Selective Synchronous Recording of the Batlistocardiogram and Electrocardiogram on a Single Channel

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Abstract
Identification of ballistocardiographic waves is difficult unless reference can be made to another simultaneously recorded event in the cardiac cycle. By hooking up an electrocardiographic lead in parallel circuit with the ballistocardiograph and interposing a rheostat of variable resistance in series in one of the electrocardiographic lead wires, the electrocardiogram may be selectively tuned in or out of the circuit. At resistances of 50,000 to 100,000 ohms the QRS complex appears only as a small spike preceding the ballistocardiographic waves and readily permits their identification. This simple expedient renders unnecessary the use of multiple recording channels in clinical ballistocardiography.