Method and apparatus for providing ventilatory assistance
View Patent ↗The apparatus provides for the determination of the instantaneous phase in the respiratory cycle, subject's average respiration rate and the provision of ventilatory assistance. A microprocessor ( 16 ) receives an airflow signal from a pressure transducer ( 18 ) coupled to a port ( 17 ) at a mask ( 11 ). The microprocessor ( 16 ) controls a servo ( 19 ), that in turn controls the fan motor ( 20 ) and thus the pressure of air delivered by the blower ( 10 ). The blower ( 10 ) is coupled to a subject's mask (ii) by a conduit ( 12 ). The invention seeks to address the following goals: while the subject is awake and making substantial efforts the delivered assistance should be closely matched in phase with the subject's efforts; the machine should automatically adjust the degree of assistance to maintain at least a specified minimum ventilation without relying on the integrity of the subject's chemoreflexes; and it should continue to work correctly in the presence of large leaks.
1. A method for providing ventilatory assistance in a spontaneously breathing subject, comprising:
determining a measure of the subject's ventilation;
setting, with a processor, an instantaneous phase in a respiratory cycle based on the measure of the subject's ventilation, the phase being set to a value based on the subject's respiratory airflow when the subject's ventilation is adequate, the phase being set according to a preset rate when the subject's ventilation is inadequate; and
calculating, with the processor, a delivery pressure as a function of the phase.
2. The method of claim 1 , wherein the preset rate is a target respiratory rate.
3. The method of claim 1 , wherein the processor calculates the phase in a respiratory cycle as a continuous variable from 0 to 1 revolution.
4. The method of claim 1 , further comprising delivering the delivery pressure at the calculated delivery pressure.
5. The method of claim 1 , wherein the processor calculates the pressure as a function of an end expiratory pressure plus a desired pressure modulation amplitude multiplied by a value of a waveform template function at the set phase.
6. The method of claim 5 , wherein the desired pressure modulation amplitude includes a fixed amplitude.
7. The method of claim 5 , wherein the desired pressure modulation amplitude includes a component equal to an elastance multiplied by an estimate of the subject's tidal volume.
8. The method of claim 5 , wherein the desired pressure modulation amplitude includes a component chosen to servo-control the ventilation to at least exceed a specified ventilation.
9. The method of claim 8 , wherein the processor calculates the component by:
calculating an error term proportional to an absolute value of an estimated respiratory airflow minus twice the specified ventilation; and
setting the component proportional to a time integral of the error term.
10. The method of claim 9 , wherein the time integral is clipped to fall between a preset minimum and a preset maximum.
11. The method of claim 5 , wherein the processor determines a component of the desired pressure modulation amplitude by:
specifying an expected breath duration;
specifying a preset pressure modulation amplitude to apply for the expected breath duration;
calculating an actual breath duration of the subject; and
calculating the component of the desired pressure modulation amplitude as a function of at least the specified preset pressure modulation amplitude multiplied by the calculated actual breath duration divided by the specified expected breath duration.
12. The method of claim 1 , wherein the processor sets the phase incrementing at the preset rate when the subject's ventilation is inadequate.
13. An apparatus for providing ventilatory assistance in a spontaneously breathing subject, comprising:
a blower adapted to couple to a mask to supply breathable air to a subject's airway;
a pressure transducer to generate a flow signal representative of respiratory airflow; and
a processor configured to:
determine a measure of the subject's ventilation;
set an instantaneous phase in a respiratory cycle based on the measure of the subject's ventilation, the phase being set to a value based on the subject's respiratory airflow when the subject's ventilation is adequate, the phase being set according to a preset rate when the subject's ventilation is inadequate; and
calculate a delivery pressure as a function of the phase.
14. The apparatus of claim 13 , wherein the preset rate is a target respiratory rate.
15. The apparatus of claim 13 , wherein the processor calculates the phase in a respiratory cycle as a continuous variable from 0 to 1 revolution.
16. The apparatus of claim 13 , wherein the processor controls the blower to supply the breathable air at the calculated delivery pressure.
17. The apparatus of claim 13 , wherein the processor calculates the pressure as a function of an end expiratory pressure plus a desired pressure modulation amplitude multiplied by a value of a waveform template function at the set phase.
18. The apparatus of claim 17 , wherein the desired pressure modulation amplitude includes a fixed amplitude.
19. The apparatus of claim 17 , wherein the desired pressure modulation amplitude includes a component equal to an elastance multiplied by an estimate of the subject's tidal volume.
20. The apparatus of claim 17 , wherein the desired pressure modulation amplitude includes a component chosen to servo-control the ventilation to at least exceed a specified ventilation.
21. The apparatus of claim 20 , wherein the processor calculates the component by:
calculating an error term proportional to an absolute value of an estimated respiratory airflow minus twice the specified ventilation; and
setting the component proportional to a time integral of the error term.
22. The apparatus of claim 21 , wherein the time integral is clipped to fall between a preset minimum and a preset maximum.
