PHONOCARDIOGRAPHY 



699 



valve is closed they are dissimilar. In the same way, 

 note that comparison of the atrial and ventricular pres- 

 sures reveals that they, too, are similar during the 

 period of time that the atrioventricular valve is open, 

 and are dissimilar when it is closed. This consideration 

 of similarity and dissimilarity will become important 

 when the subject of valvular pathology is discussed. 

 For, here, pressures that were similar ijccome dissimilar 

 and vice versa, and the degree of change is related to 

 theseverityof the valvular lesion, which, in turn, is re- 

 lated to the acoustic manifestations produced. 



It should be further noted that there are three posi- 

 tive (upward) deflections in the atrial tracing and two 

 negative (downward) deflections. With the onset of 

 mechanical activity of the atrium (mechanical systole) 

 there is a rise in the atrial pressure. This is the first 

 positive wave, the a wave, and it carries with it the 

 ventricular pressure curve. Early in mechanical ven- 

 tricular systole there is the second positive wave, 

 the c wave, cvurently ascribed to transmission of ven- 

 tricular pressure through the closed atrioventricular 

 \alve which at this point is said to be bulging back 

 into the atrium. This is followed by the first negative 

 wave, the x descent ascribed to the movement of the 

 atrioventricular ring away from the atrial cavity which 

 makes for a potential enlargement of the atrial cavity. 

 This explanation, it should be noted, has been chal- 

 lenged by Wood (107, p. 48). This is followed by the 

 gradual rise of atrial pressure as the atrium fills up to 

 the third positive wave, the v wave. At the time of the 

 opening of the atrioventricular valve the atrial pres- 

 sure falls along with the ventricular pressure and pro- 

 duces the second negative wave, the v descent. The 

 importance of these waves to acoustics will be con- 

 sidered in more detail when the subject of vahular 

 pathology is discussed. They also are of importance in 

 understanding the nature of the waxes of the jugular 

 venous pulse. 



With this abbreviated background of the natm'e of 

 the intravascular pressure phenomena, consider now 

 the factors that would be responsible for acceleration 

 and deceleration of blood at specific loci within the 

 cardiovascular svstem, and thereby result in vibra- 

 tions of blood and heart structures. Reference has al- 

 ready been made to the consideration of valves as the 

 major vibratory structures. A moment's reflection 

 will recall that many factors play a role in the manner 

 in which tlie valves move. For example, the closure of 

 the atrioventricular valve depends certainly on the 

 nature of the valve structure, on the chordae ten- 

 dineae, and on the papillary muscles. It surely is 

 dependent on the time course of mechanical ventricu- 



lar activity, on the state of the ventricle in the preced- 

 ing diastole, and on the contribution of atrial contrac- 

 tion to ventricular filling, and, undoubtedly, on other 

 factors too. The mere fact that all of these events con- 

 tribute to the manner of closure of the atrioventricular 

 valve suggests that perhaps some type of analysis of 

 this heart sound has the potential of yielding valuable 

 physiological information on these various factors. 

 We may never learn how to extract these data from 

 the first sound, or similar information from other 

 acoustic events, but to attempt to pinpoint cause and 

 effect, when the information is obviously so scanty, in 

 this author's opinion is nol helpful at present. 



FIRST HEART SOUND. Wlicreas it is true, therefore, that 

 no single structure can be considered to be vibrating 

 independently, it appears from our data and from 

 those of others that the first heart sound complex 

 occurs at the time of valve motion, during the period 

 of ventricular contraction. There is a component 

 which coincides with the closure of the atrioventricular 

 valve, and a second component associated with the 

 opening of the semilunar valve. These appear to be 

 the major components \isihle on a phonocardiogram 

 and represent the acoustic events that may be audible, 

 though not necessarily separable into two distinct 

 events. The relationship of the sound components to 

 valve motion becomes clearer when circumstances, 

 such as disease, alter the time at which the \arious 

 mechanical and acoustic events occur. For example, in 

 the normal, the beginning of mechanical activity of 

 the ventricle, the rise of ventricular pressure above 

 atrial pressure, and the closure of the atrio\ entricular 

 valve are very closely related in time. When there is 

 stenosis of the atrio\entricular valve, there is a readily 

 measurable gradient of pressure between atrium and 

 \entricle at the onset of mechanical activity of the 

 ventricle. It is possible in this situation to see that the 

 first component of the first sound complex occurs not 

 with the onset of mechanical activity of the ventricle 

 but rather with the rise of ventricular pressure above 

 atrial pressure. Of further interest in this regard is the 

 complementary observation that when the valve is 

 prevented by disease from closing as in the case of 

 atrioventricular regurgitation (or insufficiency), de- 

 spite the fact that mechanical contraction is forceful, 

 there may be no noticeable first component to the 

 first sound complex. The value of such observations in 

 disease is that they represent experiments of nature 

 not wholly reproducible in the human physiology 

 laboratory at this time, and permit a glimpse into the 

 situation in which contraction of the mvocardivim 



