Heart rate detector

• US 4,549,551 A
• Filed: 11/18/1983
• Issued: 10/29/1985
• Est. Priority Date: 11/24/1982
• Status: Expired due to Fees

• Current Assignee: Her Majesty The Queen Represented By The Minister of National Defence of Her Majesty's Canadian Government
• Original Assignee: Her Majesty The Queen In Right of Canada As Represented By The Minister of National Defence
• Inventors: Dyck, Walter R., Eirich, Ronald A.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/553,116
• Time in Patent Office: 711 Days
• Field of Search: 128/680, 128/687, 128/689, 128/690, 128/695, 128/700, 128/701, 128/706, 128/715
• US Class Current: 600/502
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R

Abstract

An electronic heart sound detector in which a transducer detects the two primary heart beats of the heart cycle to produce a signal which is converted to a digital signal, filtered and the intervals between adjacent transitions determined and stored. The intervals are compared with previous values, successive values added if found substantially different and the stored or added values displayed if substantially the same as a previous correct value. The functions may be carried out by a microprocessor.

Claims

1. An electronic heart rate detector, comprising:

a transducer for converting sounds to electrical signals;

a first amplifier for amplifying said electrical signals and producing first amplified electrical signals;

a second amplifier for amplifying said first amplified electrical signals, a second transducer for converting said second amplified electrical signals to sounds;

a low pass filter having an upper cut-off frequency of 25 Hz for filtering said first amplified electrical signals and providing filtered electrical signals;

a variable gain amplifier for amplifying said filtered electrical signals and providing amplified filtered electrical signals, said variable gain amplifier maintaining the amplitude of said amplified electrical signals within predetermined limits;

means for sampling said filtered electrical signals and said amplified filtered electrical signals at a predetermined sampling frequency and producing a first series of digital signals representative of said filtered electrical signals and a second series of digital signals representative of said amplified filtered electrical filters;

means responsive to said first series of digital signals for detecting the peak-to-peak value thereof and providing a gain control signal to said variable gain amplifier;

first digital filter means for filtering said second series of digital signals and providing a series of once filtered digital signals, said first filter means having a passband of about 16 Hz to 42 Hz;

converter means for converting said series of once filtered digital filters to a series of DC signals;

second digital filter means for filtering said series of DC signals and providing a series of filtered DC digital signals;

a first comparator for comparing each signal of said series of filtered DC signals with its immediately preceding signal and producing a clock signal indicative of a negative-going transition when the magnitude of said most recent signal is less than the magnitude of its immediately preceding signal;

timer means responsive to said first detector means output signal for producing signals representative of the time interval between negative-going transitions;

second comparator means for comparing a most recent timer means output signal against immediately preceding output signal and providing a first output signal representative of a heart rate when said most recent timer means signal and its immediately preceding signal are substantially the same and a second output signal representative of the sum of said timer means output signals when said timer means signals are substantially different; and

means for displaying said first or said second comparator means output signals as a BPM heart rate count.

3. A detector as in claim 1 wherein display means includes a time-frequency converter for receiving said display and store signal and said another display signal, a display driver connected to the output to said time-frequency converter and a display connected to the output to said display driver.

2. An electronic heart sound detector comprising:

a transducer for producing an electrical signal in response to each of the two primary heart beats of the heart cycle;

means for converting the electrical signals produced by said transducer into a sequence of digital signals;

means for digitally filtering the converted signals;

first and second buffers;

means for determining and storing in said first buffer the time interval between the last two detected signals defining the most recent period and in said second buffer the time interval between the second and third last detected signals defining the second most recent period;

means for comparing the stored periods in said first and second buffers to produce a store and display signal when the periods are substantially the same and an add signal when the periods are substantially different;

a third buffer for storing said time interval in said first buffer in response to said store and display signal;

means for adding the stored periods in said first and second buffers in response to said add signal, said comparing means then comparing the period in said third buffer with the sum to produce another display signal when said sum and said period stored in said third buffer are substantially the same and disregarding said sum when said sum and said period in said third buffer are substantially different; and

display means for producing a display of the period in said first buffer in response to said store and display signal and a display of the sum in response to said another display signal.

4. A detector as in claim 2 wherein said determining and storing means includes means for detecting negative-going transitions and a timer for determining the intervals between successive transitions.

5. A detector as defined in claim 2,

said filtering means including a first digital filter having a first passband for filtering said digital signals and producing filtered digital signals and a second digital filter having a second passband for filtering said filtered digital signals for producing twice filtered digital signals.

6. A detector as defined in claim 5,

said first passband being about 16-42 Hz and said second passband being about 0-3 Hz.

7. A detector as defined in claim 2 wherein said determining and storing means includes:

means for determining the absolute value of the amplitude of said filtered electrical signals and means for comparing the absolute value of the amplitude of said filtered electrical signals at small time intervals and producing an output signal indicative of a heart sound at the first occurrence of a signal having a reduced amplitude following a sequence of signals having increasing amplitudes.