Diagnosis and monitoring of cardio-respiratory disorders
Methods and systems estimate cardio-respiratory parameter(s), such as from in-phase and quadrature channels. The channels may represent patient chest movement and may be generated with a sensor, such as a contactless sensor that may sense movement with radio-frequency signals. In the methods/systems, the in-phase and quadrature channels may be processed, such as in a processor(s), using relative demodulation to generate cardio-respiratory parameter estimate(s). Optionally, the processing produces a jerk signal that may be filtered for producing a heart rate estimate, such as from zero-crossings of the filtered signal. Optionally, the processing produces a chest velocity signal that may be filtered for producing a respiratory rate estimate, such as from zero-crossings of the filtered signal. Optionally, a respiratory volume, such as tidal volume, may be estimated from an intrapulmonary pressure signal generated by applying a function to a chest displacement signal where the function relates intrapulmonary pressure and chest displacement.
1. A method of estimating a heart rate of a patient from an in-phase channel and a quadrature channel, each channel representing chest movement of the patient, the method comprising:
in one or more processors,
processing the in-phase channel and the quadrature channel by relative demodulation to generate a jerk signal, wherein the relative demodulation comprises numerically differentiating the in-phase channel and the quadrature channel to produce a numeric derivative of the in-phase channel and a numeric derivative of the quadrature channel, and generating a chest velocity signal from the numeric derivative of the in-phase channel and the numeric derivative of the quadrature channel;
filtering the jerk signal with a cardiac band-pass filter to produce a cardiac jerk signal; and
generating a heart rate estimate from zero-crossings of the cardiac jerk signal.
2. A method according to claim 1 , wherein the generating the heart rate estimate comprises:
detecting systole phases of heartbeats by determination of the zero-crossings of the cardiac jerk signal; and
calculating the heart rate estimate from a number of detected systole phases in a window of the cardiac jerk signal.
3. A method according to claim 1 , wherein the generating the heart rate estimate comprises:
detecting diastole phases of heartbeats by determination of the zero-crossings of the cardiac jerk signal; and
calculating the heart rate estimate from a number of detected diastole phases in a window of the cardiac jerk signal.
4. A method according to claim 1 , wherein the jerk signal is a third derivative of chest displacement of the patient.
5. A method according to claim 1 , wherein the relative demodulation further comprises:
numerically differentiating the chest velocity signal to generate the jerk signal.
6. A method according to claim 1 , wherein the generating the chest velocity signal comprises:
dividing the numeric derivative of the quadrature channel by the in-phase channel to obtain a first ratio signal;
dividing the numeric derivative of the in-phase channel by the quadrature channel to obtain a second ratio signal; and
subtracting the second ratio signal from the first ratio signal multiplied by a scaling factor.
7. A method according to claim 6 , wherein the scaling factor is a ratio of amplitude gain constants of the in-phase channel and the quadrature channel.
8. A method according to claim 6 , further comprising subtracting respective offsets from the in-phase channel and the quadrature channel before the dividing steps.
9. A method according to claim 1 , wherein the cardiac band-pass filter comprises a band-pass filter with a pass-band of 0.7 to 1.6 Hz.
10. A method according to claim 9 , wherein the band-pass filter is a sixth-order Butterworth filter.
11. A method according to claim 1 , wherein the in-phase channel and the quadrature channel are generated by a contactless motion sensor.
12. A method according to claim 11 , wherein the contactless motion sensor is a radio-frequency sensor that generates the in-phase channel and the quadrature channel by processing of signals representing transmitted radio-frequency waves and received reflected ones of the transmitted radio-frequency waves.
13. A method according to claim 1 , wherein the one or more processors controls a display to output the heart rate estimate.
14. A method according to claim 1 , wherein the one or more processors controls a change to a control parameter of a treatment device in response to the heart rate estimate.
15. A method according to claim 1 , wherein the jerk signal is a second derivative of the chest velocity signal.
16. A method according to claim 15 , wherein the jerk signal describes changes in acceleration.
17. Apparatus for estimating heart rate of a patient, the apparatus comprising:
a contactless motion sensor configured to generate an in-phase channel and a quadrature channel, wherein the in-phase channel and the quadrature channel each represent chest movement of the patient when the contactless motion sensor is generally directed toward a chest of the patient; and
a processor configured to analyse the in-phase channel and the quadrature channel to generate a heart rate estimate, the analysis comprising:
processing the in-phase channel and the quadrature channel by relative demodulation to generate a jerk signal, wherein the relative demodulation comprises numerically differentiating the in-phase channel and the quadrature channel to produce a numeric derivative of the in-phase channel and a numeric derivative of the quadrature channel, and generating a chest velocity signal from the numeric derivative of the in-phase channel and the numeric derivative of the quadrature channel;
filtering the jerk signal with a cardiac band-pass filter to produce a cardiac jerk signal; and
generating a heart rate estimate from zero-crossings of the cardiac jerk signal.
18. Apparatus according to claim 17 , wherein the processor is co-located with the contactless motion sensor.
19. Apparatus according to claim 17 , further comprising communications circuitry configured to transfer data to an external computing device via a connection.
20. Apparatus according to claim 19 , wherein the processor is a processor of the external computing device.
21. Apparatus according to claim 17 , wherein the contactless motion sensor is a radio-frequency sensor that generates the in-phase channel and the quadrature channel by processing of signals representing transmitted radio-frequency waves and received reflected ones of the transmitted radio-frequency waves.
