Automatic threshold compensating demand pacemaker

Claim 2

Cardiac pacer apparatus having first means for providing timed cardiac stimulation pulses, second means for sensing natural heartbeats, means connecting the second means to the first means for inhibiting stimulation pulses when a natural heartbeat is sensed, and electrode means connected to the first and second means and adapted to be connected to a heart, the apparatus including: third means connected to the electrode means for sensing stimulated heartbeats; fourth means connected to the first and third means and responsive to each sensing of a stimulated heartbeat for decreasing the energy of the succeeding stimulation pulse by a predetermined amount, the fourth means responsive to each failure to sense a stimulated heartbeat for increasing the energy of the succeeding stimulation pulse to an amount greater than the preceding stimulation pulse but normally less than maximum energy; and energy source means connected to all the means.

Claim 3

The apparatus of claim 1 including; further means connected to the first and third means and responsive to each failure to sense a stimulated heartbeat for providing an extra stimulation pulse prior to the normal succeeding stimulation pulse.

Claim 4

The apparatus of claim 2 in which: the further means provides the extra stimulation pulse at the maximum energy level.

Claim 5

The apparatus of claim 2 in which the electrode means comprises: stimulating electrode means connected to the first means and adapted to be connected to a heart; sensing electrode means connected to the second means and adapted to be connected to a heart; and further electrode means electrically common to the first and second means and the stimulating and sensing electrode means, and adapted to be connected to a portion of the body.

Claim 6

The apparatus of claim 4 in which: the further electrode means includes dimensioned conductive surface means for minimizing polarization effects of stimulation pulses.

Claim 7

The apparatus of claim 1 in which the second and third means comprise: a single sense amplifier means having input means connected to the electrode means and output means connected to the first and fourth means.

Claim 8

The apparatus of claim 6 including: further means connected to the first and third means and responsive to each failure to sense a stimulated heartbeat for providing an extra stimulation pulse prior to the normal succeeding stimulation pulse.

Claim 9

The apparatus of claim 7 in which: the further means provides the extra stimulation pulse at the maximum energy level.

Claim 10

The apparatus of claim 1 including: fifth means connecting the first means to the fourth means for inhibiting operation of the fourth means in the absence of a stimulation pulse.

Claim 11

The apparatus of claim 9 including: further means connected to the first and third means and responsive to each failure to sense a stimulated heartbeat for providing an extra stimulation pulse prior to the normal succeeding stimulation pulse.

Claim 12

The apparatus of claim 10 in which: the further means provides the extra stimulation pulse at the maximum energy level.

Claim 13

The apparatus of claim 10 in which the fifth means includes: means responsive to a stimulation pulse for enabling operation of the fourth means for a limited time period following each stimulation pulse.

Claim 14

The apparatus of claim 9 in which the fifth means includes: means responsive to a stimulation pulse for enabling operation of the fourth means for a limited time period following each stimulation pulse.

Claim 15

The apparatus of claim 1 in which the electrode means comprises: stimulating electrode means connected to the first means and adapted to be connected to a heart; sensing electrode means connected to the second means and adapted to be connected to a heart; and further electrode means eLectrically common to the first and second means and the stimulating and sensing electrode means, and adapted to be connected to a portion of the body.

Claim 16

The apparatus of claim 14 in which: the further electrode means includes dimensioned conductive surface means for minimizing polarization effects of stimulation pulses.

Claim 17

An implantable demand cardiac pacer comprising: sense means for sensing electrical signals from a heart; first timed pulse generator means; energy storage means; controllable output means connected across the energy storage means; controllable energy charge path means connected to the energy storage means; second timed pulse generator means; stimulation electrode means connected to the output means and adapted to be connected to a heart; sense electrode means connected to the sense means and adapted to be connected to a heart; means connecting the sense means to the first and second timed pulse generator means for resetting the first and second generator means on the sensing of an electrical signal from the heart; means connecting the first generator means to the output means for controlling stimulation output pulses; means connecting the second generator means to the controllable energy charge path means; the the charge path means including means responsive to the second generator means for controlling charging of the energy storage means such that the energy level to which the storage means is charged is proportional to the energy in the storage means following the last stimulation output pulse; and all the means adapted to be connected to a source of energy.

