U.S. patent application number 09/931572 was filed with the patent office on 2002-03-07 for ventilator control system and method.
Invention is credited to Biondi, James W., Gilmore, Donald D., Johnston, Douglas M., Reynolds, Robert, Schroeder, Gerhardt P..
Application Number | 20020026941 09/931572 |
Document ID | / |
Family ID | 21938021 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020026941 |
Kind Code |
A1 |
Biondi, James W. ; et
al. |
March 7, 2002 |
Ventilator control system and method
Abstract
The invention features an exhalation assist device for adjusting
the airway resistance in an exhalation circuit of a medical
ventilator. The device includes a set of pressure, airflow and
airway sensors, a controlling processor, a user interface, and a
ventilatory unit in communication with a medical ventilator. Data
relating to pressure within the ventilatory unit and data relating
to exhalation airflow, exhalation circuit pressure and exhalation
circuit resistance are provided to the controlling processor by the
sensors. The controlling processor compares measured and calculated
values for airway pressure, airflow, airway resistance and applied
negative pressure with desired values that have been entered by a
clinician. Based on these calculations, the controlling processor
transmits a signal that will change the applied negative pressure
applied to the exhalation circuit by the ventilatory unit. The
amount of negative pressure applied during the breathing cycle is
varied by the controlling processor so that the amount of
exhalation assist increases proportionately with the amount of
exhalation flow and so that the amount of pressure within the
patient airway remains constant at a level greater that zero and
less than PEEP.
Inventors: |
Biondi, James W.; (North
Haven, CT) ; Johnston, Douglas M.; (Winchester,
MA) ; Schroeder, Gerhardt P.; (Londonderry, NH)
; Gilmore, Donald D.; (Kiehi, HI) ; Reynolds,
Robert; (New Haven, CT) |
Correspondence
Address: |
TESTA, HURWITZ & THIBEAULT, LLP
HIGH STREET TOWER
125 HIGH STREET
BOSTON
MA
02110
US
|
Family ID: |
21938021 |
Appl. No.: |
09/931572 |
Filed: |
August 14, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09931572 |
Aug 14, 2001 |
|
|
|
09660820 |
Sep 13, 2000 |
|
|
|
09660820 |
Sep 13, 2000 |
|
|
|
09045461 |
Mar 20, 1998 |
|
|
|
6158432 |
|
|
|
|
09045461 |
Mar 20, 1998 |
|
|
|
08569919 |
Dec 8, 1995 |
|
|
|
5931160 |
|
|
|
|
Current U.S.
Class: |
128/204.21 ;
128/204.18 |
Current CPC
Class: |
A61M 16/1015 20140204;
A61M 2016/0042 20130101; A61M 16/0051 20130101; A61M 2205/505
20130101; A61M 16/0009 20140204; A61M 16/0081 20140204; G16H 40/63
20180101; A61M 2016/0027 20130101; A61M 2016/0039 20130101; G16Z
99/00 20190201; A61M 16/026 20170801; A61M 2016/0021 20130101; A61M
16/0012 20140204 |
Class at
Publication: |
128/204.21 ;
128/204.18 |
International
Class: |
A62B 007/00; A61M
016/00; F16K 031/02 |
Claims
1. A method of compensating for the gas flow resistance in a
ventilatory apparatus, the method comprising the steps of:
determining the peak exhalation flow rate; determining the airway
resistance; calculating the effective airway pressure; and applying
a negative airway pressure to an exhalation circuit such that the
effective circuit pressure is greater than zero and less than
PEEP.
2. A method of claim 1, further comprising adjusting the amount of
negative pressure to generate a predetermined effective circuit
pressure with a measured value between zero and PEEP.
3. A method of claim 1 further comprising measuring an exhaled
tidal volume and adjusting the amount of applied negative airway
pressure such that the effective pressure in the exhalation circuit
remains constant.
4. A method of claim 3 wherein the steps of measuring the exhaled
tidal volume and adjusting the amount of applied negative pressure
comprise the steps of: determining the effective airway pressure
and the air flow in the exhalation circuit; determining
instantaneous changes in pressure and flow; sensing the initiation
of an active breathing cycle by comparing said instantaneous
changes with predetermined parameters; and storing these data in a
database.
5. A ventilator assist device comprising: a reservoir for inhaled
and exhaled gas in communication with a breathing apparatus adapted
for attachment to a patient; a source of negative pressure in
communication with said reservoir; a data processing unit in
electrical communication with said negative pressure source and
also in electrical communication with an exhalation flowmeter and a
circuit resistance sensor; said exhalation flowmeter and said
circuit resistance sensor in communication with said breathing
apparatus; and a user interface in electrical communication with
said negative pressure source allowing direct setting of a value
for desired negative airway pressure by a user.
6. The ventilator assist device of claim 5 further comprising: a
flexible canister attached to gas inflow and outflow circuits of a
ventilator in pneumatic communication with the exhalation circuit
adapted for connection to the patient being ventilated; an airtight
housing surrounding the canister; a Venturi valve in pneumatic
communication with said housing and in pneumatic communication with
an external source of pressurized gas; a controlling processor in
electrical communication with the Venturi valve, said controlling
processor controlling the flow of said pressurized gas; a pressure
sensor in electrical communication with said controlling processor
and in pneumatic communication with said housing; a control panel
in electrical communication with said controlling processor, said
control panel allowing direct input of a value for desired negative
pressure by the user; the exhalation flowmeter in electrical
communication with said controlling processor, said exhalation
flowmeter in pneumatic communication with the airway tubing capable
of attachment to a patient and also in electrical communication
with the control panel; the circuit resistance sensor in electrical
communication with said controlling processor and said control
panel, said circuit resistance sensor in communication with said
airway tubing; wherein said controlling processor adjusts the flow
through the Venturi apparatus in response to the flow and
resistance determined by said exhalation flowmeter and said circuit
resistance sensor to yield a negative pressure around said canister
such that a pressure is generated in said airway tubing that is
greater than zero and less than PEEP.
7. The controlling processor of claim 6 further comprising: a first
data processor in electrical communication with said exhalation
flowmeter and said circuit resistance sensor; a second data
processor in electrical communication with said pressure sensor; a
third data processor that compares input data with predetermined
values and calculates the amount of negative pressure to be applied
to generate a pressure in said airway tubing greater than zero and
less than PEEP; said third data processor further calculating from
the data input from said exhalation flowmeter and said circuit
resistance sensor instantaneous values for pressure, flow and
resistance in the airway tubing capable of attachment to the
patient; a gas flow controller in electrical communication with
said third data processor and in communication with the Venturi
valve, said gas flow controller regulating the flow through said
Venturi valve in response to data parameters as processed by said
third processor; the database in electrical communication with said
first, second and third data processors, wherein said database is
adapted for storing data processed by said first, second and third
data processors.
8. The user interface of claim 5 further comprising: a display
screen and the control panel, whereby said display screen provides
graphic representation of said data parameters contained in the
database, and whereby additional values can be entered by the user
using said control panel; said control panel further comprising a
plurality of controls; said plurality of controls in electrical
communication with the gas flow controller; and said user interface
in electrical communication with the database, with the third data
processor and with the gas flow controller.
9. The controlling processor of claim 6 further comprising: an
alarm system in electrical communication with the third data
processor and with the user interface that is triggered by a level
of pressure in said airway tubing less than zero or greater than
PEEP; and an override device in electrical communication with said
alarm system and with said user interface that discontinues the
alarm signal in response to a command input by the user.
10. The controlling processor of claim 7 wherein said first, second
and third data processors are independent.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to the field of respiratory
assist devices such as ventilators. In particular, the invention
relates to a ventilator control system and method for controlling a
ventilator pneumatic system.
BACKGROUND OF THE INVENTION
[0002] A medical ventilator delivers gas to a patient's respiratory
tract and is often required when the patient is unable to maintain
adequate ventilation. Mechanical ventilation is the single most
important therapeutic modality in the care of critically ill
patients. Known ventilators typically include a pneumatic system
that delivers and extracts gas pressure, flow and volume
characteristics to the patient and a control system (typically
consisting of knobs, dials and switches) that provides the
interface to the treating clinician. Optimal support of the
patient's breathing requires adjustment by the clinician of the
pressure, flow, and volume of the delivered gas as the condition of
the patient changes. Such adjustments, although highly desirable,
are difficult to implement with known ventilators because the
control system demands continuous attention and interaction from
the clinician.
