Determining suitable ventilator settings for patients with alveolar hypoventilation during sleep

• US 6,644,312 B2
• Filed: 03/05/2001
• Issued: 11/11/2003
• Est. Priority Date: 03/07/2000
• Status: Active Grant

• Current Assignee: ResMed Pty Ltd. (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Berthon-Jones, Michael, Malouf, Gordon, Bassin, David, Bateman, Peter
• Primary Examiner(s): Lo, Weilun
• Assistant Examiner(s): Mitchell, Teena
• Application Number:
  US09/799,260
• Publication Number:
  US 20010027792A1
• Time in Patent Office: 981 Days
• Field of Search: 128/200.24, 128/204.18, 128/204.21, 128/204.23, 128/207.14, 128/207.15, 128/207.18, 600/323, 600/300, 600/301
• US Class Current: 128/204.23
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/0066 Blowers or centrifugal pumps
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• 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 16/06 Respiratory or anaesthetic masks
• CPC Class Codes: A61M 16/0858 Pressure sampling ports
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase

Abstract

A method and apparatus for determining suitable settings for a servo-ventilator to be used during sleep. Respiratory characteristics of a patient are measured during an awake learning period. With these measured characteristics, a target ventilation setting may be calculated by alternative methods. The calculated setting may then be used for enforcing a minimum ventilation during a treatment period where ventilatory support is provided with a servo-controlled ventilator.

Claims

1. A method for determining at least one setting of a ventilator to be used during sleep comprising the steps of:

measuring at least one respiratory characteristic of a patient during at least a latter portion of a learning period while the patient is awake; and

determining at least one setting value from said at least one respiratory characteristic to be used for the operation of said ventilator during a subsequent treatment period of sleep.

2. The method of claim 1 wherein said at least one respiratory characteristic is a measure of ventilation.

3. The method of claim 2 wherein at least one setting value is a target ventilation.

4. The method of claim 3 wherein said measure of ventilation is an average minute ventilation.

5. The method of claim 4 wherein said target ventilation is a target minute ventilation.

6. The method of claim 5 wherein said target minute ventilation is a function of said average minute ventilation.

7. The method of claim 6 wherein said function is a fixed proportion.

8. The method of claim 7 wherein said fixed proportion is about 90%.

9. The method of claim 2 wherein another said respiratory characteristic is arterial hemoglobin oxygen saturation.

10. The method of claim 9 wherein at least one setting value is calculated from the relationship between said oxygen saturation and said measure of ventilation.

11. The method of claim 10 wherein said measure of ventilation is a minute ventilation.

12. The method of claim 2 wherein at least one setting value is derived through a fuzzy expert system with input variables including a target ventilation derived from said measure of ventilation and patient estimation information.

13. The method of claim 3 further comprising the step of delivering ventilatory support during a treatment period in accordance with at least one setting value.

14. The method of claim 3 further comprising the step of:

analyzing patient estimation information to determine an estimated target ventilation;

wherein said setting value is a calculated weighted average of said estimated target ventilation and a second target ventilation derived from said measure of ventilation.

15. The method of claim 3 wherein said step of measuring at least one respiratory characteristic includes deriving measures of spontaneous ventilation and measures of arterial oxygen saturation.

16. The method of claim 15 wherein said step of determining a setting value includes an analysis of a graph of said measures of spontaneous ventilation and measures of arterial oxygen saturation.

17. The method of claim 16 wherein said graph includes a fitted curve derived from said measures of spontaneous ventilation and measures of arterial oxygen saturation using least squares nonlinear regression.

18. The method of claim 17 wherein said curve is an exponential function.

19. The method of claim 15 wherein said step of determining a setting value includes an application of a function to said measures of spontaneous ventilation and measures of arterial oxygen saturation, said function being derived using a method of least squares nonlinear regression.

20. The method of claim 19 wherein said function is an equation of an exponential curve.

21. The method of claim 15 wherein said measures of spontaneous ventilation are delayed and low-pass filtered to associate changes in said arterial oxygen saturation with changes in said measures of spontaneous ventilation.

22. The method of claim 2 wherein said measure of ventilation is a tidal volume ventilation.

23. The method of claim 22 wherein said target ventilation is a tidal volume ventilation.

24. The method of claim 1 further comprising delivering a degree of ventilatory support to a patient during said learning period wherein said degree of ventilatory support is set at a fixed minimum.

25. The method of claim 24 wherein the degree of ventilatory support includes a fixed level of supplemental oxygen wherein said steps are repeated in a subsequent learning period with said degree of ventilatory support set at a different fixed minimum from a prior learning period and said ventilatory support includes a different fixed level of supplemental oxygen from said prior learning period.

