METHOD AND APPARATUS FOR CONTINUOUSLY MONITORING HEARTBEAT RATE

• US 3,841,315 A
• Filed: 03/14/1973
• Issued: 10/15/1974
• Est. Priority Date: 03/14/1973
• Status: Expired due to Term

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: Keith A. Kopp
• Inventors: Kopp, Keith A.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/341,158
• Time in Patent Office: 580 Days
• Field of Search: 128/2.5R,2.5T,2.6A,2.6B,2.6F,2.6R
• US Class Current: 600/519
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61B 5/02455 provided with high/low alarm devices
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A wearable heart rate monitor for continuously monitoring the heart rate of an ambulatory wearer and alerting him whenever his heart rate rises above a preselected maximum level or falls below a preselected minimum level is disclosed. More particularly, the monitor includes means for monitoring the heart beat of the wearer and generating output pulses coincident therewith and means for averaging the output pulses to develop an average signal having an amplitude level directly proportional to the heartbeat rate. The electrical signal is coupled to comparator means which applies a drive potential to an alarm device whenever the averaged signal exceeds or drops below preselected maximum and minimum heart rate threshold levels. Gating means enable the alarm device coincident with the output pulses thereby permitting the alarm device to generate an interrupted audio tone having a frequency corresponding to the monitored heartbeat rate whenever the heartbeat rate exceeds the maximum threshold level. When the heart rate falls below the minimum level, the alarm means is continuously enabled by the gating means to produce a continuous audio tone responsive to the drive potential from the comparator means. In either event, the wearer is alerted to the abnormal heart condition so that corrective action can be taken.

Claims

1. A cardiac rate monitor for continuously monitoring the heartbeat rate of the wearer, said monitor including an alarm device for alerting said wearer whenever a maximum desirable heartbeat rate is exceeded, said monitor comprising:

means for monitoring said heartbeat of said wearer, said means including pulse means for generating output pulses substantially coincident with corresponding ones of said heartbeats monitored by said monitoring means;

averaging means coupled to said pulse means for averaging said output pulses to develop an averaged signal having an amplitude level directly proportional to said heartbeat rate;

cOmparator means coupled to said averaging means for selectably establishing a maximum threshold level corresponding to said maximum desirable heartbeat rate, said comparator means applying a drive potential to said alarm device whenever said averaged signal exceeds said maximum threshold level; and

gating means having an input coupled to said pulse means and an output coupled to said alarm device, said gating means disabling said alarm device during intervals between said output pulses and enabling said alarm device to generate an alarm signal responsive to said drive potential only during intervals corresponding to said output pulses thereby causing said alarm device to generate a repetitive alarm signal occurring at a rate coincident with said heartbeat rate whenever said averaged signal exceeds said maximum threshold level.

2. A cardiac rate monitor for continuously monitoring the heartbeat rate of the wearer, said monitor including an alarm device for alerting said wearer whenever a maximum desirable heartbeat rate is exceeded and whenever said heartbeat rate falls below a minimum desirable heartbeat rate, said monitor comprising:

means for monitoring said heartbeat of said wearer, said means including pulse means for generating output pulses substantially coincident with corresponding ones of said heartbeats monitored by said monitoring means;

averaging means coupled to said pulse means for averaging said output pulses to develop an averaged signal having an amplitude level directly proportional to said heartbeat rate;

window comparator means coupled to said averaging means for selectably establishing a maximum threshold level corresponding to said maximum desirable heartbeat rate and a minimum threshold level corresponding to said minimum desirable heartbeat rate, said window comparator means applying separate drive potentials to said alarm device whenever said averaged signal exceeds said maximum threshold level and whenever said averaged signal is below said minimum threshold level; and

gating means having inputs coupled to said pulse means and said maximum drive potential of said window comparator means and an output coupled to said alarm device, said gating means disabling said alarm device during intervals between said output pulses and enabling said alarm device to generate an alarm signal responsive to said drive potential only during intervals corresponding to said output pulses whenever said averaged signal exceeds said maximum threshold level thereby causing said alarm device to generate a repetitive alarm signal occurring at a rate coincident with said heartbeat rate, said gating means continuously enabling said alarm device responsive to said window comparator means in response to an absence of said maximum drive potential whenever said averaged signal is below said minimum threshold level thereby causing said alarm device to generate a continuous alarm signal.

3. A cardiac rate monitor in accordance with claim 2 wherein said window comparator means comprises first amplifier means and second amplifier means having respective inputs coupled to said averaging means and respective outputs coupled to said alarm device, said window comparator means further comprising maximum threshold means coupled to said first amplifier means and minimum threshold means coupled to said second amplifier means for respectively determining said maximum threshold level and said minimum threshold level, said first amplifier means generating said drive potential when said averaged signal exceeds said maximum threshold level and said second amplifier means generating said drive potential when said averaged signal is below said minimum threshold level, and wherein said gating means comprises a logic gate having inputs coupled to said pulse means and said second amplifier means output and an output coupled to said alarm device, said logic gate enabling said alarm device during intervals corresponding to said output pulses so that said alarm device generatEs said repetitive alarm signal at said heartbeat rate when said first amplifier means generates said drive potential, said logic gate continuously enabling said alarm device responsive to said second amplifier means generating said drive potential so that said drive potential from the second amplifier means is then effective to drive said alarm device to produce said continuous alarm signal.

