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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



time, whereas that produced by the coarctation itself 

 depends upon the severity of tlie obstruction. 



Effect of Respiration on Murmurs 



Consider first the effect of inspiration on tlie riglit 

 heart. In the discussion on lieart sounds a train of 

 events was pictured that began with the decrease in 

 intrathoracic pressure and led to an increase in the 

 flow into and the stroke volume from the right 

 ventricle. There is also an increase in the flow into 

 the pulmonary vascular bed. If one returns to the 

 suggestion that the prime correlate of murmur in- 

 tensity (and presence) is the volume (and time-course) 

 of the flow, then it follows from this that murmurs 

 originating in and exclusively limited to the right 

 heart would be expected to increase in intensity with 

 inspiration. Thus, the increased inflow into the right 

 heart increases the intensity of the murmur of tri- 

 cuspid stenosis. The increase in right ventricular 

 stroke volume increases the intensity of the murmur 

 of tricuspid insufficiency [pointed out some time ago 

 by Rivero Carvallo (84)] and of murmurs created 

 at the pulmonic valve. The increase in flow into the 

 pulmonary tree will increase the intensity of the 

 murmur of pulmonary arteriovenous fistula. Our own 

 experience with this phenomenon indicates a number 

 of additional features. We have had the greatest 

 experience with the murmur of tricuspid insufficiency 

 and will use this as an example. First, there is not 

 always an exact correlation between what is heard 

 inside the heart at the site of murmur production and 

 what is heard on the thorax. Intensity may clearly 

 increase at the site of production, and yet it may be 

 difficult from recordings on the thorax to decide that 

 this has occurred. Second, the change with inspiration 

 may manifest itself more clearly by a change in 

 quality than by a change in intensity. This can best be 

 described by noting that the murmur assumes a 

 harsher cjuality. 



In considering the effect of inspiration on the left 

 heart it will be remembered that the train of events 

 from the initial effect of the lowering of intrathoracic 

 pressure proceeded via the increased vascular volume 

 of the lung to a decreased left ventricular filling and 

 stroke \olume, and a decrease in aortic flow. As a 

 result, murmurs that originate in the left side of the 

 circulation and are limited thereto can be expected 

 to decrease in intensity with inspiration. Therefore, 

 the reduced \entricular inflow decreases the intensity 

 of the murmur of mitral stenosis. The reduced stroke 

 ()ui]iut decreases the intensity of the murmur of 



mitral insufficiency and of murmurs from the aortic 

 valve. One can expect also a decrease in intensity of 

 murmurs dependent upon aortic flow for their gener- 

 ation. 



Conversely, one may consider that the effect of 

 expiration will be to decrease the intensity of murmurs 

 from the right side and increase the intensity of those 

 from the left side. 



Additional information on the site of murmur pro- 

 duction can be obtained by utilizing the \'alsalva 

 maneuver (109). When the forced expiratory phase 

 is maintained for a sufficiently long time, the reduced 

 inflow into the right heart causes not only a reduced 

 right output but as a consequence a decreased left 

 heart output. In this situation murmurs originating 

 in either side of the heart will decrease in intensity. 

 From this new equilibrium point one can then observe 

 the time-course of the return of murmur intensity to 

 the control level following the cessation of the forced 

 expiration. There is first an increase in right heart 

 output followed later by an increase in left heart 

 output. Thus the time inter\-al for the right heart 

 murmurs to return will be shorter than those from the 

 left heart. 



The same appreciation of the effects of normal 

 respiration can be used to deduce the effects of both 

 inspiration and expiration on the intensity of murmurs 

 arising out of abnormal communications. Consider 

 first communications at corresponding levels where 

 the shunt is left-to-right. For these lesions inspiration, 

 which raises right heart pressure and flow and lowers 

 left heart pressure and flow, can be expected to 

 produce a decreased gradient across the defect, a 

 decreased shunting, and consequently a decrease in 

 murmur intensity. The situation in shunts at the 

 le\el of the great vessels and ventricle appears clear- 

 cut. The situation in shunts at the atrial level is 

 complicated by the fact that the right ventricular 

 inflow depends upon systemic venous return, which 

 would appear to be increasing, and upon flow through 

 the defect. This latter might decrease due to the 

 decrease in return to the left atrium, though it is fair 

 to say that more knowledge on this point is required. 

 Depending therefore on the relative efl"ects upon 

 systemic inflow, pulmonary venous return, and flow 

 through the shunt, the right heart inflow may increase, 

 decrease, or remain the same. Efforts to analyze the 

 resultant effects is complicated by this lack of precise 

 knowledge. In many cases, as discussed alcove on the 

 section on heart sounds, it appears that the duration 

 of mechanical systole of the right ventricle remains 

 unchans;ed. This mav be due to a balanced alteration 



