JPH0211267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an output stage for a biostimulator, and more particularly to a directly coupled output stage for outputting rapidly changing signals such as those generated by a cardiac pacemaker. It is.

In a typical cardiac pacemaker, charge is stored on one or more capacitors. When a pacing pulse is desired, a charge storage capacitor is connected directly to the stimulation and neutral electrode leads and the capacitor is discharged through the leads and the electrode/electrolyte interface into the patient's tissue. (Generally, it is not necessary for two electrodes to be placed in close proximity to the heart tissue, but at least one is necessary.)
A capacitor connected directly to the stimulation electrode lead recharges through the battery power supply and the stimulation electrode.
It is a generally accepted design goal that no net charge is output to the heart. Providing an AC coupling ensures that there is no net amount of current through the stimulation electrode since the average current through the capacitor is zero.

There are at least two major drawbacks to using this type of AC coupling. First, in addition to the high cost of coupling capacitors, they are bulky, increasing the size and weight of the pacemaker. This is not a significant disadvantage in the case of external biostimulators (cardiac pacemakers or other types). Other disadvantages apply equally to external tissue stimulators. (External stimulator means a device that is external to the living body but provides signals through internal leads.) At least in the case of cardiac pacemakers, electrode leads detect electrical activity in the heart. used to. The potential on the stimulation electrode changes rapidly at the beginning of the pacing pulse and gradually returns when the capacitor connected to the electrode recharges. During this charging process the cardiac operating signals are masked. Typically, the potential of the stimulating electrode relative to the neutral electrode (ground) is several hundred millivolts during a charging cycle, while the electrical activity of the heart results in a signal of only a few millivolts. Filters used with typical cardiac pacemaker sensing circuits are designed to block charging current signals while minimizing signals that affect cardiac operation. There is usually a dead period at the beginning of a sensing cycle, followed immediately by the generation of a pacing pulse. This period lasts 50 to 100 milliseconds,
There are even longer ones. This problem is not particularly important in the case of single room shakedowns. This is because cardiac activity should be ignored by the sensing circuitry during the cardiac refractory period, which is at least as long as the dead period. However, the problem is more severe in the case of a two-chamber pacemaker, where completely independent pairs of electrodes are not provided for the two chambers, and electrical activity in one chamber is transmitted to another chamber. It must be detected shortly after the pulse is applied. In such cases, rapid charging is important to reduce the dead period.

It should be understood that there are tissue stimulation devices that have a directly coupled output stage. For example, skeletal growth stimulators apply direct current to the fracture site where skeletal growth is to be stimulated. Obviously, a direct current output stage is essential in this case. The tissue stimulators involved provide rapidly changing signals, with any signal (AC, pulse, etc.) changing appreciably (so as to have a biological effect) within 10 seconds. A typical stimulator of this type is a cardiac pacemaker, in which stimulation pulses are generated every second or so.

The general object of this invention is to provide a directly connected output stage for a rapid signal biostimulator, thus eliminating the need for coupling capacitors and eliminating the attendant disadvantages thereof. .

Despite the above-mentioned disadvantages of using a coupling capacitor, omitting an output coupling capacitor is almost considered heretical, for example in the field of cardiac pacemakers. For example, American
Journal of Cardiology
See Fisher et al., "Pacemaker Failure Characterized by Continuous Direct Current Leakage," American Journal of Cardiology, June 1976. The belief that coupling capacitors are essential is so ingrained in the minds of cardiac pacemaker designers that even today little clear thought has been given as to whether capacitors are actually necessary. do not have. However, if carefully analyzed,
This raises not only the question of whether a coupling capacitor is necessary, but also whether it really does the job it is supposed to do.