22. Apparatus according to claim 17 , wherein the jerk signal is a second derivative of the chest velocity signal.
23. Apparatus according to claim 22 , wherein the jerk signal describes changes in acceleration.
24. A method of estimating a respiratory rate of a patient from an in-phase channel and a quadrature channel, each channel representing chest movement of the patient, the method comprising:
in one or more processors,
processing the in-phase channel and the quadrature channel by relative demodulation to generate a chest velocity signal, wherein the relative demodulation comprises numerically differentiating the in-phase channel and the quadrature channel to produce a numeric derivative of the in-phase channel and a numeric derivative of the quadrature channel, and generating the chest velocity signal from the numeric derivative of the in-phase channel and the numeric derivative of the quadrature channel;
filtering the chest velocity signal with a respiratory band-pass filter to produce a respiratory velocity signal; and
generating a respiratory rate estimate from zero-crossings of the respiratory velocity signal.
25. A method according to claim 24 , wherein the generating the respiratory rate estimate comprises:
detecting inspiration phases of respiration by determination of the zero-crossings of the respiratory velocity signal; and
calculating the respiratory rate estimate from a number of detected inspiration phases in a window of the respiratory velocity signal.
26. A method according to claim 24 , wherein the generating the respiratory rate estimate comprises:
detecting expiration phases of respiration by determination of the zero-crossings of the respiratory velocity signal; and
calculating the respiratory rate estimate from a number of detected expiration phases in a window of the respiratory velocity signal.
27. A method according to claim 24 , wherein the chest velocity signal is a first derivative of chest displacement of the patient.
28. A method according to claim 24 , wherein the generating the chest velocity signal comprises:
dividing the numeric derivative of the quadrature channel by the in-phase channel to obtain a first ratio signal;
dividing the numeric derivative of the in-phase channel by the quadrature channel to obtain a second ratio signal; and
subtracting the second ratio signal from the first ratio signal multiplied by a scaling factor.
29. A method according to claim 28 , wherein the scaling factor is a ratio of amplitude gain constants of the in-phase channel and the quadrature channel.
30. A method according to claim 28 , further comprising subtracting respective offsets from the in-phase channel and the quadrature channel before the dividing steps.
31. A method according to claim 24 , wherein the respiratory band-pass filter comprises a band-pass filter with a pass-band of 0.2 to 0.5 Hz.
32. A method according to claim 31 , wherein the band-pass filter is a sixth-order Butterworth filter.
33. A method according to claim 24 , wherein the in-phase channel and the quadrature channel are generated by a contactless motion sensor.
34. A method according to claim 33 , wherein the contactless motion sensor is a radio-frequency sensor that generates the in-phase channel and quadrature channel by processing of signals representing transmitted radio-frequency waves and received reflected ones of the transmitted radio-frequency waves.
35. A method according to claim 24 , wherein the one or more processors controls a display to output the respiratory rate estimate.
36. A method according to claim 24 , wherein the one or more processors controls a change to a control parameter of a treatment device in response to the respiratory rate estimate.
37. Apparatus for estimating respiratory rate of a patient, the apparatus comprising:
a contactless motion sensor configured to generate an in-phase channel and a quadrature channel, each channel representing chest movement of the patient when the contactless motion sensor is generally directed toward a chest of the patient; and
a processor configured to analyse the in-phase channel and the quadrature channel to generate a respiratory rate estimate, the analysis comprising:
processing the in-phase channel and the quadrature channel by relative demodulation to generate a chest velocity signal, wherein the relative demodulation comprises numerically differentiating the in-phase channel and the quadrature channel to produce a numeric derivative of the in-phase channel and a numeric derivative of the quadrature channel, and generating the chest velocity signal from the numeric derivative of the in-phase channel and the numeric derivative of the quadrature channel;
filtering the chest velocity signal with a respiratory band-pass filter to produce a respiratory velocity signal; and
generating a respiratory rate estimate from zero-crossings of the respiratory velocity signal.
38. Apparatus according to claim 37 , wherein the processor is co-located with the contactless motion sensor.
39. Apparatus according to claim 37 , further comprising communications circuitry configured to transfer data to an external computing device via a connection.
40. Apparatus according to claim 39 , wherein the processor is a processor of the external computing device.
41. Apparatus according to claim 37 , wherein the contactless motion sensor is a radio-frequency sensor that generates the in-phase channel and the quadrature channel by processing of signals representing transmitted radio-frequency waves and received reflected ones of the transmitted radio-frequency waves.
42. A patient monitoring system comprising:
means for generating an in-phase channel and a quadrature channel, each channel representing chest movement of a patient; and
means for analysing the in-phase channel and the quadrature channel to generate a heart rate estimate of the patient, the analysing comprising:
processing the in-phase channel and the quadrature channel by relative demodulation to generate a jerk signal, wherein the relative demodulation comprises numerically differentiating the in-phase channel and the quadrature channel to produce a numeric derivative of the in-phase channel and a numeric derivative of the quadrature channel, and generating a chest velocity signal from the numeric derivative of the in-phase channel and the numeric derivative of the quadrature channel;
filtering the jerk signal with a cardiac band-pass filter to produce a cardiac jerk signal; and
generating a heart rate estimate from zero-crossings of the cardiac jerk signal.
43. A patient monitoring system comprising:
means for generating an in-phase channel and a quadrature channel, each channel representing chest movement of a patient; and
means for analysing the in-phase channel and the quadrature channel to generate a respiratory rate estimate of the patient, the analysing comprising:
processing the in-phase channel and the quadrature channel by relative demodulation to generate a chest velocity signal, wherein the relative demodulation comprises numerically differentiating the in-phase channel and the quadrature channel to produce a numeric derivative of the in-phase channel and a numeric derivative of the quadrature channel, and generating the chest velocity signal from the numeric derivative of the in-phase channel and the numeric derivative of the quadrature channel;
filtering the chest velocity signal with a respiratory band-pass filter to produce a respiratory velocity signal; and
generating a respiratory rate estimate from zero-crossings of the respiratory velocity signal.