Demand cardiac pacer

• US 3,927,677 A
• Filed: 07/12/1974
• Issued: 12/23/1975
• Est. Priority Date: 07/12/1974
• Status: Expired due to Term

• Current Assignee: David H. Gobeli, John Minor Adams
• Original Assignee: David H. Gobeli, John Minor Adams
• Inventors: Gobeli, David H., Adams, John M.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/488,045
• Time in Patent Office: 529 Days
• Field of Search: 128/2.6A,2.6F,2.6R,419P,421,422
• US Class Current: 607/9
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: H03K 5/01 Shaping pulses discrimination against noise or interference H03K5/125
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A demand cardiac pacer of the type having a resettable pulse generator and electrode means adapted to be connected to the heart for sensing heart activity. The pacer is provided interference discrimination circuitry including a rectifier section responsive to the repetition rate and amplitude of the signals sensed by the electrodes for establishing a reference level representative of sensed extraneous repetitive noise and a second level representative of sensed heart activity. A detector section of the interference discrimination circuitry responds to a difference between the reference level and second level to generate a signal indicative of the sensing of heart activity when that difference exceeds a predetermined value. In a preferred embodiment, the rectifier and detector sections of the interference discrimination circuitry include differential amplifiers, the rectifying differential amplifier acting to control the charge on a capacitor with the capacitor charge establishing both the reference and second levels. The signal indicating the sensing of heart activity triggers a reset signal generator which is provided with a refractory period to limit the repetition rate of the reset signals.

Claims

1. In a demand cardiac pacer of the type having input and output means adapted to be connected to the heart, the input means including means for sensing natural heart activity, having a resettable pulse generator and having means for generating a pulse generator reset signal in response to the sensing of natural heart activity, the improvement which comprises:

first means connected to said heart activity sensing means for establishing a reference level representative of sensed extraneous repetitive noise and a second level, said second level being greater in absolute value than said reference level by an amount representative of sensed heart activity; and

second means connected to said first means and differentially responsive to said reference level and said second level for generating a signal indicative of the sensing of heart activity when the difference between said reference level and said second level exceeds a predetermined value.

2. The apparatus of claim 1 wherein said first means comprises rectifier means.

3. The apparatus of claim 1 wherein said first means comprises:

capacitance means; and

means for charging said capacitance means to said reference level in response to extraneous repetitive noise and to said second level in response to sensed heart activity.

4. The apparatus of claim 3 wherein said capacitance means charging means comprises:

differentiator means; and

means responsive to said differentiator means for controlling the charge level of said capacitance means.

5. The apparatus of claim 4 wherein said charge controlling means comprises differential amplifier means.

6. The apparatus of claim 4 wherein said charge controlling means comprises rectifier means.

7. The apparatus of claim 1 wherein said second means comprises differential amplifier means.

8. The apparatus of claim 7 wherein said second means further comprises means responsive to said differential amplifier means for generating a signal indicative of heart activity.

9. The apparatus of claim 8 wherein said first means comprises:

capacitance means; and

means for charging said capacitance means to said reference level in response to sensed repetitive extraneous noise and to said second level in response to sensed heart activity.

10. The apparatus of claim 1 wherein said reset signal generating means comprises refractory means for limiting the repetition rate of said reset signals.

11. In a demand cardiac pacer of the type having input and output means adapted for connection to the heart, the input means including means for sensing natural heart activity, having a resettable pulse generator and having means for generating a pulse generator reset signal in response to the sensing of natural heart activity, the improvement which comprises;

differentiator means connected to said sensing means for providing a signal having an amplitude and repetition rate representative of the signals sensed by said sensing means;

capacitance means;

means connected to said differentiator means for charging said capacitance means to a first level representative of sensed repetitive extraneous noise and a second level which exceeds said first level by an amount representative of sensed heart activity; and

means connected to said capacitance charging means and differentially responsive to said first and second levels for generating a pulse generator reset signal, said reset signal generating means including refractory means for limiting the repetition rate of said reset signals.

12. The apparatus of claim 11 wherein said charging means comprises rectifier means.

13. The apparatus of claim 11 wherein said charging means and said reset signal generating means comprise differential amplifier means.

14. The apparatus of claim 11 wherein said differentiator means comprises active circuit means.

15. The apparatus of claim 11 wherein said differentiator means comprises passive circuit means.