, is provided
to the mixed gas line.
[0340] As depicted in FIG. 10, the air flow controller and the
oxygen flow controller can be configured to use feedback loops to
control respective modulators, e.g. as depicted in FIG. 6A and FIG.
6B, respectively.
[0341] FIG. 6A depicts a feedback control loop that can optionally
be used by the air flow controller, e.g. the air flow controller of
step H in the feedback loop detailed in the example above. As
depicted in FIG. 6A, the feedback control loop comprises the
following steps:
[0342] G. The air flow target is provided.
[0343] H1. Summing junction of air flow target and air flow
feedback. A comparison is made between the air flow target and the
air flow feedback, e.g. the actual air flow measured in the air
line or calculated based on the difference between measured oxygen
flow and measured gas mixture flow.
[0344] H2. An air flow error is calculated from the comparison of
the air flow target and the air flow feedback. Specifically, the
air flow error is the difference between the air flow target and
the air flow feedback.
[0345] H3. The air flow error becomes the input to the air flow
controller which corrects the air flow command, i.e. modifies the
previous air flow command, based on the air flow error. The
feedback control mechanism can be, e.g. proportional, integral,
derivative, PI, PID, feedforward, or a modified form thereof.
[0346] H4. The air flow command is provided to the air flow
modulator. The air flow command is, for example, a signal such as a
voltage provided to the air flow modulator.
[0347] H5. The air flow modulator receives the air flow command and
assumes a position (e.g. pump speed or valve position), e.g. that
is dependent on the signal level of the command. The air flow
modulator is, for example, a variable speed pump (e.g. variable
speed dynamic pump) in the air line or downstream of the air/oxygen
junction or a proportional valve in the air line downstream of a
pump (e.g. fixed speed dynamic pump).
[0348] K. Air flow output--Air flows downstream from the air flow
modulator
[0349] H6. The air flow sensor, provided in the air line, measures
the actual air flow. As an alternative to using an air flow sensor,
an air flow calculator can be used to calculate the air flow
feedback, e.g. as the difference between measured oxygen flow and
measured gas mixture flow.
[0350] H7. The actual air flow (e.g. measured by the air flow
sensor) is provided to the controller as air flow feedback for
comparison with the target air flow in the summing junction, as
detailed in step H1, and the feedback loop is continuously repeated
in real time.
[0351] FIG. 6B depicts a feedback control loop that can optionally
be used by the oxygen flow controller, e.g. the oxygen flow
controller of step J in the feedback loop detailed in the example
above.
[0352] G. The oxygen flow target is provided
[0353] J1. Summing junction of oxygen flow target and oxygen flow
feedback. A comparison is made between the oxygen flow target and
the oxygen flow feedback, i.e. the actual oxygen flow measured in
the oxygen line or calculated based on the difference between
measured air flow and measured gas mixture flow.
[0354] J2. An oxygen flow error is calculated from the comparison
of the oxygen flow target and the oxygen flow feedback.
Specifically, the oxygen flow error is the difference between the
oxygen flow target and the oxygen flow feedback.
[0355] J3. The oxygen flow error becomes the input to the oxygen
flow controller which corrects the oxygen flow command, i.e.
modifies the previous oxygen flow command, based on the oxygen flow
error. The feedback control mechanism can be, e.g. proportional,
integral, derivative, PI, PID, feedforward, or a modified form
thereof.
[0356] J4. The oxygen flow command is provided to the oxygen flow
modulator. The oxygen flow command is, for example, a signal such
as a voltage provided to the oxygen flow modulator.
[0357] J5. The oxygen flow modulator receives the oxygen flow
command and assumes a position (e.g. valve position), e.g. that is
dependent on the signal level of the command. The oxygen flow
modulator is, for example, a proportional valve in the oxygen line
downstream of the oxygen inlet.
[0358] L. Oxygen flow output--Oxygen flows downstream from the
oxygen flow modulator
[0359] J6. The oxygen flow sensor, provided in the oxygen line,
measures the actual oxygen flow. As an alternative to using an
oxygen flow sensor, an oxygen flow calculator can be used to
calculate the oxygen flow feedback, e.g. as the difference between
measured air flow and measured gas mixture flow.
[0360] J7. The actual oxygen flow (e.g. measured by the oxygen flow
sensor) is provided to the controller as oxygen flow feedback for
comparison with the target oxygen flow in the summing junction, as
detailed in step J1, and the feedback loop is continuously repeated
in real time.
[0361] Accordingly, this example details how volume or flow
targeting can be used to deliver a mixed gas to a patient with
feedback control of oxygen and flow modulators. Such volume- or
flow-targets can be, e.g. provided as an alternative to pressure
targeting for choosing by a user of the ventilator.
