Influence of vagal stimulation on ventricular contractility, O2 consumption, and coronary flow

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Abstract
A right-heart bypass preparation, in which aortic pressure, cardiac input, and heart rate were held constant, was used to study reactions of 15 dogs to stimulation of the efferent vagal nerves. Stimulation during synchronized atrioventricular pacing produced the following statistically significant changes in indices of ventricular performance; left ventricular end-diastolic pressure, +6.6 cm H2O; maximal rate of rise of left ventricular pressure, -357 mm Hg/sec; right ventricular contractile force, -4.8 units; duration of systole, +10 msec. The left ventricular function curve was shifted to the right. Coronary blood flow increased, but there was no significant change in myocardial O2 consumption. Comparable results were obtained during stimulation under conditions of I) controlled coronary blood flow; 2) surgically induced heart block; 3) beta adrenergic receptor blockade; 4) unchanging pathways of ventricular activation. Atropine abolished the effects of vagal stimulation. These data support the view that changes in efferent vagal activity can directly influence ventricular contractility and suggest the presence of vagal cholinergic innervation of canine cardiac ventricles.