EKG based heart rate monitor with digital filter and enhancement signal processor
First Claim
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1. Apparatus for determining heart rate from electrical signals generated within a body, comprising:
- at least two electrical contacts for detecting said electrical signals when placed in contact with said body;
an analog circuit that conditions said electrical signals;
an analog-to-digital converter coupled to receive an analog output signal from said analog circuit and convert said analog signals to a plurality of digital samples;
a digital filter for receiving said digital samples and suppressing noise signals that have frequencies below about 5-15 Hertz, and signals having frequencies above about 25-40 Hertz to generate filtered data, said digital filter being a recursive filter having integer coefficients;
an enhancement signal processor to receive said filtered data and highlight signals therein that have predetermined characteristics of QRS complexes in human heartbeat signals so as to generate enhanced digital data, said enhancement signal processor comprising a squaring processor that applies a squaring operation at least twice; and
a post-processing heart rate determination signal processor that analyzes said enhanced digital data and determining the heart rate therefrom.
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Abstract
A convenient low-cost heart rate monitor. In one embodiment, a digital filter structure includes a low pass filter having a notch at 60 Hz and a bandpass filter which amplifies signals in a frequency range from 10-40 Hz and has a notch at 60 Hz. This digital filter has a recursive structure and uses integer coefficients to simplify and speed up the calculations. A four bit microcontroller may implement the digital filter. The output of the digital filter is subject to enhancement signal processing to emphasize QRS complexes indicative of human heartbeats.
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Citations
21 Claims
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1. Apparatus for determining heart rate from electrical signals generated within a body, comprising:
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at least two electrical contacts for detecting said electrical signals when placed in contact with said body; an analog circuit that conditions said electrical signals; an analog-to-digital converter coupled to receive an analog output signal from said analog circuit and convert said analog signals to a plurality of digital samples; a digital filter for receiving said digital samples and suppressing noise signals that have frequencies below about 5-15 Hertz, and signals having frequencies above about 25-40 Hertz to generate filtered data, said digital filter being a recursive filter having integer coefficients; an enhancement signal processor to receive said filtered data and highlight signals therein that have predetermined characteristics of QRS complexes in human heartbeat signals so as to generate enhanced digital data, said enhancement signal processor comprising a squaring processor that applies a squaring operation at least twice; and a post-processing heart rate determination signal processor that analyzes said enhanced digital data and determining the heart rate therefrom. - View Dependent Claims (2, 3, 4, 5, 6)
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5. The apparatus of claim 3 wherein said moving average processor comprises means for calculating said moving average as a stream of digital data samples with the most recent digital data sample representing the moving average represented by YN and for calculating each YN in said moving average data stream by summing the 8 most recent data samples in said stream of data samples representing said filtered data and dividing the sum by 64.
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6. The apparatus of claim 1 further comprising a display for displaying said heart rate determined by said post-processing heart rate determination signal processor means.
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7. Apparatus for determining heart rate from electrical signals generated within a body, comprising:
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at least two electrical contacts for detecting said electrical signals when placed in contact with said body; an analog circuit that conditions said electrical signals; an analog-to-digital converter coupled to receive an analog output signal from said analog circuit and convert said analog signals to a plurality of digital samples; a digital filter for receiving said digital samples and suppressing noise signals that have frequencies below about 5-15 Hertz, and signals having frequencies above about 25-40 Hertz to generate filtered data, said digital filter being a recursive filter having integer coefficients; an enhancement signal processor to receive said filtered data and highlight signals therein that have predetermined characteristics of ORS complexes in human heartbeat signals so as to generate enhanced digital data; and a post-processing heart rate determination signal processor that analyzes said enhanced digital data and determining the heart rate therefrom; and wherein said analog circuit comprises; a differential amplifier having a gain of from approximately 1-10 coupled to said electrical contact means for amplifying any signals detected by said electrical contact means and suppressing any common mode noise; and an analog bandpass filter coupled to receive the output of said differential amplifier and having a passband from approximately 5 to 40 Hertz, said bandpass filter comprising a low pass analog active filter having a first order rolloff characteristic with a corner frequency between 25 and 40 Hertz, and a high pass analog active filter having a second order rolloff characteristic with a corner frequency between 5 and 15 Hertz.
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8. A method of detecting a heartbeat rate among unwanted signals, comprising the steps of:
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sensing signals from a body using electrodes in contact, with the skin of the body; amplifying said signals while cancelling common mode noise therein; filtering out noise below and above the frequency range in which the desired heartbeat rate will lie; converting the filtered analog signal to a plurality of digital samples; digitally filtering the digital samples to remove further remnants of frequencies above and below the range of frequencies in which said heartbeat will lie and to suppress powerline hum at approximately 50-60 Hertz so as to generate filtered digital samples; digitally processing said filtered digital samples to enhance heartbeat peaks in the signals represented by said filtered digital samples to generate enhanced digital samples; processing said enhanced digital samples to determine said heartbeat rate. - View Dependent Claims (9, 10, 11)
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12. Apparatus for determining heart rate from electrical signals generated within a body, comprising:
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at least two electrical contacts for detecting said electrical signals when placed in contact with said body; an analog circuit that conditions said electrical signals; an analog-to-digital converter coupled to receive an analog output signal from said analog circuit and convert said analog signals to a plurality of digital samples; a digital filter for receiving said digital samples and suppressing unwanted signals; an enhancement signal processor to receive said filtered data and highlight signals therein that have predetermined characteristics of QRS complexes in human heartbeat signals so as to generate enhanced digital data, said enhancement signal processor comprising; a differentiator for determining the slope of peaks in said filtered data and generating a slope signal which defines the magnitude and sign of the slopes of each portion of each said peak; a squaring processor for squaring the results from said differentiator at least twice; and a moving average processor for computing a moving average of said positive values only signal and outputting a moving average signal which defines said moving average over time.
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13. In a heart rate monitoring system wherein heart activity is converted to electrical signals, a method for distinguishing pulses caused by heartbeats from other pulses comprising the steps of:
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a) discarding pulses that arrive at times inconsistent with plausible beat-to-beat variation in heartbeat rate as representing artifacts rather than heartbeats; b) discarding pulses having amplitudes varying more than a predetermined amount from previously received pulses representing heartbeats; c) identifying an artifact pulse arriving before an expected arrival time of a heartbeat pulse; and d) identifying a pulse that arrives at said expected arrival time as a heartbeat pulse only if said artifact pulse has subsided. - View Dependent Claims (14, 15, 16)
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17. In a heart rate monitoring system wherein heart activity is converted to electrical signals, a post-processing heartbeat determining system that distinguishes heartbeat pulses from other pulses said system comprising:
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an analog to digital converter that converts said electrical signal to digital samples; and a digital circuit adapted to digitally process said digital samples to determine times of said pulses;
discard pulses that arrive at times inconsistent with plausible beat-to-beat variation in heartbeat rate as representing artifacts rather than heartbeats; anddiscard pulses having amplitudes varying more than a predetermined amount from previously received pulses representing heartbeats. - View Dependent Claims (18, 19, 20, 21)
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Specification