Pressure sensor evaluation for respiratory apparatus
A respiratory apparatus evaluates accuracy of a pressure sensor, such as when only a single pressure sensor is provided. The accuracy of the pressure sensor may be assessed based on pressure measurement obtained from the pressure sensor and a subordinate or secondary characteristic of the respiratory device such as altitude or atmospheric pressure. A controller or processor may calculate the altitude of the respiratory device based in part on the pressure measurement. In some embodiments, the assessment of the pressure sensor may involve an evaluation of the calculated altitude. In some cases, the assessment of the pressure sensor may involve determining an estimated pressure based on a calculated altitude, and comparing the pressure measurement obtained from the pressure sensor with the estimated pressure.
1. A respiratory apparatus configured to provide a respiratory treatment, the respiratory apparatus comprising:
a flow generator having a blower to generate a flow of breathable gas for a patient interface at a pressure above atmospheric pressure;
a pressure sensor configured to measure the pressure;
a controller coupled to the pressure sensor and the flow generator, the controller configured to control a delivery of respiratory treatment from the flow generator in a first mode according to a pressure control loop with a signal from the pressure sensor;
the controller further configured to:
test accuracy of the pressure sensor;
upon detection that the pressure sensor is inaccurate, change control of the delivery of the respiratory treatment with the flow generator from the first mode to an operational safe mode; and
thereafter control delivery of respiratory treatment according to the operational safe mode, wherein the operational safe mode comprises a pressure controlled mode using the pressure sensor detected to be inaccurate.
2. The respiratory apparatus of claim 1 , wherein, in the operational safe mode, the controller is configured to:
determine a desired pressure level setting of flow generator;
set a motor speed threshold;
obtain a pressure reading from the pressure sensor; and
increase a motor speed of the flow generator to a next motor speed if (i) the pressure reading does not exceed the desired pressure level and (ii) the next motor speed does not exceed a maximum motor speed.
3. The respiratory apparatus of claim 2 , wherein the maximum motor speed is a motor speed corresponding to the desired pressure level.
4. The respiratory apparatus of claim 2 , wherein the maximum motor speed is a motor speed corresponding to a maximum pressure level.
5. The respiratory apparatus of claim 2 , wherein the controller is configured to repeatedly increase a motor speed of the flow generator to a next motor speed unless increasing the motor speed (i) causes the pressure reading to exceed the desired pressure level or (ii) causes the next motor speed to exceed the maximum motor speed.
6. The respiratory apparatus of claim 1 , wherein the controller is further configured with another operational safe mode wherein the another operational safe mode is a speed controlled mode, wherein the controller is further configured to:
determine a desired pressure level setting of the flow generator;
determine a desired motor speed based on the desired pressure level; and
control delivery of respiratory treatment at the desired motor speed.
7. The respiratory apparatus of claim 6 further comprising a memory containing a look up table for defining one-on-one mappings between a plurality of different motor speeds and a plurality of different pressure levels, and wherein the controller is configured to determine the desired motor speed based on the look up table.
8. The respiratory apparatus of claim 6 , wherein the desired pressure level is a constant pressure value maintained throughout a session of the respiratory treatment.
9. The respiratory apparatus of claim 6 , wherein the desired pressure varies throughout a session of the respiratory treatment based on one or more detected breathing conditions.
10. The respiratory apparatus of claim 1 , wherein the controller is configured to test the accuracy of the pressure sensor based on based a measured pressure and an altitude of the respiratory apparatus.
11. The respiratory apparatus of claim 10 , wherein the controller is configured to calculate the altitude of the respiratory apparatus as a function of (a) the pressure measured by the pressure sensor and one or both of (b1) a measured flow rate of the flow of breathable gas and (b2) a measured motor speed of the flow generator.
12. The respiratory apparatus of claim 11 , wherein the controller is configured to calculate the altitude of the respiratory apparatus as a function of a measured temperature of the flow of breathable gas.
