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EKG based heart rate monitor

  • US 5,738,104 A
  • Filed: 11/08/1995
  • Issued: 04/14/1998
  • Est. Priority Date: 11/08/1995
  • Status: Expired due to Term
First Claim
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1. A heart rate monitor for sensing EKG signals and displaying a heart rate based upon the frequency of occurrence of ORS complexes in said EKG waveform, comprising:

  • at least two electrical contacts for making electrical contact with different areas of a user'"'"'s body;

    an amplifier coupled to said at least two electrical contacts for amplifying any signals picked up by said contacts and suppressing any common mode noise;

    a plurality of bandpass filters coupled to receive the output of said amplifier, each bandpass filter having a passband from approximately 5 to 40 Hertz, each said bandpass filter comprising a low pass analog filter having a first order rolloff characteristic with a corner frequency between 25 and 40 Hertz, and a high pass analog filter having a second order rolloff characteristic with a corner frequency between 5 and 15 Hertz;

    an amplifier coupled to receive the output of said bandpass filter(s);

    an analog-to-digital converter coupled to receive the output signal of said amplifier and convert said output signal to a plurality of digital samples;

    a computer coupled to receive said digital samples and programmed to process said digital samples by digitally filtering said samples to suppress frequencies below about 5-15 Hertz and to suppress frequencies of about 25-40 Hertz and above to generate filtered data, and programmed to process said filtered data so as to suppress artifacts while enhancing or at least not suppressing R peaks in QRS waveforms in EKG signals picked up by said electrical contact and encoded in said filtered data to generate enhanced data, and programmed to process said enhanced data to find R peaks therein which have a heart rate period which is within a range from about 40 to about 220 beats per minute and which is not changing by more than about 12.5% between adjacent beats, and programmed to learn the background noise characteristics of the enhanced data and the maximum amplitude and heart rate period characteristics of said R peaks so located in said enhanced data and programmed to set the level of an adaptive discrimination threshold using said learned characteristics, and, after said characteristics are learned, programmed to use said adaptive threshold to locate further candidate peaks in new incoming enhanced data which are possibly R peaks in a QRS complex and subject said candidate peaks to a plurality of validity tests to determine which candidate peaks are probably actual R peaks and programmed to compute an average maximum amplitude and an average head rate period and a refractory period for a plurality of R peaks that pass said validity tests, and to use the results of at least said average maximum amplitude computation to adjust the level of said adaptive discrimination threshold and said refractory period, and to continue to compute a running average maximum amplitude and a running average heart rate period and new refractory periods for each new R peak that passes said validity tests on an ongoing basis, and for outputting for display heart rate data encoding at least said head rate period, said validity tests to which candidate peaks are subjected including at least a test to determine whether the new heart rate period which is defined by a new candidate peak represents more than a predetermined change from the average head rate period previously determined;

    a display coupled to receive said head rate data from said computer and to display a head rate indication encoded in said head rate data* and further comprising a wristwatch housing said heart rate monitor, said wristwatch having a face a back, and wherein said said at least two electrical contacts comprise three electrical contacts and wherein at least two of said three electrical contacts are on said face of said wristwatch and wherein at least one of said three electrical contact is on said back of said wristwatch.

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