In any biostimulator with rapid signals,
At least a stimulating electrode is implanted in close proximity to the tissue to be stimulated. A neutral electrode may be implanted nearby or in tissue remote from it. However, the signal current necessarily flows between the two electrodes. What happens here is that the electronic current in the electrode lead is converted into an ionic current at the interface with the biological electrolyte (the biological fluid is usually a salt). The equivalent impedance at the electrode/electrolyte interface is not the same as that of the biological tissue itself between the electrodes, and the latter can be expressed as a separate resistance. At the interface of each electrode the impedance is actually a distributed RC network,
An infinite number of resistors are connected in series and an effective capacitor is connected in parallel across each resistor. This is the equivalent circuit through which the pacing current pulse flows and the allocated capacitance charges. There should be no net charge transfer to the tissue to minimize electrochemical effects. This requires that the charge accumulated at the electrode/electrolyte interface be recovered. By ensuring that there is no net current flow, the coupling capacitor theoretically provides total charge recovery.

However, since they are in series with the coupling capacitor, zero net current flow through the electrode leads is of no practical importance. Theoretically, charge is stored in a distributed capacitance at each electrode/electrolyte interface, this charge is collected after the pacing pulse as a charge storage capacitor is recharged through the battery, and then transferred back through the electrode leads. Current flows in the direction. However, just because there was no net current through the coupling capacitor does not mean that ion flow did not occur within the stimulated tissue.

At a purely theoretical level, consider the case of a 1 second, 10 milliamp current pulse delivered through an electrode. Assume further that the current flow in the opposite direction can be operatively controlled to have the same duration and the same amount. A symmetrical square wave current signal flows through the electrodes, where the average current through the coupling capacitor is zero. When current flows in one direction, the charge at the electrode/electrolyte interface is
stored in distributed capacitors. However, this charge does not remain there until it is recovered by a current flowing in the opposite direction. Instead, some charge leaks through the distributed capacitor,
It flows through living tissues and disappears irretrievably. When the same current pulse is made to flow in the opposite direction, the charge remaining on the distributed capacitance is recovered. However, some of the original charge leaks out and the remainder of the recovered charge must be extracted from elsewhere within the tissue. The net current through the coupling capacitor is zero, but there are actually two unwanted ion flows within the tissue. One is due to inherent leakage and the other is due to recovery to compensate for lost charge. While the initial leak is undesirable, nothing is gained by mixing the problem with additional ion flow through the tissue. Any damage caused by leakage is not covered.
Instead, a guaranteed ion flow will cause more damage. Although the net charge flowing through the coupling capacitor is zero, the net ion current or charge transfer is not zero. These are two bad cases that don't actually do the right thing.

In summary, the most possible “charge balance” within the tissue
(minimum net charge transfer) is not necessarily affected by zero net current flow through the electrodes.

Consider another example in which no coupling capacitor is used, ie the output stage is not connected in series with the electrodes. The example illustrates the principles of the invention. A typical pacing pulse is 10 milliamps in volume and has a duration of 0.5 milliseconds. Assume that the electrode leads are shorted together instead of allowing the coupling capacitor to recharge through the electrodes to an integral value equal to the current-time product or 5 milliamps-milliseconds. Experiments have shown that 99% of the charge output through the electrodes during the pacing pulse is recovered via the leads during the first 8 milliseconds following electrode shorting. This means that the net current flow within the tissue is only about 1% of the peak pulse current.

If a coupling capacitor is used, charge recovery is relatively slow because the coupling capacitor typically returns to the battery power supply through a resistor. During relatively long charge recovery times, e.g. 100 milliseconds, some of the charge on the distributed capacitance leaks out, and therefore this charge is transferred to additional sources within the tissue at the end of the charge recovery process. can simply be recovered by a stream of ions. It is the capacitor itself that causes this undesired ion flow, and the reason is that the only way to achieve zero net current through the capacitor is to add additional This is because an ion flow is generated. However, if the electrode leads are shorted together, the capacitance distributed across the short will rapidly discharge. Since the discharge is very fast,
As mentioned above, about 99% of the charge is recovered within about 8 milliseconds. Although about 1% of the charge leaks out of the distributed capacitance and adds to its damage, not only is there less leakage because the distributed capacitance discharge is rapid, but also the overall dissipation within the tissue. The damage is not mixed by the fact that the necessary ion flow occurs in the opposite direction.