Claim 18

An implantable demand cardiac pacer comprising: sense means for sensing electrical signals from a heart; first timed pulse generator means; energy storage means; controllable output means connected across the energy storage means; controllable energy charge path means connected to the energy storage means; second timed pulse generator means; stimulation electrode means connected to the output means and adapted to be connected to a heart; sense electrode means connected to the sense means and adapted to be connected to a heart; means connecting the sense means to the first and second timed pulse generator means for resetting the first and second generator means on the sensing of an electrical signal from the heart; means connecting the first generator means to the output means for controlling stimulation output pulses; means connecting the second generator means to the controllable energy charge path means; the the charge path means including means responsive to the second generator means for controlling charging of the energy storage means such that the energy level to which the storage means is charged is proportional to the energy in the storage means following the last stimulation output pulse; and all the means adapted to be connected to a source of energy.

Claim 19

The apparatus of claim 16 in which: the energy storage means comprises a capacitor; and the charge path means includes time constant means connected in series with the capacitor.

Claim 20

The apparatus of claim 17 in which the time constant means includes inductance means.

Claim 21

The apparatus of claim 16 including: inhibit means connected between the first generator means and the second generator means; the inhibit means including means normally operative for inhibiting operation of the second generator means and means responsive to a pulse from the first generator means for allowing operation of the second generator means for a predetermined time period.

Claim 22

The apparatus of claim 19 in which: the second timed pulse generator has a pulse repetition rate less than the predetermined time period.

Claim 23

The apparatus of claim 19 including; further means connecting the first generator means to the second generator means for resetting the second generator means in response to a pulse from the first generator means.

Claim 24

The apparatus of claim 19 including: means connected between the output means and the second generator means and responsive to a pulse from the second generator means for connecting the stimulation electrode means across the source of energy.

Claim 25

The apparatus of claim 16 in which: the sense means includes amplifier means having a refractory period not greater than 20 milliseconds.

Claim 26

In an implantable cardiac demand pacer having a source of energy, sensing means connected to the source of energy, periodic pulse generator means connected to the source of energy, and means connecting the sensing means to the generator means for resetting the generator means, the improvement comprising: sense electrode means connected to the sensing means and adapted to be connected to a heart; capacitor means; time constant means; first switch means; means connecting the time constant means, the first switch means and the capacitor means in series across the source of energy; output means including stimulation electrode means adapted to be connected to a heart; second switch means; means connecting the output means and the second switch means in series across the capacitor means; means connecting the pulse generator means to the second switch means; second periodic pulse generator means connected to the source of energy; means connecting the sensing means to the second pulse genErator means for resetting the second pulse generator means; and means connecting the second pulse generator means to the first switch means for controlling connection of the capacitor means and the time constant means to the source of energy.

Claim 27

In an implantable cardiac demand pacer having a source of energy, sensing means connected to the source of energy, periodic pulse generator means connected to the source of energy, and means connecting the sensing means to the generator means for resetting the generator means, the improvement comprising: sense electrode means connected to the sensing means and adapted to be connected to a heart; capacitor means; time constant means; first switch means; means connecting the time constant means, the first switch means and the capacitor means in series across the source of energy; output means including stimulation electrode means adapted to be connected to a heart; second switch means; means connecting the output means and the second switch means in series across the capacitor means; means connecting the pulse generator means to the second switch means; second periodic pulse generator means connected to the source of energy; means connecting the sensing means to the second pulse genErator means for resetting the second pulse generator means; and means connecting the second pulse generator means to the first switch means for controlling connection of the capacitor means and the time constant means to the source of energy.

Claim 28

The apparatus of claim 24 in which: the time constant means includes inductance means.

Claim 29

The apparatus of claIm 24 including: third switch means connected between the second pulse generator means and the source of energy for normally inhibiting operation of the second pulse generator means; window timing means connected between the periodic pulse generator and the third switch means for allowing operation of the second pulse generator means for a limited window period of time following a pulse output from the periodic pulse generator.

Claim 30

The apparatus of claim 26 in which: the periodic pulses from the second generator are at a repetition rate less than the window period of time.

Claim 31

The apparatus of claim 26 including: means connected between the first switch means and the output means for connecting the output means across the source of energy when the first switch means is actuated.