4. A cardiac rate monitor in accordance with claim 3 wherein said logic gate comprises a NOR gate.

5. A cardiac rate monitor in accordance with claim 2 wherein said monitoring means includes input amplifier means having a pair of inputs for monitoring said heartbeats, said input amplifier means developing an output signal representative of said heartbeats, said pulse means generating said output pulses substantially coincident with said heartbeats responsive to said input amplifier means output signal being coupled thereto, said input amplifier means having a high common mode rejection ratio for reducing interference from electromyographic signals and electromagnetic radiation.

6. A cardiac rate monitor in accordance with claim 5 wherein said input amplifier means comprises a capacitive cross-coupling network and first, second and third operational amplifiers having respective input pairs and outputs, respective ones of said first and second operational amplifier inputs monitoring said heartbeats while said first and second operational amplifier outputs are coupled to corresponding ones of said third operational amplifier inputs, said third operational amplifier output being coupled to said pulse means, the other ones of said first and second operational amplifiers being interconnected by said capacitive cross-coupling network, said capacitive cross-coupling network comprising first and second pairs of parallel coupled capacitors and a resistor interposed in series between said first and second capacitor pairs;

said capacitive cross-coupling network reducing the differential gain of said input amplifier means at frequencies outside the expected range of said heartbeat rate while maintianing a high common mode rejection ratio and constant input impedance.

7. A cardiac rate monitor in accordance with claim 5 including a non-linear voltage divider coupling said input amplifier means to said pulse means, said non-linear voltage divider improving the signal-to-noise ratio of said input amplifier output signal.

8. A cardiac rate monitor in accordance with claim 7 including a DC reference potential and wherein said non-linear voltage divider comprises a plurality of diodes and a resistor connected in series between said input amplifier means and said DC reference potential, said pulse means being coupled to the junction of said diode series and said resistor, said diodes having a dynamic resistance decreasing with increasing potential applied thereacross so that small amplitude interfering signals are attenuated at the junction of said diode series and said resistor by a greater factor than that portion of said input amplifier means output signal representative of said heartbeats and having larger amplitudes.

9. A cardiac rate monitor in accordance with claim 2 including a low amplitude ripple filter having an input coupled to said averaging means and an output coupled to said comparator means, said filter suppressing residual ripple in said averaged signal while responding quickly to variations in said averaged signal amplitude level resulting from changes in said heartbeat rate.

10. A cardiac rate monitor in accordance with claim 9 having a DC reference potential and wherein said low amplitude ripple filter comprises a pair of diodes coupled in parallel between said filter input and said filter output and a pair of capacitors, one of said capacitors being coupled between said filter input and said DC reference potential and the other of said capacitors being coupled between said filter output and said DC reference potential, the cathode of one of said diodes being cOupled to the anode of the other of said diodes and the anode of said one diode being coupled to the cathode of said other diode, said filter time constant being a function of said averaged signal amplitude level applied across said diodes.

11. A cardiac rate monitor in accordance with claim 2 wherein said pulse means comprises a monostable multivibrator.

12. In a cardiac rate monitor having first means for continuously monitoring the heartbeat rate of the wearer and developing a signal having an amplitude level directly proportional to said heartbeat rate and second means for selectably establishing a maximum threshold level corresponding to a particular heartbeat rate and developing a drive potential for driving an alarm device whenever said signal exceeds said maximum threshold level said monitor also providing a DC reference potential, the improvement comprising:

a low amplitude ripple filter comprising a pi -filter for coupling said signal from said first means to said second means, said pi -filter comprising a pair of diodes coupled in a parallel arrangement between said first means and said second means and a pair of capacitors, said capacitors being coupled at opposite ends of said parallel diode arrangement to said DC reference potential, the cathode of one of said diodes being coupled to the anode of the other of said diodes and the anode of said one diode being coupled to the cathode of said other diode, said filter time constant being a function of said averaged signal amplitude level applied across said diodes whereby said low amplitude ripple filter is able to respond quickly to changes in the frequency of said heartbeat rate.

13. The method of continuously monitoring heartbeat rate sounding an alarm device to alert the wearer whenever a maximum desirable heartbeat rate is detected, said method comprising:

monitoring said heartbeats;

generating output pulses substantially coincident with corresponding ones of said heartbeats;

averaging said output pulses to develop an averaged signal having an amplitude level directly proportional to said heartbeat rate;

establishing a selectable maximum theshold level corresponding to said maximum desirable heartbeat rate;

applying a drive potential to said alarm device whenever said averaged signal exceeds said maximum threshold level;

gating said alarm device responsive to said output pulses to disable said alarm device during intervals between said output pulses and enable said alarm device to generate an alarm signal responsive to said drive potential only during intervals corresponding to said output pulses thereby causing said alarm device to generate a repetitive alarm signal occurring at a rate coincident with said heartbeat rate, whenever said averaged signal exceeds said maximum threshold level.

14. The method of claim 13 which includes establishing a selectable minimum threshold level, applying said drive potential to said alarm device responsive to said averaged signal dropping below said minimum threshold level and continuously enabling said alarm device whenever said averaged signal is below said minimum threshold level thereby causing said alarm device to generate a continuous alarm signal.