Method and Device for Generating of a Signal that Reflects Respiratory Efforts in Patients on Ventilatory Support

• US 20090221926A1
• Filed: 05/12/2006
• Published: 09/03/2009
• Est. Priority Date: 05/12/2006
• Status: Active Grant

• Current Assignee: YRT Limited
• Original Assignee: YRT Limited
• Inventors: Younes, Magdy
• Granted Patent: US 8,920,333 B2
• Time in Patent Office: Days
• US Class Current: 600/529
• CPC Class Codes: A61B 5/085 Measuring impedance of respiratory organs or lung elasticity
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• 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 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2016/0042 in the expiratory circuit
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

A method and device for generating a signal that mirrors changes in the level of effort exerted by respiratory muscles of patients on mechanical ventilatory support comprising: monitoring and storing airway pressure (P_aw), rate of gas flow (F), and volume of gas flow (V), and generating a composite pressure signal using resistive pressure units (K_F) determined from elapsed data and selected to minimize step changes in the calculated signal and elastic pressure units (K_v) determined from elapsed data by steps comprising: scanning stored F or P_aw during exhalation and identifying where their trajectory transiently reverses direction to detect transients; selecting points within the exhalation that are at preselected distances away from the transients; calculating the value of K_v required to force the values of the calculated signal at said selected points in elapsed breaths to be substantially equal when the selected value of K_F is used as the flow coefficient.

Claims

1. A method for generating a signal that mirrors changes in the level of effort exerted by respiratory muscles of patients on mechanical ventilatory support (Signal), comprising:

monitoring airway pressure (P_aw), rate of gas flow (F), and volume of gas flow (V) of the patient;

storing P_aw, F and V data collected in computer memory;

generating a composite pressure signal (Signal) from the relationship;

Signal=current V*K_V+current F*K_F−

current P_aw,

wherein, K_F is a coefficient that converts flow into equivalent resistive pressure units and K_F is calculated from elapsed data and selected to minimize step changes in calculated Signal at the time of ventilator triggering and/or cycling-off, and K_V is a coefficient that converts volume into equivalent elastic pressure units and K_V is determined from elapsed data by steps comprising;

scanning of stored F or P_aw information, and/or the time derivative thereof, during the exhalation phase of elapsed breaths and identifying instances where the trajectory of either F or P_aw transiently reverses direction during said exhalation phase, thereby detecting transients;

selecting two or more points within the exhalation phase that are at preselected distances away from identified transients,

calculating the value of K_V required to force the values of Signal calculated at said selected points in elapsed breaths to be substantially equal when said selected value of K_F is used as the flow coefficient.

2. The method of claim 1 wherein the term F*K_F is replaced by other functions that allow for non-linear relation between flow and said resistive pressure units.

3. The method of claim 2 wherein F*K_F is replaced by [F*K_F1+(F*absolute F*K_F2)], wherein K_F2 is a constant and K_F1 is calculated from elapsed data and selected to minimize step changes in calculated Signal at the times of ventilator triggering and/or cycling-off.

4. The method of claim 3 wherein K_F2 is assigned a value corresponding to the K₂ constant of an endotracheal tube in place in the patient.

5. The method of claim 1 wherein K_V, K_F, K_F1 and/or K_F2 are adjusted to result in a specified slope of Signal during part or all of the expiratory phase.

6. The method of claim 1 wherein a default value of K_F or K_F1 is used.

7. The method of claim 1 wherein the K_F or K_F1 value used is a known or estimated value of patient'"'"'s respiratory system resistance.

8. The method of claim 7 wherein K_V is also a known or estimated value of patient'"'"'s respiratory system elastance.

9. The method of claim 1 wherein the K_V value used is a known or estimated value of patient'"'"'s respiratory system elastance.

10. The method of claim 1 wherein a default value of K_V is used while the value of K_F or K_F1 required to obtain the desired baseline Signal trajectory is obtained through the same steps specified in claim 1 to estimate the required K_V.

11. The method of claim 10 wherein the K_V value used is a known or estimated value of patient'"'"'s respiratory system elastance.

