DE2811325C2 - Cardiac surgery fibrillator - Google Patents

Description

The invention relates to a fibrillator for cardiac surgery with two application electrodes and one for Generation of fibrillation pulses specific pulse generator, as in the preamble of claim 1 outlined in more detail.

It is known that when the human body is exposed to low-frequency currents Corresponding strength or with direct current impulses the heart and other muscle fibers into a continuous one disorderly activity (fibrillation). It consists of rhythmic, but not synchronous Stretching and contractions of individual fibers, so that the function of the entire system is disturbed, e.g. B. Ventricular fibrillation.

In open heart surgery, this fact is used to induce ventricular fibrillation through electrical stimuli. For this purpose, electrodes with a ^{surface area of approximately 1 cm 2 are} attached to two points on the surface of the heart and a 50 Hz voltage is applied to the electrodes. The electrical current stimulates and depolarizes a large part of the heart muscle at the same time. At the same time, the impulses that normally reach the heart depolarize the endocardial surface. The interlocking of the two processes results in an irregular depolarizer !, which puts different zones of the myocardium into different states of excitement and is responsible for fibrillation. To achieve this, high current densities are required, since a sufficiently large area must be depolarized. Up to 10 volts are required to achieve fibrillation. For one smooth complete fibrillation, the tension has to be increased with this method. Included however, there is a risk that the myocardium will be damaged.

To generate fibrillation, the electrodes are either briefly attached to the surface of the heart Brought into contact or connected to the surface of the heart during the entire surgical phase.

Corresponding devices that are battery-operated and thus operate independently of the mains are already known

For example, in "Medical and Biological Engineering", July 1975, pages 586 and 587, a battery-operated one Cardiac fibrillator of the type mentioned above.

This contains two pairs of mutually complementary transistors that have a relatively complicated one Network that also contains two operational amplifiers that are connected to each other and to the batteries. In addition to the operational amplifiers, the device contains another thermistor and a bridge rectifier. The device is therefore very complex in terms of circuitry. This is also expressed in the fact that the entire Circuit must be housed in a box-shaped housing, from which the electrodes means long lines. The well-known fibrillator is therefore, due to the complex Circuit, relatively unwieldy.

From US-PS 36 50 275 a device is known also for the purpose of stimulating one Body muscle is created. It is about however, not around the heart muscle, but the anal sphincter muscle. A-jch this device has two pairs transistors complementary to each other and it is also battery operated. However, also falls here as a disadvantage that the circuit is relatively complex as a whole. So is in addition to the two transistor pairs with the network connecting these an additional circuit is provided which has a unijunction transistor Also in this case the device is used for Voltage generation spatially separated from the application electrodes and with a longer duration flexible lines connected.

The invention is based on the object of providing a fibrillator for cardiac surgery of the type mentioned at the beginning Kind to provide, which is characterized by a simple circuit structure and a Characterizes the least possible expenditure on circuit components and can thus be manufactured as a small, handy, fully sterilizable device.

So this object is achieved according to the invention solved that each transistor of the first transistor pair via its collector electrode directly with the base electrode excluding the complementary to it Transistor of the second transistor pair is connected, its emitter electrodes each with opposite poles of the series connection of the batteries and its Collector electrodes both with each other and via a capacitor with the base electrodes of the first Transistor pair as well as with the one application electrode are connected, while the other The application electrode is led to the center tap of the series connection of the batteries,

The proposed circuit structure is thus very simple, and apart from the two Transistor pairs is another use of expensive and potentially fragile circuit building blocks not provided. The space requirement of this circuit is so small that the new fibrillator as a whole as a small,

pen-shaped, mains-independent device in the form a surgical set with built-in electrodes can be performed. So it can be how treat such surgical instruments, especially keep them fully sterilized at the operating table. the Handy embodiment enables a quick stroke of the heart muscle, with a stimulation takes place in several places of the heart muscle and thereby the fibrillation is achieved with certainty. The new fibrillator is very economical in terms of power consumption, because it only switches on automatically when the electrodes are placed on the surface of the heart. Furthermore he is short-circuit proof.

Another possible embodiment of the fibrillator is given by the dependent claim.

