A Cardiovascular Injector

The use of peripheral angiography and selective angiocardiography has rapidly increased during the past few years. For the injection of contrast medium through a cardiac catheter, high pressures are needed, making the use of a power injector mandatory. Peripheral angiography and also cerebral angiography can be satisfactorily performed by hand, but with considerable radiation hazard to the operator if done repeatedly. Controlled pressure, exact timing, and protection from radiation can be achieved by means of a simple, automatic syringe. Commercially available manually-operated injectors do not deliver the high pressures required for selective cardioangiography, and the operator is exposed to secondary radiation during the time of injection. The rather expensive automatic power injectors are usually employed only for selective cardioangiography, since they are large, complicated machines which cannot be easily adapted for peripheral angiographic work. We have attempted to bridge this gap in available equipment by designing and constructing a simple portable injector suitable both for peripheral and cardioangiographic studies. In this power injector, as in almost all of the others, compressed gas is used to activate the piston in the pressure cylinder. Our inexpensive source of power is a carbon dioxide cartridge, of the type which is generally carried by drug stores for the preparation of charged water. These cartridges contain a fairly large amount of carbon dioxide under a pressure of approximately 750 pounds per square inch, depending on the room temperature. For operation of the injector, one cartridge is placed in the cartridge holder as shown in Figure 1(a) and perforated by the puncture needle. The desired pressure is selected and set by the reducing valve (b), which is directly mounted to the pressure cylinder. The force is then transmitted to the syringe at a power factor of 1.45. Since glass syringes do not withstand the required high pressures, a stainless steel syringe was constructed with a total capacity of 90 c.c. Perfect sealing of the piston is achieved by use of physiologically inert silicone-rubber piston rings, resulting in low internal friction. The syringe, after it has been loaded and the air has been expelled, as in the conventional glass syringe, is placed in the injector, which is kept at constant body temperature by a heating jacket (c) and thermoswitch. By depression of the three-way valve (d), the contrast medium is ejected; the stroke in the pressure cylinder is adjusted so that 20 C.c. of contrast medium remains in the syringe as a safety precaution against any possible injection of air. The x-ray exposure is triggered automatically by setting a spacer on the calibrated piston rod and can be started anywhere from the very beginning to the end of the injection period.