There is no compelling reason to keep the electrodes shorted for more than 8 milliseconds in this case. No more than 99% of the initial charge is recovered; approximately 1 of the initial charge is recovered during the first 8 milliseconds.
% will not leak and be recovered. The current flowing in the opposite direction drops to a low level by the time the 8 milliseconds expire. Although shorting electrodes do not cause any harm as they do not create unnecessary ion currents (charge recovery is passive and not active),
There is no reason to keep the electrodes shorted for much longer.
This means not only avoiding the use of expensive and large coupling capacitors, but also greatly reducing dead periods (in the context of cardiac pacemakers). Once the short circuit, the mechanism used to couple the electrodes together and allow passive charge dissipation, is opened, the electrodes can be used to sense the movement of the heart, and the resulting signal is It is not masked by the output capacitor recharging current flow (although the interface voltage component still remains due to unrecoverable charge).

Of course, the electrodes remain shorted in this manner for more than 9 milliseconds, providing an automatic refractory period of the desired duration. In a typical ventricular arrest (VVI) cardiac pacemaker, the sensing circuit should not respond to cardiac movement for perhaps 50 milliseconds or so after the pacing pulse is generated, and the shorting circuit that recovers the charge This is a convenient mechanism for disabling the sensing circuit. Generally, the present invention contemplates shorting the electrodes for between 0.01 and 400 milliseconds. For short periods at the lower end of the range, short circuits can be made within sharp narrow pulses, ie one pulse intermittently followed by several short circuits, allowing for sensing at intervals. A short-circuit pause period of 8 to 50 milliseconds is preferred, particularly in the case of cardiac pacemakers.

The invention is particularly useful when used in implantable devices where it is desired to eliminate some elements such as large capacitors. It should be appreciated that this invention is highly effective in the case of typical cardiac pacemakers where only one voltage source is provided. It is conceivable that if two voltage sources of opposite polarity are provided, the use of a coupling capacitor can be avoided by switching the two voltage sources to the stimulation electrodes. One voltage source is used to control the application of pulses to the stimulation electrode, and the other voltage source is used to control the actual discharge of the apportioned capacitance. However, common cardiac pacemakers are not provided with two voltage sources. It has been believed that only one polarity voltage source is used and that a coupling capacitor is necessary for charge balancing purposes. For the reasons mentioned above, the capacitor is in fact not needed or even undesirable.

All this does not mean that the use of capacitors can be avoided. In fact, in the illustrated embodiment of the cardiac pacemaker of this invention:
Two large capacitors are used. One capacitor, typically 5 to 15 μF, is connected across the battery within the pacemaker to stabilize the voltage bus. This capacitor is independent of pacing pulse output or charge recovery.
It is used only to ensure that transients resulting from the pacing pulses do not affect the energization of other circuits within the pacemaker. a second capacitor,
Typically 15 μF is used to store the charge to be output during the application of the pacing pulse. Conventional batteries used in cardiac pacemakers are not capable of supplying the relatively large currents required for pacing pulses. A common technique for obtaining this relatively large current is to charge a storage capacitor from a battery and then rapidly discharge this capacitor into the electrode leads whenever a pacing pulse is desired. Although this invention uses such a capacitor, it is not a coupling capacitor. This is because although the coupling capacitor outputs the pacing pulse directly to the stimulation electrode, no charge is recovered through it at the end of the pulse. The capacitor does not recharge through the electrodes between pacing pulses. Rather, the capacitor is charged once more through circuitry within the pacemaker in preparation for another pacing pulse, and current flow through the electrode leads is not involved. Charge balance is achieved by shorting the two electrodes together. The storage capacitor does not act as a coupling capacitor because all the current flowing through the stimulation lead does not flow through it.

