Intravenous infusion of nitroglycerin: effects upon cardiovascular dynamics and regional blood flow distribution in conscious dogs.

We have studied both central and peripheral hemodynamic changes induced by infusion of nitroglycerin (55 micrograms/kg per minute) over a 15-min period in conscious dogs to clarify its mechanism of action. Dogs were prepared with an electromagnetic flow probe positioned at the root of the aorta, and microspheres (9 microns) were used to measure regional blood flow distribution before and after 15 min of infusion. Controlled hypotension (-15 to -20 mmHg (1 mmHg = 133.322 Pa)) was maintained throughout the infusion period and this hypotensive state was associated with a significant decrease in stroke volume (-30%), cardiac index (-20%), and left ventricular work (-43%). Regional blood flow studies showed that at the 15th min of infusion, nitroglycerin induced significant decrease in blood flow to all components of the myocardium (range -12 to -20%) while their vascular resistances were not affected significantly. Blood perfusion to liver (hepatic artery), spleen, and intestine was also modified significantly (-22, -18, and -16%, respectively) while their vascular resistances remained close to control values. By the time measurements were made, blood flow and vascular resistance of cerebral and renal tissues remained normal. For each organ studied, blood perfusion was uniform. These results indicate that nitroglycerin elicits both central and peripheral hemodynamic changes and that local reflex adjustments modify the vasodilator effect of the drug in most vascular beds that we have studied.