The Effect of Nitroglycerin on the Capacitance of the Human Pulmonary “Venous” System

Abstract

We performed a computer simulation of four bouts of successive left-sided heart failure aggravated at intervals of one week. Each bout resulted in a decrease in the level of the left ventricular output curve to 70% of the preceding output curve level, while the right ventricular output curve was maintained unchanged. At each bout of acute left-sided heart failure, there occurred a transient oliguria and a gradual increase in the left atrial pressure. When the ordinate was the pulmonary “venous” volume and the abscissa was left atrial pressure, the pulmonary “venous” volume and left atrial pressure increased linearly (obliquely to the right), with progress of left-sided heart failure every week. By definition, the unstressed volume of the pulmonary “venous” system was unchanged.

It was shown that the occurrence of a simultaneous pulmonary venodilation and systemic venodilation produced a shift, near horizontally to the left, of the volume—pressure relationship.

We reviewed our previous paper where we showed that the volume—pressure (V–P) relation of the human pulmonary “venous” system could be constructed, in the form of V–P lines, by performing radionuclide angiocardiography with passive leg elevation, and using a floating catheter to record the pulmonary capillary wedge pressure (PCW). In 50 patients, most of whom had ischemic heart disease, the sublingual administration of nitroglycerin in a dose of 0.3–0.6 mg caused V–P lines to shift a little downward to the left and become steeper, indicating, in the light of the abovementioned computer simulation, a simultaneous pulmonary and systemic venodilation. The effective unstressed volume of the pulmonary “venous” system was virtually unchanged by nitroglycerin.