Method and apparatus for controlling a medical ventilator

• US 6,390,091 B1
• Filed: 02/03/1999
• Issued: 05/21/2002
• Est. Priority Date: 02/03/1999
• Status: Expired due to Term

• Current Assignee: University of Florida Research Foundation, Incorporated (State University System of Florida)
• Original Assignee: University of Florida (State University System of Florida)
• Inventors: van Oostrom, Johannes H., Banner, Michael Joseph, Blanch, Paul Bradford, Melker, Richard Joel
• Primary Examiner(s): Weiss, John G.
• Assistant Examiner(s): WEISS JR, JOSEPH
• Application Number:
  US09/243,258
• Time in Patent Office: 1,203 Days
• Field of Search: 122/202.22, 122/204.18, 122/204.21, 122/204.22, 122/204.23, 122/204.26, 122/205.23
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/003 with a flowmeter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2205/8206 battery-operated
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

An open- or closed-loop method and corresponding medical ventilator for providing breathing gas to a patient such that the patient exerts a desired work of breathing during pressure support ventilation, and such that the work of breathing of the patient is monitored and the pressure and/or flow rate of the breathing gas provided to the patient is controlled throughout the inspiratory phase to provide a pressure support ventilation level that provides the desired work of breathing in the patient. The medical ventilator includes at least a pressure sensor and a flow rate sensor, disposed in a functionally open ventilator conduit in fluid communication with the lungs of the patient, electrically coupled to a microprocessor to monitor the average respiratory muscle pressure of the patient and to predict the patient work of breathing as a function of the current value of the average respiratory muscle pressure of the patient, to detect when the patient work of breathing is not within a predetermined work of breathing range, and to generate a response signal thereof. Further, the medical ventilator has a driver circuit electrically coupled to the microprocessor and to an actuator of a pneumatic system which, responsive to the response signal, may adjust the selected pressure support ventilation level of the breathing gas provided to the patient by the ventilator until a pressure support ventilation level is reached such that the patient work of breathing is within the predetermined work of breathing range.

Claims

1. A medical ventilator for providing pressure support ventilation to a patient, the medical ventilator in fluid communication with a gas source of one or ignore breathing gases and in flow communication with a functionally open ventilator flow conduit having a patient breathing attachment in fluid communication with the patient, the medical ventilator comprising:

a) pressure sensing means disposed within the ventilator conduit for sensing the pressure of the gas within the ventilator conduit;

b) flow rate measuring means disposed within the ventilator conduit for measuring the flow rate of the gas within the ventilator conduit;

c) monitoring means, connected to the pressure sensing means and the flow rate measuring means, programmed for;

a) monitoring a patient work of breathing, and b) determining a selected pressure support ventilation level to maintain the patient work of breathing within a predetermined work of breathing range; and

d) gas delivery means for controlling a supply of the gas so that the gas is delivered to the patient at the selected pressure support ventilation level.

2. The medical ventilator of claim 1, wherein the monitoring means detects when the patient work of breathing is not within the predetermined work of breathing range.

3. The medical ventilator of claim 1, wherein the monitoring means, responsive to the flow rate measured by the flow rate measuring means, determines a measured tidal volume of the breathing gas.

4. The medical ventilator of claim 3, wherein the monitoring means, responsive to the measured tidal volume of the gas in the ventilator conduit, the flow rate of the gas in the ventilator conduit, and the pressure of the gas in the ventilator conduit sensed by the pressure sensing means, determines an average respiratory muscle pressure of the patient, and wherein the monitoring means, responsive to the determined average respiratory muscle pressure, determines the patient work of breathing.

5. The medical ventilator of claim 2, further comprising alarm means responsive to the response signal to generate an alarm suitable for alerting an operator that the patient work of breathing is not within the predetermined work of breathing range.

6. The medical ventilator of claim 2, further comprising a regulating means connected to the monitoring means and the gas delivery means, the regulating means responsive to the response signal of the monitoring means to control the gas delivery means so that the selected pressure support ventilation level of the gas supplied to the patient is regulated in response to the monitoring means.

7. The medical ventilator of claim 6, wherein the gas delivery means comprises a pneumatic system having at least one electrically coupled actuator, in fluid communication with the gas source for regulating the supply of the breathing gas so that the breathing gas may be delivered to the patient at the selected pressure support ventilation level.

8. The medical ventilator of claim 7, wherein the regulating means comprises at least one driver circuit electrically coupled to the monitoring means and to each actuator, wherein the driver circuit adjusts the actuator based on electrical signals received from the monitoring means, thereby varying a pressure, a flow rate, or a combination of both to regulate the supply of the breathing gas so that the selected pressure support ventilation level is supplied to the patient.

