Apparatus and method for measuring heart rate

• US 5,365,934 A
• Filed: 04/26/1993
• Issued: 11/22/1994
• Est. Priority Date: 06/28/1991
• Status: Expired due to Term

• Current Assignee: Brunswick Corporation
• Original Assignee: Life Fitness (Brunswick Corporation)
• Inventors: Leon, Tomas, Hong, Teng Y. E., Golen, Emil S., Alexander, Donald J.
• Primary Examiner(s): MANUEL, GEORGE C
• Application Number:
  US08/053,511
• Time in Patent Office: 575 Days
• Field of Search: 128/695, 128/696, 128/698, 128/700, 128/702, 128/703, 128/706, 128/704, 128/708, 128/715, 128/713, 128/666, 128/661.07
• US Class Current: 600/517
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/222 combined with detection or measurement of physiological parameters, e.g. heart rate
• CPC Class Codes: A61B 5/7246 using correlation, e.g. template matching or determination of similarity

Abstract

An exercise apparatus for measuring heart rate is provided which comprises a sensor for generating a signal which includes the biopotential signal produced by a heart. This signal is filtered, amplified and digitized. A computer autocorrelates the digitized signal. A plurality of signal indication routines then scan the autocorrelated output for the presence of periodic signals. Each of the signal indication routines uses different search or filter criteria, such as peak and wave form detection, and generates one (and in some cases, several) candidate heart rates. An arbitrator then selects one of the candidate heart rates according to predetermined criteria. These criteria include the value of previously selected heart rates. In one embodiment, the signal indication and arbitration routines are especially well-suited for measuring the heart rate of a user while exercising on a stair climbing machine or treadmill.

Claims

1. An apparatus for measuring the heart rate of a person during exercise, comprising:

a biopotential sensor adapted for contact with the user and capable of generating an input signal that includes the biopotential signal produced by the user'"'"'s heart;

an autocorrelator responsive to the input signal, the autocorrelator generating an autocorrelation signal of the input signal;

signal processing means for detecting the indications of periodic signals in the autocorrelation signal and generating candidate signals corresponding to each of the detected indications, the indications being pulses in the autocorrelation signal which meet all of a predetermined plurality of filtering criteria;

arbitration means for selecting that one of the candidate signals which is most likely a true heart rate in accordance with a plurality of predetermined arbitration criteria; and

memory means for storing a current heart rate value, the memory means being responsive to the arbitration means for setting the current heart rate value to the value of the candidate signal selected by the arbitration means.

2. The apparatus of claim 1, wherein the predetermined filtering criteria include selecting those pulses having:

(a) a pulse height greater than a predetermined threshold value,

(b) a pulse width that is within a predetermined range, and

(c) a pulse shape that has a local peak between, and in close proximity to, two local minimums.

3. The apparatus of claim 2, wherein the predetermined filtering criteria further include selecting those pulses which are substantially vertically symmetrical.

4. The apparatus of claim 1 further comprising raw ECG means for detecting a raw ECG signal corresponding to heart rate in the input signal, wherein at least one of the predetermined arbitration criteria is the value of the signal.

5. The apparatus of claim 1 wherein the biopotential sensor includes an amplifier that is adjustable in response to a variable gain control signal, and the signal processing means includes means for generating the gain control signal, and wherein the arbitration means selects one of the candidates signals only if the gain control signal is in a steady state.

6. The apparatus of claim 1 wherein the arbitration criteria include selecting the candidate signal with the largest pulse height, selecting the candidate with the strongest harmonics, and selecting the candidate which is closest to the current heart rate value.

7. A method for measuring the heart rate of a person during exercise, comprising:

generating an input signal that includes the biopotential signal produced by the user'"'"'s heart;

generating an output signal that is the autocorrelation of the input signal;

detecting the indications of periodic signals in the autocorrelation output signal, said detection being accomplished by selecting as candidate signals those detected indications which meet all of a plurality of predetermined filtering criteria;

selecting one of the candidate signals as the current heart rate in accordance with a plurality of predetermined arbitration criteria; and

maintaining in memory the value of the current heart rate.

8. The method of claim 7, wherein the predetermined filtering criteria include selecting those pulses having:

(a) a pulse height greater than a predetermined threshold value,

(b) a pulse width that is within a predetermined range, and

(c) a pulse shape that has a local peak between, and in close proximity to, two local minimums.

9. The method of claim 8, wherein the predetermined filtering criteria further include selecting those pulses which are substantially vertically symmetrical.

10. The method claim 7 further comprising the steps of detecting a raw ECG signal from the input signal, and using the value of the raw ECG signal as one of the predetermined arbitration criteria.

11. The method of claim 7 wherein the step of selecting one of the candidate signals is performed in accordance with a plurality of first-tier arbitration criteria, which include

(a) selecting as the largest candidate that candidate with the largest pulse height,

(b) selecting as the strongest candidate that candidate with the strongest harmonics, and

(c) selecting as the closest candidate that candidate which is closest to the current heart rate value.

12. The method of claim 11 wherein the step of selecting one of the candidate signals includes the step of selecting one of the largest, strongest and closest candidate signals in accordance with second-tier arbitration criteria.

13. The method of claim 12 wherein the second-tier arbitration criteria include a first and second sets of second-tier arbitration criteria, wherein the step of selecting one of the largest, strongest and closest candidate signals is initially performed in accordance with the first set of second-tier arbitration criteria, and then, after a predetermined time period, is performed in accordance with the second set of second-tier arbitration criteria.

14. The method of claim 7, further comprising the steps of

generating a variable gain control signal in accordance with the amplitude of the input signal;

amplifying the input signal in accordance with a gain control signal to maintain the amplitude of the input signal within a predetermined range; and

determining if the gain control signal is at a steady state;

wherein the step of selecting one of the candidate signals in accordance with predetermined arbitration criteria is performed only when the gain control signal is at a steady state.

15. A method for measuring the heart rate of a person during exercise, comprising:

generating an input signal that includes the biopotential signal produced by the user'"'"'s heart;

determining whether the input signal has exceeded predetermined positive and negative voltage limits, and setting the input signal to a null value when such limits are exceeded;

generating an output signal that is the autocorrelation of the input signal;

detecting the indications of periodic signals in the autocorrelation output signal, and selecting as candidate signals those indications which meet predetermined filtering criteria;

selecting one of the candidate signals in accordance with a plurality of predetermined arbitration criteria.

16. The method of claim 15 further comprising the steps of:

detecting the peak amplitude in the input signal over a predetermined time span;

generating a variable gain control signal in accordance with the detected peak amplitude;

amplifying the input signal in accordance with the gain control signal.

17. The method of claim 16 further comprising the step of:

counting the times the number of times the input signal is set to a null value during a predetermined time period;

decrementing the variable gain control signal by a predetermined amount if the count exceeds a predetermined threshold for a predetermined number of time periods.

18. The method of claim 15 wherein if the variable gain control is in a steady state, then the step of generating the variable gain control signal is performed in accordance with the average of the most-recently detected peak amplitude and at least one previously detected peak amplitude.