[0003] Further, patients requiring ventilatory assistance must
overcome airway resistance in the breathing circuit during
exhalation. This resistance, combined with the stiffness of the
lungs and the thoracic cage under certain pathological conditions,
imposes a significant workload upon a patient whose reserves may
already be compromised by underlying disease processes. The present
invention reduces patient work of breathing without compromising
patient ventilation requirements.
SUMMARY OF THE INVENTION
[0004] The invention relates to a ventilatory assist device that
decreases the resistance to exhalation in the exhalation circuit of
a medical ventilator. The device adjusts the resistance within the
exhalation circuit by generating a negative pressure around a gas
exchange reservoir. The negative pressure is then transmitted to
the exhalation circuit. In order to keep the resistance constant
with varying amounts of exhalation flow, the device varies the
amount of applied negative pressure proportionately with increases
in exhalation flow.
[0005] In one embodiment of the invention, the clinician enters a
desired set of values relating to airway pressure, airway
resistance or applied negative pressure through a control panel. A
microprocessor within the data processing unit of the device
compares these values with data for airway pressure, airway
resistance and applied negative pressure that have been measured or
calculated by sensors within the device. The microprocessor then
adjusts the amount of negative pressure to be created within the
gas exchange reservoir that communicates with the patient airway.
In one embodiment of the device, negative pressure around the gas
exchange reservoir is produced within a rigid canister by varying
the airflow through a Venturi valve. In this embodiment, a gas flow
controller regulates the flow through the Venturi valve in response
to signals it receives from the microprocessor within the data
processing unit that calculates the amount by which the applied
negative pressure is to be changed. A pressure sensor in
communication with the ventilatory unit measures the negative
pressure applied to the gas exchange reservoir and transmits these
data to the data processing unit.
[0006] A method of exhalation assist compensates for resistance to
gas flow encountered by a patient requiring assisted or controlled
ventilation. The method accomplishes this by first determining the
instantaneous flow of exhaled gas, the instantaneous pressure
within the exhalation circuit and the instantaneous resistance to
air outflow so that these data can be compared with desired values
entered by a clinician. Negative pressure is applied to the
exhalation circuit so as to alter the measured values to reach the
desired values.
[0007] The term "ventilator control setting structure" is defined
as a collection of information sufficient to control one parameter
of ventilation including one or more of: high alarm level, high
alarm active, control level, control level active, low alarm level,
low alarm active, range level, range level active, and a range
target control structure. The range target control structure
defines how and why the parameter is to be adjusted automatically
within the specified range. The term "cycle control structure" is
defined as a collection of waveform samples and a ventilator
control setting Structure for each parameter. The term "phase
control structure" is defined as a collection of phase switching
rules that defines how the ventilator control settings are to be
utilized and a ventilator control setting for each controllable
parameter that exists in the ventilator. Each phase has one or more
triggers that are tested every cycle (4 Msecs per cycle) to decide
which ventilator control setting to use.
[0008] The term "breath control structure" is defined as a
collection of phase switching rules that defines how and when one
ventilatory breath phase is to switch to another ventilatory breath
phase and a phase control structure for each phase of breath
defined by the specified breath. Breath phases break up a
ventilatory breath into as many phases as desired in order to
control inspiration, pause, expiration assist and PEEP with any
desired level of control for the specified breath. Each breath has
one or more triggers that are tested every cycle (4 Msecs per
cycle) to decide whether or not to jump to the beginning of a new
phase control structure.
[0009] The term "mode control structure" is defined as a collection
of breath switching rules that defines how and when one ventilatory
breath is to switch to another ventilatory breath and a breath
control structure for each type of breath defined by the specified
mode of ventilation. Each mode has one or more triggers that are
tested every cycle (4 Msecs per cycle) to decide whether or not to
jump to the beginning of a new breath control structure.
[0010] The term "therapy control structure" is defined as a
collection of mode switching rules that defines how and when one
mode of ventilation is to switch to another mode of ventilation and
one mode control structure for each ventilation mode defined by the
specified therapy. Also, the term "breath parameter" is defined as
at least one of a control setting and an alarm setting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing and other objects, features and advantages of
the invention will become apparent from the following more
particular description of preferred embodiments of the invention,
as illustrated in the accompanying drawings.
[0012] FIG. 1 is a block diagram of an embodiment of a ventilator
of the invention.
[0013] FIG. 2 is a detailed block diagram of a display
controller.
[0014] FIG. 3 is a detailed block diagram of an embedded
controller.
[0015] FIG. 4 is a detailed block diagram of a ventilator pneumatic
unit.
[0016] FIG. 5 is a diagram illustrating an embodiment of the
adjustment of negative pressure applied to a patient as performed
by an embodiment of the invention.
[0017] FIG. 6 is psuedocode of an embodiment of a triggering
algorithm used by the ventillator of the invention.
[0018] FIG. 6a is a pressure and flow diagram of the patient airway
gas flow and patient airway pressure used by the algorithm of FIG.
6 to determine patient ventilation triggering.
[0019] FIG. 7 is an illustration of a display screen when the
ventilator control system is in the operational mode.
[0020] FIG. 8 is an illustration of a section of the display
screening showing a minute volume wheel.
[0021] FIG. 9 is an illustration of a section of the display
screening showing a control slider.
[0022] FIG. 10 is an illustration of a section of the display
screening showing a numerical controller.
[0023] FIG. 110 is a flow chart of the data structure hierarchy
employed by the ventilator control system.
[0024] FIG. 12 is an embodiment of a flow chart of an exhalation
assist algorithm executed by an embodiment of the invention.
[0025] FIG. 13 is an illustration of a simulation mode display
screen for the ventilator control system.
[0026] FIG. 14 is a functional block diagram of the simulator
portion of the ventilator control system FIG. 15 is an illustration
of a section of the display screening showing a waveform
shaper.
[0027] FIG. 16 is an illustration of a therapy programming screen
for the ventilator control system.
DETAILED DESCRIPTION
[0028] 1. Ventilator Control System-The invention features a
ventilator control system for controlling a ventilator pneumatic
system in a medical ventilator. The ventilator control system
provides a clinician with complete control of a patient's airway
flow and pressure throughout the respiratory cycle, and thereby
enables the clinician to determine the optimal therapy for the
patient. In order to decrease the work of exhalation in this
situation, negative pressure can be applied to the exhalation
circuit of the patient's ventilator to reduce the resistance to
airflow.
[0029] Because resistance to airflow is an exponential function of
flow, negative pressure must be adjusted to compensate for
resistance as increases and decreases in airflow and airway
resistance occur. If too much negative pressure is applied to the
conducting airways dynamic collapse of the conducting airways can
occur and this may result in alveolar gas trapping. Varying the
applied negative pressure according to airflow and airway
resistance allows maximum assist to be applied during peak
expiration, when resistance and work of breathing is greatest. By
decreasing the applied negative pressure at lower airflow rates,
airway collapse can be averted.
[0030] If airway pressure rises above the clinically indicated
level of positive end-expiratory pressure (PEEP), the lung will be
overpressurized thus the effective airway pressure throughout the
expiratory cycle is titrated throughout the expiratory phase under
precise algorithmic control. The clinical benefit of a certain PEEP
level will be diminished. Thus, the effective airway pressure
throughout the expiratory cycle must remain greater than zero and
less than PEEP.
[0031] FIG. 1 is a block diagram of a ventilator including a
ventilator control system 10 incorporating the features of the
invention. The ventilator control system 10 includes a display
controller 12 and an embedded controller 14. The display controller
12 provides an interface to the clinician 16, and the embedded
controller 14 provides an interface with a ventilator 17 providing
ventilation to a patient 20. The display controller 12 and the
embedded controller 14 each include memory (not shown) and are
electrically coupled via a shared memory interface 15. Data from
the display controller 12 and the embedded controller 14 are stored
in a database 13.
