General and Local Heat Developed in Living Animal Body by Passage of High Frequency Currents.

Abstract

The present wide use of clinical diathermy has led us to a study of the deep heat produced in tissues by the passage of alternating currents of high frequency. Most of our experiments have been made on dogs anesthetized by the intravenous injection of barbital sodium. The deep temperature was measured by means of specially prepared thermocouples soldered to the tips of Luer needles which could be inserted into the body cavities. These thermocouples, which were of copper and constantan, were connected with a galvanometer through a constant temperature junction obtained by a thermos bottle thermostat as described by Clark. 1

The high frequency current was passed through the body by placing the electrodes usually on the sides of the shaved thorax. Great care was taken to have the electrodes parallel to each other and the thermocouple needles at right angles to the electrical field. This is very important, otherwise there is a concentration of current at the needle point which results in false readings. This source of error was excluded in all experiments. In some instances the temperature was measured by mercury thermometers as well. The current strength usually employed was between 1200 and 1500 milliamperes, with a concentration not greater than 100 milliamperes per square inch of electrode surface. Under these conditions no damage to the skin resulted.

The passage of such a current through a dog's thorax results in a general elevation of body temperature (rectal), with an equivalent rise of temperature in the lung. This is shown in Fig. 1. In this figure it is likewise shown that with the passage of the current the lung at first gradually warms more than the rectum, but later cools below the rectal temperature until the current strength is increased, when it again crosses the rectal temperature.