Ventricular response to increased outflow resistance in absence of elevated intraventricular end-diastolic pressure.

• Classically, the adaptation of the ventricle to increased outflow resistance is considered to be associated with increased end-diastolic pressure and volume.' Recent studies by Rosenblueth and his co-workers have shown, however, that when the right ventricle is forced to contract against an augmented outflow pressure, after an initial dilatation, the right ventricle gradually resumes its original volume while maintaining its full degree of compensation. Similarly, Sarnoff and his associates' have demonstrated that initially, the end-diastolic pressure in the left ventricle increases when outflow resistance is suddenly augmented; however, the end-diastolic pressure shortly returns to or toward the control level with no detectable reduction in the degree of cardiac adaptation to the maintained increase of resistance. Many years earlier, Anrep had observed a slight, similar response to increased arterial resistance; with the addition of eptiiephrine to the blood, however, this reaction was much more fully developed.