Method and device for pulse rate detection

• US 20030065269A1
• Filed: 09/26/2002
• Published: 04/03/2003
• Est. Priority Date: 09/28/2001
• Status: Active Grant

• Current Assignee: CSEM Centre Suisse D'Electronique et de Microtechnique SA, Mendel Biotechnology, Inc. (KOCH Industries Incorporated)
• Original Assignee: CSEM Centre Suisse D'Electronique et de Microtechnique SA
• Inventors: Vetter, Rolf, Renevey, Philippe, Krauss, Jens, Gentsch, Roland, Depeursinge, Yves
• Granted Patent: US 7,018,338 B2
• Time in Patent Office: Days
• US Class Current: 600/503
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured

Abstract

There is described a device and a method for detecting the pulse rate. The measuring principle consists of emitting radiant energy at the surface of or through human body tissue (5) by means of a light-emitting source (10), measuring the intensity of the radiant energy after propagation through the human body tissue by means of at least first and second light detectors (21, 22, 23, 24) located at a determined distance from the light-emitting source and providing first and second input signals (y₁(t), y₂(t)) representative of this propagation. Simultaneously, a motion detecting device (40), such as a three dimensional accelerometers, provides a motion reference signal (a_x(t), a_y(t), a_z(t)) representative of motion of the detecting device on and with respect to the human body tissue (5). The input signals are then processed in order to remove motion-related contributions due to motion of the detecting device (1) on and with respect to the human body tissue (5) and to produce first and second enhanced signals. This processing basically comprises the elaboration of a model of the motion-related contributions based on the motion reference signal and the subtraction of this model from each of the input signals. Pulse rate is then extracted from the enhanced signals using for instance a maximum likelihood histogram clustering technique.

Claims

1. Portable pulse rate detecting device (1) intended to be worn on and in contact with the human body tissue (5), comprising

a light-emitting source (10) for emitting radiant energy at the surface of or through the human body tissue (5);

at least first and second light detectors (21, 22, 23, 24) for detecting the intensity of said radiant energy after propagation through the human body tissue (5) and for providing first and second input signals (y₁(t), y₂(t)) representative of said propagation;

a device (40) for measuring motion of the detecting device (1) on and with respect to the human body tissue (5) and for providing a motion reference signal (a_x(t), a_y(t), a_z(t)) representative of said motion; and

processing means (50) for removing, from said first and second input signals (y₁(t), y₂(t)), motion-related contributions due to movement of the detecting device (1) on and with respect to the human body tissue and producing first and second enhanced signals,

said processing means being arranged to elaborate a model of said motion-related contributions based on said motion reference signal (a_x(t), a_y(t), a_z(t)) and to subtract this model from each of said first and second input signals (y₁(t), y₂(t)).

2. Portable pulse rate detecting device (1) according to claim 1, wherein said model is a nonlinear model such as a third order polynomial moving average model.

3. Portable pulse rate detecting device (1) according to claim 2, wherein the model is selected using a Minimum Description Length (MDL) criterion.

4. Portable pulse rate detecting device (1) according to any one of claims 1 to 3, wherein said processing means (50) are further arranged to remove measurement noise and residual non-modelled contributions from said first and second enhanced signals using a noise reduction algorithm.

5. Portable pulse rate detecting device (1) according to claim 4, wherein said noise reduction algorithm is based on Principal Component Analysis (PCA).

6. Portable pulse rate detecting device (1) according to any one of the preceding claims, wherein said processing means (50) are arranged to detect peaks in said first and second enhanced signals and to extract inter-beat intervals from said detected peaks to provide a pulse rate measurement, the detection of said peaks being inhibited during the refractory period of cardiac cells.

7. Portable pulse rate detecting device (1) according to any one of the preceding claims, wherein said detecting device comprises a strap (3) for being worn around the wrist, said light-emitting source (10) and said light detectors (21, 22, 23, 24) being disposed on a bottom side (2a) of said detecting device in contact with the human body tissue (5).

8. Portable pulse rate detecting device (1) according to any one of the preceding claims, wherein said first and second light detectors (21, 22) are located on each side of the light-emitting source (10) along a first axis (A), this detecting device further comprising third and fourth light detectors (23, 24) located on each side of the light-emitting source (10) along a second axis (B) substantially perpendicular to the first axis (A).

