PHONOCARDIOGRAPHY 



721 



nary artery throughout the cycle, one can expect 

 flow throughout the cycle and a murmur throughout 

 the cycle. In this circumstance, then, one expects and 

 does find a continuous murmur, or a so-called ma- 

 chinery murmur. Furthermore, the gradient of pres- 

 sure increases during systole and decreases during 

 diastole which yields the expected effect on murmur 

 intensity. 



When the normal relationship between the two 

 pressures is disturbed for any reason, then there may 

 be a change in the time-course of flow and conse- 

 quently of the murmur. Here again the pressure 

 gradient yields a first approximation as an acoustic 

 correlate, the prime correlate remaining the flow. 

 With a lessening of the pressure gradient, due most 

 often clinically to increased pulmonary \ascular re- 

 sistance, a number of hemodynamic situations are 

 possible. Perhaps the most common situation is the 

 retention of a systolic gradient with the loss of the 

 diastolic gradient. Here, as might be expected, the 

 diastolic component of the murmur is lost. The 

 reverse, retention of the diastolic gradient alone, is 

 much less common. \Vhen the two pressures become 

 identical and there is little or no flow, the murmur 

 disappears. For completeness it should be pointed out 

 that identity of the pressure carries with it three 

 possible hemodynamic situations; a left-to-right shunt, 

 no shunt, or a right-to-left shunt. It is only in the 

 second case that there is no potential for murmur pro- 

 duction. In the first case there is the potential for the 

 production of a murmur originating in the pulmonary 

 artery. In the third case there is the potential for 

 murmur production, but here it would be directed 

 into the aorta. This might well be localized by re- 

 cording at the site of murmur production but would 

 be expected to be difficult from recordings taken on 

 the thorax. With pressure in the pulmonary artery in 

 excess of that in the aorta, one would have to expect 

 that a murmur, if present, would be produced in the 

 aorta. This is an unusual circumstance but has been 

 observed (18). It should be remembered that the 

 above discussion of murmur production and locali- 

 zation deals only with murmtu's produced by the flow 

 through the lesion itself and is not meant to include 

 other murmurs that may be present as a result of the 

 altered hemodynamics. 



One final consideration that applies particularly to 

 patent ductus arteriosus should be noted. For this 

 lesion there are two circumstances in which the mur- 

 mur may appear with only the systolic component. 

 The first, as discussed, is due to a rise in pulmonary 



artery pressure, due most often to an increased pulmo- 

 nary vascular resistance, such that the diastolic 

 pressure gradient and flow are abolished. The .second 

 is due to closure of the ductus during diastole. This 

 mav occur when the communication is small and the 

 movement of the heart or the ductus itself twists off 

 the passageway. Here the two pressures (aorta and 

 pulmonary artery) are widely different and, although 

 a gradient is present, a communication is not. Differ- 

 entiation between these two similar acoustic events 

 can be based on the very dissimilar accompanying 

 hemodynamic and therefore clinical presentation. 



A defect in the ventricular septum may arise out 

 of a congenital cardiac malformation or be acquired 

 following myocardial infarction (88) or trauma. In 

 the normal, the left \entricular pressure is between o 

 and 10 mm Hg in diastole and rises to appro.ximately 

 I 20 mm Hg in systole, whereas the right ventricular 

 diastolic pressure is between o and 5 mm Hg and the 

 systolic pressure rises to 30 mm Hg. At the onset of 

 systole left ventricular pressure rises before right ven- 

 tricular pressure, and begins to fall first at the end. 

 The result is that from the time of the initial valve 

 component of the first sound until at least the aortic 

 valve component of the second sound, left ventricular 

 pressure exceeds right ventricular pressure. In fact a 

 gradient may exist throughout the cycle, since the 

 diastolic pressure in the left ventricle may be higher 

 than that in the right, but more information is needed 

 on this point. From the acoustic standpoint, the above 

 circumstance would be expected to produce a systolic 

 murmur that begins with the first sound and goes at 

 least up to and perhaps beyond the aortic component 

 of the second .sound. Fmthermore, since the ven- 

 tricular pressures rise rapidly to peak value there is 

 little variation of the gradient throughout systole. 

 The result is that the murmur shows little variation 

 in intensity througliout systole. Such a murmur meets 

 all three criteria for a regurgitant type of systolic 

 murmur and may be classified as such. 



The usual type of deviation of the dynamics from 

 the normal is an increased right ventricular systolic 

 pressure. So long as the normal order of events is 

 preserved, there will remain a gradient of pressure 

 from left ventricle to right ventricle that begins with 

 mitral closure and persists up to aortic closure, for all 

 right ventricular pressures below left. Therefore, 

 so long as right ventricular systolic pressure does 

 not equal left x^entricular systolic pressure, the cir- 

 cumstances will be present for the potential pro- 

 duction of a regurgitant type of systolic murmur. We 



