PHONOCARDIOGRAPHY 



705 



warnings about the "false apex impulse" in right 

 ventricular enlargement are well worth remembering 

 in this regard (85). 



The feature of the so-called apex cardiogram most 

 commonly utilized in diagnosis is the nature of the 

 outward (toward the thorax) mo%'ement of the ven- 

 tricle during diastole. During this period the record- 

 ing, as traditionally obtained, shows a continuous rise 

 from the onset of ventricular filling to the end of the 

 phase of rapid filling when the outward movement 

 either ceases or is impeded. It is at this latter point 

 that the third sound and/or the protodiastolic gallop 

 sound occur. It is also the point at which the diastolic 

 sound of constrictive pericarditis occurs. Tiie opening 

 snap of the atriox'entricular valve coming before the 

 end of rapid filling precedes this point. Since it heralds 

 the opening of the atrio\entricular valve and the onset 

 of ventricular filling it occurs at the bottom (o point) 

 of the recording which denotes the beginning of the 

 early filling pha.se. 



The feature of the vibrations recorded over the 

 great vessels (e.g., pulmonary artery cardiogram) 

 most frequently used is the recording of semilunar 

 valve closiu-e. In this respect, the tracing is a counter- 

 part of the tactile sensation called the diastolic shock 

 felt, at times, over the thorax in the region of the pul- 

 monary artery in certain disease states. Other me- 

 chanico-acoustical correlates have been studied. These 

 include the ballistocardiogram (65) and the electro- 

 kvmogram (66). These will not be discussed here. 



Effect of Rfspiration on Heart Sounds 



The major effect of respiration on heart sounds has 

 been noted on the second sound. Whereas there are 

 certainh- changes in intensity of the other sounds with 

 respiration (as will be discussed below Ijriefly), and 

 there may well be changes in their appearance time, 

 the greatest study thus far has centered around semi- 

 lunar \al\e closure. The effect of respiration on the 

 appearance time of the components of semilunar valve 

 closiu'e is now well known, but at present the precise 

 mechanism of this effect in humans can only be sur- 

 mised. This is due mainly to the lack of methods for 

 precise measurements of stroke output, beat by beat. 



Consider first the train of events that might be 

 expected to occur on the right side of the heart follow- 

 ing inspiration. Inspiration lowers intrathoracic pres- 

 sure. Since the vessels returning blood to the right 

 heart connect with vessels that lie outside the thorax, 

 and since they are exposed to atmospheric pressure. 



the gradient of pressure between extrathoracic and 

 intrathoracic vessels increases. This is somewhat 

 greater when one considers the return from the intra- 

 abdominal vessels, since inspiration tends to increase 

 intra-abdominal pressure. The result is that inspira- 

 tion increases venous return to the right heart. The re- 

 sponse of the right ventricle to this increase in venous 

 return is an increase in stroke otitput (Starling). As 

 the stroke volume increases, and thereby the right 

 ventricular work, the duration of mechanical systole 

 increases. The increase in the duration of mechanical 

 systole results in a delay in the appearance time of the 

 pulmonic component of the second sound. Clonsider 

 now the effect of inspiration on the left ventricle. Here 

 again one must start with the lowering of intrathoracic 

 pressure. However, in this case the venous supply to 

 this ventricle lies wholly within the thorax. One must 

 consider the effect of inspiration on the \a.scular 

 volume of the lung to find the answer to the effect of 

 inspiration on return to the left ventricle. This in- 

 formation is far from complete, h\xt some studies in 

 the past h\ a number of workers have suggested that 

 with inspiration the volume of blood in the pulmonary 

 capillar\- l^ed decreases (7, 80, 98), that blood is, per- 

 haps, squeezed out of these vessels. Such an eff'ect 

 would be expected to result in an increa.se in return 

 to the left \entricle. As will be seen below, this is not 

 in keeping with the effect of inspiration giving an 

 earlier time of aortic valve closure. This observation 

 fits lietter with inspiration resulting in a decrease in 

 return to the left heart. A way out of this seeming 

 paradox has been provided by Howell el at. (42), who 

 suggest that the effect of inspiration on the pulmonary 

 vessels depends in large part on the particular segment 

 invohed. Since the capillaries run in the alveolar 

 septa, it is reasonable to suppose that they may be 

 squeezed during alveolar expansion and thereby con- 

 tain less blood. However, the arteries and \eins which 

 lie in the interstices of the lung will tend to be pulled 

 open as the lung expands and their vascular volume 

 thereby increased. One needs only to suggest that the 

 volume of these vessels is greater than that of the 

 capillaries, and overbalances them, to arrive at the 

 hoped-for conclusion that inspiration increases the 

 vascular volume of the lung. \'erification of this 

 hypothesis is much needed. If we use this supposition 

 for the moment, then, since there is a greater potential 

 room for blood in the lung, inspiration would be 

 expected to reduce venous return to the left heart. 

 From this it follows that stroke volume and thereby 

 stroke work and therebv the duration of mechanical 



