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Med. & bioL Engng. Vol. 9, p. 143. Pergamon Press, 1971. Printed in Great Britain
TECHNICAL NOTE
T H E E L E C T R O - A C O U S T I C S T E T H O S C O P E ; A N I N S T R U M E N T F O R T H E
S I M U L T A N E O U S A U S C U L T A T I O N O F H E A R T S O U N D S A N D A U D I O S I G N A L S *
WITH the advent of electrical devices such as the doppler- cardiophone (ABELSON, 1968), oscillophone (ABELSON et aL, 1971) and electrocardiophone (GREEN, 1967), which present various cardiac phenomena in terms of audible signals, the need frequently arises for a time-marker to assist in the identification of the different signals at the bedside. For this purpose the heart sounds are superior to the carotid pulse, because (1) there is no pulse delay time, and (2) there are two reference points instead of one,-- the second sound, for example, is particularly useful in identifying the diastolic signal heard with the doppler- cardiophone.
Figure la shows a simple modification of the standard stethoscope which enables the physician to listen to heart sounds and electrically produced signals simultaneously. The two metal tubes of a 'Telex' headset are sawn off, leaving about 1 in. of tubing projecting. The unit is then connected to both sides of the main 'Y' limb of the stethoscope, using two metal connectors and two short lengths of rubber tubing. In this way the acoustic path- way from the stethoscope chest-piece to both ears remains uninterrupted.
In use the stethoscope is placed on the chest at a point where the two heart sounds can be heard most distinctly, and the transducer (e.g. Doppler probe) is placed at the point selected for study. The volume control of the electronic device is adjusted so that the signals are loud enough for interpretation without drowning the heart sounds.
When two electrical signals are to be monitored
simultaneously, a second unit is incorporated in the tubing (Fig. lb). If desired, a clip can then be placed on the left limb from one unit and the right limb from the other, diverting most of the sound to the right and left ears respectively. This 'acoustic mixing' is also suitable for listening to stereophonic tape recordings (of heart sounds and Doppler signals, for instance), and may be preferable to electronic mixing circuits, in which com- patibility requirements must be considered.
Acknowledgement This work was supported by the John A. Hartford Foundation.
DENIS ABELSON t Department o f Clinical Cardiology Royal Postgraduate Medical School London W.12, England
REFERENCES
AnELSON, D. (1968) Ultrasonic Doppler auscultation of the heart; with observations on atrial flutter and fibrillation. J. Am. med. Ass. 204, 438--443.
AnEt.SON, D., SLTLLrVA~, J. and Fox, J. G. C. (1971) The oscillophone; an instrument for the audible registration of the apex beat or peripheral pulses. Med. biol. Engng 8, 145.
GREEN, H. L. (1967) The electrocardiophone. A new instrument for rapid bedside diagnosis of cardiac arrhythmias. Circulation 36, 975-979.
* Received 3 November 1970. t Present address: Lankenau Hospital, Lancaster and City Line Avenues, Philadelphia, Pennsylvania 19151, U.S.A.
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