PHONOCARDIOGRAPHY 



697 



decrease the fluid viscosity have the capacity to 

 produce nonlaminar flow, which, in turn, has the po- 

 tential for producing noise. Whereas it appears that 

 we must abandon turbulence for vortex formation as 

 the type of nonlaminar flow responsible for murmurs, 

 perhaps more experimentation, especially in vivo 

 studies, ought to be carried out to confirm this opin- 

 ion. Furthermore, although the switch-over from 

 thinking "turbulence" to thinking "vortex formation" 

 is desirable for the sake of accuracy and for what addi- 

 tional data will follow from this, it may well be that, 

 in vivo, circumstances w hich produce vorte.x formation 

 simultaneously produce turbulence, as defined here. 



PHYSICAL BASIS FOR THE TRANSMISSION OF 

 SOUNDS AND MURMURS 



The information on the transmission of heart 

 sounds and murmurs is at present sketchy. It is only 

 with the development of techniques for recording the 

 various acoustic events from their site of origin that 

 any systematic study of this subject has been begun. 

 It must be kept in mind that we are not here using 

 the word transmission in the same sense as used by 

 the clinician. Clinically, the word transmission has 

 been used to signify those areas on the chest other 

 than the area of maximum intensity over which a par- 

 ticular event is heard. For example, one would say 

 that the murmur of mitral insuflicienc\' is heard 

 loudest at the apical region on the chest and is trans- 

 mitted to the left axilla. Such usage of the word 

 transmission is not in keeping with our present under- 

 standing and should be abandoned. Indeed, the 

 murmur of mitral insufficiency is transmitted from 

 its site of origin within the heart to both the apical 

 region of the chest and to the left axilla. 



It has been known for a long time that there are 

 areas on the chest wall to which the various acoustic 

 events are preferentially transmitted. For example, 

 all books on human cardiac acoustics show a diagram 

 indicating where the four valves are located within 

 the thorax, and, in addition, the areas on the thorax 

 to which events occurring at these valves are usually 

 preferentially transmitted. Thus, the aortic valve area 

 is at the upper right sternal border. The mitral valve 

 area is in the region of the apical impulse. The pul- 

 monic valve area is at the upper left sternal border, 

 and the tricuspid valve area is variously described at 

 the lower sternal border, right or left, or at the xiphoid. 

 Other sources of acoustics have their own preferential 

 areas. 



The factors responsible for this preferential trans- 

 mission to the chest wall are not completely under- 

 stood. First and foremost among the apparent causes 

 are the size and position of the heart in the thorax. 

 One can assign so-called valve areas on the thorax be- 

 cause in most patients tlie heart is in about the same 

 place in the thorax. Howe\er, important exceptions 

 occur so that this point must be kept in mind. For 

 example, in minor image dextrocardia, since the 

 position of the heart is a mirror image of the normal, 

 it is logical to expect that the chest wall areas are 

 also a mirror image of the normal, and such is the 

 case. Of importance too is the direction of blood flow. 

 This appears to be of greater importance for the 

 transmission of murmurs than for heart sounds, but 

 the extent to which each type of acoustic event de- 

 pends upon blood flow for its transmission remains to 

 be settled. Studies of murmurs from within the heart 

 by a number of groups demonstrate clearly that mur- 

 murs are, in the main, transmitted in the bloodstream 

 from their point of origin downstream and not up- 

 stream. Thus, for example, the murmur of aortic 

 stenosis created at the aortic valve during systole when 

 the blood is flowing away from the heart is transmitted 

 not only to the aortic area on the chest but also to the 

 neck. On the other hand, the murmur of aortic 

 insufficiency, created at the aortic valve during diastole 

 when blood is flowing abnormally back into the left 

 ventricle, is transmitted not only to the aortic area, 

 but often more loudly to the left sternal ijorder and 

 to the apical region. 



There are other factors known which determine 

 the transmission of .sounds to the chest. These affect, 

 bv and large, the over-all intensity and perhaps the 

 frequencv that reaches the chest wall and would ap- 

 pear to alter the distribution of noise on the thorax 

 only as they affect the above considered factors of 

 heart size, position, and direction of blood flow. The 

 presence of fluid in or fibrous thickening of the peri- 

 cardium may reduce the intensity of sound that 

 reaches the chest wall. It has generally been assumed 

 that this is due to interference with sound transmis- 

 sion, but interference with sound production has not 

 been ruled out. On two occasions we have had the 

 opportunity of studying the intracardiac sounds in pa- 

 tients with pericardial thickening. In neither did it 

 appear that the sound intensity within the heart was 

 diminished. However, the sound intensity on the 

 thorax in both cases was not remarkably reduced and 

 this point remains unsettled in our minds. 



The position and degree of aeration of the lungs 

 also seem to play a role in sound transmission. It has 