9. Portable pulse rate detecting device (1) according to claims 7 and 8, wherein said first and second axes (A, B) are respectively perpendicular and parallel to a longitudinal direction of said strap (3).

10. Portable pulse rate detecting device (1) according to any one of claims 7 to 9, wherein said light-emitting source (10) is located in a substantially central area of the bottom side (2a) of the detecting device and said light detectors (21, 22, 23, 24) are disposed around said light-emitting source (10).

11. Portable pulse rate detecting device according to any one of the preceding claims, wherein the distance between said light-emitting source (10) and said light detectors (21, 22, 23, 24) is approximately 10 mm.

12. Portable pulse rate detecting device according to any one of the preceding claims, wherein said light-emitting source (10) is an infrared light-emitting device and said light detectors (21, 22, 23, 24) are photodiodes.

13. Portable pulse rate detecting device according to any one of the preceding claims, wherein said processing means (50) are in the form of a digital signal processor DSP housed within said detecting device (1).

14. Portable pulse rate detecting device according to any one of the preceding claims, wherein said device (40) for providing the motion reference signal (a_x(t), a_y(t), a_z(t)) is a three dimensional accelerometer.

15. Portable pulse rate detecting device according to any one of the preceding claims, further comprising means (226) for detecting non-stationary signal segments in said motion reference signal (a_x(t), a_y(t), a_z(t)) and for disabling said light-emitting source (10), said light detectors (21, 22, 23, 24) and/or said processing means (50) when non-stationary signal segments are detected.

16. Portable pulse rate detecting device according to any one of the preceding claims, further comprising means for outputting an indication of the detected pulse rate in the form of an optical, audible or other sensorial signal and/or for outputting an alarm when the detected pulse rate reaches a determined threshold.

17. Method for detecting a pulse rate comprising the steps of:

a) emitting radiant energy at the surface of or through human body tissue (5) by means of a light-emitting source (10);

b) measuring the intensity of said radiant energy after propagation through the human body tissue (5) by means of at least first and second light detectors (21, 22, 23, 24) located at a determined distance from said light-emitting source (10) and providing first and second input signals (y₁(t), y₂(t)) representative of said propagation;

c) measuring motion of the detecting device (1) on and with respect to the human body tissue (5) during propagation of said radiant energy through the human body tissue (5) by means of a motion detecting device (40) and providing a motion reference signal (a_x(t), a_y(t), a_z(t)) representative of said motion;

d) processing said first and second input signals (y₁(t), y₂(t)) to remove motion-related contributions due to motion of the detecting device (1) on and with respect to the human body tissue (5) and producing first and second enhanced signals,

said processing comprising elaborating a model of said motion-related contributions based on said motion reference signal (a_x(t), a_y(t), a_z(t)) and subtracting this model from each of said first and second input signals (y₁(t), y₂(t)); and

e) extracting the pulse rate from said first and second enhanced signals.

18. Method according to claim 17, wherein said model is a nonlinear model such as a third order polynomial moving average model.

19. Method according to claim 18, wherein said processing step (d) includes selecting the model using a Minimum Description Length (MDL) criterion.

20. Method according to any one of claims 17 to 19, further comprising, after subtracting said model from each of the first and second input signals (y₁(t), y₂(t)):

d1) removing measurement noise and residual non-modelled contributions from said first and second enhanced signals using a noise reduction algorithm.

21. Method according to claim 19, wherein said noise reduction algorithm is based on Principal Component Analysis (PCA).

22. Method according to any one of claims 17 to 21, wherein said extracting step (e) includes detecting peaks in said first and second enhanced signals and extracting inter-beat intervals from said detected peaks to provide a pulse rate measurement, the detection of said peaks being inhibited during the refractory period of cardiac cells.

23. Method according to any one of claim 22, further comprising the step of performing a maximum likelihood histogram clustering of said inter-beat intervals.

24. Method according to claim 23, further comprising the step of determining a reliability measure of the pulse rate measurement of each one of said first and second enhanced signals and performing a nonlinear mapping of the two pulse rate measurements in function of their reliability measures.