12. The method of claim 1 wherein the term V*K_V is replaced by another term that allows for a non-linear relation between volume and. equivalent elastic pressure units, said non-linear function being of the form [ƒ

V*K_V], wherein ƒ

is a specified mathematical function to be applied to the volume data, or [V*variable K_V], and value of K_V is a function of volume [K_V=ƒ

V], wherein ƒ

is a specified mathematical function, and the specified function (ƒ

) is derived from the P_aw, F and V data measured at said selected two or more points within said exhalation phase.

13. The method of claim 1 wherein said transients are classified into a number of types by reference to specified criteria.

14. The method of claim 13 wherein said preselected distances are set according to identified transient type.

15. The method of claim 1 wherein K_F or K_F1 required to minimize step changes in Signal is calculated both at the time of ventilator triggering and time of cycling-off and wherein, if differences exist between the two determinations, one or the other is chosen based on pre-specified criteria.

16. The method of claim 15 wherein if differences exist between the two determinations, a simple or weighted average value is obtained for use in calculating Signal.

17. The method of claim 1 wherein the generated Signal is further processed to identify the onset of Signal'"'"'s rising phase (T_ONSET) and/or onset of Signal'"'"'s declining phase (T_END).

18. The method of claim 17 wherein identification of T_ONSET is precluded for a specified period in the ventilator'"'"'s exhalation phase (T_ONSET Window Delay) and/or identification of T_END is precluded for a specified period in the ventilator'"'"'s inflation phase (T_END Window Delay).

19. The method of claim 18 wherein a minimum value for T_ONSET Window Delay is specified.

20. The method of claim 19 wherein said minimum value for T_ONSET Window Delay is a function of patient'"'"'s respiratory rate.

21. The method of claim 18 wherein a minimum value for T_END Window Delay is specified.

22. The method of claim 20 wherein said minimum value for T_END Window Delay is a function of patient'"'"'s respiratory rate.

23. The method of claim 17 wherein said generated T_ONSETs and/or T_ENDs are used to effect triggering and/or cycling-off of ventilator cycles.

24. The method of claim 17 wherein generated Signal is further processed to obtain information about patient-ventilator interaction and wherein said information is communicated to a user through display on a monitor or by other forms of communication.

25. The method of claim 24 wherein said information includes at least one of display of the Signal itself, T_onset and Tend markers, trigger delay, cycling-off delay, patient'"'"'s respiratory rate, number or rate of ineffective efforts.

26. The method of claim 1 wherein said calculated value of K_F and/or K_V is/are communicated to a user through display on a monitor or by other forms of communication.

27. The method of claim 26 wherein said communicated information is accompanied by narrative/commentary providing interpretation of the findings and/or suggestions for ventilator adjustment that might improve patient-ventilator interaction.

28. A device for generating a signal that mirrors changes in the level of effort exerted by respiratory muscles of patients on mechanical ventilatory support (Signal), comprising:

sensors and associated circuitry for obtaining information regarding airway pressure (P_aw), rate of gas flow (F), and volume of gas flow (V) of such a patient; and

a computer that executes the following functions;

storing collected P_aw, F and V data in computer memory;

calculating a composite pressure signal (Signal) from the relationship;

Signal=current V*K_V+current F*K_F−

current P_aw,

wherein, K_F is a coefficient that converts flow into equivalent resistive pressure units and K_F is calculated from elapsed breath data using algorithms that calculate the K_F value required to minimize step changes in calculated Signal at the time of ventilator triggering and/or cycling-off, and K_V is a coefficient that converts volume into equivalent elastic pressure units and K_V is calculated from elapsed breath data by steps comprising the following functions;

scanning of stored F or P_aw information, and/or the time derivative thereof, during the exhalation phase of elapsed breaths and identifying instances where the trajectory of either F or P_aw transiently reverses direction during said exhalation phase thereby detecting transients;

selecting two or more points within the exhalation phase that are at preselected distances away from identified transients, and

calculation functions to determine the value of K_V required to force the values of Signal calculated at said selected points in elapsed breaths to be substantially equal when said selected value of K_F is used as the flow coefficient.

29. The device of claim 28 wherein the term F*K_F is replaced by other functions that allow for non-linear relation between flow and said resistive pressure units.