Common conventional cardiac pacemakers often include voltage doubler circuits. Such a circuit results in the use of two large storage capacitors (in addition to the third filter capacitor across the battery). The two capacitors are separately charged to the battery potential; one capacitor is a coupling capacitor and is therefore charged for charging balance through the electrode leads. When a pacing pulse is required, and if double the amount of pulse is desired, two capacitors are connected in series with the electrode leads. A voltage doubler is also provided in the illustrated embodiment of the invention. However, instead of using two large 30μF storage capacitors, only one
A 15μF component is used with a small pump capacitor, typically 0.1μF. The pump capacitor controls the potential of the storage capacitor equal to twice the battery power supply. The net result is therefore that one large capacitor can be omitted, reducing the size of the other by half. However, although two large capacitors were used to achieve voltage doubling, not using either of them to control charge balance would avoid undesired ion flux in the biological tissue. In other words, there is no net decrease in the component;
From a physiological point of view it is good to provide direct coupling, even if it is not to say that the use of DC coupling makes it possible to reduce the dead period considerably.

In one experiment conducted in the past, the electrodes were 9
It was placed in a gram/liter salt solution to simulate living tissue. 0.5 millisecond, 10 milliamp pulses were generated at a repetition rate of 1 per second, and the net current in the lead was measured during different short-circuit rest periods following the application of each pulse. The table below shows the net current, ie the charge imbalance, for different rest periods of the short circuit.

Short circuit rest period net current 1 ms 1.40 μA 1.75 ms 0.62 μA 2 ms 0.44 μA 2.75 ms 0.15 μA 3.2 ms 0.13 μA 5 ms 0.07 μA 8 ms 0.04 μA Further objects, features, and The advantages will become apparent upon consideration of the following detailed description in conjunction with the drawings.

The output stage of the pacemaker of FIG. 2 includes a 3 volt voltage source 72 and a filter capacitor 68 connected across it. Two voltage buses for energizing the pacemaker circuit are designated V+ and V-. Capacitor 68 is typically 5 to 15 μF, and its use, as discussed above, is necessary for reasons other than pacing pulse output or charge balancing.

The other parts of the circuit shown in FIG. 2 are themselves output stages; the circuitry for sensing cardiac activity and synchronizing the pacing pulses is not shown. Between the pacing pulses the two transistors 11
and 19 are kept off. capacitor 1
5 is charged between the two voltage buses through resistors 13 and 17. There is another one on the right side of that capacitor.
is sufficiently negative to the left before there is a need to generate two pacing pulses. At the same time, capacitor 25 is charged via resistor 23, the stimulation and neutral electrode leads, the two electrodes, and the heart tissue. It is during this period that charge is recovered from the distributed capacitance at the electrode/electrolyte interface, and the right side of capacitor 25 is charged to a negative voltage with respect to the left side. Zener diode 70 is a common protection diode to prevent excessive voltages from building up across the two electrodes and does not need further explanation here. When a pacing pulse is to be output, a positive pulse is
given on the basis of. That transistor turns on, shorting the left side of capacitor 15 through it to the negative voltage bus. This negative voltage step is applied through capacitor 15 to the emitter of transistor 19, which also turns on. Capacitors 15 and 25 are now connected in series between the neutral electrode IND and the stimulating electrode STIM, and a negative pulse is applied to the stimulating electrode to pace the heart.

At the end of the pulse, transistor 11 is turned off, and with it transistor 19 is also turned off. Capacitor 15 now recharges through resistors 13 and 17. Capacitor 25 recharges through resistor 23 and the heart tissue. (Resistor 23 is typically 15 kilohms. It should not be too large, otherwise capacitor 2
5 would take too long to charge. )
This technique of charging each of the capacitors to the full supply voltage and then connecting them in series when a pacing pulse is to be output makes the pulse amplitude twice that of the battery. Each of capacitors 15 and 25 has a size of 30 μF, and the two capacitors have a capacitance equivalent to 15 μF when they are connected in series to output the pacing pulse.

Capacitor 25 serves two functions. Firstly, one of the two storage capacitors is used to achieve voltage doubling and store enough charge for large current pulses. Second
is that the capacitor 25 is used as an AC coupling capacitor. Since the net current through the capacitor must be zero, the net current flow through the electrodes is necessarily zero. As mentioned above, however, despite the fact that a coupling capacitor was considered necessary, it does not provide charge balancing. fact,
At each electrode/electrolyte interface, perfect charge balance is not possible due to leakage from the apportioned capacitance, and capacitor 25 actually absorbs unwanted ions at the electrode/electrolyte interface. Create a flow. By controlling the net current of zero,
This results in a greater net transfer of charge than would otherwise occur.

