A Method Of Fibrillating A Heart And Apparatus Therefor

Abstract

Fibrillation of a heart by inducing arrhythmias in the heart muscle fibers separately and successively in small groups by the application of a multiple of low voltage electrical pulses across the surface of the heart. The flow of electrical current is concentrated along the outer surface of the heart. A fibrillator comprising pulse-generating means housed within a small casing having a pair of electrodes on the outer surface of the casing and connected operatively to the pulse-generating means, the fibrillator being in the form of a single self-contained unit and being sterilizable as a whole by introduction into a sterilizing zone.

Description

This invention relates to the stimulation of tissues, such as nerves and muscle fibers in human beings and in animals.

It is sometimes desirable to bring a heart into a state of fibrillation for surgery to take place. Also, it may be desirable to stimulate a bowel or bladder muscle, or a nerve.

According to the invention, a method of stimulating tissues includes the step of applying a multiple of electrical pulses to a number of different tissue fibers.

The electrical pulses may be of a low voltage, of the order of 1 to 10 volts. The pulses may last for periods of about 1 to 10 milliseconds. The pulses may be applied at intervals of about 10 to 50 milliseconds, and the energy input per pulse may be about 80 microwatt seconds.

In the following paragraphs the description will be directed specifically to the stimulation of hearts. It must be understood, however, that the method and the apparatus described may be employed also for stimulating fibers such as nerves and other muscles, e.g. smooth and skeletal muscles. The apparatus must therefore not be understood as being limited to use in the fibrillation of hearts.

Still according to the invention, a method of fibrillating a heart muscle includes the step of applying a plurality of electrical pulses to a number of different fibers of the heart.

The fibers may be disposed along the outer surfaces of the heart. The current path through the heart muscle may be short relative to the heart itself.

Further according to the invention, a method of fibrillating a heart muscle includes the steps of wiping a pair of electrodes across the surface of the heart and of applying successive electrical pulses to the electrodes.

Yet further according to the invention, a method of fibrillating a heart muscle includes the step of inducing arrhythmias in a number of different fibers of the heart. The fibers may be disposed along the heart surface.

Still further according to the invention, a tissue stimulator has a plurality of electrodes, and means for applying a number of electrical pulses to the electrodes.

The invention includes also a portable self-contained fibrillator, powered by dry cell batteries.

The pulses may be provided by electronic circuitry, such as a multivibrator, suitably energized. The circuitry may be energized by a battery, and the battery and circuitry may be sealed in a casing, thus providing a completely sealed unit independent of power leads. It may be in the shape of a small pear, the electrodes being provided at the small end. Alternatively, it may be of rod or wand or probe shape. The battery may be housed in one end constituting a handle.

The device may be provided with an automatic or attitude-sensitive switch, e.g. by a mercury or gravity switch which switches off automatically when the device is at rest or in a predetermined attitude, but is energized immediately as its attitude changes. Alternatively, the circuitry may be energized as soon as the resistance across the electrodes falls below a predetermined value.

The electrodes may be in the form of horseshoe formations disposed in closely spaced parallel planes. The spacing between electrodes may be of the order of 3 to 10 millimeters.

In applying electrical pulses to the heart muscle, current flow is restricted substantially to the heart muscle only.

For the hearts of human beings, it has been found that the duration of the electrical pulses advantageously are about 3 milliseconds. The time interval between pulses conveniently matches the speed at which wiping takes place so that successive pulses will be applied to the adjacent zones of the heart muscle. Thus if the time intervals between pulses are relatively short, the wiping rate may be high. And if the time intervals between pulses are relatively long, the wiping rate should be low.

The invention will now be described by way of example, with reference to the accompanying drawings.

In the drawings:

FIG. 1 shows a circuit diagram of a first embodiment of the invention having one type of pulse generator;

FIG. 2 shows a three-dimensional view of a fibrillator embodying the circuitry of FIG. 1;

FIG. 3 shows a side elevation of another embodiment of rod or wand shape;

FIG. 4 shows a section at IV--IV of FIG. 3; and

FIG. 5 shows a circuit diagram of the electrical circuitry of the embodiment of FIGS. 3 and 4.

