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HANDBOOK OF PHYSIOLOGY "^ CIRCULATION I 



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FIG. 21. LA = left atrial pressure. 



from 54 to 156 mm Hg while the vagus was stimu- 

 lated. In panel B, the relation between mean left 

 atrial pressure and stroke work (VTCla) was shifted 

 to the right. Schreiner et al. (109) did not find evi- 

 dence that efferent vagal stimulation altered the rela- 

 tionship between mean atrial pressure and stroke 

 work and concluded that such stimulation does not 

 modify the contractility of the ventricle, a conclusion 

 reaffirmed by the above experiments. It is not en- 

 tirely clear, however, why they did not obtain a 

 higher mean left atrial pressure for any given level of 

 left ventricular stroke work as shown in figure 20. 



The above experiments on vagal stimulation are 

 not consonant with the experiments of Wang et al. 

 (122) or with the suggestion of Peterson (74) that 



vagal fibers produce a negative inotropic effect on 

 the ventricle. They do support the recent observa- 

 tions of Carlsten et al. (21) in man suggesting that 

 vagal stimulation does not influence the ventricular 

 myocardium and are in essential agreement with the 

 experiments of Gesell (42), who attributed the 

 changes in arterial pressure during vagal stimulation 

 to the diminished contribution of the atrium to 

 \entricular filling. 



/). Influence of Efferent Vagal Xerre Stimulation 

 on the Atrium 



In view of the abo\e it appeared worthwhile to 

 make a direct and detailed re-examination (42, 124) 



