Magnetic tape recording electrocardiograph.

R ECORDING the electrocardiogram for prolonged intervals presents difficulties from the standpoint of economy and convenience. One 200 foot roll of paper for a direct writing instrument is used in 40 minutes of continuous recording at 25 mm. per second, and reviewing this long electrocardiographic record is a cumbersome procedure. A convenient method of recording electrocardiograms and fied electrocardiographic impulses. Figure 1 shows a block diagram of the apparatus which has been developed. Details of the circuit will be reported in a separate communication. Figure 2 is a photograph of the instrument. A differential amplifier is employed, which minimizes the effect of 60 cycle interference. A 250 cycle square wave carrier which is amplitude modulated is used. The frequency of the square