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HANDBOOK OF PHVSIOLOGV 



CIRCULATION I 



tation from the work of Braunvvald et al. (lo), shows 

 the order of mechanical acti\ity of the four chambers. 



Whereas the electrical activity and mechanical ac- 

 tivity of the atria begin first on the right side, the elec- 

 trical and mechanical activity of the ventricles begin 

 first on the left. Since the initial depolarization is on 

 the left side of the interventricular septum (72, 8g), 

 considered to be part of the left ventricle, it is not un- 

 reasonable, therefore, that mechanical activity begins 

 first on the left. However, whereas the onset of me- 

 chanical activity occurs first on the left side, ejection 

 begins first on the right side. With these two pieces of 

 information it is possible to construct the order of 

 events of \alve motion at the onset of systole and from 

 the order of the acoustic e\ents of the first sound com- 

 plex. As stated, the first event is the onset of left 

 ventricular contraction, followed by the onset of right 

 ventricular contraction, then right \entricular ejec- 

 tion begins, followed, finally, by the onset of left \en- 

 tricular ejection. From this, the order of valve motion, 

 and the four apparent components of the first heart 

 sound complex would be : closure of the mitral valve 

 (MC), closure of the tricuspid valve (TC), opening of 

 the pulmonic valve (PO), and the opening of the 

 aortic \'alve (AO) (64, 67). What relationship these 

 four separate events bear to the make-up of the first 

 sound complex, as seen in the usual chest phonocardio- 

 gram, remains to be determined. Classically, four 

 sets of vibrations have been described for the first heart 

 sound complex as seen in the chest phonocardiogram 

 (77) and it might seem at first that a ready explana- 

 tion is available, since there are four distinct valve 

 motions. This, however, has not been the classical 

 explanation. Moreover, although there may be several 

 sets of small vibrations, the major ones most often 

 appear to be only two in number. Our thought in this 

 matter has been that most often the first loud vibra- 

 tion can be associated with closure of the mitral valve. 

 In the normal there appears to be difficulty in assign- 

 ing any given vibration to closure of the tricuspid 

 valve. Since the acoustic events from the left side of 

 the heart are louder than those from the right side, it 

 may be that valve motion of this side predominates in 

 the acoustic representation of the first sound. Again, 

 it is difficult to say what part opening of the pulmonic 

 valve plays in this. The physiological value of such a 

 precise mechanical-acoustical correlation resides in the 

 fact that proper identification of \alve motion at the 

 time of ventricular contraction provides a relatixely 

 simple way of quantitating the duration of isometric 

 contraction. 



Figure 3 also shows that the cessation of ventricular 



mechanical activity occurs first on the left side. Conse- 

 quently, it is to be expected that closure of the aortic 

 valve (AC) precedes closure of the pulmonic valve 

 (PC). From this asynchronous occurrence of semilunar 

 vahe closure it would be expected that there would 

 be two components to the second sound, and such is 

 the case. The importance of this observation rests in 

 the physiological correlates possible. First, the pres- 

 ence of two coinponents to the second sound identifies 

 the presence of two semilunar valves. Second, proper 

 identification of the source of each component allows 

 for certain deductions about the state of affairs on that 

 side of the heart. Third, since conclusions made from 

 point two depend on the source of the acoustic event 

 and not on the site on the chest wall to which the 

 event is transmitted, they are more rigorous. Further- 

 more, consideration of this point leads to the conclu- 

 sion that terminology based solely on the site on the 

 chest to which the acoustic e\ent is transmitted is not 

 in keeping with the breadth of current knowledge and 

 deprives one of potentially valuable information. It 

 has, therefore, been suggested that the terminology re- 

 garding the second sound be altered to refer not to 

 location on the chest but to site of origin within the 

 heart (50). 



The information regarding the order of events of 

 atrioventricular \alve opening is small but it would 

 appear that the opening of the tricuspid valve pre- 

 cedes the opening of the mitral valve (67). This point 

 will be dealt with in more detail when the correlation 

 between the acoustic events and the jugular venous 

 pulse is discussed. It must also be stated that only a 

 small amoimt of information regarding the order ol 

 events with respect to the early diastolic sound in the 

 normal is available. Simultaneous ob.scrvations from 

 within each ventricle by Luisada and associates (64) 

 indicate that the third sound from the right ventricle 

 precedes that from the left. Our studies suggest that 

 the third soinid is not commonly observed within the 

 cavity of the right ventricle. 



In summary then, comparison of the order of events 

 of all I 2 of the theoretically possible normal sounds 

 indicates that starting vvith the depolarization of the 

 sinoatrial node there occurs: /) the right atrial com- 

 ponent of the fourth heart sound, 2) the left atrial 

 component of the fourth heart sound, 3) the mitral 

 valve clo.sure component of the first heart sound, 4) 

 the tricuspid valve closure component of the first heart 

 sound, 5) the pulmonic valve opening component of 

 the first heart sound, 6) the aortic valve opening com- 

 ponent of the first heart sound, 7) the aortic valve 

 closure component of the second heart sound, S) the 



