THE DIFFERENTIAL EFFECTS OF RESPIRATION ON THE LEFT AND RIGHT VENTRICLES

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Abstract
Direct vol. changes of dogs hearts were made by means of an oncometer during normal breathing, with the ventricles exposed to intrathoracic pressure changes. During inspiration, there was an increase in total diastolic size and stroke vol. of the 2 ventricles, even though systemic arterial pressure dropped at the same time. Motion pictures were taken of the heart during normal respiration, through a ventral chest window. Successive single frames were enlarged, the area of each ventricle measured in each frame, and these areas plotted together with simultaneous intrathoracic and carotid pressures. The diastolic size and stroke vol. of the right ventricle increased during inspiration, while the size and output of the left ventricle decreased; the reverse was true during expiration. Each ventricle responded according to the Starling principle, regardless of the size of the other ventricle. The results indicate that the main factor responsible for the arterial blood pressure fluctuations with respiration in the dog is the changing output of the left ventricle. Sinus arrhythmias and direct influences of intrathoracic pressure may modify somewhat these blood pressure changes.

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