23. The apparatus of claim 17 , wherein the processor determines a component of the desired pressure modulation amplitude by:
specifying an expected breath duration;
specifying a preset pressure modulation amplitude to apply for the expected breath duration;
calculating an actual breath duration of the subject; and
calculating the component of the desired pressure modulation amplitude as a function of at least the specified preset pressure modulation amplitude multiplied by the calculated actual breath duration divided by the specified expected breath duration.
24. The apparatus of claim 13 , wherein the processor sets the phase incrementing at the preset rate when the subject's ventilation is inadequate.
25. A method for providing ventilatory assistance in a spontaneously breathing subject, comprising:
determining a measure of a mask leak stability;
setting, with a processor, an instantaneous phase in a respiratory cycle based on the measure of the mask leak stability, the phase being set to a value based on the subject's respiratory airflow when the mask leak is stable, the phase being set according to a preset rate when the mask leak is instable; and
calculating, with the processor, a delivery pressure as a function of the phase.
26. The method of claim 25 , wherein the preset rate is a target respiratory rate.
27. The method of claim 25 , wherein the processor calculates the phase in a respiratory cycle as a continuous variable from 0 to 1 revolution.
28. The method of claim 25 , further comprising delivering the delivery pressure at the calculated delivery pressure.
29. The method of claim 25 , wherein the processor calculates the pressure as a function of an end expiratory pressure plus a desired pressure modulation amplitude multiplied by a value of a waveform template function at the set phase.
30. The method of claim 29 , wherein the desired pressure modulation amplitude includes a fixed amplitude.
31. The method of claim 29 , wherein the desired pressure modulation amplitude includes a component equal to an elastance multiplied by an estimate of the subject's tidal volume.
32. The method of claim 29 , wherein the desired pressure modulation amplitude includes a component chosen to servo-control ventilation to at least exceed a specified ventilation.
33. The method of claim 32 , wherein the processor calculates the component by:
calculating an error term proportional to an absolute value of an estimated respiratory airflow minus twice the specified ventilation; and
setting the component proportional to a time integral of the error term.
34. The method of claim 33 , wherein the time integral is clipped to fall between a preset minimum and a preset maximum.
35. The method of claim 29 , wherein the processor determines a component of the desired pressure modulation amplitude by:
specifying an expected breath duration;
specifying a preset pressure modulation amplitude to apply for the expected breath duration;
calculating an actual breath duration of the subject; and
calculating the component of the desired pressure modulation amplitude as a function of at least the specified preset pressure modulation amplitude multiplied by the calculated actual breath duration divided by the specified expected breath duration.
36. The method of claim 25 , wherein the processor sets the phase incrementing at the preset rate when the mask leak is instable.
37. An apparatus for providing ventilatory assistance in a spontaneously breathing subject, comprising:
a blower adapted to couple to a mask to supply breathable air to a subject's airway;
a pressure transducer to generate a flow signal representative of respiratory airflow; and
a processor configured to:
determine a measure of a mask leak stability;
set an instantaneous phase in a respiratory cycle based on the measure of the mask leak stability, the phase being set to a value based on the subject's respiratory airflow when the mask leak is stable, the phase being set according to a preset rate when the mask leak is instable; and
calculate a delivery pressure as a function of the phase.
38. The apparatus of claim 37 , wherein the preset rate is a target respiratory rate.
39. The apparatus of claim 37 , wherein the processor calculates the phase in a respiratory cycle as a continuous variable from 0 to 1 revolution.
40. The apparatus of claim 37 , wherein the processor controls the blower to supply the breathable air at the calculated delivery pressure.
41. The apparatus of claim 37 , wherein the processor calculates the pressure as a function of an end expiratory pressure plus a desired pressure modulation amplitude multiplied by a value of a waveform template function at the set phase.
42. The apparatus of claim 41 , wherein the desired pressure modulation amplitude includes a fixed amplitude.
43. The apparatus of claim 41 , wherein the desired pressure modulation amplitude includes a component equal to an elastance multiplied by an estimate of the subject's tidal volume.
44. The apparatus of claim 41 , wherein the desired pressure modulation amplitude includes a component chosen to servo-control ventilation to at least exceed a specified ventilation.
45. The apparatus of claim 44 , wherein the processor calculates the component by:
calculating an error term proportional to an absolute value of an estimated respiratory airflow minus twice the specified ventilation; and
setting the component proportional to a time integral of the error term.
46. The apparatus of claim 45 , wherein the time integral is clipped to fall between a preset minimum and a preset maximum.
47. The apparatus of claim 41 , wherein the processor determines a component of the desired pressure modulation amplitude by:
specifying an expected breath duration;
specifying a preset pressure modulation amplitude to apply for the expected breath duration;
calculating an actual breath duration of the subject; and
calculating the component of the desired pressure modulation amplitude as a function of at least the specified preset pressure modulation amplitude multiplied by the calculated actual breath duration divided by the specified expected breath duration.
48. The apparatus of claim 37 , wherein the processor sets the phase incrementing at the preset rate when the mask leak is instable.