[0032] A sensor monitoring system 19, including an exhalation
flowmeter 11 a circuit resistance sensor 9 and a pressure sensor 7
in communication with the airway 21, provide signals to a embedded
controller 14 relating to airway pressure, flow and resistance.
These measured values are stored in a database 13. These values are
also compared with values preselected by a user by way of the
embedded controller 14 to calculate the amount of negative pressure
to be generated in the ventilator 17 in order to produce an airway
pressure greater than zero and less than positive end-expiratory
pressure. A pneumatic system 41 regulates the flow of gas delivered
from the source of pressurized gas 45 through a Venturi valve
within the ventilator 17 to produce this negative pressure. One
embodiment of such a pneumatic system 41 is described in U.S. Pat.
No. 5,664,563, owned by the assignee of the present invention,
incorporated herein by reference. A pressure sensor 51 measures the
amount of negative pressure produced within the ventilator 17 and
transmits these data to the embedded controller 14. These data are
stored in the database 13 and displayed on the display 24 of the
display controller 12.
[0033] Initially, the clinician 16 enters target values into the
system 10 by way of the input device 26 of the display controller
12. Each of these target values is compared with a corresponding
current value of ventilatory unit pressure, airway pressure, airway
flow and airway resistance by the embedded controller 14. Upon
determining that there is a difference between current pressure,
flow and resistance values and those values entered by the
clinician 16, the embedded controller 14 generates a signal to the
pneumatic system 41 so that the pneumatic system 41 changes the
amount of negative pressure produced by the ventilator 17. The
ventilator 17 is in pneumatic communication with a flexible tubing
21 capable of attachment to a patient 20. The clinician 16 can also
directly adjust the pneumatic system 41 by manipulating a plurality
of controls on the input device 26 of the display controller
12.
[0034] The clinician 16 enters numerical data at the display
controller 12 relating to the desired level of airway resistance in
the flexible airway tubing 21 or relating to the desired amount of
negative pressure in the pneumatic system 41. These entered values
signal the pneumatic system 41 to change the amount of negative
pressure on a per breath basis within the pneumatic system 41 until
the pressure in the pneumatic system 41 or the resistance in the
airway tubing 21 equals the value entered by the clinician 16.
[0035] The pneumatic system 41 controls gas flow and pressure in
the patient's airway using a patient circuit. An electromechanical
fresh gas flow control and measurement system provides a metered
blend of oxygen and air via a heated, humidified gas delivery
system. A high speed pneumatically driven, electronically
controlled proportional valve and dual Venturi system provides
bi-directional flow and pressure control as described in U.S. Pat.
No. 5,664,563 incorporated herein by reference. Pressure 7 and flow
11 sensors provide feedback control of the desired breathing
pattern and verify operation within safe limits. The pneumatic and
electronic systems and patient circuit are described in extensive
detail in commonly assigned patent application, Ser. No.
08/352,658, incorporated herein by reference.
[0036] The safe performance of the ventilator 10 is enhanced by the
redundancy of the two independent display controller 22 and
embedded controller 30 processors, which continually check each
other's performance via the shared memory interface 15. The
embedded controller 14 communicates its status, and that of the
patient, to the display controller 12. The embedded controller 14
maintains a non-volatile record of the therapy control structure
and continues to operate at the last known good settings if
communication becomes lost. The two systems which comprise the
ventilator control system 10 give both audible and visual messages
when an alarm condition exists, and maintain an alarm history. The
systems provide alarms and mandatory patient support upon detection
of apnea (i.e., the detected absence of breathing). During
operation, both systems perform background tests to detect system
faults. The ventilator provides a series of reduced operation modes
to provide life support if system capability is compromised.
[0037] In more detail, FIG. 2 is a block diagram of the display
controller 12. The display controller 12 includes a processor 22, a
display 24 and an input device 26. In one embodiment, the input
device 26 is a touchscreen used in conduction with the display 24.
The processor 22 collects input information from the clinician 16,
validates the input, creates a therapy control structure from the
input information and sends the resulting structure to the embedded
controller 14. The therapy control structure is a hierarchical
arrangement of similar data structures which includes one or more
mode control structures, one or more breath control structures, one
or more phase control structures and one or more cycle control
structures. Data generated and collected by the processor 22 are
stored in the database 13. The display 24 maintains and displays
the patient's history in a graphical format which highlights the
patient's status. In one embodiment, the display 24 is a CRT. In
another embodiment, the display 24 is a flat panel display. More
specifically, the display 24 provides a visual indication of the
current breath control parameters, alarm and fault conditions, and
the current status of the patient's pulmonary system, including gas
pressure, flow and volume. In one embodiment, the touchscreen 26
covers the surface of the CRT display 24 and provides a
straightforward, highly flexible means to change control
settings.
[0038] The display controller 12 is a powerful graphics workstation
with hardware and software components. In one embodiment, the
clinician interacts with the display controller 12 via a color CRT
monitor 24 and a touchscreen 26. The display 24 is modified to run
from an isolated power supply, and the touchscreen power supply and
controller are built in to the monitor. In one embodiment, the
processor 22 is included in a single board computer which also
includes RAM, an integrated high speed graphics driver, and an
integrated dual port memory. The display controller 12 also
includes a hard disk drive 23.
[0039] While the display controller 12 provides interpretation and
decision support information on the display 24, the ventilator 17
does not change any breath control parameters unless directed by
the clinician 16. Nevertheless, the display controller 12 provides
a flexible user interface with multiple interactive levels, from
simple text menus of controls for inexperienced users, to complete
visual feedback for clinicians who understand the patient models
and can intervene more aggressively and effectively.
[0040] In more detail, and referring also to FIG. 3 a block diagram
of the embedded controller 14 is depicted. In one embodiment, the
embedded controller 14 includes a system board 28, a real time data
processor 30, a ventilator processor 32 and an airway processor 31.
The real time processor 30 manages sensor data collection from the
sensor monitoring system 19, processes measured data, performs
alarm/fault detection and provides control data to the ventilator
17. The embedded controller 14 further receives data input by the
clinician 16 and accesses with the database 13.
[0041] A first data processor 31, an airway processor, receives
signals from the patient sensor monitoring system 19 relating to
airway pressure, flow and resistance. A second data processor 32, a
ventilatory unit processor, receives signals from the pressure
sensor 51 in communication with the ventilatory pneumatic system
18. Signals from both data processors 31 and 32 are transmitted to
a third data processor, a real time data processor 30. This data
processor 30 calculates the amount of negative pressure that must
be generated by the pneumatic system 41 to change the airway
resistance to exhalation. This calculation is made by comparing the
data relating to airway pressure, flow and resistance to
preselected values and then calculating the change in ventilatory
unit negative pressure required to affect the desired change in
airway resistance.
[0042] In more detail, and referring also to FIG. 4, a block
diagram of the ventilator 17 in communication with the flexible
airway 21 that is the conduit for inhalation from the patient 20 is
depicted. The pneumatic system 41 regulates the amount of negative
pressure produced within a rigid chamber 43 by adjusting the flow
of gas from a source of pressurized gas 45 through a Venturi valve
47. Within the rigid chamber 43 is a flexible canister 49. Negative
pressure produced within the rigid chamber 43 is transmitted to the
flexible canister 49 and thus to the patient airway 21 which is in
pneumatic communication with the flexible canister 49. In this way,
negative pressure is applied to the patient airway 21 to assist the
patient's exhalation through the canister 49 into the medical
ventilator 7. Pressure within the flexible canister 49 is measured
by a pressure sensor 51. These data are transmitted to the embedded
controller 14.
[0043] Now referring also to FIG. 5 a detailed functional block
diagram of the ventilator control system 10 is depicted. As shown,
the clinician 16 manipulates a control setting slider 34 to change
or set one or more breath parameters. A change alert panel 36 on
the display 24 informs the clinician 16 of the process, from input
to implementation, to assure him that his input information is
being processed properly. As noted previously, a change to one or
more breath parameters will lead to changes in one or more data
structures of the therapy control structure hierarchy. It is noted
that FIG. 5 provides an example of a breath parameter change which
results in a change at the level of the breath control structure.