Capacitor 25 may be needed for other reasons, ie, if the switching transistor in the pacemaker fails to prevent continuous DC voltage from being applied to the stimulating electrode. However, switches are usually more reliable than capacitors, especially in integrated circuit pacemakers.

The pacemaker of FIG. 1 is shown more specifically than the conventional pacemaker shown in FIG. 2, and although all of the components necessary for pacemaker operation are shown, Some are simply shown as blocks as they are well known to those skilled in the art. Stimulatory and neutral electrodes STIM and IND are connected to leads 66 and 64, respectively, with a similar Zener diode 70 placed across them. Second
Unlike resistor 23 in the figure, resistor 62 is typically
100K ohm high impedance element,
It is not used to recharge the storage capacitor. Capacitor 68 of FIG. 1 serves the same function as capacitor 68 of FIG. 2, which is a filter capacitor for a 3 volt power supply. 1st
The illustrated capacitor 36 is a storage capacitor that, when discharged, causes a pacemaker pulse to be output. All of the charge applied to the stimulation electrode is output from this capacitor 36. Therefore, two 30 μF capacitors 15 and 25 are used in the conventional circuit of Figure 2.
I am giving a series capacitor equivalent to 15μF,
Capacitor 36 only requires 15 μF. This capacitor 36 is charged to twice the battery voltage as will be explained below, and as with the two 30 μF capacitors in the circuit of FIG.
Outputs stimulation current pulses with the same shape. Capacitor 30 in FIG. 1 is a very small pump capacitor of 0.1 μF. This capacitor is used to inject capacitor 36 to a voltage equal to twice the supply voltage, as will be explained hereinafter.

Amplifier 48 is a conventional sense amplifier and responds to electrical activity within the heart, which detects natural heart beats. The output of timer 50 is normally low. Pacemakers are “on demand” (VVI) in that pacing pulses are generated only when requested.
mode). If timer 50 is set to 1 minute
If adjusted to provide a pacing rate of 60 heartbeats, the timer output will remain low as long as a natural heartbeat is detected at least once every second. However, whenever one second passes without a heartbeat occurring, the output of timer 50 is
High for 0.5ms. This results in the generation of a pacing pulse.

As long as the heart is beating normally and the output of timer 50 is low, the output of inverter 14 is at a high potential, enabling one input of NAND gate 12. The other input of gate 12 is connected to a 1KHz oscillator 10. The output of gate 12 is therefore pulsed alternately between high and low potentials at a rate of 1KHz. When the gate output is at a low potential, transistor 20 is kept on and transistors 18A and 18B are kept off. These latter two transistors 18A and 18B have conventional transmission gates and are controlled by inverter 16 to provide opposite potential levels to their gate terminals. The output of gate 12 is also connected to the input of level translator 40. This conventional device operates to output a low potential at its output when its input (output of gate 12) is at a low potential. Therefore, transistor 20 is on and transistors 18A and 18
When B is off, level translator and inverter 42 connects transistors 32A and 32
B remains on and capacitors 34A and 34B remain off. Current therefore flows from the positive power supply bus through transistor 20, capacitor 30 and transistors 32A and 32B to the negative bus, charging capacitor 30 and making the left side of the capacitor positive with respect to the right side.

The only reason for level translator 40 is that in order to completely turn off N-channel transistor 34B, its gate must be held at the most negative potential in the circuit. The most negative potential is not necessarily the potential of the V-bus. This is because capacitor 36 charges to twice the battery power supply, so the bottom of that capacitor is more negative than the V- potential of the negative bus. Therefore, the potential on the lower side of the capacitor 36 is extended to the level translator 40,
When the output of the NAND gate 12 is at a low potential,
The output of the level translator is the input of its two negative potentials, i.e. the V-potential or the capacitor 36.
is always the lower of the lower potentials.
When the output of NAND gate 12 is at a high potential, the output of level translator 40 is equal to the potential of the V+ bus.