30. The device of claim 29 wherein F*K_F is replaced by [F*K_F1+(F*absolute F*K_F2)], wherein K_F2 is a constant and K_F1 is calculated from elapsed data and selected to minimize step changes in calculated Signal at the times of ventilator triggering and/or cycling-off.

31. The device of claim 30 wherein K_F2 is assigned a value corresponding to the K₂ constant of an endotracheal tube in place in the patient.

32. The device of claim 28 wherein K_V, K_F, K_F1 and/or K_F2 are adjusted to result in a specified slope of Signal during part or all of the expiratory phase.

33. The device of claim 28 wherein a default value of K_F or K_F1 is used.

34. The device of claim 28 wherein the K_F or K_F1 value used is a known or estimated value of patient'"'"'s respiratory system resistance.

35. The device of claim 34 wherein K_V is also a known or estimated value of patient'"'"'s respiratory system elastance.

36. The device of claim 28 wherein the K_V value used is a known or estimated value of patient'"'"'s respiratory system elastance.

37. The device of claim 28 wherein a default value of K_V is used while the value of K_F or K_F1 required to obtain the desired baseline Signal trajectory is obtained through the same calculations specified in claim 28 to estimate the required K_V.

38. The device of claim 37 wherein the K_V value used is a known or estimated value of patient'"'"'s respiratory system elastance.

39. The device of claim 28 wherein the term V*K_V is replaced by another term that allows for a non-linear relation between volume and equivalent elastic pressure units, said non-linear function being of the form [ƒ

V*K_V], wherein ƒ

is a specified mathematical function to be applied to the volume data, or [V*variable K_V], and value of K_V is a function of volume [K_V=ƒ

V], wherein ƒ

is a specified mathematical function, and the specified function (ƒ

) is derived from the P_aw, F and V data measured at said selected two or more points within said exhalation phase.

40. The device of claim 28 wherein said transients are classified into a number of types by reference to specified criteria.

41. The device of claim 40 wherein said preselected distances are set according to identified transient type.

42. The device of claim 28 wherein K_F or K_F1 required to minimize step changes in Signal is calculated both at the time of ventilator triggering and time of cycling-off and wherein, if differences exist between the two determinations, one or the other is chosen based on pre-specified criteria.

43. The device of claim 42 wherein, if differences exist between the two determinations, a simple or weighted average value is obtained for use in calculating Signal.

44. The device of claim 28 wherein the computer executes the additional features of further processing the generated Signal to identify the onset of Signal'"'"'s rising phase (T_ONSET) and/or onset of Signal'"'"'s declining phase (T_END).

45. The device of claim 44 wherein the computer executes the additional features of precluding identification of T_ONSET for a specified period in the ventilator'"'"'s exhalation phase (T_ONSET Window Delay) and/or precluding identification of T_END for a specified period in the ventilator'"'"'s inflation phase (T_END Window Delay).

46. The device of claim 45 wherein a minimum value for T_ONSET Window Delay is specified.

47. The device of claim 46 wherein said minimum value for T_ONSET Window Delay is a function of patient'"'"'s respiratory rate.

48. The device of claim 46 wherein a minimum value for T_END Window Delay is specified.

49. The device of claim 47 wherein said minimum value for T_END Window Delay is a function of patient'"'"'s respiratory rate.

50. The device of claim 44 wherein said computer executes the additional features of using generated T_ONSETs and/or T_ENDs to effect triggering and/or cycling-off of ventilator cycles.

51. The device of claim 44 wherein the computer executes the additional features of further processing generated Signal to obtain information about patient-ventilator interaction and wherein said information is communicated to a user through display on a monitor or by other forms of communication.

52. The device of claim 51 wherein said information includes at least one of display of the Signal itself, T_onset and T_end markers, trigger delay, cycling-off delay, patient'"'"'s respiratory rate, number or rate of ineffective efforts.

53. The device of claim 28 wherein the computer executes the additional features of communicating said calculated value of K_F and/or K_V to a user through display on a monitor or by other forms of communication.

54. The device of claim 53 wherein said communicated information is accompanied by narrative/commentary providing interpretation of the findings and/or suggestions for ventilator adjustment that might improve patient-ventilator interaction.