Abstract

Since the dimensions of the ventricles are related to both myocardial tension and myocardial oxygen consumption (MVO2), the effects of nitroglycerin on the left ventricular volumes and left ventricular haemodynamics were studied in patients with ischaemic heart disease. The ventricular volumes were estimated using the constant infusion technique (indocyanine green) of Shaffer (1964). Sublingual administration of nitroglycerin (0.6 mg.) resulted in a significant reduction in cardiac output (27%), mean systolic pressure (21%), left ventricular end-diastolic pressure (63%), stroke volume (27%), left ventricular end-diastolic volume (26%), and left ventricular work (41%). Both calculated circumferential myocardial force (40%) and the myocardial tension (33%) decreased during systole, while the pressure-time index decreased by 27%. A similar decrease was also found in the contractile element work (42%), and mean circumferential fibre shortening rate (22%). Thus, this study has shown that the major determinants of MVO2, i.e. myocardial wall tension, the velocity of contraction, and contractile element work, decrease significantly after administration of nitroglycerin.