The output of level translator and inverter 42 keeps transmission gate containing devices 34A and 34B off while transmission gate containing devices 32A and 32B are on.

Therefore, capacitor 30 is not coupled to capacitor 36 while capacitor 30 is being charged.

During the AC half cycle of oscillator operation, the output of gate 12 is at a high potential. The high potential applied to the gate of device 20 keeps the device off. Devices 32A and 32B are also off at that time, and conducting are devices 18A and 18.
B, 34A and 34B. As a result, V+
and capacitors 30 and 36 between V and bus,
Then there is a series connection consisting of two transmission gates. The charge on capacitor 30 is transferred to capacitor 36 and the voltage across capacitor 36 increases. The rise is step-like. Capacitor 30 is charged during an AC half cycle of operation.
During these cycles the charge on capacitor 30 is transferred to capacitor 36. Capacitor 30 is always charged such that its left end is positive with respect to its right end, so that each time a charge is output to capacitor 36, the bottom end of that capacitor 36 becomes negative with respect to its top end. Become. The voltage change across capacitor 36 becomes smaller and smaller as capacitor 36 charges, but in much less than one second capacitor 36 becomes charged to twice the battery power.

When the sense amplifier circuit determines that a pacing pulse is required, the output of timer 50 goes high for 0.5 milliseconds. The output of inverter 14 is at a low potential, and the output of gate 12 is at a high potential. This then translates into level translator 40
The output of gate 44 is brought to a high potential and one input of gate 44 is enabled. The other input of gate 44 is timer 5
0 and hence gate 4
The output of 4 is at high potential for 0.5 milliseconds. The output of its gate 44 is connected to the gate of transistor 38, so that this transistor conducts and the charge on storage capacitor 36 is transferred to this device 38.
A current is applied to the stimulating electrode through the heart tissue and to the V+ power supply through the neutral electrode. The duration of this pulse, the time during which capacitor 36 is discharged, is 0.5 milliseconds, since that is the period during which the output of gate 44 is at a high potential. It should be noted that transistor 38 is a 50N device, which means that its on-resistance is so far less than the on-resistance of other possible transistors, by a factor of 50. When stimulation pulses are to be delivered to the patient's heart, very low resistance in the electrode leads is required, and for this reason transistor 38 is a large device.

During the time that the pacing pulse is being output, the output of gate 12 is at a high potential. Therefore capacitor 3
6 is connected to the stimulation electrode lead via transistor 38 as well as transmission gates 34A, 3
4B, capacitor 30, and transmission gate 18
It is also connected to the negative power supply bus through A and 18B. However, this is not important. This is because only a negligible current is directed from the stimulation electrode lead to the capacitor 30 due to the relatively small size of the capacitor 30.

Pulser 46 is triggered on the trailing edge of a 0.5 millisecond positive pulse applied to its input. When the pulser is triggered, it generates a negative pulse whose duration controls the duration of shorting the electrode leads 64, 66 and is therefore stored in the distributed capacitor at the electrode/electrolyte interface. The accumulated charge can be recovered. The output of the pulse is applied to the gate of transistor 60, and the device turns on when the pulser output goes low. Transistor 60 is also large and has a very low on-impedance so that the fastest discharge, or recovery of allocated capacity, occurs through the shorted electrode leads. As soon as the pulsar output becomes high potential again, transistor 60 turns off. The period of electrode lead shorting is independent of capacitor 36 recharging. At the end of the 0.5 millisecond pacing pulse, the output of gate 44 is at a low potential, so transistor 38 is turned off. This is 2
isolate one electrode lead from the rest of the circuit,
Capacitor 30 in preparation for another pacing pulse
Start charging.

