THE CONTROL OF THE FUNCTION OF THE HEART 517 



n LA '::::-;-zr:::z34 \ \\\ L gqin 



200 



CS.P 

 mm 



Hg 







150 



A.P. 

 mm 



Hg 







40 



UA. 



cm 





 40 1- 



LV.D. 

 cm 



H2O 



0,5" 



\ 



■V 



-A 



\y 





FIG. 23 



can be seen, such closure took place in the absence of 

 any ventricular activity. That mitral valve closure was 

 a direct result of the consequences of atrial activity is 

 clear from the subsequent portion of the same tracing. 

 That is, the diminution of atrial systole during 

 efferent vagal nerve stimulation (interval shown bv 

 the signal) eliminated the valve closure as evidenced 

 by the abolition of the ventriculo-atrial pressure 

 gradient. After cessation of vagal stimulation the 

 original pattern returned. 



When, in the dog with heart block, the control 

 atrial and ventricular tracings are such as to indicate 

 that mitral valve closure is not taking place after each 

 atrial systole, atrially induced closure of the mitral 

 valve can often be induced by stimulation of the 

 stellate ganglion and the resulting augmentation of 



atrial systole. Although this is not a consistent finding, 

 as can be seen from figure 19 (upper), it is frequently 

 observed. Examples of atrially induced mitral valve 

 closure by reflex sympathetic stimulation is shown in 

 figure 23B. During carotid hypertension (sympathetic 

 inhibition), evidence of atrially induced mitral valve 

 closure was not present (left panel). When the carotid 

 pressure was lowered (sympathetic stimulation), the 

 pattern indicative of valve closure took place (right 

 panel). Similar results are shown in figure 28. Figure 

 19 (lower) suggests that the ability of the atrium to 

 induce mitral valve closure is not limited to conditions 

 of atrioventricular dissociation. In the right panel of 

 that figure, during stellate ganglion stimulation, the 

 peak of atrial systole precedes the onset of ventricular 

 systole by 60 msec, then declines substantially while 



