Vasomotor dynamics associated with cardiac operations. I. Venous tone and the effects of vasodilators.

Vasomotor dynamics were studied in 52 patients undergoing direct coronary revascularization or mitral valve replacement utilizing cardiopulmonary bypass. Emphasis was placed on the study of venous tone. Operation resulted in a general vasoconstrictive response with increased arterial resistance and reduced venous capacitance. These changes were magnified in patients who underwent mitral valve replacement for mitral valve stenosis related or partially related to reduced cardiac performance before and after operation. Nine patients became hypertensive following coronary artery bypass and were treated with nitroprusside; eight patients were given nitroglycerin to reduce venous tone and prevent hypertension. A comparison of these two vasodilators, with their somewhat different actions on the vascular bed, reveals that afterload reduction and increase of cardiac output were equivalent with both. However, nitroglycerin had the effect of increasing venous capacitance, while nitroprusside had little effect on the venous circulation. In addition, nitroglycerin was especially effective in reducing venous tone and left ventricular preload following mitral valve replacement. Relative merits of pharmacologic reduction of venous tone as a part of overall relief of increased vascular resistance following cardiac operation should be considered when attempting to obtain an optimal hemodynamic state.