Automatic Control System For Mechanical Ventilation For Active Or Passive Subjects

• US 20110017214A1
• Filed: 07/25/2009
• Published: 01/27/2011
• Est. Priority Date: 07/25/2009
• Status: Active Grant

• Current Assignee: Fleur T Tehrani
• Original Assignee: Fleur T Tehrani
• Inventors: Tehrani, Fleur T.
• Granted Patent: US 8,701,665 B2
• Time in Patent Office: Days
• US Class Current: 128/204.22
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61B 5/085 Measuring impedance of respiratory organs or lung elasticity
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity
• CPC Class Codes: A61B 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0033 electrical
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2230/202 partial carbon oxide pressure, e.g. partial dioxide pressure (P-CO2)
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

A method and an apparatus for controlling a ventilator to automatically adjust ventilation assistance to an active or passive subject. The method includes determining volume and flow rate of gas to the patient during inspiration on an ongoing basis, and generating control signals in proportion to the volume and flow rate of gas to the patient wherein proportionality factors, and support levels for the elastic and resistive components of pressure are automatically adjusted by the ventilator. The ongoing pressure applied by the ventilator is a sum of elastic and resistive pressures that are automatically controlled by the system. When the patient breathes spontaneously, the support levels are automatically adjusted based on the patient'"'"'s requirements. If the patient does not breathe spontaneously, the ventilator provides ventilation at an optimal level and rate. The method may be used in weaning or in a management phase of ventilation.

Claims

1. A method for automatically controlling a ventilator, comprising:

(a) determining ongoing volume and flow rate of gas to a patient during inspiration;

(b) providing respiratory elastance, K, and airway resistance, K′

, of the patient;

(c) generating control signals controlling pressure applied by the ventilator as a sum of elastic and resistive components of pressure, the elastic component of pressure having a proportionality factor, K₁, proportional to the determined volume of the inspiratory gas, and the resistive component of pressure having a proportionality factor, K₂, proportional to the determined flow rate of the inspiratory gas; and

(d) automatically adjusting a support level for elastic component of pressure, α

=K₁/K, a support level for resistive component of pressure, α

′

=K₂/K′

, and the proportionality factors K₁ and K₂, based on a comparison between a work of breathing for the patient determined by the ventilator and a previously determined work of breathing.

2. The method of claim 1 wherein the previously determined work of breathing is a specified constant level, and adjustments in the support levels, α

and α

′

, and proportionality factors, K₁ and K₂, are proportional to a difference between the specified constant level and the patient'"'"'s determined work of breathing.

3. The method of claim 1 wherein the previously determined work of breathing is a work of breathing previously determined for the patient by the ventilator, and adjustments in the support levels, α

and α

′

, and proportionality factors, K₁ and K₂, are proportional to a difference between the patient'"'"'s previously determined work of breathing and an updated determined work of breathing.

4. The method of claim 1 further comprising determining whether the patient is breathing spontaneously, and if the patient is not breathing spontaneously, then skipping steps (c) and (d), determining a required ventilation for the patient, and based on the patient'"'"'s required ventilation and the patient'"'"'s respiratory elastance and airway resistance, determining an optimal breathing rate for the patient, and providing mandatory ventilation to the patient according to the determined required ventilation and optimal breathing rate.

5. The method of claim 4 wherein the patient'"'"'s required ventilation is determined based on a data indicative of an ideal body weight of the patient.

6. The method of claim 4 wherein the patient'"'"'s required ventilation is determined based on a measured carbon dioxide level of the patient.

7. The method of claim 4 wherein the patient'"'"'s optimal breathing rate is determined to minimize respiratory work rate.

8. The method of claim 7 wherein the following equation is used to calculate the optimal breathing rate:

9. A method for automatically controlling a ventilator, comprising:

(a) determining ongoing volume and flow rate of gas to a patient during inspiration;

(b) providing respiratory elastance, K, and airway resistance, K′

, of the patient;

(c) generating control signals controlling pressure applied by the ventilator as a sum of elastic and resistive components of pressure, the elastic component of pressure having a proportionality factor, K₁, proportional to the determined volume of the inspiratory gas, and the resistive component of pressure having a proportionality factor, K₂, proportional to the determined flow rate of the inspiratory gas; and

(d) automatically adjusting a support level for elastic component of pressure, α

=K₁/K, a support level for resistive component of pressure, α

′

=K₂/K′

, and the proportionality factors K₁ and K₂, based on a comparison between a required ventilation for the patient and a measured ventilation for the patient.

10. The method of claim 9 further comprising determining the required ventilation for the patient based on data indicative of an ideal body weight of the patient.

11. The method of claim 9 further comprising determining the required ventilation for the patient based on a measured carbon dioxide level of the patient.

12. The method of claim 11 wherein the required ventilation for the patient is determined according to the following equations:

VAC=K₃[K₅(P_CO2−

K₄−

P1)+P1]−

K₆,

VALV=VALV(rest)×

VAC,

VDt=VD+VDE, and

MV=VALV+f×

VDt

where VAC is a factor representing a net effect of the patient'"'"'s CO₂ level on alveolar ventilation, and VAC cannot be negative, zero, or less than a predefined value, K₅ is a smoothing constant parameter less than or equal to 1, P_CO2 is the measured carbon dioxide level of the patient, P1 is a normal level of P_CO2, K₄ is a difference between an acceptable level of P_CO2 for the patient and P1, and K₄ is chosen to set a desired level of patient'"'"'s P_CO2, K₃ and K₆ are constants, VALV(rest) is patient'"'"'s alveolar ventilation at rest in liters per minute proportional to patient'"'"'s ideal body weight, VALV is patient'"'"'s required alveolar ventilation in liters per minute, VD is patient'"'"'s physiological dead space determined as VD=C₁×

VALV+C₂ where C₁ and C₂ are constants, VDE is a dead space due to tubes and connections to the ventilator, VDt is total dead space volume, f is a patient'"'"'s rate of spontaneous breathing measured by the ventilator per minute, and MV is the patient'"'"'s required ventilation in liters per minute.