Example 7
Controller for a Ventilator with a Mixing Chamber
[0362] One embodiment of the invention provides a ventilator having
an oxygen feed line, an air feed line, an oxygen flow modulator,
and an air flow modulator, wherein the flow modulators modulate the
flow of the respective gases to a junction comprising a mixing
chamber, e.g. as detailed in Example 3. In this embodiment, the
parameters of the mixing chamber gas depend on the flow through
each line that feeds the mixing chamber. Specifically, the oxygen
content of the gas mixture is a function of the ratio or relative
flow through the feed lines, and given a fixed physical volume of
the mixing chamber, the pressure in the mixing chamber is a
function of the cumulative flow through the feed lines. The
ventilator comprises a controller that controls the oxygen flow
modulator and the air flow modulator to produce a mixing chamber
gas having a set of parameter targets comprising a target oxygen
content and target mixing chamber pressure. To pressurize the
mixing chamber to a target mixing chamber pressure and target
oxygen content, the controller can use one or more feedback loops,
e.g. as detailed in Example 4 or in Example 5 and shown in FIG. 5,
FIG. 6A, FIG. 6B, or FIG. 7.
[0363] The ventilator further comprises a mixed gas line that
transmits gas from the mixing chamber to the patient and a mixed
gas control valve in the mixed gas line that modulates flow of gas
released from the mixing chamber to patient, e.g. as detailed in
Example 3. In addition to the aforementioned feedback loops to
control delivery of gas to the mixing chamber, the controller can
be configured to use another feedback control loop for error
correction of the mixed gas control valve to control delivery of
mixed gas to the patient. An example of such a feedback control
loop is depicted in FIG. 8. Accordingly, in this embodiment, the
controller is optionally configured to use a first feedback loop
(e.g. FIG. 5 or FIG. 7) to control the delivery of gas to the
mixing chamber and a second feedback loop to control the delivery
of gas from the mixing chamber to the patient (e.g. FIG. 8 or FIG.
11).
[0364] As depicted in the feedback loop of FIG. 8, the controller
can be configured to perform the following steps to control
delivery of gas from the mixing chamber to the patient:
[0365] Q. A target mixed gas pressure (e.g., a constant pressure
value, or one of various pressure shapes such as adjustable rise
time setting) is obtained, e.g. set by user input (e.g. by a
clinician).
[0366] R. Summing junction of pressure target and pressure
feedback. A comparison is made between the pressure target and the
pressure feedback, i.e. actual pressure measured via a pressure
sensor downstream of the mixed gas control valve.
[0367] S. A pressure error is calculated from the comparison of the
pressure target and the pressure feedback. Specifically, the
pressure error is the difference between the pressure target and
the actual pressure.
[0368] T. The pressure error becomes the input to the mixed gas
flow controller which corrects the mixed gas control valve command,
i.e. modifies the previous mixed gas valve command, based on the
pressure error. The feedback control mechanism can be, e.g.
proportional, integral, derivative, PI, PID, feedforward, or a
modified form thereof.
[0369] U. The mixed gas valve command is provided to the mixed gas
control valve. The mixed gas valve command is, for example, a
signal such as a voltage provided to the mixed gas control
valve
[0370] V. The mixed gas control valve receives the mixed gas valve
command and assumes a position (e.g. valve position), e.g. that is
dependent on the signal level of the command. The mixed gas control
valve is, for example, a proportional valve the downstream of the
mixing chamber.
[0371] W. The mixed gas is output, i.e., gas flows from the mixing
chamber downstream towards the patient. The actual pressure of the
mixed gas is function of the flow of the gas mixture, specifically
the volume delivered which is an integration of flow. However, the
actual pressure is also affected by other factors such as
compliance of the patient system (e.g. static and/or dynamic
compliance) such as patient-lung compliance and tubing compliance.
The patient system comprises the patient and the patient interface
and includes, for example, a patient circuit, inline humidifier,
inline bacteria filter, mask and any optional component inline with
the patient tubing. These features can introduce disturbances which
can be corrected by feedback control of the pressure.
[0372] X. The pressure sensor measures the actual pressure of the
mixed gas and provides feedback to the controller. The pressure
sensor can be located, e.g., either in the patient circuit or
upstream in the ventilator.
[0373] Y. Pressure feedback--The actual pressure of the mixed gas
measured by the pressure sensor is obtained by the controller for
comparison with the target pressure in the summing junction, as
detailed in step R, and the feedback loop is continuously repeated
in real time.
[0374] As an alternative to the feedback loop depicted in FIG. 8,
which modulates a mixed gas control valve to impart a target
pressure in the mixed gas line, the controller can be configured to
use a feedback loop which modulates the mixed gas control valve to
impart a target flow or target volume (e.g. a target volume shape
defined by one or more target flows). In this embodiment, the
pressure target, pressure error, pressure detection, pressures
sensor, and pressure feedback steps detailed above and shown in
FIG. 8 can be substituted with a flow target, flow error, flow
detection, flows sensor, and flow feedback, respectively.