The validation process includes the processor 22 validating 38 the
clinician's inputs and creating 40 a breath control structure which
is stored in memory. The display controller 12 transmits the breath
control structure to the embedded controller 14 and informs the
clinician 16 of successful transmission via the change alert panel
36. The embedded controller 14 initially stores 44 the breath
control structure in local memory. The embdded controller 14
re-validates 46 the settings within the breath control structure.
The embedded controller 14 implements 48 the validated breath
control structure 48 using a breath control algorithm 50 and
provides signals to the pneumatic system 41 for simultaneously
changing one or more control settings at the appropriate time. This
process enables the user to change or implement a new therapy so
that the therapy delivered to the patient is essentially
uninterrupted, and the new therapy is synchronized with the next
inspiration. If, however, any step in the process is not completed,
the clinician is alerted via the panel 36 to the cause of the error
and the process is terminated.
[0044] The ventilator control system 10 provides two independent
feedback paths to assure the clinician 16 that his setting change
has been properly implemented. First, the embedded controller 14
calculates a series of breath monitoring values and sends them to
the display controller 12, where the values are displayed 60
contiguous to the desired setting controls. The breath monitoring
values can be, for example, set breath rate, measured breath rate,
set tidal volume, measured inhaled volume, and measured exhaled
volume. The display controller 12 also displays 60 a series of
measurements (e.g., peak airway pressure, peak airway flow, and
PEEP) from the waveform data both numerically and graphically.
Second, the display controller 12 displays 54 the continuous
waveforms on the display 24. The waveforms are derived 56 from raw
data from the sensors 19, returned from the embedded controller 14
and passed directly to the display 24.
[0045] One feature of the ventilator control system 10 is that it
can be configured to provide an assisted phase of a breath to the
patient 20. As noted previously, the accumulated volume of gas
inhaled by the patient as a result of his spontaneous respiratory
muscle activity can be monitored. To accomplish this, the sensor
monitoring system 19 measures the flow of gas inhaled by the
patient 20 at the beginning of the inspiration phase of the breath
and integrates the flow to provide the measured volume. The
embedded controller 14 compares the measured volume to a trigger
volume set by the clinician 16, and adjusts the plurality of
controls within the pneumatic system 41 when the measured
accumulated volume exceeds the trigger volume to provide an
assisted phase of a breath. The embedded controller 14 also may
adjust the trigger volume dynamically according to measured patient
flow and pressure signals indicating the phase of the respiratory
cycle. In particular, the embedded controller 14 may increase the
trigger volume set by the clinician 16 during periods of the breath
where increases in the pressure at the airway of the patient 20 may
be induced by changes in the pneumatic system 41, and not by
spontaneous efforts of the patient.
[0046] Another feature of the ventilator control system is its
ability to distinguish between active inspiratory effort and
passive reverse airflow due to the elastic rebound of the chest
wall and lungs. The present system is configured such that if the
patient's spontaneous inspiratory efforts are being assisted,
passive reverse airflow can not erroneously trigger an assisted
breath. To accomplish this pressure and flow data provided by the
sensor monitoring system 19 are analyzed by the imbedded controller
14 to discriminate between passive airflow and active initiation of
inspiration. Specifically, referring to FIG. 6 and 6a, the
clinician sets the trigger volume needed to initiate a breath. The
system 10 then determines the baseline pressure and flow for the
patient.
[0047] As the patient exhales, the system 10 monitors both the
patient airway flow and the patient airway pressure. Referring to
FIG. 6, if the gas flow is seen to flow into the patient, and the
pressure slope is positive, the flow into the patient is considered
to be a result of overshoot and no inhalation is triggered (FIG.
6a). If the pressure decreases and the gas flow is into the patient
(Step 300), then the total amount of gas inhaled by the patient is
measured, and compared to the trigger volume (Step 310).
[0048] If the total amount of gas inhaled is greater than the
trigger volume and this value has been reached in less than 200
msec, a breath is initiated. If the trigger volume has not been
reached and it is taking more than 200 msec, the volume of inhaled
gas is continued to be measured until the trigger volume has been
reached (Steps 320, 330).
[0049] Another feature of the ventilator control system is its
ability to compensate for gas flow resistance into and out of the
lungs of the patient 20. Using the input device 26, the clinician
16 can set a resistance parameter of the patient's respiratory
system to a selected value. Alternatively, the display controller
12 may calculate a value for the gas flow resistance from gas flow
and pressure measurements provided by the sensor monitoring system
19. The gas flow resistance is described by the equation::
[0050] Gas Flow Resistance=(Inspiration Peak Pressure-End
Inspiration Plateau Pressure)/(Inspiration Flow at Peak).
[0051] The selected or calculated resistance value is provided to
the embedded controller 14 by the display controller 12. The
embedded controller 14 adjusts one or more controls of the
pneumatic system 41 to compensate for the resistance to flow. The
compensation for resistance to flow may be selected to occur during
any one or more of the inspiration, exhalation or post-breath
phases of a breath. Further, the controls may be adjusted to
compensate for different selected or calculated resistance during
different phases of a breath.
[0052] 2. Display Controller-The display controller 12 is an
intelligent assistant for the clinician 16. The display controller
12 quickly informs the clinician 16 of the effects of intervention,
provides fast, graphical feedback, and presents information in a
manner that requires minimal training to understand.
[0053] Referring also to FIG. 7 an illustration of a display screen
64 provided by the display controller 12 is depicted. The display
controller 12 uses software-generated waveforms and
software-generated icons for control and alarms settings. The
bottom row of touch sensitive on/off buttons 66 includes: a Power
button that controls the ventilator control system; a Freeze button
to pause the display; a Modes button to display various modes; a
History button to play back a database of historical patient
protocols; a 100% O.sub.2 button to flush the ventilator with
oxygen; Help and Save buttons; and an Others button to display
other capabilities.
[0054] The left side of the screen includes a list of the
publically available ventilator control settings. The top area
displays the current mode of ventilation 67 (e.g., Backup). Below
the current mode display, each row in the list has three columns.
The left column is the current set value. If a row in the left
column is inactive, it displays an OFF indication. Important
current set values are highlighted. The middle column is a touch
sensitive display showing the abbreviated title of the setting. The
right column is the actual value of the setting as measured during
the previous breath. If the actual value exceeds an alarm limit,
the exceeded value turns red and a large alarm message is displayed
on the screen. By touching a row, a control slider (not shown)
appears on the right side of the screen. The control slider enables
the clinician to change various parameters (e.g., alarm levels,
control settings) and is described in detail below.
[0055] The middle area of the display screen is divided into top
and bottom regions (70, 72). The bottom region 72 can include a
variety of virtual instruments including: additional user-defined
waveforms, trendlines, an events log, measured minute averages and
other options. The top region 70 includes real time airway flow and
pressure waveforms (74, 76), which are displayed over different
shades of gray to indicated the breath phase. The airway flow
waveform 74 illustrates flow into the patient, or inspiration
(positive flow), and flow out of the patient, or exhalation
(negative flow). The pressure waveform 76 illustrates that the
patient's airway rises above ambient for inspiration and falls
during exhalation. The waveforms are tracked by a cursor that can
be programmed to follow a peak, average, plateau or manually set
position. The waveforms are displayed in fixed axis, moving erase
bar format. The time axis resolution is user adjustable and
displays time in seconds. Overwriting of the display starts at the
beginning of an inspiration, so that the first displayed breath
starts at a fixed point on the screen. The vertical axes are scaled
to keep the displayed waveforms and settings in clear view.
[0056] The right side 77 of the display screen normally includes a
flow-volume loop 78, a pressure-volume loop 80 and a minute volume
wheel 82. A control slider and other optional panels can overlay
this side when a user so desires. The flow-volume loop 78 is
updated each breath to show the timing of delivered airflow. The
vertical axis of the loop shares a common range and alignment with
the airway flow waveform 74. The pressure volume loop is updated
each breath to show the condition of the lungs. The vertical axis
of the loop shares a common range and alignment with the pressure
waveform 76. Calculated resistance and compliance are also
displayed.