While the two electrode leads are shorted together,
It should be noted that sense amplifier 48 is inactive. Although not shown, this amplifier responds to a potential difference between the stimulus and neutral leads;
While they are shorted together, sensing operation is disabled. An absolute refractory period of approximately 100 milliseconds is desired for a typical demand-type pacemaker. The sense amplifier should not detect cardiac activity resulting from the stimulation pulse itself, nor should the stimulation pulse be detected or interpreted as a natural heart beat. Refractory period control is "automatic" in that no additional circuitry must be provided to disable the sense amplifier while the leads are shorted together. For regular VVI pacemakers,
The pulse period at the output of pulser 46 is 300 mm,
It can be adjusted to be as high as seconds. In other cases where a short refractory period is desired, the pulses should be shorter. As mentioned above, pulses on the order of 8 milliseconds effectively result in total charge recovery.

The importance of low "on" impedance for transistor 60 should be appreciated. Even if the transistor is kept on for 300 milliseconds, it is necessary to quickly recover the charge. One of the problems with conventional pacemaker circuits, as mentioned above, is that during actual charge recovery, there is leakage from the allocated capacitance, and the leaked charge is not recoverable. Conventional circuits unnecessarily create opposing ion flows that serve no practical purpose other than controlling zero net current through the electrodes, which is not useful in itself. In the circuit of Figure 1, the charge balancing process is passive (charge shorting) rather than active, so that no charge leaks out of the distributed capacitance at the electrode/electrolyte interface, and the opposite ion While not unnecessarily compensating for flow, it is also desirable to minimize charge leakage. For this reason, most effective shorting of the electrode leads is desired, and this is achieved by providing a very low "on" impedance to device 60.

Both switches 38 and 60 should have an "on" impedance of less than 200 ohms. These switches, as well as condenser pumps, are part of a pending patent application filed by the applicant on the same date as the present application entitled "Direct Coupled Output Stage for Rapid Signal Biostimulators." Further details are provided in Application Serial No. 1, which is incorporated herein by reference.

Although the invention has been described with respect to a particular embodiment, it should be understood that this embodiment is merely illustrative of the application of the principles of the invention. Many changes may be made and other arrangements may be devised without departing from the spirit of the invention.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a cardiac pacemaker according to an embodiment of the present invention, and Fig. 2 is a circuit diagram showing a conventional typical pacemaker.
FIG. 2 is a circuit diagram partially showing the output stage of an AC-coupled pacemaker. In the figure, 10 is an oscillator,
12 is a NAND gate, 14, 16 and 42 are inverters, 18A, 18B, 20, 32A, 3
2B, 34A, 34B, 38 and 60 are transistors, 30, 36 and 68 are capacitors, 4
0 is a level translator, 44 is a gate, 46
48 is an amplifier, 50 is a timer, 62 is a resistor, 64 and 66 are electrode leads, 70 is a Zener diode, and 72 is a voltage source.

Claims (1)

