700 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



and valve motion are separable. We have attempted 

 such a separation in normals, but with little success. 

 It seemed possible that the technique of Reale et al. 

 (82) developed for the purpose of measuring valve 

 area in \ivo could t)e applied to this problem. They 

 suggested that the area of the tricuspid \al\e could be 

 measured in man if a balloon on a catheter in the 

 right ventricle was inflated and drawn back through 

 the valve into the atrium. The size that could be just 

 gotten back across the valve could then be used to 

 calculate valve area by reproducing the experiment 

 with the same volume in the balloon outside the body. 

 We felt that recording sounds, both within the heart 

 and on the thorax, when the balloon was in the valve 

 orifice and preventing the valve from closing, but not 

 interfering with myocardial contraction (in the first 

 cycle), would allow for the separation of these two 

 events and cast some further light on the first sound. A 

 few tries at this revealed the technical difficulties in- 

 volved and no conclusive results were obtained. How- 

 ever, further experimentation along this or similar 

 lines might well reveal some interesting information. 



SECOND HEART SOUND. The sole mechanical event that 

 can be related to the second heart sound is the closure 

 of the semilunar valve. Since both closing of the atrio- 

 ventricular valve and opening of the semilunar valve 

 are considered to play a part in the make-up of the 

 first sound complex, there would appear to be no 

 physiological reason to limit tiie second heart sound 



SOUNDS 



0. snd 



FIG. 2. Suggested mechanism of third sound indicating 

 transient A-V valve closure. The pressures are of ventricle and 

 atrium. Only that part of the cycle from shortly after the closure 

 of the semilunar valve (not shown here) to mid-diastole is 

 shown. The \cntricular pressure falls below atrial pressure at 

 which time the atrioventricular valve opens as indicated on the 

 sound tracing as the time of the opening sound (o. snd). Early 

 in diastole the ventricular pressure according to this suggested 

 mechanism rebounds at which time the protodiastolic sound 

 (3) occurs. The dotted line is the normal course of the ventricu- 

 lar pressure. [Adapted from the work of Warren el al. (102).] 



to closure of the semilunar valve and not include the 

 immediately following event of opening of the atrio- 

 ventricular valve. However, traditionally, opening of 

 the atrioventricular \alve, if audible or even if only 

 seen on a phonocardiogram, is not considered part of 

 the second heart complex. It will not be considered so 

 here. Again, in the case of the second sound, the evi- 

 dence that acoustics is closely related to valve motion 

 is strong. For example, the absence of the semilunar 

 valve or its failure to close when disease is present is 

 associated with absence of the second sound. 



THIRD HEART SOUND. Although the relationship be- 

 tween valve motion and acoustics can be demonstrated 

 for the "systolic" sounds (i.e., first and second sounds), 

 the precise physical correlate for the "diastolic" 

 sounds (i.e., third and fourth sounds) remains the 

 subject of vigorous investigation. Both of these sounds 

 occur at periods of rapid ventricular filling. The earlier 

 third heart sound occurs during the initial rapid filling 

 phase when the ventricle fills passively in relation to 

 the atrioventricular gradient. The latter, fourth sound, 

 occurs during the second phase of rapid filling, when, 

 near the end of ventricular diastole, the ventricle re- 

 ceives additional blood by acti\e atrial contraction. 



For the third heart sound it has long been held that 

 the vibrations heard are those set up by the motion of 

 the mass of ventricular muscle (along with the blood) 

 caused by the rapid inrush from the atrium (77, 104). 

 The time of occurrence of the sound, at the end of the 

 rapid filling phase (46-48) fits with the concept that 

 the sound is associated with or caused by the "check- 

 ing" of ventricular motion, as it reaches the limit of 

 free distensibility. 



In recent years, this mechanism has been chal- 

 lenged. It has been shown that at the end of the rapid 

 filling phase, \entricular pressure may transiently rise 

 above atrial pressure, thus setting the stage for tran- 

 sient closure of the atrioventricular valve (27, loi, 102) 

 (see fig. 2). From this observation it has been suggested 

 that, like the first and second sounds, the third sound 

 is the product of \alve closure. At the present time, it 

 does not appear that all investigators agree as to 

 what part \alve motion and/or \entricular "checking" 

 play in the causation of the vibrations that produce a 

 sound in early diastole, both in the normal and in dis- 

 ease. In our own studies we have observed a sound in 

 early diastole when it would appear that \entricular 

 pressure did not rise above atrial pressure, but we 

 have also seen situations in which there was a marked 

 rebound of ventricular pressure early in diastole cer- 

 tainly great enough to carry it above atrial pressure 