[0057] The minute volume wheel 82 provides a comprehensive summary
of the patient's breathing for the last minute. The minute volume
wheel displays a wealth of historical breath information (e.g.,
minute volume, inspiration phase, exhalation phase,
inspiration/exhalation ratio, breathing rate, spontaneous minute
volume, inhale tidal volume, exhale tidal volume, leakage) on a
single integrated graphic circle so that the clinician can readily
evaluate ventilation during the last minute.
[0058] Referring to FIG. 8, a minute volume wheel 84 represents one
minute of ventilation as a circle with an area corresponding to
measured minute volume. The measured minute volume is represented
numerically, as the center number, and graphically, as a circle 86
drawn over a background circle 88 that has an area corresponding to
the target minute volume. When the measured minute volume is
exactly equal to the target minute volume, the two circles are
blended in color and appear as one circle. When the measured volume
is larger than the target volume, the background circle bleeds
through and is visible. When the measured volume is smaller than
the target volume, an uncovered portion of the background circle is
visible.
[0059] One minute of ventilation is drawn as a circle 90, one wedge
at a time, and is redrawn once a minute. Like the face of a watch,
each degree of the circle 90 corresponds to one sixth of a second.
Each inspiration is drawn as a wedge 92 with an area corresponding
to delivered volume. This wedge is drawn over an inspiration spoke
94 that extends to maximum minute volume. Each exhalation is drawn
as a wedge 96 with an area corresponding to exhaled volume. This
wedge is drawn over an exhalation spoke 98 that extends to maximum
minute volume. The spokes indicate breathing regularity and inhale
to exhale (I:E) time ratio, and the wedges indicate tidal volumes.
Difference between the radius of inspiration and exhalation wedges
indicates the I:E ratios. The I:E ratio and breathing rate are also
represented numerically (100, 102). The pairs of inspiration and
exhalation wedges are coded by color to indicate spontaneous
breaths, those triggered and partially controlled by the patient,
and mandatory breaths, those triggered and controlled by the
ventilator. The ratio of the colored areas indicates the ratio of
spontaneous to mandatory breathing during the minute just past.
[0060] Referring, again to FIG. 7, the display controller provides
a method for clinician control of the displayed waveforms. Each
waveform (74, 76) is continuously measured and displayed on a
background that changes color to indicate the phase of a breath.
The rectangular area 200 for any phase of the waveform (74, 76) is
used as a target for the touchscreen. When the clinician selects a
phase of a waveform, the display controller displays the associated
ventilator controls for available for adjustment by the
clinician.
[0061] The display controller provides cursors 201 which are
actually floating windows. More specifically, windows of one or two
pixels width float over the waveforms (74, 76), thereby creating
cursors 201. Since the cursors are independent of the background
waveform graphics, numerous advantages result including drawing
optimization, dynamic repositioning based on changing waveform
values, positioning based on user interface gestures.
[0062] The background of the waveform (74, 76) includes color
shading to indicate breath phase, title, units and scale
information. Redrawing these graphics as new waveform samples are
displayed generally requires substantial computer time, and the
display controller performs this function efficiently
notwithstanding the complexity of the background image. To perform
this task efficiently, background images are created once. A narrow
rectangular region 202 is removed from these images and pasted in
front of the moving waveform to clear out the previous waveform and
refresh the background prior to the new waveform. The width of the
rectangular area 202 is kept sufficiently small so that the refresh
is smooth in appearance. The x-axis coordinate of the current
waveform position is used to control the x-axis position from which
to remove a strip of background image. Multiple color coded
background images can be maintained (e.g., three gray shades for
the breath phases) and images removed from the desired one
depending on the state of the waveform.
[0063] By selecting one of the control buttons on the touch
display, the clinician 16 can display the control slider 106 for
the control setting in a fixed location at the right of the screen,
as shown in FIG. 9. A scroll bar title 108, located near the top of
the slider 106, indicates the name of the control setting. The full
vertical range 108 indicates the allowed set limits. The center
slider indicates the current position 110 and the range 112 of the
control setting. The upper and lower sliders (114, 116) indicate
the current alarm limit settings. The position 110 of the current
setting within the allowable range 112 and within the alarm limits
(114, 116) is readily apparent to the clinician. The clinician can
move any of the sliders to change the set values in steps of
approximately 1% of the allowable range, or with the "Exact" button
selected, approximately ten times more precision (i.e., about 0.1%
of the allowable range). When the desired value is reached, the
clinician depresses the Accept Changes button to change the
parameter.
[0064] Alarm settings are matched with control settings in the
appropriate control sliders. Some control settings have two
associated alarms, others have only one associated alarm or do not
have any associated alarms. For example, both high and low
inspiratory pressure alarms are provided on the Airway Pressure
control slider. If an alarm limit is exceeded during operation, the
alarm is displayed in an alarm window, and an audio alarm turns on.
Alarms are non-latching, i.e., the alarm indication turns off when
the detected level no longer violates the set limit. Available
control settings and ranges, alarm settings and ranges, and
measured parameters are listed in the following table:
1 Control Settings Tidal Volume (Compliance Compensated) 50 to 2000
mL Breathing Rate 2 to 150 bpm Peak Inspiratory Flow (BTPS
Compensated) 10 to 120 L/min Oxygen Percentage 21 to 100% Peak
Inspiratory Pressure 2 to 120 cmH.sub.2O Exhalation Assist 0 to 30
cmH.sub.2O/L/sec PEEP 0 to 20 cmH.sub.2O Inspiratory Time 0.2 to 4
sec Inspiratory Pause Time 0 to 1 sec Sensitivity (Patient Effort
Trigger) 0 to 250 mL Flow Drop-Off Percentage (Percent 5% to 80% of
Peak) Humidifier Temperature 30 to 60.degree. C. Airway Temperature
15 to 40.degree. C. Waveform Shape (clinician modifiable) custom,
square decelerating, modified fine Monitored and Displayed
Parameters Exhaled Tidal Volume (Compliance 50 to 2500 mL
Compensated) Measured Breathing Rate 2 to 150 bpm Peak Inspiratory
Flow (BTPS Compensated) 10 to 120 L/min Oxygen Percentage 21 to
100% Peak Inspiratory Pressure 0 to 120 cmH.sub.2O PEEP 0 to 20
cmH.sub.2O Mean Airway Pressure 0 to 120 cmH.sub.2O Inspiratory
Time 0.1 to 4 sec Inspiratory:Expiratory Ratio 0.1 to 10.0 Minute
Ventilation - Controlled 0 to 99 L/min Minute Ventilation -
Spontaneous 0 to 99 L/min Airway Temperature 15 to 40.degree. C.
Lung Compliance 10 to 150 mL/cmH.sub.2O Airway Resistance 1 to 60
cmH.sub.2O/L/s Leak 0 to 20 L/min Airway Flow Waveform -120 to
.+-.120 L/min Airway Pressure Waveform -20 to +60 cmH.sub.2O
Flow-Volume Graph, Pressure Volume Graph see text Fresh Gas Flow
Bar Graph see text Minute Volume Wheel see text Alarms and
Indicators High/Low Exhaled Tidal Volume Alarm 50 to 2000 mL
High/Low Respiratory Rate Alarm 2 to 150 bpm Low Oxygen Fresh Gas
Flow Automatic, % O.sub.2 dependent Low Air Fresh Gas Flow
Automatic, % O.sub.2 dependent Low Oxygen Supply Pressure Alarm 25
psig High/Low Airway Pressure Alarm 2 to 120 cmH.sub.2O High/Low
Inspiratory Time Alarm 0.2 to 4 High/Low Inspiratory:Expiratory
Ratio Alarm 0.1 to 4.0 High/Low Minute Volume Alarm 1 to 40 L/min
Airway Leak Alarm 1 to 20 L/min Patient DisconnectAlarm Automatic
Apnea Alarm/Backup Ventilation 30 Internal Battery Notification
Alarm Battery in Use % Remaining Pneumatic System Fault Alarm
Automatic Alarms Silence 120 High/Low Oxygen Alarm 18-100%
O.sub.2
[0065] In one embodiment, the display screen 24 is covered by a
resistive touchscreen. Known touchscreen interfaces require that
the user touch a graphic object on the screen, but this action
generally obscures the object. The touchscreen interface of the
present invention defines an area whose shape, size and position is
dynamically computed based on the characteristics of the associated
graphic object. The interface interprets touching by the user as a
manipulation of the associated graphic object. More specifically, a
dragging motion moves the associated object, or change its value or
other attributes.
