Effect of Decreasing the Force of Right Atrial Contraction on Right Ventricular Stroke Volume

The effect of reducing the force of right atrial contraction on right ventricular stroke volume was determined in anesthetized open-chest dogs. Atrial contractile force, measured directly with a strain-gauge arch, was decreased by electrical stimulation of the right vagus nerve; right ventricular stroke volume was measured with an electro-magnetic flowmeter. Heart rate was maintained constant by electrical stimulation of the right atrium. Vagal stimulation decreased atrial contractile force by an average of 47±2.6 (SEM)% of the control, and stroke volume fell by 4.0±0.9%. During vagal stimulation, no change was observed in right ventricular contractile force. In addition, no consistent change was noted in mean right atrial or right ventricular pressures. The relation between the decrease in atrial force and stroke volume was not altered significantly by the rate of right atrial pacing. In 7 of 10 experiments, increasing the inhibition of atrial force produced a further decrease in stroke volume. Since neural, mechanical, and humoral factors modify atrial contractile force in the intact animal, the present study provides more definitive evidence that the ability to alter atrial force represents another adaptive mechanism in the regulation of cardiac performance.