9. The medical ventilator of claim 6, wherein the regulating means, in response to the response signal of the monitoring means, adjusts the selected pressure support ventilation level of the ventilator.

10. The medical ventilator of claim 9, wherein the regulating means, in response to the response signal of the monitoring means:

a) increments the selected pressure support ventilation level of the medical ventilator if the patient work of breathing is greater than the predetermined work of breathing range;

or

b) decrement the selected pressure support ventilation level of the medical ventilator if the patient work of breathing is less than the predetermined work of breathing range.

11. The medical ventilator of claim 9, wherein the monitoring means detects when the patient work of breathing is within the predetermined work of breathing range and generates a level signal thereof.

12. The medical ventilator of claim 11, further comprising a display means for displaying the selected pressure support ventilation level in response to the level signal so that the operating clinician is advised of the selected pressure support ventilation level that will maintain the patient work of breathing within the predetermined work of breathing range.

13. The medical ventilator of claim 12, wherein the monitoring means stores an initial value of the selected pressure support ventilation level so that the initial value of the selected pressure support ventilation level prior to adjustment of the selected pressure support ventilation level is stored, and wherein the regulating means, responsive to the level signal generated by the monitoring means, adjusts the selected pressure support ventilation level of the ventilator so that the selected pressure support ventilation level is adjusted to the initial value of the selected pressure support ventilation level.

14. A method of providing pressure support ventilation to a patient supplied with a breathing gas from a medical ventilator having a selectable pressure support ventilation level, the gas being received into the medical ventilator from a gas source of one or more breathing gases, and the gas exiting the medical ventilator being in flow communication with a functionally open ventilator flow conduit having a patient breathing attachment in fluid communication with the patient, wherein a supply of the gas is controlled by the medical ventilator, the method comprising the steps of:

a) delivering the breathing gas from the ventilator to the patient breathing attachment at a selected pressure support ventilation level;

b) sensing the pressure of the breathing gas within the ventilator conduit and generating a pressure signal representative of that pressure;

c) measuring the flow rate of the breathing gas within the ventilator conduit and generating a flow signal representative of that flow rate; and

d) providing a program for;

i) processing the flow signal and the pressure signal to determine the patient work of breathing;

ii) monitoring the patient work of breathing; and

iii) determining the pressure support ventilation level for which the patient work of breathing is maintained within a predetermined work of breathing range.

15. The method of claim 14, wherein the step of monitoring comprises determining when the patient work of breathing is not within the predetermined work of breathing range.

16. The method of claim 15, and further comprising the step of generating an alarm when it is determined that the patient work of breathing is not within the predetermined work of breathing range.

17. The method of claim 15, and further comprising the step of controlling the selected pressure support ventilation level of the ventilator when it is determined that the patient work of breathing is not within the predetermined work of breathing range.

18. The method of claim 17, wherein the step of controlling the pressure support ventilation level of the ventilator further comprises the steps of:

a) incrementing the selected pressure support ventilation level of the ventilator if the patient work of breathing is greater than the predetermined work of breathing range; and

b) decrementing the selected pressure support ventilation level of the ventilator if the patient work of breathing is less than the predetermined work of breathing range.

19. The method of claim 17, further comprising the steps of:

a) prior to the controlling step, storing an initial value of the selected pressure support ventilation level;

b) displaying the selected pressure support ventilation level, as a target pressure support ventilation level, to the operator when the patient work of breathing is within the predetermined work of breathing range; and

c) restoring delivery of the breathing gas to the patient to the stored initial value of the selected pressure support ventilation level when the patient work of breathing is within the predetermined work of breathing range.

20. The method of claim 17, further comprising the step of displaying the selected pressure support ventilation level to the operator when the patient work of breathing is within the predetermined work of breathing range.

21. The method of claim 14, further comprising the step of displaying the determined work of breathing to the operator.

22. The method of claim 14, wherein the step of sensing the pressure of the gas is performed in a flow path of the gas within the ventilator conduit;

and wherein the step of sensing the flow rate of the gas is performed in the flow path of the gas within the ventilator conduit.

23. The method of claim 14, wherein the step of measuring the flow rate of the gas exhaled by the patient comprises continuously measuring the flow rate of the breathing gas during an inhalation and exhalation effort by the patient.

24. The method of claim 14, wherein the step of sensing the pressure of the gas comprises continuously sensing the pressure of the breathing gas during an inhalation and exhalation effort by the patient.

25. The method of claim 14, wherein the step of processing comprises the steps of:

a) extracting a measured tidal volume of the breathing gas from the flow signal;

b) calculating a real-time respiratory muscle pressure according to;

26. The method of claim 25, wherein the selected number of serial breaths is five so that the determined average respiratory muscle pressure is a serial five breath average.

