THE PHONOCARDIOGRAPHY OF HEART MURMURS PART I. APPARATUS AND TECHNIQUE

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Abstract
Because the standard instrument for phonocardiography was incapable of recording the majority of relatively high pitched systolic and diastolic murmurs, a new apparatus was constructed, consisting of a crystal microphone, a 2-stage valve amplifier, and a Cambridge double-string Einthoven galvanometer. One fiber of this galvanometer is used for the ecg. in the normal way; the other, which is used for the phonocardiogram, is tightened to its full extent in order to raise its high-frequency response. In this condition its sensitivity is about 1 mv./mm.

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