13. The method of claim 9 wherein updated support levels and proportionality factors are determined according to:

14. The method of claim 9 wherein updated support levels and proportionality factors are determined according to:

15. The method of claim 9 further comprising determining whether the patient is breathing spontaneously, and if the patient is not breathing spontaneously, then skipping steps (c) and (d), determining a required ventilation for the patient, and based on the patient'"'"'s required ventilation and the patient'"'"'s respiratory elastance and airway resistance values, determining an optimal breathing rate for the patient, and providing mandatory ventilation to the patient according to the determined required ventilation and optimal breathing rate.

16. The method of claim 15 wherein the patient'"'"'s required ventilation is determined based on data indicative of an ideal body weight of the patient.

17. The method of claim 15 wherein the patient'"'"'s required ventilation is determined based on a measured carbon dioxide level of the patient.

18. The method of claim 15 wherein the patient'"'"'s optimal breathing rate is determined to minimize respiratory work rate.

19. The method of claim 18 wherein the following equation is used to calculate the optimal breathing rate:

20. An apparatus for automatically controlling a ventilator, comprising:

a computing system;

digital readable memory coupled to the computing system;

one or more transducers providing data to the computing system representing a patient'"'"'s respiratory elastance and airway resistance values and ongoing volume and flow rate of a gas to the patient during inspiration; and

a program stored in the memory, the program when executed by the computing system determining support levels for elastic and resistive pressures based on a comparison between a work of breathing for the patient determined by the program and a previously determined level of work of breathing, and determining a level of ongoing pressure support to the patient as a sum of the elastic and resistive pressures based on the determined support levels and the data provided by the transducers, and the computing system generating control signals to the ventilator to achieve the determined support levels for elastic and resistive pressures and the level of ongoing pressure support.

21. The apparatus of claim 20 wherein the previously determined level of work of breathing is a specified constant level and the program stored in the memory determines the support levels and the level of ongoing pressure support to the patient based on a difference between the specified constant level and the patient'"'"'s determined work of breathing.

22. The apparatus of claim 20 wherein the previously determined level of work of breathing is a work of breathing previously determined for the patient by the program, and the program determines the support levels and the level of ongoing pressure support to the patient based on a difference between the patient'"'"'s updated work of breathing and the patient'"'"'s previous work of breathing determined by the program.

23. The apparatus of claim 20 wherein if the patient does not breathe spontaneously, the program stored in the memory does not determine the support levels and instead determines a required ventilation for the patient and an optimal respiration rate for the patient wherein the patient'"'"'s optimal respiration rate is determined according to the following equation:

24. The apparatus of claim 23 wherein the patient'"'"'s required ventilation is determined by the program stored in the memory also on the basis of a measured level of carbon dioxide of the patient provided to the computing system by a carbon dioxide analyzer.

25. The apparatus of claim 24 wherein the carbon dioxide analyzer is selected from the group comprising an end-tidal gas analyzer, an arterial gas analyzer, and a transcutaneous CO₂ analyzer.

26. The apparatus of claim 20 further comprising one or more A/D converters connected between the transducers and the computing system for converting analog signals from the transducers into digital form.

27. The apparatus of claim 20 further comprising one or more D/A converters for converting digital signals from the computing system to analog signals and supplying the analog signals to the ventilator as the control signals.

28. An apparatus for automatically controlling a ventilator, comprising:

a computing system;

digital readable memory coupled to the computing system;

one or more transducers providing data to the computing system representing ongoing volume and flow rate of a gas to a patient during inspiration; and

a program stored in the memory, the program when executed by the computing system determining support levels for elastic and resistive pressures and a level of ongoing pressure support to the patient as a sum of the elastic and resistive pressures, wherein the support levels for elastic and resistive pressures are determined based on a comparison between a required ventilation for the patient and a measured ventilation for the patient performed by the program, and the ongoing pressure support to the patient is determined based on the support levels for elastic and resistive pressures and the data provided by the transducers, and the computing system generating control signals to the ventilator to achieve the determined support levels for elastic and resistive pressures and the level of ongoing pressure support.

29. The apparatus of claim 28 wherein the transducers further include one or more monitors for measuring respiratory elastance and airway resistance of the patient.

30. The apparatus of claim 29 wherein the required ventilation for the patient is determined by the program stored in the memory based on data indicative of an ideal body weight for the patient.

31. The apparatus of claim 29 wherein the required ventilation for the patient is determined based on a measured level of carbon dioxide of the patient provided to the computing system by a carbon dioxide analyzer.

32. The apparatus of claim 31 wherein the carbon dioxide analyzer is selected from the group comprising an end-tidal gas analyzer, an arterial gas analyzer, and a transcutaneous CO₂ analyzer.

33. The apparatus of claim 29 wherein if the patient does not breathe spontaneously, the program stored in the memory does not determine the support levels and instead determines a required ventilation for the patient and an optimal respiration rate for the patient wherein the patient'"'"'s optimal respiration rate is determined according to the following equation:

34. The apparatus of claim 29 further comprising one or more A/D converters connected between the transducers and the computing system for converting analog signals from the transducers into digital form.

35. The apparatus of claim 28 further comprising one or more D/A converters for converting digital signals from the computing system to analog signals and supplying the analog signals to the ventilator as the control signals.