13. The respiratory apparatus of claim 11 , wherein the controller is configured to test the accuracy of the pressure sensor based on an average of calculated altitudes.
14. The respiratory apparatus of claim 13 , wherein the controller determines the pressure sensor is accurate when the average of calculated altitudes satisfies a threshold comparison.
15. The respiratory apparatus of claim 10 , wherein the altitude of the respiratory apparatus is a first altitude, and wherein the controller is configured to test accuracy of the pressure sensor by:
calculating a second altitude of the respiratory apparatus using a measured flow rate of the flow of breathable gas, a measured motor speed of the flow generator, and the pressure measured by the pressure sensor; and
comparing the second altitude of the respiratory apparatus with the first altitude of the respiratory apparatus.
16. The respiratory apparatus of claim 15 , wherein the controller is configured to detect that the pressure sensor is inaccurate when a difference between the first altitude and the second altitude exceeds a predetermined threshold.
17. The respiratory apparatus of claim 16 , wherein the predetermined threshold is 600 feet.
18. The respiratory apparatus of claim 15 , wherein the controller is configured to read a measurement of the pressure from the pressure sensor and to calculate the second altitude based on the measurement at a predetermined frequency over a predetermined period of time.
19. The respiratory apparatus of claim 18 , wherein the controller is configured to detect that the pressure sensor is inaccurate when an average of the second altitude calculated during the predetermined period of time differs from the first altitude by an offset greater than a predetermined threshold.
20. The respiratory apparatus of claim 1 , wherein the controller is configured to test the accuracy of the pressure sensor by:
calculating expected pressure of the gas generated by the respiratory apparatus; and
comparing the expected pressure with the pressure measured by the pressure sensor.
21. The respiratory apparatus of claim 20 , wherein the controller is configured to calculate the expected pressure using an altitude of the respiratory apparatus, a measured flow rate of the flow of breathable gas, and a measured motor speed of the flow generator.
22. The respiratory apparatus of claim 21 , wherein the controller is configured to calculate the expected pressure using a measured temperature of the flow of breathable gas.
23. The respiratory apparatus of claim 21 , wherein the controller is configured to detect that the pressure sensor is inaccurate when a difference between the expected pressure and the pressure measured by the pressure sensor exceeds a predetermined threshold.
24. The respiratory apparatus of claim 23 , wherein the predetermined threshold is 5 cmH2O.
25. The respiratory apparatus of claim 20 , wherein the controller is configured to read measurement of pressure from the pressure sensor, calculate the expected pressure, and compare the expected pressure with the measured pressure at a predetermined frequency over a predetermined period time of time.
26. The respiratory apparatus of claim 25 , wherein the controller is configured to detect that the pressure sensor is inaccurate based on a plurality of comparisons between measured pressures and expected pressures.
27. A control method in respiratory apparatus for a respiratory treatment comprising:
controlling settings of respiratory treatment with a flow generator in a first mode according to a pressure control loop with a signal from a pressure sensor;
testing accuracy of the pressure sensor;
upon detection that the pressure sensor is inaccurate, changing mode of operations for the respiratory treatment with the flow generator from the first mode to an operational safe mode; and
thereafter controlling operations according to the operational safe mode, wherein the operational safe mode comprises a pressure controlled mode using the pressure sensor detected to be inaccurate.
28. The control method of claim 27 , wherein, in the operational safe mode, the control method comprises:
determining a desired pressure level setting for the flow generator;
setting a motor speed threshold;
obtaining a pressure reading from the pressure sensor; and
increasing a motor speed of the flow generator to a next motor speed if (i) the pressure reading does not exceed the desired pressure level and (ii) the next motor speed does not exceed a maximum motor speed.
29. The control method of claim 28 , wherein the maximum motor speed is a motor speed corresponding to the desired pressure level.
30. The control method of claim 28 , wherein the maximum motor speed is a motor speed corresponding to a maximum pressure level.
31. The control method of claim 28 , wherein the control method further comprises repeatedly increasing a motor speed of the flow generator to a next motor speed unless increasing the motor speed (i) causes the pressure reading to exceed the desired pressure level or (ii) causes the next motor speed to exceed the maximum motor speed.
