THE CONTROL OF THE FUNCTION OF 1 HE HEART 



505 



25 



LA. 

 cm 

 H2O 





 250 



Ao. 



mm 



Hg, 



4MHMI 



tiiifittl"" 



50 



40 



30 



20 - 



10 



5 10 15 20 25 30 35 



FIG. 13. LA = mean left atrial pressure, RA = mean right atrial pressure, PA = mean pulmonary 

 artery pressure, AF = total aortic flow (cardiac output minus coronary flow). 



increase in stroke volume. The calculated external 

 xentricular stroke work thus rises with each increase 

 in stimulus frequency while mean atrial pressure 

 falls. The same type of result is also obtained when 

 the stimulus voltage is varied from zero to the level 

 of maximal response while the stimulation frequency 

 is held constant. 



At the end of the series of oljser\ations shown in the 

 left panel of figure I4.-1, stellate stimulation was 

 stopped and an interval of 6 min allowed to pass; 

 during this period each of the hemodynamic values 

 returned to control levels. An infusion of i oo ml of 

 blood was then made. This resulted in a modest 

 elevation of atrial and arterial pressures, cardiac 

 output, stroke volume, and stroke work, as can be 

 seen by comparing the first segment of the left panel 

 of figure i^A (before infusion) with the first segment 

 of the right panel (after one infusion). The same series 

 of frequency graded stimuli were then once again 

 applied with the results seen in the right panel of 

 figure 14.4. This sequence of interventions was re- 

 peated until six sets of six points each were obtained. 

 Heart rate was held constant throughout. 



The plot of mean left atrial pressure against left 

 ventricular stroke work (VTCla) resulting from these 

 data is shown in figure 14B (left). The number ad- 

 jacent to each curve indicates the stimulus frequency. 

 Worthy of note is the magnitude of the changes in 

 the ventricular work produced at a given mean left 

 atrial pressure level under the influence of left stellate 

 stimulation (especially since only a portion of the 

 cardiac sympathetic nerves were stimulated) and 

 also the systematic manner in which the position of 

 the curve shifts with the change in the frequency of 

 cardiac sympathetic nerve stimulation. One hour and 

 fifteen minutes later the experiment was repeated, 

 and the resulting curves are shown in figure 14^ 

 (right). The effects of left stellate stimulation on the 

 performance of the right ventricle (VFCra) are simi- 

 lar to the effects observed on the left ventricle (105). 



It remained to be demonstrated whether the syste- 

 matic alteration in myocardial contractility produced 

 by an increasing frequency of cardiac sympathetic 

 nerve stimulation is accompanied by a graded libera- 

 tion of catecholamine in the heart. Recently acquired 

 data (109a), from a type of experiment in which 