27. The method of claim 25, wherein the step of determining the patient work of breathing is determined according to:

28. A medical ventilator for providing pressure support ventilation of a patient, the medical ventilator comprising:

a gas source of one or more breathing gases in flow communication with the medical ventilator;

a ventilator flow conduit in flow communication with the medical ventilator and in fluid communication with the patient;

a pneumatic system having at least one actuator for controlling a supply of the breathing gas so that a selected pressure support ventilation level of pressure support ventilation is provided to the patient;

a pressure sensor disposed in the ventilator flow conduit which senses the pressure of the breathing gas proximate the pressure sensor and which provides a pressure signal representative of that pressure;

a flow rate sensor disposed in the ventilator flow conduit which senses the flow rate of the breathing gas within the ventilator flow conduit and which provides a flow signal representative of that flow rate;

a microprocessor programmed for controlling the selected pressure support ventilation level of the ventilator, the microprocessor being electrically coupled to the output of the pressure sensor and flow rate sensor, wherein the microprocessor determines a work of breathing of the patient, compares the work of breathing to a predetermined work of breathing range, generates a response signal based on the comparison, and communicates the response signal to at least one of the actuators of the pneumatic system so that the selected pressure support ventilation level of the ventilator is adjusted to bring the work of breathing of the patient within the predetermined work of breathing range.

29. The medical ventilator of claim 28, wherein the microprocessor generates the response signal when the patient work of breathing is not within the predetermined work of breathing range.

30. The medical ventilator of claim 28, further comprising an audible, a visible alarm, or a combination of both, that, in response to the response signal, generates an alarm suitable for alerting an operator that the patient work of breathing is not within the predetermined work of breathing range.

31. The medical ventilator of claim 28, wherein the actuator, responsive to the response signal:

a) increments the selected pressure support ventilation level provided by the ventilator if the patient work of breathing is greater than the predetermined work of breathing range;

or

b) decrements the selected pressure support ventilation level provided by the ventilator if the patient work of breathing is less than the predetermined work of breathing range.

32. The medical ventilator of claim 28, wherein the microprocessor detects when the patient work of breathing is within the predetermined work of breathing range and generates a level signal thereof.

33. The medical ventilator of claim 32, wherein the microprocessor, in response to level signal, stores the selected pressure support ventilation level as a target pressure support ventilation level.

34. The medical ventilator of claim 33, wherein the microprocessor, in response to the response signal, stores an initial value of the selected pressure support ventilation level so that the initial value of the selected pressure support ventilation level prior to adjustment is stored, and wherein the actuator, responsive to the level signal, adjusts the selected pressure support ventilation level of the ventilator of the gas provided to the patient back to the initial value of the selected pressure support ventilation level.

35. The medical ventilator claim 28, wherein the microprocessor:

a) extracts and stores a measured tidal volume of the breathing gas from the flow signal;

b) determines and stores a real-time respiratory muscle pressure (Pmus(t)) of the patient from the stored measured tidal volume, the stored inspiratory flow rate sensed, and the stored pressure sensed;

c) calculates an average respiratory muscle pressure for the inspiratory period of a single breath (Pmus_avg(t)) from the stored real-time respiratory muscle pressure (Pmus(t));

d) calculates an average respiratory muscle pressure of the patient (Pmus_avgN(t)) from the stored Pmus_avg(t) over a serial number of breaths; and

e) determines the patient work of breathing (WOB) from the calculated average respiratory muscle pressure (Pmus_avgN(t)).

36. The medical ventilator of claim 28, further comprising a first digitizer which receives the flow signal from the flow sensor and converts the flow signal into a digitized flow signal which is received by the microprocessor and a second digitizer which receives the pressure signal and converts the pressure signal into a digitized pressure signal which is received by the microprocessor.

37. The medical ventilator of claim 36, wherein the flow sensor continuously senses the flow rate of the breathing gas and the first digitizer continuously converts the flow signal into the digitized flow signal, and wherein the pressure sensor senses the pressure of the breathing gas continuously and the second digitizer continuously converts the pressure signal into the digitized pressure signal.

38. The medical ventilator of claim 35, wherein the microprocessor further comprises a memory means for storing at least one of:

the signal data, the determined tidal volume, Pmus(t), Pmus_avg(t), Pmus_avgN(t), the work of breathing of the patient, the selected pressure support ventilation level, the target pressure support ventilation level, and the initial value of the selected pressure support ventilation level.

39. The medical ventilator of claim 35, further comprising a monitor for displaying at least one of:

the signal data, the determined tidal volume, Pmus(t), Pmus_avg(t), Pmus_avgN(t), the work of breathing of the patient, the selected pressure support ventilation level, the target pressure support ventilation level, and the initial value of the selected pressure support ventilation level for concurrent review by an operator of the system.