[0066] Referring again to FIG. 9, the display controller includes
software for manipulating the characteristics of the breath
parameter Airway Pressure 106 displayed in the control slider 104
on the touch-sensitive display 24. When the clinician 16 selects a
control button to display the control slider 106 for Airway
Pressure, the display controller 12 dynamically defines a touch
zone on the touch-sensitive display. More specifically, touch zones
are defined for each slider (i.e., high alarm, low alarm, position
and allowable range) within the control slider. Each touch zone is
slightly larger than the displayed slider. By way of example only,
the touch zone for high alarm may extend into regions 118 to either
side of the color coded high alarm region 114. The display
controller 12 receives a touch signal when the clinician 16 touches
any location within the touch zone and changes the range of the
high alarm slider breath parameter in response to the touch signal.
In other words, the display controller 12 increases the high alarm
limit in response to the clinician 16 touching a location within
the region 118 and dragging his finger in a upward path. Because
his finger does not obscure the high alarm limit, the clinician can
actually see the limit being change as it happens.
[0067] Referring also to FIG. 10, the display controller 12
includes software for providing precise numerical control without
the requirement of a keyboard. The display controller 12 displays a
window 120 that looks like a numeric text field, but has a
background color to distinguish the left region 122 from the right
region 124, relative to the decimal point. Once either numeric
region 122, 124 has been touched, a larger touch sensitive area
126, 128 respectively is associated with each of the numeric
regions. When the clinician 16 touches a touch sensitive area and
moves in a vertical path, the interface provides continuous numeric
feedback by increasing or decreasing the displayed value.
[0068] 3. Embedded Controller-Referring again to FIG. 1, the
embedded controller electronics 14 is based around microprocessors
31, 32. The microprocessor 32 is in electrical communication with
the ventilatory unit 17 and the microprocessor 31 is in electrical
communication with the sensor monitoring system 19. The embedded
controller relies on industry standard bus based modules to perform
certain functions and custom printed circuit boards to perform
other functions. The modules, the printed circuit boards, the
ventilatory unit pressure processors 32 and the airway processor 31
are mounted on or connected to on a main printed circuit board 28.
A real time operating system is the foundation of the embedded
controller software, which runs the algorithms required for
measurement and control. A power system converts line power and
provides battery backup for a average of one hour.
[0069] The embedded controller 14 has microprocessor and associated
input/output hardware to provide for closed loop control of
pneumatic system 41 and the acquisition of patient data. The
embedded controller 14 communicates the status of the patient and
its own status to the display controller 12. The embedded
controller 14 responds to commands and setting changes received
from the display controller 12, and maintains a non-volatile record
of instrument settings to maintain operation in the absence of both
communication from the display controller and line power.
[0070] The embedded controller 14 performs real time data
acquisition of twenty three different analog input signals
including:
2 1. Flow Oxygen, 2. Flow Air, 3. Flow Third Gas, 4. Flow Canister,
5. Flow Exhaust, 6. Pressure Patient Airway, 7. Pressure Canister,
8. Flow Low Exhaust, 9. Temperature Airway, 10. Temperature
Humidifier, 11. Voltage Battery, 12. Current 5 Volts, 13. CO.sub.2
Airway, 14. Voltage ECG, 15. Voltage QRS, 16. Temperature Patient
Temperature 2, 17. Pressure Patient Pressure 1, 18. Pressure
Patient Pressure 2, 19. Signal PT34, 20. Voltage Aux 1, 21. Voltage
Aux 2, 22. Voltage Aux 3, 23. Voltage Aux 4. The embedded
controller 14 also monitors six switches: 1. Pressure Oxygen, 2.
Pressure Air, 3. Pressure Third Gas, 4. Pressure Safety Valve, 5.
Voltage Power Switch, 6. Voltage No AC Line.
[0071]
3 The embedded controller controls nine digital outputs: 1.
Solenoid Exhaust Flow Zero, 2. Solenoid Canister Flow Zero, 3.
Solenoid Safety Valve, 4. Solenoid Direction (I/E), 5. Heater
Canister, 6. Heater Fresh Gas Tube and Humidifier, 7. Power CRT
Display, 8. Alarm Beeper, 9. Battery Backup. The embedded
controller 14 controls four duty cycle modulated digital outputs:
1. Flow valve Canister, 2. Flow valve Air, 3. Flow valve Oxygen, 4.
Flow valve Third Gas.
[0072] The embedded controller 14 communicates with the display
controller 12. via a shared memory interface 15 at a data
transmission rate exceeding 100K bytes per second.
[0073] 4. Data Structures-This section describes the architecture
for software utilized in the embedded controller and shared with
the display controller. The architecture of the software is built
around the concepts of therapy controls, mode controls, breath
controls, phase controls and cycle controls. A data structure
driven state machine determines the control parameters for each
therapy control, mode control, breath control, phase control, cycle
control and exhalation assist.
[0074] Referring to FIGS. 1 and 11, the figures illustrate the data
structure hierarchy for the ventilator control system. Using an
input device 26 such as the touch-sensitive display 24 within the
display controller 12, a clinician can change ventilation control
settings to create a new therapy comprising a therapy control
structure 140. The settings are validated by the display controller
12, placed into a new therapy control structure and sent to the
embedded controller 14. The embedded controller 14 validates the
settings again and checks the integrity of the new structure before
the new therapy control is accepted. Also, the clinician 16 may
simulate the behavior of the new therapy control using a simulator
and may allow others to utilize the therapy control by adding it to
the database 13. In any case, the clinician 16 sends the new
therapy control structure to the memory for use by the embedded
controller 14 in controlling the pneumatic system 41. A therapy
control structure 142 (or a mode control) 140 is defined as a
collection of mode control structures 142 and mode switching rules
144. A mode control structure (or a breath control) is defined as a
collection of breath control structures 146 and breath switching
rules 148. A breath control structure 146 (or a phase control) is
defined as a collection of phase control structures 150 and phase
switching rules 152. A phase control structure 150 (or a cycle
control) is defined as a collection of ventilator control settings
154 and an array of waveform samples 156. Phase definitions and
requirements for transitions between phases are tied directly to
measurable system performance, and correlate closely to published
descriptions of the desired behavior of mechanical ventilators.
[0075] More specifically, the therapy control structure 140 is a
nested hierarchy of increasingly complex control structures. A
cycle (e.g., a 4 msec time slice) occurs within cycle control,
which occurs within phase control, which occurs within breath
control, which occurs within mode control, which occurs within
therapy control, which is the clinically specified therapy that
drives the ventilator pneumatic system 41. Once each cycle,
ventilation control moves from one control state to another control
state.
[0076] After each cycle, when the hierarchy of rules is tested and
the state is set for the next cycle, a new therapy control
structure 140 may cause a branch to the first cycle of the first
phase of the first breath of the first mode of ventilation within
the new therapy control structure, or the new therapy control
structure may be delayed a few cycles until better patient
synchrony can be achieved. Within a therapy, there is a collection
of mode control structures 142 and a collection of rules specifying
how and when to switch from one mode of ventilation to another one.
Thus, a therapy may define several different modes of ventilation
and mode switching rules 144 for the transition from one mode of
ventilation to another.
[0077] After each cycle, when the hierarchy of rules is tested and
the state is set for the next cycle, the mode switching rules 144
may cause a branch to the first cycle of the first phase of the
first breath of another mode of ventilation within the therapy
control structure 140. Within a mode, which is within a therapy,
there is a collection of breath control structures 146 and a
collection of breath switching rules 148 specifying how and when to
switch from one breath type to another breath type within the same
mode. Thus, a mode of ventilation may have several different types
of breaths defined, and rules specified for how to go from one
breath type to another.