[Scope of Claims] 1. A battery power source, a pair of electrodes for applying stimulation pulses to the patient's heart, a sensing device connected to at least one of the electrodes for sensing the operation of the heart, and a storage capacitor. a device and a connecting device responsive to the sensing device to determine the need for a stimulation pulse and responsive thereto to connect the storage capacitor device across the electrode to provide a stimulation pulse to the patient's heart; an apparatus for charging the storage capacitor from the battery power supply following applying a stimulation pulse to the patient's heart; and directly coupling the electrodes to each other following applying a stimulation pulse to the patient's heart. a coupling device operative to allow charge accumulated at an interface between the electrode and the patient's tissue as a result of the stimulation pulse to be largely recovered through the electrode, independent of the battery power supply; A pacemaker for the heart. 2. The cardiac pacemaker of claim 1, wherein the coupling device operates for a period of time within the range of 0.01 to 400 milliseconds. 3. The connection device removes the storage capacitor device from the electrode simultaneously with the operation of the coupling device,
3. A cardiac pacemaker as claimed in claim 2, wherein the storage capacitor device is therefore capable of being charged from the battery power source while charge stored in the patient's heart is being recovered through the electrodes. 4. The cardiac pacemaker of claim 2, wherein the coupling device shorts the electrodes together. 5 an electrode device for providing a stimulating current to the patient's heart, a sensing device for sensing the movement of the heart, and responsive to said sensing device to determine the need for the stimulating current; a control device for causing a flow of the electrode device through the electrode device; and an enabling device operable, following operation of the control device, to enable passive discharge of the distributed volume within the patient's heart. pacemaker. 6. The enabling device is operated for a time period in the range of 0.01 to 400 milliseconds.
Cardiac pacemaker as described in Section. 7. A cardiac pacemaker as claimed in claim 5, wherein the electrode arrangement consists of two electrodes, and the enabling device is operative to short the two electrodes together. 8. The cardiac pacemaker of claim 5, wherein the pacemaker is energized from only one voltage source and the control device is operative to cause current flow in only one direction through the electrode device. 9. The cardiac pacemaker of claim 5, wherein the sensing device is connected to the electrode device to disable sensing of cardiac motion while the enabling device is operating. 10. Claim 9, wherein the enabling device operates for a time period within the range of 0.01 to 400 milliseconds.
Cardiac pacemaker as described in Section. 11. The cardiac pacemaker of claim 10, wherein the electrode device comprises two electrodes, and the enabling device is operative to short-circuit the two electrodes together. 12. The cardiac pacemaker of claim 11, wherein the pacemaker is energized from only one voltage source and the control device is operative to pass current through the electrode device in only one direction. 13. A biological tissue stimulator for applying a rapidly changing signal to a site to which a minimum net charge is to be transferred, the device comprising: an electrode device for applying a stimulating current to said site; A biological tissue comprising: a control device for causing a stimulating current to flow through said electrode device; and, following operation of said control device, a device operative to enable passive discharge of a distributed capacitance at said site. Stimulator. 14. Claim 13, wherein the enabling device operates for a time period in the range of 0.01 to 400 milliseconds.
The biological tissue stimulator described in . 15. The biological tissue stimulation device of claim 13, wherein the electrode device comprises two electrodes, and the enabling device operates to short-circuit the two electrodes together. 16. The biological tissue stimulator of claim 13, wherein the stimulator is energized from only one voltage source and the control device is operative to pass current through the electrode device in only one direction. 17. Claim 13, wherein the control device is inoperable while the enabling device is in operation.
The biological tissue stimulator described in . 18. The enabling device is operated for a time period in the range of 0.01 to 400 milliseconds.
The living tissue stimulation device according to item 7. 19. The biological tissue stimulation device of claim 18, wherein the electrode device comprises two electrodes, and the enabling device is operative to short-circuit the two electrodes together. 20 The stimulator is energized from only one voltage source;
Claim 1, wherein the control device is operative to cause current to flow in only one direction through the electrode device.
The living tissue stimulation device according to item 9. 21 a pair of electrodes for passing a current through the site to stimulate the site where low net charge transfer is desired; a charge storage device; An output circuit for a living tissue stimulation device, comprising a connecting device connected in series with an electrode of the device, and a coupling device coupling the pair of electrodes to each other following operation of the connecting device. 22. The connecting device is connected between the charge storage device and one of the electrodes, and the coupling device couples the other of the electrodes to a connection point between the connecting device and the one electrode. An output circuit for the biological tissue stimulation device according to scope 21. 23. An output circuit for a biological tissue stimulation device according to claim 22, wherein the coupling device operates for a period of time in the range of 0.01 to 400 milliseconds. 24. The biological tissue stimulation of claim 23, wherein the stimulator is energized from only one voltage source and the charge storage device is connected to the electrode only when current flows in one direction through the electrode. Output circuit for the device. 25. The biological tissue stimulation of claim 22, wherein the stimulator is energized from only one voltage source and the charge storage device is connected to the electrode only when current flows in one direction through the electrode. Output circuit for the device. 26. An output circuit for a biological tissue stimulation device according to claim 21, wherein the coupling device operates for a period of time in the range of 0.01 to 400 milliseconds. 27. The biological tissue of claim 21, wherein the stimulation device is energized from only one voltage source and the charge storage device is connected to the electrode only when current flows in one direction through the electrode. Output circuit for the stimulator.