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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



sharply into heart sounds and heart murmurs, it would 

 seem wise, at the outset, to define our terms. To the 

 uninitiated and to the musically inclined everything 

 seems reallv to be noise and, indeed, it is. The division 

 into sounds and murmurs, howe\-er, not only is useful 

 clinicallv and physiologically, but also has some basis 

 in fact, in that it appears that they are caused by 

 different mechanisms, as will be discussed below. 



PHYSICAL BASIS FOR THE PRODUCTION OF HEART SOUNDS 



The phvsical factors responsible for the genesis of 

 heart sounds have always been and continue to be 

 an intriguing question for both physiologists and 

 clinicians. It must be admitted that despite the great 

 interest displayed in this subject and the wealth of 

 available published material, there is no explanation 

 universally agreed upon. Many conclusions about 

 cause and effect in heart sound production have been 

 based upon a consideration of those events of the 

 cardiac cycle that occur at the time of the particular 

 acoustic event tmder .scrutiny. Although such evidence 

 is necessary to prove cause and effect, it is, however, 

 not sufficient. A great deal of dispute has arisen per- 

 haps from a desire on the part of many investigators 

 to pinpoint one single responsible factor to the exclu- 

 sion of all others. The ingenious experiments of Dock 

 (24-26) have pointed toward the valves as the major 

 vibratory structures responsible for the production of 

 \'ibrational energy sufficiently great to be audible. 

 Rushmer (86) has rightly pointed out that, "Since the 

 chambers of the heart are filled with blood, none of 

 these structures can vibrate independenth- without 

 producing movements of the blood. Similarly, vibra- 

 tions in the blood must be transmitted to the surround- 

 ing structures. If the sounds can be picked up from the 

 external surface of the body, all structures between the 

 heart and thoracic wall must be vibrating." 



Whereas no unified thesis for all heart sounds ap- 

 pears wholly justifiable at this time, it seems likely 

 that the genesis of sounds is related to the acceleration 

 and deceleration of the blood at specific loci within 

 the cardiovascular system, and that associated with 

 such velocity changes vibrations of blood and heart 

 structures are set up. As will be discussed below, each 

 sound is created by specific velocity changes and 

 system vibrations based on the particular physiological 

 circumstances at that time in the cardiac cvcle. 



PHYSICAL BASIS FOR THE PRODUCTION OF MURMURS 



There is general agreement that the source of mur- 

 mur formation is the development of nonlaminar 

 blood flow. W'ith laminar flow, the fluid particles flow 

 miidirectionally downstream and all the energy is in a 

 direction parallel to the long axis of the vessel. Indeed, 

 the layer that adjoins the wall of the tube does not 

 flow. Consequently, there is no source for the develop- 

 ment of vibrations of either the fluid or the \essel in 

 which it flows. With the development of nonlaminar 

 flow, some of the particles move in directions other 

 than parallel to the long axis of the tube. These par- 

 ticles flowing, for example, at right angles to the long 

 axis of the tube (i.e., toward the wall), even flowing di- 

 rectly upstream temporarily, or in any direction, have 

 the potential of setting up \ibrations of the fluid and 

 of the vessel in which the\- are contained. When such 

 vibrations are in the audible frequency range of the 

 human ear they may be perceived as sound. 



For many years, physiologists have assumed that 

 the tvpe of nonlaminar flow responsible for murmur 

 genesis was turbulence. Turbulence, for this purpose, 

 may be described as a random distribution of those 

 energies not directed downstream parallel to the long 

 axis of the tube. The flow of the stray particles is 

 "irregularly irregular"; they show no pattern to 

 their "irregularity." This concept has recently been 

 challenged by Bruns (15). He found, in model experi- 

 ments, that there was insufficient energy produced by 

 these "irregularly irregular" stray particles to produce 

 audible noise. However, the development of non- 

 laminar flow with what might be called a "regular 

 irregularitv" (e.g., vortex formation) could yield 

 sufficient energy to produce \ibrations of the fluid and 

 of the vessel wall to create audible noise. One other 

 important source of nonlaminar flow was considered 

 and discarded ijy Bruns, namely, cavitation. Here he 

 suggested that whereas cavitation would yield suffi- 

 cient energy to cause audible noise, the hemodynamic 

 circumstances seen in vivo were insufficient to produce 

 cavitation. 



At the present time, one might take the following 

 position regarding the physical factors responsible for 

 the genesis of murmurs. Any circumstance that 

 changes the pattern of flow from laminar to nonlami- 

 nar has the potential for producing noise (i.e., mur- 

 mur). Nonlaminar flow is produced under conditions 

 where there is a disparity between the flow rate and 

 the tube (or vessel or chamber) size. Circumstances 

 that increase the flow rate (e.g., exercise, anemia, 

 shunts) or decrease the tube size (e.g., stenosis) or, 



