Synchronous Heart Sound Recording by Application of a Second Channel to the Cossorrobertson Cardiograph.

By using a microphone to provide the input, the standard Cossor-Robertson cardiograph can be used to record heart sounds instead of the electrocardiogram, but such a record is of little value unless it is recorded synchronously with an electrocardiogram. For this purpose two separate recording channels are necessary. The double-beam cathode ray tube with two amplifying channels has been developed by Donovan (1943). With the addition of stationary spots and a moving-film camera to avoid loss of focus and definition due to curvature of the tube face, this is the method of choice. The possibility of replacing the standard singlebeam tube of the Cossor-Robertson cardiograph with a double-beam tube was therefore investigated, but unfortunately it was found that the necessary alterations involved almost complete rebuilding of the instrument. It is possible, however, to record simultaneously two different wave forms with a singlebeam tube by using two valve amplifiers and an automatic switch which connects their outputs alternately to the single deflecting plate of the tube. The effect which this gives is illustrated in Fig. 1. If the switching rate is sufficiently high the gaps in the traces become small com-