Effect of nitroglycerin on ventricular oxygen extraction during aortic occlusion

Nitroglycerin (NTG) is often administered to improve hemodynamics during aortic occlusion (AO). This investigation was designed to characterize the effect of NTG on left ventricular oxygen extraction during thoracic aortic occlusion. Open-chest dogs (n = 12) underwent measurement of mean arterial pressure, heart rate, and coronary blood flow. The great cardiac vein (GCV) was cannulated. AO was produced by a balloon in the descending aorta. Arterial and GCV oxygen content were determined before, 30 seconds, and 10 minutes after AO (control occlusions). Oxygen extraction (A-V)O2, oxygen consumption, and cardiac work were calculated. AO was repeated during NTG infusion (2 micrograms/kg/min IV) in seven animals. (A-V)O2 was decreased 10% at 30 seconds in control occlusions. NTG exacerbated these decreases in oxygen extraction. With NTG, (A-V)O2 decreased by 33% despite a 12% increase in cardiac work. The fact that early decreases in oxygen extraction occurring after AO are accentuated by NTG may predispose patients undergoing aortic reconstruction who receive NTG to myocardial ischemia.