The Bell System Technical Journal 



October. 1924 



"The Stethophone," An Electrical Stethoscope 



By H. A. FREDERICK and H. F. DODGE 



1. AcorsTic Stethoscopes 



ArSd'I.TATION is commonly practiced by means of ilic 

 ordinary stethoscope, a device with which the physician is 

 al)ie to study sounds produced within the heart, lungs, f)r other por- 

 tions of the btxly and to determine whether such abnormal con- 

 ditions exist as are evidenced by abnormal sounds. Of particular 

 importance are the characteristics of the normal heart sounds, heart 

 murmurs, breathing sounds and rales.' It is well known that the 

 intensity of certain of these sounds is not in itself of fundamental 

 significance, that, for example, certain very faint murmurs may 

 represent serious organic lesions; hence it is of pathological im- 

 portance that these sounds be heard and understood. 



Most acoustic and mechanical \ibratory systems introduce dis- 

 tortion by discriminating in favor of certain frequency bands. Ex- 

 treme distortion may alter a sound beyond recognition. If a mod- 

 crate amount of distortion is unavoidable, it may be possible to 

 control it judiciously so as to give most accurate reproduction in 

 the frequency region of major importance. 



From this standpoint it is of interest to consider the fre(|uency 

 characteristics of the two common types of stethoscopes shown in 

 Figs. 1 and 2. The stethoscopes used in these tests were equipped 

 with thick-walled soft rubber tubing such that the distance from 

 the chest piece to the ear pieces was approximately 55 cm. The 

 characteristic of the open bell stethoscope was obtained by picking 

 up sound from the surface of a piece of fresh beef and measuring 

 the relative intensity of sound on a condenser transmitter- with antl 



' The presence of any one of several types of lesions in or near the valves of the 

 heart "gives rise to etldies in the bloofi current and thereby to the almornial sounds 

 to which we give the name murmurs." "So one of the various blowing, whistling, 

 rolling, rumbling or piping noises to which the term refers, sounds anything like 

 a 'murmur' in the ordinar>- sense of the word." (R. C. Cabot — Physical Diagnosis, 

 pp. 182-,?, \')2i.) 



"The term 'rales' is applied to sounds produced by the passage of air through 

 bronchi (windpipes! which contain mucus or pus, or which are narrowed by swelling 

 of their walls." i R. C. Cabot— Physical Diagnosis, p. 163) Rales niay appear 

 either as bubbling sounds, occurring singly or in showers, or as musical squeaks 

 and groans. 



• E. C. Wente, "The Sensitivity and Precision of the Electrostatic Transmitter 

 for Measuring Sound Intensities," Phys. Rev. 19, No. 5, p. 498, 1922. 



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