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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



microphone was an adaptation of transducers used in 

 underwater detection of sound, in submarine warfare, 

 for example. About 1951 Soulie's group in Paris, 

 wliile working with a newly designed micromanom- 

 eter of the inductance type for registration of intra- 

 cardiac pressure, were impressed with its high- 

 frequency response. Vibrations in the auditory range 

 were recorded when frequencies Jjelow '^o cycles per 

 sec were cut out. 



Beginning with the carbon-granule microphone of 

 EinthoN'en, phonocardiographers have used a variety 

 of transducers. The crystal microphone was popular 

 for many years. The capacitance, or condenser, 

 microphone seems to have been first used in phono- 

 cardiography by Trendelenberg. Selection (1953) of 

 a condenser microphone of improved design (Altec) 

 for use in spectral phonocardiography has led to its 

 wide use in phonocardiography generally (8). 



THE NATURE OF THE PHENOMENON 



Physiologic Considerations 



Cardiovascular sounds tend to be divisible rather 

 sharply into two major categories: /) transients, 

 referred to as "heart sounds," and 2) more prolonged 

 noises, referred to as "murmurs,"' which may be 

 partially or purely musical. (Musicality is a subjective 

 quality which is said to be present when harmonic 

 organization is demonstrated by the spectral phono- 

 cardiogram. ) 



The heart sounds are considered to be the expres- 

 sion of hydraulic pressure transients associated with 

 abrupt deceleration, and in some instances perhaps 

 acceleration, in blood flow. For example, the first and 

 second heart sounds are mainly the result of \'alve 

 closure and more specifically the result of abrupt 

 deceleration of the local flow which is responsible for 

 coaptation of the valve cusps. 



Noisy murmurs are essentially the expression of 

 turbulence uf blood flow. The soft elements of the 

 heart and vessel walls undoubtedly interplas', in a 

 complex manner, with the hemodynamic phenome- 

 non.' 



In the generation of musical murmurs a specific 

 structural member, such as a pathologically altered 



' Bruns (3) suE;gests that vortex or wake formation rather 

 than turbulence is the mechanism of all murmurs. In this view 

 musical murmurs owe their harmonic organization to the 

 regular, periodic shedding of vortices in contrast to the unor- 

 ganized vortication in the generation of noisy murmurs. 



valve cusp, seems to be involved. The proper combina- 

 tion of hemodynamic factor and structural factor 

 seems essential for the periodic generation of \ortices' 

 resulting in musical murmurs. Unusually great 

 intensity is a feature of musical murmurs as a class. 



Physical Considerations 



The vibrations at the skin surface which are in the 

 audible range of frequency are of essentially the same 

 nature as the grosser precordial movements of lower 

 frequency accompanying and resulting from cardiac 

 action. It seems most accurate to view the generation 

 of cardiovascular sound as a setting into vibration, a 

 "shaking," if you will, of the blood and wall struc- 

 tures, and to consider the propagation of cardio- 

 vascular sound as the transmission of these vibrations 

 to contiguous structures lying between the site of 

 generation and the site of detection. Specifically, the 

 analogy to sound in air or even water, with alternate 

 zones of condensation and rarefaction, is probably not 

 appropriate. Although a rather philosophical one, the 

 question might be raised as to whether cardiovascular 

 sound is really sound, at least up to the point that the 

 vibrations we so designate are translated into sound 

 at the skin surface. Is the phenomenon recorded in 

 intracardiac phonocardiography "sound"? 



The record from sonic catheters is dominated by 

 pressure fluctuations in a rapidly flowing stream con- 

 taining obstructions. This flow is neither laminar nor 

 turbulent, but vortical, i.e., filled with small waves 

 and moving eddies, which excite a stationary pressure 

 transducer in passing. In addition to these dynamical 

 flow transients (of amplitude i to 10 mm Hg = 10^ 

 to 10^ dynes /cm'-), there should indeed be true sound- 

 pressure waves as well, at a much lower amplitude 

 (.001 to .01 mm Hg = 10 to 10- dynes/cm-) generated 

 by interaction of vortices with the walls. However, 

 these sound waves are all below the threshold (i mm 

 Hg) of existing sonic catheters. 



Another factor which distinguishes between cardio- 

 vascular sound and what sonic catheters record is the 

 great variation of the observed pressure pattern with 

 position; it changes rapidly within centimeters, both 

 across the lumen and up and down stream. Sound does 

 not behave this way, but travels as a compressional 

 wave largely unaffected by flow or, at these fre- 

 quencies, by turbulence. Thus within the right 

 ventricle, the catheter records predominantly the 

 tricuspid valve "sound" rather than the pulmonic, 

 showing that one senses here the fluid motion rather 

 than transmitted sound. An analogy would be to put 



