Method and apparatus for determining a respiration signal

Patent metadata

Field	Value
Publication number	US-9675282-B2
Application number	US-201113575969-A
Country	US
Kind code	B2
Filing date	Feb 7, 2011
Priority date	Feb 11, 2010
Publication date	Jun 13, 2017
Grant date	Jun 13, 2017

Abstract

The invention relates to a method and apparatus for determining a respiration of a subject ( 305 ) in which, with a single multi-axial accelerometer ( 310 ) positioned on a body of the subject ( 305 ), accelerometer signals are generated ( 101 ) indicative of the acceleration of the subject ( 305 ) along different spatial axes, a vector magnitude signal of the acceleration of the subject ( 305 ) along the different spatial axes is calculated ( 102 ) from the accelerometer signals, a non-respiratory motion contribution to the acceleration along the different spatial axes is identified ( 103, 203 ) from the vector magnitude signal, which non-respiratory motion contribution is not caused by the respiration, and a respiration signal indicative of the respiration of the subject is determined ( 104, 204 ) by filtering the non-respiratory motion contribution from at least one of the accelerometer signals. In this way a method is provided which determines the respiration of a subject ( 305 ) with a single accelerometer ( 310 ) in an efficient and, for a patient, comfortable way.

First claim

The invention claimed is:

1. A method for monitoring a respiration of a subject comprising the steps of:
generating, with a single multi-axial accelerometer positioned on a body of the subject, accelerometer signals indicative of the acceleration of the subject along different spatial axes,
calculating, with at least one processor, a vector magnitude signal of the acceleration of the subject as a magnitude of the vector sum of the accelerometer signals along the different spatial axes,
identifying, with the at least one processor, from the vector magnitude signal of the acceleration a non-respiratory motion contribution to the acceleration along the different spatial axes which non-respiratory motion contribution is not caused by the respiration, the non-respiratory motion being indicative of at least a motion of a thorax due to cardiac activity of the subject,
filtering, with the at least one processor, the non-respiratory motion contribution from at least one of the accelerometer signals;
determining, with the at least one processor, a respiration signal indicative of the respiration of the subject with the at least one filtered accelerometer signal; and
displaying the determined respiration signal on a display.

2. The method as defined in claim 1 , wherein the step of determining the respiration signal includes the steps of:
filtering the non-respiratory motion contribution from each of the accelerometer signals separately,
determining the respiration signal from a combination of the filtered accelerometer signals.

3. The method as defined in claim 1 , wherein the step of identifying the non-respiratory motion contribution comprises the steps of:
calculating a power spectrum of the vector magnitude signal,
extracting a characteristic frequency of the non-respiratory motion from the power spectrum,
and wherein the step of determining the respiration signal comprises a step of filtering the characteristic frequency from the accelerometer signals with an adaptive notch filter.

4. The method as defined in claim 1 , wherein the step of identifying the non-respiratory motion contribution comprises the steps of:
calculating a coherence spectrum of the vector magnitude signal and one of the accelerometer signals,
extracting a characteristic frequency of the non-respiratory motion contribution from the coherence spectrum,
and wherein the step of determining the respiration signal comprises a step of filtering the characteristic frequency from the accelerometer signals with an adaptive notch filter.

5. The method as defined in claim 1 , further comprising a step of extracting a respiration rate of the subject from the respiration signal.

6. The method as defined in claim 1 , further comprising a step of filtering a frequency range from the vector magnitude signal which filtered vector magnitude signal is used in the step of identifying the non-respiratory motion contribution.

7. The method as defined in claim 1 , wherein the step of identifying the non-respiratory motion contribution comprises a step of extracting a characteristic frequency of the non-respiratory motion contribution from the vector magnitude signal.

8. The method as defined in claim 7 , wherein the characteristic frequency of the non-respiratory motion contribution comprises a heart beat frequency of the subject.

9. The method as defined in claim 7 , wherein the characteristic frequency of the non-respiratory motion contribution comprises a step frequency of a moving subject.

10. The method as defined in claim 1 , wherein the step of identifying the non-respiratory motion contribution comprises a step of extracting a noise reference signal representative for the unwanted noise contribution from the vector magnitude signal.

11. The method as defined in claim 10 , wherein the noise reference signal is extracted from the vector magnitude signal with a digital filtering technique.

12. The method as defined in claim 10 , wherein the noise reference signal comprises a cardiac interference signal.

13. The method as defined in claim 10 , wherein the step of determining the respiration signal comprises a step of filtering the accelerometer signals with an adaptive noise filter with the noise reference signal.

14. The method as defined in claim 10 , wherein the step of identifying the non-respiratory motion contribution further comprises a step of extracting a characteristic frequency of the non-respiratory motion contribution from the noise reference signal and wherein the step of determining the respiration signal comprises a step of filtering the characteristic frequency from the accelerometer signals with an adaptive notch filter.

15. A respiration monitoring apparatus for monitoring a respiration of a subject, wherein the respiration monitoring apparatus comprises:
a single multi-axial accelerometer configured to be positioned on a body of the subject, wherein the multi-axial accelerometer is adapted to generate accelerometer signals x(t), y(t), and z(t) indicative of the acceleration of the subject along orthogonal x, y, and z spatial axes respectively,
a signal processing unit programmed to calculate a vector magnitude signal m(t) of the acceleration of the subject as m(t)=√{square root over (x(t) 2 +y(t) 2 +z(t) 2 )} and for identifying a non-respiratory motion contribution to the acceleration along different spatial axes from the vector magnitude signal m(t), the non-respiratory motion being indicative of at least a motion of a thorax due to a cardiac activity of the subject,
a respiration signal determination unit programmed to:
filter the non-respiratory motion contribution from at least one of the accelerometer signals; and
determine a respiration signal indicative of the respiration of the subject with the at least one filtered accelerometer signal; and
a display on which the determined respiration signal is displayed.

16. The respiration monitoring apparatus of claim 15 , wherein the respiration signal determination unit is further programmed to:
filter the non-respiratory motion contribution from each of the accelerometer signals separately,
determine the respiration signal from a combination of the filtered accelerometer signals.

17. The respiration monitoring apparatus of claim 15 , wherein the signal processing unit is further programmed to
extract a characteristic frequency of the non-respiratory motion contribution from the vector magnitude signal;
wherein the characteristic frequency of the non-respiratory motion contribution comprises a heart beat frequency of the subject.

18. The respiration monitoring apparatus of claim 15 , wherein the signal processing unit is further programmed to:
extract a noise reference signal representative for the unwanted noise contribution from the vector magnitude signal
wherein the noise reference signal comprises a cardiac interference signal.

19. A respiration monitoring apparatus for determining a respiration of a subject, wherein the respiration monitoring apparatus comprises:
a single multi-axial accelerometer configured to be positioned on a body of the subject, wherein the multi-axial accelerometer is adapted to generate accelerometer signals indicative of the acceleration of the subject along different spatial axes,
a signal processor programmed to calculate a vector magnitude signal of the acceleration of the subject as a magnitude of the vector sum of the accelerometer signals along the different spatial axes and for identifying a non-respiratory motion contribution to the acceleration along

Assignees

• Morren Geert Guy Georges
• Koninklijke Philips Nv

Inventors

• Morren Geert Guy Georges

Classifications

• A61B5/721

  using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured · CPC title

• A61B5/113 Primary

  occurring during breathing · CPC title

• A61B2562/0219

  Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches · CPC title