32. The control method of claim 27 , wherein, in another operational safe mode comprising a speed controlled mode, the control method comprises:
determining a desired pressure level setting of the flow generator;
determining a desired motor speed based on the desired pressure level; and
controlling delivery of respiratory treatment at the desired motor speed.
33. The control method of claim 32 , wherein determining the desired motor speed is further based on a look up table defining one-on-one mappings between a plurality of different motor speeds and a plurality of different pressure levels.
34. The control method of claim 32 , wherein the desired pressure level is a constant pressure value maintained throughout a session of the respiratory treatment.
35. The control method of claim 32 , wherein the desired pressure varies throughout a session of the respiratory treatment based on one or more detected breathing conditions.
36. The control method of claim 27 , wherein testing the accuracy of the pressure sensor is based on based a measured pressure and an altitude of the respiratory apparatus.
37. The control method of claim 36 , wherein the control method further comprises calculating the altitude of the respiratory apparatus as a function of (a) the pressure measured by the pressure sensor and one or both of (b1) a measured flow rate of a flow of breathable gas and (b2) a measured motor speed of the flow generator.
38. The control method of claim 37 , wherein the control method further comprises calculating the altitude of the respiratory apparatus as a function of a measured temperature of the flow of breathable gas.
39. The control method of claim 37 , wherein the control method further comprises testing the accuracy of the pressure sensor based on an average of the calculated altitudes.
40. The control method of claim 39 , wherein the control method further comprises determining the pressure sensor is accurate when an average of the calculated altitudes satisfies a threshold comparison.
41. The control method of claim 37 , wherein the control method further comprises testing the accuracy of the pressure sensor by:
calculating expected pressure of gas generated by the respiratory apparatus; and
comparing the expected pressure with the pressure measured by the pressure sensor.
42. The control method of claim 41 , wherein the control method further comprises calculating the expected pressure using an altitude of the respiratory apparatus, a measured flow rate of the flow of breathable gas, and a measured motor speed of the flow generator.
43. The control method of claim 42 , wherein the control method further comprises calculating the expected pressure using a measured temperature of the flow of breathable gas.
44. The control method of claim 42 , wherein the control method further comprises detecting that the pressure sensor is inaccurate when a difference between the expected pressure and the pressure measured by the pressure sensor exceeds a predetermined threshold.
45. The control method of claim 44 , wherein the predetermined threshold is 5 cmH2O.
46. The control method of claim 41 , wherein the control method further comprises reading measurement of pressure from the pressure sensor, calculating the expected pressure, and comparing the expected pressure with the measured pressure at a predetermined frequency over a predetermined period time of time.
47. The control method of claim 46 , wherein the control method further comprises detecting that the pressure sensor is inaccurate based on a plurality of comparisons between measured pressures and expected pressures.
48. The control method of claim 46 , wherein the altitude of the respiratory apparatus is a first altitude, and wherein the control method further comprises testing accuracy of the pressure sensor by:
calculating a second altitude of the respiratory apparatus using a measured flow rate of the flow of breathable gas, a measured motor speed of the flow generator, and the pressure measured by the pressure sensor; and
comparing the second altitude of the respiratory apparatus with the first altitude of the respiratory apparatus.
49. The control method of claim 48 , wherein the control method further comprises detecting that the pressure sensor is inaccurate when a difference between the first altitude and the second altitude exceeds a predetermined threshold.
50. The control method of claim 49 , wherein the predetermined threshold is 600 feet.
51. The control method of claim 48 , wherein the control method further comprises reading a measurement of the pressure from the pressure sensor and calculating the second altitude based on the measurement at a predetermined frequency over a predetermined period of time.
52. The control method of claim 51 , wherein the control method further comprises detecting that the pressure sensor is inaccurate when an average of the second altitude calculated during the predetermined period of time differs from the first altitude by an offset greater than a predetermined threshold.