40. The medical ventilator of claim 28, wherein the actuator regulates a pressure, a flow rate, or a combination of both to regulate the supply of the breathing gas.

41. A method of providing pressure support ventilation to a patient supplied with a breathing gas from a medical ventilator having a selectable pressure support ventilation level, the gas being received into the medical ventilator from a gas source of one or more breathing gases, and the gas exiting the medical ventilator being in flow communication with a functionally open ventilator flow conduit having a patient breathing attachment in fluid communication with the patient, wherein a supply of the gas is controlled by the medical ventilator, the method comprising the steps of:

a) delivering the breathing gas from the ventilator to the patient breathing attachment at a selected pressure support ventilation level;

b) sensing the pressure of the breathing gas within the ventilator conduit and generating a pressure signal representative of that pressure;

c) measuring the flow rate of the breathing gas within the ventilator conduit and generating a flow signal representative of that flow rate;

d) processing the flow signal and the pressure signal to determine the patient work of breathing by;

i) extracting a measured tidal volume of the breathing gas from the flow signal;

ii) calculating a real-time respiratory muscle pressure according to;

42. The method of claim 41, wherein the selected number of serial breaths is five so that the determined average respiratory muscle pressure is a serial five breath average.

43. The method of claim 41, wherein the step of determining the patient work of breathing is determined according to:

44. A medical ventilator for providing pressure support ventilation of a patient, the medical ventilator comprising:

a gas source of one or more breathing gases in flow communication with the medical ventilator;

a ventilator flow conduit in flow communication with the medical ventilator and in fluid communication with the patient;

a pneumatic system having at least one actuator for controlling a supply of the breathing gas so that a selected pressure support ventilation level of pressure support ventilation is provided to the patient;

a pressure sensor disposed in the ventilator flow conduit which provides a pressure signal representative of the pressure of the gas proximate the pressure sensor;

a flow rate sensor disposed in the ventilator flow conduit which provides a flow signal representative of the flow rate of the breathing gas within the ventilator flow conduit;

a microprocessor programed for controlling the selected pressure support ventilation level of the ventilator, the microprocessor being electrically coupled to the output of the pressure sensor and flow rate sensor, wherein the microprocessor;

a) extracts and stores a measured tidal volume of the breathing gas from the flow signal;

b) determines and stores a real-time respiratory muscle pressure (Pmus(t)) of the patient from the stored measured tidal volume, the stored inspiratory flow rate sensed, and the stored pressure sensed;

c) calculates an average respiratory muscle pressure for the inspiratory period of a single breath (Pmus_avg(t)) from the stored real-time respiratory muscle pressure (Pmus(t));

d) calculates an average respiratory muscle pressure of the patient (Pmus_avgN(t)) from the stored Pmus_avg(t) over a serial number of breaths;

e) determines a patient work of breathing (WOB) from the calculated average respiratory muscle pressure (Pmus_avgN(t));

f) compares the work of breathing to a predetermined work of breathing range;

g) generates a response signal based on the comparison; and

h) communicates the response signal to at least one of the actuators of the pneumatic system so that the selected pressure support ventilation level of the ventilator is adjusted to bring the work of breathing of the patient within the predetermined work of breathing range.

45. A medical ventilator for providing pressure support ventilation of a patient, the medical ventilator comprising:

a gas source of one or more breathing gases in flow communication with the medical ventilator;

a ventilator flow conduit in flow communication with the medical ventilator and in fluid communication with the patient;

a pneumatic system having at least one actuator for controlling a supply of the breathing gas so that a selected pressure support ventilation level of pressure support ventilation is provided to the patient;

a pressure sensor disposed in the ventilator flow conduit which provides a pressure signal representative of the pressure of the gas proximate the pressure sensor;

a flow rate sensor disposed in the ventilator flow conduit which provides a flow signal representative of the flow rate of the breathing gas within the ventilator flow conduit;

a microprocessor programmed for controlling the selected pressure support ventilation level of the ventilator, the microprocessor being electrically coupled to the output of the pressure sensor and flow rate sensor, wherein the microprocessor;

a) determines and stores a real-time respiratory muscle pressure (Pmus(t)) of the patient from the flow signal and the pressure signal;

b) calculates an average respiratory muscle pressure of the patient (Pmus_avgN(t)) from the stored real-time respiratory muscle pressure (Pmus(t)) over a serial number of breaths;

c) determines a patient work of breathing (WOB) from the calculated average respiratory muscle pressure (Pmus_avgN(t));

d) compares the work of breathing to a predetermined work of breathing range;

e) generates a response signal based on the comparison; and

f) communicates the response signal to at least one of the actuators of the pneumatic system so that the selected pressure support ventilation level of the ventilator is adjusted to bring the work of breathing of the patient within the predetermined work of breathing range.