Cardiac monitoring apparatus

• US 4,221,223 A
• Filed: 05/24/1978
• Issued: 09/09/1980
• Est. Priority Date: 05/24/1978
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Linden, Rolf W.
• Primary Examiner(s): Michell, Robert W.
• Assistant Examiner(s): Jaworski, Francis J.
• Application Number:
  US05/909,229
• Time in Patent Office: 839 Days
• Field of Search: 128/2.05 T, 128/2.05 R, 128/2.05 P, 128/2.06 F, 128/687-690, 128/706-707, 364/417, 364/701, 328/37, 328/51, 324/78 D, 235/92 T, 235/92 TF
• US Class Current: 600/519
• CPC Class Codes: A61B 5/332 Portable devices specially adapted therefor

Abstract

There is disclosed herein a wristwatch size cardiac monitoring apparatus which is worn on the wrist of one arm. A conductive material housing acts as one electrode when held firmly in contact with the wrist of the arm on which it is worn. A finger of the other limb is placed on a receiving electrode of the casing which acts as the second electrode. Together, these two electrodes provide a Lead I electrocardiac signal to electronics within the housing. The second electrode consists of a metal layer on which is placed a dielectric material and when the finger is placed on top of the dielectric material, a capacitor is formed and the electric signal on the finger is transferred to the metal layer. Additionally, there is described circuitry which is used to operate the rate monitor. This circuitry includes means for detecting a QRS complex and for causing a count in beats per minute to be displayed, manifesting the heartbeat rate. The circuitry includes means for updating the heartbeat rate displayed every two seconds and for automatically turning the system off when no heartbeats are detected for a six second interval.

Claims

1. Circuit means for a cardiac rate monitoring circuit comprising:

means for detecting a signal manifesting a heartbeat in response to an electrocardiac signal applied thereto;

means responsive to the rate of said detected signals for providing a voltage related to said rate;

integrating means for integrating said voltage and providing first and second control signals as said integrated signal increases beyond respective first and second magnitude;

counter means for being reset by said first signal to count from an initial value and to provide a signal manifesting said heart rate as related to the count therein upon the occurrence of said second signal;

wherein said counter counts to a certain count above the count therein at the time said second control signal is provided; and

wherein said circuit means further includes means responsive to said counter reaching said certain count for resetting said integrating means.

2. The invention according to claim 1:

wherein said circuit means further includes clock means for providing constant frequency clock signals to be counted to said counter means; and

wherein said circuit means further includes means for inhibiting the provision of said clock signals upon said counter reaching said certain count.

3. The invention according to claim 2 wherein said means for inhibiting the provision of said clock signals is operative until said first control signal is provided by said integrating means.

4. Circuit means for a cardiac rate monitoring circuit comprising:

means for detecting a signal manifesting a heartbeat in response to an electrocardiac signal applied thereto;

means responsive to the rate of said detected signals for providing a voltage related to said rate;

integrating means for integrating said voltage and providing first and second control signals as said integrated signal increases beyond respective first and second magnitudes;

counter means for being reset by said first signal to count from an initial value and to provide a signal manifesting said heart rate as related to the count therein upon the occurrence of said second signal;

wherein said means for providing said voltage related to said heart rate includes first capacitance means for being charged at a determined rate, second capacitance means, switch means for transferring the voltage on said first capacitance means to said second capacitance means each time a heartbeat is detected, means for discharging said first capacitance means after each heartbeat is detected, and means for applying the voltage stored by said second capacitance means to said integrating means as said voltage related to said rate;

wherein said counter counts to a certain count above the count therein at the time said second control signal is provided; and

wherein said circuit means further includes means responsive to said counter reaching said certain count for resetting said integrating means.

5. The invention according to claim 4:

wherein said circuit means further includes clock means for providing constant frequency clock signals to be counted to said counter means; and

wherein said circuit means further includes means for inhibiting the provision of said clock signals to said counter reaching said certain count.

6. The invention according to claim 5 wherein said means for inhibiting the provision of said clock signals is operative until said first control signal is provided by said integrating means.

7. The invention according to claim 6 wherein said first capacitance means is charged from a constant current source providing a constant current.

8. The invention according to claim 7:

wherein said integrating means includes an amplifier having inverting and noninverting inputs, and an output, third capacitance means coupled between said output and said inverting input, resistance means coupled between said inverting input and a point of reference potential and coupling means coupling one side of said second capacitance means to said noninverting input; and

wherein the other side of said second capacitance means is coupled to said point of reference potential.

9. The invention according to claim 8 wherein heartbeat rate as manifested by said counter is directly proportional to said constant frequency, the value of said resistance means, the difference in voltage between said first and second signals, the value of said first and third capacitance means and inversely proportional to said constant current and the real time between detected heartbeats.

10. The invention according to claim 9 wherein said resistance means is functionally trimmed.

11. Circuit means for a cardiac rate monitor comprising:

means for detecting a signal manifesting a heartbeat in response to an electrocardiac signal applied thereto;

clock means for providing a series of clock signals at a constant frequency;

counter means for counting said clock signals from an initial reset count to a higher predetermined count;

control means in response to said detected heartbeats for providing a control signal to said counter means to capture a count therein, less than said predetermined count, which captured count is related to said heart rate;

shift register means, which in response to signals applied thereto when said counter reaches said predetermined count, shifts an applied data value therethrough to an output thereof;

display means having data and enable inputs for displaying a number related to signals applied to the display inputs upon application of a signal to said enable input;

means for connecting the captured count of said counter to the data input of said display means; and

means for connecting the output of said shift register to said enable input of said display means.

12. The invention according to claim 11:

wherein said circuit means includes switch means for being closed upon use of said monitor, and latch means for being set upon closure of said switch means; and

wherein said data value transferred through said shift register is related to whether said latch means is set.

13. The invention according to claim 12 wherein said data value related to said latch being set, when transferred through said shift register, enables said display means.

14. The invention according to claim 13 wherein said latch means being set enables said control means.

15. The invention according to claim 12 wherein said circuit means further comprises:

second multistage shift register means having data, clock and reset inputs and an output for shifting therethrough the data value applied to the data input each time a signal is applied to the clock input, and for resetting each stage thereof each time a signal is applied to said reset input;

gate means for providing a signal to said reset input of said second shift register means upon the coincident occurrence of said latch being set and a detected heartbeat;

means for connecting the output of said first shift register means to the data input of said second shift register means;

means for applying signals to said clock input each time said counter reaches said predetermined count; and

means for coupling the output of said second shift register to reset said latch each time said data value applied to said data input appears as the value at said output.

16. The invention according to claim 15 wherein said first shift register means includes a reset input to which is coupled the output of said second shift register.