Heart rate monitor

• US 20040186388A1
• Filed: 03/18/2003
• Published: 09/23/2004
• Est. Priority Date: 03/18/2003
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Gerasimov, Vadim
• Granted Patent: US 7,139,605 B2
• Time in Patent Office: Days
• US Class Current: 600/519
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A method for analyzing an EKG signal in real time to produce a heart rate indication. The most recent digitized samples of the EKG are stored in a buffer and evaluated to identify each R-wave peak sample value that (a) immediately precedes and is larger that the most recently stored digital sample value, (b) is larger than any other sample value in the buffer, and (c) differs from the first sample value in the buffer by more than a predetermined threshold value. The threshold is a fraction of the rise time slope of the last peak. The real time heart rate indication is calculated from the time duration separating the last two detected peaks, but rate indications outside the range of 30-200 beats per minute, and which depart from the preceding rate indication by more than 50 percent, are discarded.

Claims

1. The method of determining a heart rate from an electrocardiogram signal comprising the steps of:

identifying a series of R-wave peaks in said signal, each of which occurs at a time at which said signal;

a) begins to decrease after having increased during an immediately preceding time interval at a rate of change greater than a threshold rate of change, and

b) has a greater amplitude than at any other time in said immediately preceding time interval,

calculating a series of heart rate values from the durations separating adjacent ones of said detected R-wave peaks, and

discarding any heart rate value which differs from the preceding heart rate value by more than a predetermined amount.

2. The method as set forth in claim 1 wherein said threshold rate of change is a predetermined fraction of the rate of change of said signal during a time interval immediately preceding the time at which the prior R-wave peak was detected.

3. The method as set forth in claim 1 for further discarding any heart rate value that is less than a predetermined minimum.

4. The method as set forth in claim 3 for further discarding any heart rate value that is greater than a predetermined maximum.

5. The method as set forth in claim 2 for further discarding any heart rate value that is less than a predetermined minimum.

6. The method as set forth in claim 5 for further discarding any heart rate value that is greater than a predetermined maximum.

7. A method for deriving a heart rate value from an electrocardiogram signal having a waveform exhibiting a series of R-wave peak values, said method comprising, in combination, the steps of:

determining the time position of each of said R-wave peak values in said waveform by identifying each peak time when the amplitude of said waveform is larger than at any time in a predetermined interval immediately preceding said peak time, when the amplitude of said waveform decreases immediately after said peak time, and when the rate of change of the amplitude of said waveform during said predetermined time interval is greater than a threshold value, and

calculating heart rate values from the measured time interval between said peak time positions.

8. The method as set forth in claim 7 wherein said threshold value is a predetermined fraction of the rate of change of said signal during a time interval immediately preceding the previously determined peak time.

9. The method as set forth in claim 7 for further discarding any heart rate value that is less than a predetermined minimum.

10. The method as set forth in claim 9 for further discarding any heart rate value that is greater than a predetermined maximum.

11. The method as set forth in claim 8 for further discarding any heart rate value that is less than a predetermined minimum.

12. The method as set forth in claim 11 for further discarding any heart rate value that is greater than a predetermined maximum.

13. The method for analyzing a continuous electrocardiogram signal to produce a numerical pulse rate indication in real time, said method comprising, in combination, the steps of:

producing digital sample values representing samples of said signal taken a predetermined sampling rate,

storing a series of the most recently produced ones of said digital sample values,

evaluating said series to identify a peak sample value that (a) immediately precedes and is larger that the most recently stored digital sample value, (b) is larger than any other sample value in said series, and (c) differs from the first sample value in said series by more than a predetermined threshold amount, and

determining said numerical pulse rate indication from the time duration separating consecutive ones of said peak sample values.

14. The method as set forth in claim 13 further includes the step of establishing a new threshold amount equal to a predetermined fraction of the amount by which an identified peak sample value differs from the first sample value in said series.

15. The method as set forth in claim 13 for further discarding any numerical pulse rate indication that is less than a predetermined minimum.

16. The method as set forth in claim 15 for further discarding any numerical pulse rate indication that is greater than a predetermined maximum.

17. The method as set forth in claim 14 for further discarding any heart rate value that is less than a predetermined minimum.

18. The method as set forth in claim 17 for further discarding any heart rate value that is greater than a predetermined maximum.