[0078] After each cycle, when the hierarchy of rules is tested and
the state is set for the next cycle, the breath switching rules 148
may cause a branch to the first cycle of the first phase of another
type of breath within the mode. Within a breath, within a mode,
within a therapy there is a collection of phase control structures
150 and a collection of phase switching rules 152 specifying how
and when to switch from one breath phase to another phase within
the same breath. Thus, a breath type may have, several different
phases defined, and rules specified for how to go from one breath
phase to another. For example, breathing generally proceeds from an
inspiration phase to a pause phase to an exhalation assist phase to
a PEEP phase, but these phases may be further subdivided for a
finer granularity of control.
[0079] After each cycle, when the hierarchy of rules is tested and
the state is set for the next cycle, the phase switching rules 152
may cause a branch to the first cycle of the next phase within the
breath type. Within a phase, within a breath, within a mode, within
a therapy, there is a ventilator control setting structure 154.
This structure contains an array of samples that comprise a
specified waveform shape. During each cycle, the control logic is
driven by the waveform sample specific for the cycle, and by a
collection of ventilator control settings 154 specific for the
phase. The cycle time is in milliseconds, and is currently set to
four milliseconds.
[0080] After performing all ventilation control for the cycle, the
hierarchy of rules is tested and the state is set for the next
cycle, which is by default the next cycle within the current phase,
current breath type, current mode of ventilation and current
therapy. However, higher level rules may cause a change in breath
phase, breath type, mode of ventilation, or an entirely new therapy
may be specified by the clinician and take control at the next
cycle.
[0081] Each ventilator control setting structure 158 contains
necessary and sufficient information to control one parameter of
ventilation, including whether there is a high alarm level, whether
the high alarm is active, whether there is a control level, whether
the control is active, whether there is a low alarm level, whether
the low alarm is active, whether there is a range level, whether
the range is active, and a range target control structure to define
how and why the parameter is to be adjusted automatically within
the specified range. Each phase control structure has its own
collection of ventilator control settings, although in practice,
phases within a breath generally share the same collection.
[0082] The data structure-driven architecture described above
enhances safety and reduces the likelihood of hazardous conditions
by permitting non-programmers to review and understand the function
of the ventilator control system.
[0083] Several breath control structures are predefined in the
embedded controller. These breath control structures are used when
hazards are detected; such as apnea or patient circuit disconnect.
They are also used to support the patient if the communication link
between the display controller 12 and embedded controller 14 is
lost. Also, the embedded controller 14 checks the integrity of
every therapy control structure sent by the display controller 12.
If a requested change is invalid, the embedded controller 14
continues operation with the last known valid therapy control
structure. If no valid therapy control structure has been received,
the embedded controller 14 uses the predefined breath control
structures to continue patient support.
[0084] FIG. 12 is a flowchart of an embodiment of an algorithm
executed by the exhalation assist device embodied in FIG. 1. The
algorithm begins with the clinician 16 entering the desired values
relating to airway resistance or negative pressure in the
ventilatory unit (Step 1). These values are then compared with data
relating to airway resistance or negative pressure in the
ventilatory unit that have been measured or calculated by the data
processing unit (Step 2). It is then determined whether these sets
of data are equal to each other or are within a predetermined range
of each other (Step 3). If these values are equal or within a
predetermined range, airway flow is then measured (Step 5). If
these values are not equal or within a predetermined range, the
applied negative pressure is adjusted (Step 4), and then the airway
flow is measured (Step 5). After airway flow is measured, it is
determined whether the measured airway flow is a positive or a
negative number (Step 6). If airway flow is positive, indicating
that inspiration is occurring, a new measurement of airway flow is
obtained (Step 5). If airway flow is negative, indicating that
exhalation is occurring, airway pressure is measured (Step 7). It
is then determined whether airway pressure is greater than zero and
less than PEEP (Step 8). If airway pressure is greater than zero
and less than PEEP, airway resistance is calculated and pressure in
the ventilatory unit is measured (Step 9). After these measurements
and calculations are made, the cycle recommences (Step 2). If
airway pressure is not greater than zero and less than PEEP, it is
determined whether the alarm has been overridden (Step 10). If the
alarm has been overridden, airway flow is measured on the next
breath (Step 5). If the alarm has not been overridden, the alarm is
triggered (Step 11). If the alarm is triggered, the cycle must be
restarted with the input of desired values (Step 1).
[0085] 5. Simulator-Referring again to FIG. 1., a simulator 212 is
provided for predicting the status of the pulmonary system of a
patient and a database 13 for storing actual or simulated
historical patient protocols. The simulator 212 is electrically
connected to the display and embedded controllers 12, 14
respectively. The simulator 212 uses a set of breath parameters
provided by the clinician 16 via the input device 26 to predict the
status of the patient's pulmonary system. The simulator 212
simulates the adjustment to the ventilator pneumatic system 41 in
response to the set of breath parameters and the response of the
patient's pulmonary system to the adjusted pneumatic system 41. The
predicted status and the set of breath parameters are displayed on
the display screen 24 (FIG. 13).
[0086] An advantage of the simulator 212 is that the clinician 16
can experiment with new or old settings, while the actual settings
remain unchanged and the patient is unaffected. When the clinician
16 begins changing settings in the simulation mode, the ventilator
control system 10 predicts the effects of the change and displays
the predicted result on the display 24. The simulator 212 uses a
standard two parameter model of a respiratory system and the
current calculated values of the patient's resistance and
compliance to predict the effect. The model assumes no contribution
from the patient's respiratory muscles (i.e., a passive inspiration
and exhalation cycle). The model used is: 1 Airway Pressure = (
Delivered Volume / Lung Compliance ) + ( Airway Flow .times. Airway
Resistance ) .
[0087] A change in patient intervention in current ventilators
typically requires multiple setting changes. Implementing such
setting changes is greatly complicated by the series of
indeterminate control states as one setting is changed at a time.
Using the simulator 212, the clinician 16 can change multiple
settings until the predicted waveforms are satisfactory and then
activate all the changes simultaneously. If the clinician 16 is
dissatisfied, he can quickly and conveniently return the control
settings to their previous values without adversely affecting the
patient.
[0088] The clinician 16 can also use the simulator 212 to select a
mode of ventilation or sequence by modes, by choosing a programmed
comprehensive therapy control structure. Those breath parameters,
which are essential to the definition of the mode, are highlighted
with a color-coded background. Other controls are listed as active
or inactive. The explicit list of active controls clearly
delineates the exact function of the mode and alleviates confusion
caused by inconsistent or incomplete definitions. Moreover, the
simulator 212 can precisely replicate the behavior of modes on
preexisting ventilators. The clinician 16 can make adjustments to
the list of controls to accurately simulate the ventilator that a
hospital's staff has been trained to use. The list of controls
together with the simulated behavior can help teach the effects of
various modes on patients, rather than the ventilator-specific mode
definition.
[0089] As claimed in FIG. 13, while the simulator 212 predicts the
shape of the breaths using the two parameter model, and displays
the simulation on the display 24, many other physiological models
and predictions may be possible. Specifically, the simulator 212
may predict the effect of positive end expiratory pressure on lung
volume and functional residual capacity; it may predict the effect
of minute volume on blood oxygen and carbon dioxide levels; it may
predict the effect of mean airway pressure on pulmonary blood flow;
and it may provide other similar models.
[0090] Referring also to FIG. 1, the database 13 assists the
clinician 16 in managing the intervention and in tracking patient
status. The database 13 makes large amounts of stored patient data
available at several levels of detail and encourages comparison of
different patient data. The clinician 16 can compare stored
historical patient data with current settings to learn whether the
current intervention has been effective and whether the patient is
progressing.
[0091] The database 13 is electrically coupled to the display
controller processor 22 and stores a plurality of patient
protocols. Each patient protocol includes at least a set of breath
parameters and patient data. The breath parameter may be organized
as one or more therapy control structures. The clinician 16 selects
a patient protocol by depressing a touch zone on the display 24.