An embodiment of the invention is shown in the figures and will be described in more detail below described. It shows

F i g, 1 an electrical circuit diagram of the new fibrillator,

F i g. 2 a complete fibrillator in the form of a surgical instrument.

In Fig. 1, the emitter electrodes of two complementary transistors T \ and 73 are connected to one another via a diode D _x , Di each and are connected to the center tap O of two series-connected batteries U _x , U ₂ via a resistor R \ . The base electrodes of the two transistors Tj and T ₃ are also connected to one another and connected via a capacitor Q to the interconnected collector electrodes of two subsequent transistors Ti, Ti ₁ , which are also complementary to one another. The transistor Ti is complementary to the transistor T _x and Tt is complementary to T ₃ . The base electrode of the transistor Ti is connected to the collector electrode of the transistor Ti, the base electrode of the transistor T * is connected to the collector electrode of the transistor T ₃ . The emitter electrodes of the transistors T ₂ , T * are connected to the plus and minus poles of the series-connected batteries U _x and U ₂ . A resistor Ri can be placed between the base and emitter electrodes of the transistor T _1. The electrode E _x , which, like the electrode E _{2, is applied} to the surface of the heart, which represents a resistor Rh , is led to the connection of the two collector electrodes of the transistors T ₂ and 7}. The electrode Ei is at the center O of the series circuit of the both batteries U ₁ and U ₂ .

FIG. 2 shows a complete fibrillator in the external form of an L-shaped surgical instrument. The short leg 5 contains the electrodes E \ and £ 2. The generator is accommodated in a hollow cylinder 4 made of insulating material. The long leg 6, which is preferably made of metal with a flat-ground surface, contains the batteries U _x , U ₂ .

The electrical circuit of the fibrillator according to FIG. 1 works as follows: As soon as the heart comes into contact with the electrodes E _x , E ₂ , the capacitor C _x discharges via the heart resistance, which is represented by the resistance Rh , assuming that the capacitor C _{x is} opposite the reference potential at the center tap O at the time of contemplation

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is negatively charged by the occurring - flows

a current in the base electrode of the transistor 71, whereby the transistor T ₂ becomes conductive. The capacitor C _x is thereby positively charged (positive feedback effect). When the charging is finished, - towards 0, the

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Transistor T _x blocks and thus a v.; H transistor T ₂ . The capacitor C _x discharges sicn vieder through the heart resistance Rh with reverse current direction, so that the transistors T ₃ and 7} are conductive until the capacitor C _{x is} negatively charged occurs at a frequency given by the size of the capacitor C _x

In the event of a short circuit at the output of the fibrillator, ie when Rh = O , the capacitor C _{x is} discharged and cannot be recharged since the transistors T ₂ and T4 block. When the short circuit is removed, the capacitor C _x slowly recharges due to leakage currents.

The resistor R _x is used to limit the current. A defined initial state, ie positive or negative charge on the capacitor Q in the idle state, can be achieved by optionally installing an additional resistor R ₂ between the base and collector electrodes of the transistor T ₂ or 7}.

If diodes D _x , D _{2 are} inserted into the emitter leads of the transistors T _x and Ti , these can be used in the form of light-emitting diodes for function control.

1 sheet of drawings

Claims (2)

Claims; 1. Fibrillator for cardiac surgery with two application electrodes and a pulse generator intended to generate fibrillation pulses, which contains two pairs of mutually complementary transistors, both the base electrodes and the emitter electrodes of the transistors of a first transistor pair with each other and the emitter electrodes of this transistor pair via a resistor are connected to the center tap of a series circuit of two batteries, characterized in that each transistor of the first transistor pair (T _x , Ti) is connected via its collector electrode directly to the base electrode excluding the transistor of the second transistor pair (Ti, T *) which is complementary to it, its emitter electrodes each with opposite poles of the series connection of the batteries (LJ _x , Ui) and its collector electrodes both with each other and via a capacitor (C _x ) with the base electrodes of the first transistor pair and mi t of the one application electrode (E _x ) are connected, whereas the other application electrode (E ₂ ) is led to the center tap (O) of the series connection of the batteries 2. Fibrillator according to claim 1, characterized in that the emitter electrode of one of the transistors (T ₂ , Ta) of the second pair is connected to the base electrode of the transistor via a further ohmic resistor (Ri)