Referring to FIG. 1 of the drawings, reference numeral 10 refers generally to circuitry for a fibrillator according to the invention. It comprises a power supply 12 which is fixed or removable, an attitude-sensitive switch 14, a pulse generator 16, and electrodes 18, which may be extendable or fixed as desired. The electrodes 18 are generally of horseshoe shape.

FIG. 2 shows one embodiment of fibrillator according to the invention. It comprises an outer case 11 of synthetic plastic material, in pear-shaped form. The various integers are indicated diagrammatically and in block diagram form inside. The power supply comprises batteries in a cavity which may be sealed by epoxy resin. This seal may be translucent and may be broken to replace batteries, whereafter resealing may take place again with epoxy resin or some other suitable sealing agent.

Referring now to FIGS. 3 to 5 of the drawings, reference numeral 110 refers generally to a fibrillator according to another embodiment of the invention. This fibrillator has a casing 111 of substantially rod shape having a handle portion 112 and a curved front portion 114 provided with a pair of electrodes 116 at its end.

In the handle portion of the casing there is a cavity 118 for housing a battery 120. The casing further has another cavity 122 for housing a multivibrator 124. This multivibrator is operatively connected to the battery 120 and to the electrodes 116.

The casing is made of nylon and the battery and multivibrator are sealed in. If the battery runs down, the seal may be broken and the battery replaced and the casing resealed. Alternatively, the battery may be rechargeable, connections being provided outside the casing for connection to a suitable charger.

In use, the fibrillator will be sterilized as a whole before use. When the electrodes are not connected via a patient's heart, the circuit has only a very small battery drain. However, as soon as the electrodes 116 are bridged by contacting a patient's heart or by any other suitable fashion, transistor T1 switches on the multivibrator T3--T3-and successive 3 millisecond 20 Hz. pulses appear across the electrodes 116.

In order to induce fibrillation in a heart, the contacts are placed in contact with the surface of the heart. Thereupon the electrodes are displaced or wiped across the surface of the heart at a steady rate. As soon as contact is made, the multivibrator generates the voltage pulses. These pulses, because of the wiping action, are applied to successive zones of the heart. These zones then go into excitation which results in fibrillation of the heart.

In the second embodiment of the invention described, the casing is stated to be of nylon. It will be understood, however, that the casing may be made of any suitable material which can be sterilized. This material may conveniently be a synthetic plastic material. Another example of a synthetic plastic material which is suitable, is polyvinylchloride.

It is an advantage of this invention that fibrillation can be induced in a heart muscle with very low power inputs. This is possible because the heart muscle fibers are fibrillated separately in small groups. This is in contradistinction to conventional fibrillation apparatus in which a massive pulse is administered to electrodes placed at opposite ends of the heart, for fibrillating all muscle fibers simultaneously.

The method according to the invention has the advantage that damage to the heart is less than with conventional apparatus because of the lower voltage used. Furthermore, the fibrillation induced in accordance with the invention is "smoother" than that obtained in conventional fashion.

The voltage pulses for inducing fibrillation into the hearts of human beings, conveniently have the following characteristics:

Pulse potential 1 to 10 volts.

Pulse duration 1 to 10 milliseconds.

Time interval between pulses 10-50 milliseconds.

A fibrillator according to the invention can be made to provide pulses having these characteristics.

In general broadly, therefore, a muscle or nerve stimulator includes a portable self-contained sealed device. Such a device can be so made and be of such materials that it can be sterilized as a whole. It can also be used by a surgeon without any technical assistance.

Claims

We claim:

1. A method of fibrillating a heart which comprises the steps of generating a multiple of low voltage electrical pulses, applying the pulses to a pair of closely spaced electrodes and moving the electrodes over the surface of the heart inducing arrhythmias successively to a number of different fibers across the heart.

2. A method as claimed in claim 1 in which the pulses have a potential of the order of 1 to 10 volts, last for periods of from 1 to 10 milliseconds, and are applied at intervals of about 11 to 50 milliseconds.