The processor 22 copies the selected patient protocol into memory.
In the operational mode, the processor 22 instructs the embedded
controller 14 to simultaneously adjust the controls of the
pneumatic system 18 using the selected patient protocol. In the
simulation mode, the simulator 212 simulates the adjustment to the
ventilator pneumatic system 41 and the resulting response of the
patient's pulmonary system.
[0092] The processor 22 stores patient protocols as epochs, which
are complete "snapshots" of a particular time or event. The
processor 22 uses real time event and pattern discrimination to
determine when to store epochs of interest. In this way, the
clinician 16 does not have to decide a priori what may be
important, what to "trend", or how to process the data. Because all
the data is stored, it can be post processed to reveal any aspect
of the patient's previous condition. The saved epochs are organized
in the database. Access to the epochs can be by time, by event, or
by area of interest. The ability to overlay data from previous
epochs informs the clinician as to whether the patient is
progressing, or whether the intervention is working as
expected.
[0093] FIG. 14 is a detailed functional block diagram of the
simulator feature of the ventilator control system 210. The
clinician manipulates a control setting slider 216 to change or set
a ventilator control setting. The clinician's input are stored in a
memory 218. The simulator 220 receives the inputs and creates a
phase control structure, a breath control structure, a mode control
structure, or a therapy control structure for use in its
simulation. If, for example, the clinician 16 decides to use the
breath control structure 222 to change the patient's therapy, the
selected breath control structure (which is embedded within a mode
control structure within a therapy control structure) is
transmitted to the embedded controller (at 224) via the shared
memory interface. The embedded controller validates the settings
within the breath control structure 226. The processor implements
the validated therapy control structure 228, which includes the
breath control structure, in a breath control algorithm 230 and
provides signals 232 to the pneumatic system for simultaneously
changing one or more control settings.
[0094] 7. Waveform Shaper-The waveform shaper shown in FIG. 15 is a
graphical tool which enables a clinician to shape one or more
phases of a breath. Characteristics such as the rise time and shape
130, the plateau length and shape 132, the fall time and shape 134
can be drawn to any desired characteristics by the clinician. In
one embodiment, the phases can be shaped by touching the various
active areas dynamically created on the touchscreen display
displaying the waveform shaper and drawing the finger in the
desired direction. In another embodiment, control buttons may be
selected to add characteristics to the waveform, specifically
sinusoidal or pulse-like variations about an average level during a
phase. The waveform shaper is displayed by the display controller
12, wherein its output is used to fill the array of waveform
samples 156 in the cycle control structure of the therapy control
structure 140. The pneumatic system 41 in communication with the
embedded controller 14 can in this way be directed to follow any
arbitrary waveform "drawn" by the clinician for one or more phases
of a breath.
[0095] 8. Interface Protocol-The patient data waveforms are driven
by a data stream protocol. The data stream can be generated by
sensors, which is the usual manner in which the ventilator
operates, by the simulator 212 which uses the breath parameters and
measured patient paramoters to generate simulated sensor data, or
by the stored sensor data in epochs to show historical patient
behavior. The ability to use the same interface to display real
data, simulated data and epoch data is an important feature of the
ventilator control system.
[0096] 9. Integrated Control/Data/Alarm Display-Referring again to
FIG. 7, patient data waveforms 74,76 presented on display screen 64
of the display controller 12 combine setting control, data and
alarm displays in a single region. The association of numbers and
graphic icons with the data waveforms provide context to illuminate
the meaning of the numbers and icons without unnecessary data or
unit labels. A light line 201 is apparent as peak flow or pressure;
a heavy bar 204 is apparent as the peak pressure set level; a light
bar 203 is apparent as a high pressure alarm setting; an active
rectangular region 200 on the pressure waveform is apparent for
setting the exhalation pressure level. Differences between desired
and actual settings, and alarm margins are readily apparent. The
simplicity of these representations can be contrasted to a typical
list of controls, calculated data, and alarms, where each item on
the list is in LABEL:VALUE:UNITS format and the integration and
comparisons must be performed in the head of the clinician.
[0097] 10. Therapy Programming-Referring also to FIG. 16 is an
illustration of a therapy programming screen 205 provided by the
display controller 12. With this screen, the clinician 16 can
create or modify one or many breath parameters to prescribe a new
type of therapy for the patient. Changes made are reflected at one
or more data structure levels in the therapy control structure
created in the display controller 12. After validation, the new
therapy control structure can be sent to the embedded controller 14
for immediate implementation, or saved to a list of therapy
prescriptions for later use.
[0098] A therapy can thus be built from the simple to the complex.
Breath parameters are selected and changed to modify and combine
cycles to define a phase; to modify and combine phases to define a
breath; to modify and combine breaths to define a mode; and to
modify and combine modes to define a therapy program. The
selections are reflected in the hierarchy of structures in the
therapy control structure, as previously described. The collection
of settings are given a title by the clinician, in common use
loosely defined as a mode of ventilation. The creation process,
with its explicit connection of breath parameters to a mode
definition, helps clarify the way the therapy will affect the
patient. In contrast, modes preset by the manufacturer often have
implicit, obscure and contradictory affects on the patient.
[0099] In one embodiment, the therapy programming screen 205
enables selection and changing of related breath parameters. The
therapy prescription to be altered is selected from a list; a new
therapy prescription can be created by selecting a similar
prescription from the list, giving it a new title, and altering it
as needed. A mode within the selected therapy prescription is
selected; a breath within the selected mode is selected; a breath
parameter control setting within the selected breath is selected; a
sequence which identifies a specific, hierarchically nested breath
parameter. Features of the breath parameter are toggled on or off,
or chosen from lists which are brought forth when there are more
than two choices. Every breath parameter, within each breath,
within each mode, must be programmed to complete the therapy
prescription.
[0100] Referring to FIG. 16, a control definition section 207 is
displayed adjacent to the control slider previously described. The
control definition section 207 includes a title 209 of the therapy
prescription. The title in this example includes two modes, and the
mode (A/C pc) to which the selected breath parameter is tied is
highlighted. The control setting for the breath parameter may have
a range feature enabled 211, which, if enabled, will bring forth a
panel of selected targets appropriate for the range, and which, if
enabled, means that the ventilator control system will seek to
accomplish a range target goal 213 by varying the control setting
within the range specified in the control slider. The control
setting may be required to be on 215, meaning that it cannot be
turned off by the clinician when operating within this breath type
within this mode. It may be required to be off 217, meaning that it
cannot be turned on by the clinician when operating within this
breath type within this mode.
[0101] The therapy programming screen allows the control setting to
be shared by one or more other breath types 219 within the mode, or
within the paired modes, such that any adjustments to the control
setting will affect all such breaths. It allows control settings to
be highlighted 221 as having primary importance to clinicians
making adjustments to therapy. It allows multiple breath types to
be defined, and provides a selection of rules that will be tested
to determine which breath type to use within the mode.
[0102] The embodiment allows the clinician to select from a number
of triggers which determine the transition between modes of
ventilation 223, when a multi-mode feature is enabled 225. The
triggers for transition may be different depending on the direction
of the transition. For the example shown, the trigger for the
transition from variable pressure support (VPS) to assist control
(A/C pc) is minute volume (MV), while the trigger for the
transition from assist control to variable pressure support is
sensitivity (Sense, i.e. patient effort).
[0103] While the particular embodiment permits the programming of
two modes, due to conceptual limitations for this new capability on
the part of clinicians, another embodiment includes therapy
prescriptions which encompass many modes, with multiple triggers
for the transitions between modes. Specifically, other
prescriptions include sequences of modes which automatically change
the treatment of a patient as his condition changes, and allow the
clinician to readily control the sequence. Other prescriptions
permit time limited modes, which turn on for a period and then
revert to the mode, or combinations of modes, in effect prior to
their turn on. The therapy programming screen enables the clinician
to tune the therapy to the specific and ever changing needs of the
patient, with much more power and flexibility than selecting from a
set of simple ventilator modes preset by the manufacturer.
[0104] Equivalents
[0105] While the invention has been particularly shown and
described with reference to specific embodiments, it should be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *