Radial arterial pressure measurements may be a poor guide to the beneficial effects of nitroprusside on left ventricular systolic pressure in congestive heart failure.

The effect of nitroprusside on pressure wave transmission from ascending aorta to radial artery was studied in 10 patients with severe congestive heart failure. Nitroprusside resulted in a beneficial increase in cardiac index, reduction of pulmonary wedge pressure and reductions of aortic and radial arterial mean pressures. In 6 patients with an identifiable late systolic peak of aortic pressure (group I), nitroprusside reduced aortic systolic pressure more than radial systolic pressure, resulting in an increase in the difference between aortic and radial systolic arterial pressure (group I control 13 +/- 4, nitroprusside 20 +/- 6 mm Hg; p less than 0.025). Yet in 4 patients in whom no aortic late systolic pressure wave was apparent (group II), nitroprusside did not alter the difference between aortic and radial systolic pressures. Radial arterial pressure is often used to estimate the effect of nitroprusside on the arterial pressure load on the left ventricle. These results indicate that a reduction of radial systolic pressure induced by nitroprusside may underestimate the true reduction of aortic systolic pressure and thus the effect of the vasodilator on the arterial load on the left ventricle. The enhanced difference between aortic and radial arterial systolic pressures appears to be the consequence of nitroprusside on arterial pressure reflections.