Demand heart pacer

• US 3,926,197 A
• Filed: 01/04/1974
• Issued: 12/16/1975
• Est. Priority Date: 01/04/1974
• Status: Expired due to Term

• Current Assignee: Lawrence Everett Iii Alley
• Original Assignee: Lawrence Everett Iii Alley
• Inventors: Alley, Lawrence Everett III
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/430,827
• Time in Patent Office: 711 Days
• Field of Search: 128/419PG,419PT,419R,421,422 307/251,279,288
• US Class Current: 607/9
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371
• CPC Class Codes: H03K 3/354 Astable circuits
• CPC Class Codes: H03K 3/355 Monostable circuits

Abstract

A demand heart pacer which includes an oscillator, an amplifier for receiving and amplifying naturally occurring heart pulses, a monostable multivibrator activated by amplified naturally occurring heart pulses to generate a disabling pulse, and means for disabling the oscillator upon occurrence of a disabling pulse is of complimentary metal oxide semi-conductor devices to present a capability of operating with low power dissipation to facilitate implantable heart pacer use having an enhanced power supply lifetime. The heart pacer produces stimulation pulses in an '"'"''"'"''"'"''"'"'inhibit mode'"'"''"'"''"'"''"'"' at a first frequency and stimulation pulses in a '"'"''"'"''"'"''"'"'fixed rate mode'"'"''"'"''"'"''"'"' at a second frequency, the difference in the first and second frequencies being indicative of the power supply voltage to provide a monitor of its state or condition. The heart pacer additionally employs an oscillator inhibitor, which includes a field effect transistor biased to a level which is increased upon reception of high frequency noise, to prevent conduction, and which additionally operates to define a variable second half of a refractory period to distinguish noise at a frequency approximately twice that of an acceptable heartbeat frequency.

Claims

1. A heart pacer for producing heart stimulation pulses in the absence of naturally occurring heart pulses, comprising:

a voltage source;

a pair of electrodes, at least one of which is connectable to the heart;

means connected to said electrodes for detecting naturally occurring heart pulses and for generating an inhibiting pulse corresponding to each detected natural heart pulse;

means connected to said voltage source, including a timing capacitor, for generating stimulation pulses for delivery to said electrodes at a constant heartbeat rate independent of the voltage of said voltage source;

means connected to said stimulation pulse generating means for discharging said timing capacitor to inhibit the generation of selected stimulation pulses;

means connected to said detecting means refernced to said voltage source for generating in response to a naturally occurring heart pulse, a waveform having a time varying amplitude directly proportional to the voltage of said voltage source;

means having a threshold activating voltage to which said waveform is applied connected for activating said capacitor discharging means during the time said waveform exceeds the threshold voltage to control the time said timing capacitor is discharged, thereby changing the heartbeat rate of said stimulation pulse generating means directly proportionally to said supply voltage; and

, means for decoupling said waveform to prevent it from activating said stimulation pulse generating means to enable said stimulation pulse generating means to pulse without being inhibited to produce a reference heartbeat rate comparable to the heartbeat rate with said inhibiting means coupled, the difference between said heart beat rates being indicative of the voltage of said voltage source.

2. The heart pacer of claim 1 wherein said means for activating said capacitor discharging means is a field effect transistor having a gate, a source, and a drain, the gate being connected to receive said waveform and the source and drain being connected between said voltage source and said capacitor discharging means to apply the voltage of the voltage source to said timing capacitor discharging means to activate said capacitor discharging means, and means for biasing said field effect transistor below its threshold voltage to a normally non-conducting state whereby the waveform biases said field effect transistor above the threshold voltage to a conducting state over at least a portion of said waveform.

3. The heart pacer of claim 2 wherein said decoupling means comprises switch means interconnecting said gate of said field effect transistor and said voltage source for biasing said field effect transistor below the threshold voltage.

4. The heart pacer of claim 3 wherein said switch means is a magnetic switch.

5. The heart pacer of claim 1 wherein said means for generating a waveform includes a capacitor to which said inhibiting pulse is applied and a resistor connected to said capacitor to controllably discharge said capacitor at a rate relatable to the frequency of said inhibiting pulses, whereby the capacitor builds up a DC voltage thereupon at a frequency higher than a predetermined heartbeat frequency, thereby impressing a DC level upon said waveform to prevent saiD waveform from exceeding the threshold voltage.

6. A heart pacer for producing heart stimulation pulses in the absence of naturally occurring heart pulses, comprising:

means for generating stimulation pulses at a heartbeat rate, a pair of electrodes, at least one of which is connectable to the heart connected to said stimulation pulse genrating means, means connected to said electrodes for detecting naturally occurring heart pulses and for generating an inhibit pulse in response to the detection of a naturally occurring heart pulse, means connected between said stimulation pulse generating means and said inhibit pulse generating means for inhibiting the generation of stimulation pulses in response to said inhibit pulses, means connected to said detector for disabling said detector for a first fixed refractory period to prevent the generation of inhibit pulses during said first refractory period, and means to which said inhibit pulses are applied from said inhibit pulse generator for disabling said stimulation pulse inhibiting means for a second variable refractory period, said second refractory period being consecutive with the first and being variable in length proportional to the rate at which the inhibit pulses are applied to said disabling means for said second refractory period to detect noise pulses falling within said second period to distinguish normal heartbeat produced pulses from external noise induced pulses.

7. The heart pacer of claim 6 wherein said stimulation pulse generating means comprises a timing capacitor, and a first field effect transistor having a gate, a source, and a drain, said source and drain being connected across said capacitor to discharge it when said transistor is in a conducting state, and wherein said means for inhibiting the generation of said stimulation pulses comprises a second field effect transistor having a gate, a source, and a drain, and a voltage source, said source and drain being connected to apply the voltage of said voltage source to the gate of said first field effect transistor to cause it to conduct, and further comprising means to which said inhibit pulses are applied for producing a waveform having a voltage portion to present a bias to maintain said second field effect transistor in a non-conducting state for a period after said inhibiting pulse has been generated to define said second variable refractory period.

8. The heart pacer of claim 7 further comprising means for varying relatably with the fequency of the pulses from said inhibiting pulse generating means the period said second field effect transistor is maintained in its non-conduction state, whereby the variable refractory period produced thereby is reduced upon increasing frequency of said pulses from said inhibiting pulse generating means.