26. The method of claim 1 wherein said at least one respiratory characteristic is a measure of respiration rate.

27. The method of claim 26 wherein at least one setting value is a target respiration rate.

28. The method of claim 27 wherein said measure of respiration rate is an average respiration rate.

29. The method of claim 28 wherein said average respiration rate is averaged over about the latter 75% of the learning period.

30. The method of claim 1 wherein said at least one respiratory characteristic is a measure of arterial partial pressure of carbon dioxide.

31. The method of claim 30 wherein at least one setting value is a target ventilation which is a product of a current target ventilation and the measure of arterial partial pressure of carbon dioxide divided by a desired arterial partial pressure of carbon dioxide.

32. A ventilator comprising:

a means for delivering ventilatory support to a patient;

a means for determining the patient'"'"'s respiratory airflow;

a means for calculating a measure of ventilation from said respiratory airflow; and

a means for controlling said ventilatory support to maintain said measure of ventilation to at least equal a target ventilation,

wherein said apparatus further comprises machine control instructions for switching between a learn mode and a treat mode where said ventilator automatically calculates a target ventilation based on a learning period from said learn mode, and in said treat mode said ventilator delivers ventilatory support using said target ventilation calculated from said learn mode.

33. The ventilator of claim 32 wherein said machine control instructions further comprise machine control instructions for switching the apparatus to an inoperative mode to prevent said ventilator from operation in the treat or learn modes.

34. The ventilator of claim 33 wherein machine control instructions for switching the apparatus control the ventilator, if power is cycled off and on, to remain in the mode of operation it was in before the off and on cycle, unless the ventilator was in the learn mode, in which case the ventilator switches to the inoperable mode.

35. The ventilator of claim 32 wherein machine control instructions of the ventilator prior to said treat mode permit external input for modifying or accepting ventilator.

36. The ventilator of claim 35 wherein machine control instructions of said ventilator signals conclusion of said learn mode.

37. The ventilator of claim 32 wherein said measure of ventilation is an average minute ventilation taken over a latter portion of the learning period and said target ventilation calculated from said learn mode is a fixed proportion of said average minute ventilation.

38. The ventilator of claim 32 where in said treat mode, a target respiratory rate is set from a respiratory rate measured during the learning period of said learning mode.

39. An apparatus for determining ventilation settings comprising:

a mask;

a blower to supply pressurized air to said mask;

a servo-controller coupled to said blower;

a transducer to generate a flow signal representing air supplied to said mask; and

a processor, coupled to said transducer and said servo-controller, with program instructions;

wherein the instructions control switchable learn and treat modes in which said processor;

calculates a measure of ventilation from said flow signal during a learning period in a learn mode; and

calculates a target ventilation as a function of said measured ventilation for use in a treat mode;

calculates a pressure request during a treat mode to control delivery of said pressurized air to said mask wherein a degree of ventilatory support maintains patient ventilation to equal at least said target ventilation determined from said learn mode.

40. The apparatus of claim 39 wherein said measured ventilation is an average minute ventilation and said target ventilation is a target minute ventilation.

41. The apparatus of claim 40 wherein said function is a fixed proportion of about 90%.

42. The apparatus of claim 39 wherein said measure of ventilation is a tidal volume ventilation and said target ventilation is a tidal volume.

43. The apparatus of claim 39 wherein the instructions further cause said processor to control delivery of a fixed minimum degree of ventilatory support during said learning period.

44. The apparatus of claim 39 further comprising an oximeter coupled to said processor wherein the instructions further cause said processor to measure blood oxygen saturation during said learning period using said oximeter wherein said function is a relationship between said measure of blood oxygen saturation and said measure of ventilation.

45. The apparatus of claim 39 wherein the instructions further cause said processor to process patient estimation information to determine an estimated target ventilation and wherein said function is a weighted average of said estimated target ventilation and a second target ventilation derived from said measure of ventilation.

46. The apparatus of claim 39 wherein the instructions further cause said processor to implement an inoperative mode to prevent said apparatus from operation in the treat or learn modes.

47. The apparatus of claim 46 further comprising an input device coupled to said processor to receive signals to switch said apparatus between said treat mode, said learn mode and said inoperative mode.

48. The apparatus of claim 47 wherein the instructions further cause said processor to implement said inoperative mode if said apparatus is powered on after being powered off in the learn mode.

49. The apparatus of claim 39 wherein the instructions further cause said processor to permit external input for modifying or accepting said target ventilation or other settings calculated based on said learn mode before use of said target ventilation or other settings during said treat mode.