Additionally or alternatively, the flow target can be determined,
e.g., calculated based on a volume target, (e.g. by a flow target
controller as with flow target controller D2 of FIG. 9 which
determines gas mixture flow target E). Specifically, as depicted in
FIG. 11, the controller can be configured to perform the following
steps to control delivery of gas from the mixing chamber to the
patient:
[0375] AA. A mixed gas flow target is provided, e.g. by input by a
user or determined based on a target volume shape or real time
target volume error.
[0376] AB. Summing junction of flow target and flow feedback. A
comparison is made between the flow target and the flow feedback,
i.e. actual flow measured via a flow sensor in the mixed gas
line.
[0377] AC. A flow error is calculated from the comparison of the
flow target and the flow feedback. Specifically, the flow error is
the difference between the flow target and the actual flow.
[0378] AD. The flow error becomes the input to the mixed gas flow
controller which corrects the mixed gas control valve command, i.e.
modifies the previous mixed gas valve command, based on the flow
error. The feedback control mechanism can be, e.g. proportional,
integral, derivative, PI, PID, feedforward, or a modified form
thereof.
[0379] AE. The mixed gas valve command is provided to the mixed gas
control valve. The mixed gas valve command is, for example, a
signal such as a voltage provided to the mixed gas control
valve
[0380] AF. The mixed gas control valve receives the mixed gas valve
command and assumes a position (e.g. valve position), e.g. that is
dependent on the signal level of the command. The mixed gas control
valve is, for example, a proportional valve in the downstream of
the mixing chamber.
[0381] AG. The mixed gas is output, i.e., gas flows from the mixing
chamber downstream towards the patient.
[0382] AH. The flow sensor measures the actual flow of the mixed
gas and provides feedback to the controller.
[0383] AI. Flow feedback--The actual flow of the mixed gas measured
by the flow sensor is obtained by the controller for comparison
with the target flow in the summing junction, as detailed in step
AB, and the feedback loop is continuously repeated in real
time.
[0384] As detailed in this example, a ventilator comprising a
mixing chamber can use one or more feedback loops for pressurizing
the mixing chamber as well as one or more feedback loops for
delivering mixed gas to a patient. Also as detailed in this
example, the ventilator can be configured for delivering mixed gas
to a patient with pressure targeting, volume targeting, flow
targeting, or a combination thereof. F
Example 8
Calculation of Target Air Flow and Target Oxygen Flow
[0385] According to the present invention, a controller can
optionally be configured to use an FiO.sub.2 algorithm, e.g. as in
step F described in Example 5, to calculate a target air flow and a
target oxygen flow based on the gas mixture flow target and the
target oxygen content. The following example illustrates equations
that can optionally be used to perform such a calculation.
[0386] In the equations that follow, the following variable
definitions are used:
[0387] F.sub.A=Target flow of air through the air line
[0388] F.sub.O=Target flow of oxygen through the oxygen line
[0389] F.sub.M=Target flow of a gas mixture (e.g. mixed gas or
mixing chamber gas)
[0390] O.sub.A=Oxygen content of air
[0391] O.sub.O=Oxygen content of oxygen
[0392] O.sub.M=Target oxygen content of mixed gas
[0393] F.sub.M=Target flow of the mixed gas
[0394] The following equation relates the oxygen content and flow
rates of the three gasses (gas mixture M, air A, and oxygen O):
(O.sub.M)(F.sub.M)=(O.sub.A)(F.sub.A)+(O.sub.O)(F.sub.O) Equation
1:
[0395] The following equation relates the flow rates of the three
gasses:
F.sub.M=F.sub.A+F.sub.O Equation 2:
[0396] Substituting the identity of F.sub.M (from Equation 2) into
Equation 1, provides:
(O.sub.M)(F.sub.A+F.sub.O)=(O.sub.A)(F.sub.A)+(O.sub.O)(F.sub.O)
Equation 3:
[0397] As examplary oxygen contents, consider the oxygen content of
air O.sub.A is 0.21, the oxygen content of oxygen is 1, and an
examplary target oxygen content of the gas mixture is O.sub.M 0.26.
Under these conditions, Equation 3 can be solved as:
F.sub.A/F.sub.O=14.8
[0398] Under these examplary conditions, the ratio of air flow rate
to flow rate is, for example, 14.8 to provide a target mixed gas
oxygen content of 26%.
[0399] This example demonstrates the use of Equations 3 to
determine the relative flows of oxygen and air.
[0400] Given a target gas mixture flow rate F.sub.M (e.g.
determined based on a target pressure), Equation 2 can be used to
determine the actual flow rates of the oxygen and air. Accordingly,
this example also demonstrate the use of Equation 2 in combination
with Equation 3 to determine the target flows of air and oxygen
based on a target mixed gas flow.
[0401] The citations provided herein are hereby incorporated by
reference for the cited subject matter.
* * * * *