Underestimation of Vasodilator Effects of Nitroglycerin by Upper Limb Blood Pressure

To determine why upper limb blood pressure measurement underestimates the vasodilator effects of nitroglycerin on lowering ascending aortic systolic pressure, we studied 24 patients (58 plus/minus 11 years, mean plus/minus SD). Ascending aortic pressure and radial artery pulse calibrated by cuff blood pressure measurement at the brachial artery were recorded simultaneously before and 5 minutes after sublingual administration of 0.3 mg nitroglycerin. Waves were analyzed by a signal processor, and the fourth derivative wave was used to find the early (S1) and late (S2) systolic shoulders (S1 corresponds to the second zero crossing and S2 to the third zero crossing). Before nitroglycerin administration, maximal systolic pressure in the ascending aorta (141 plus/minus 21 mm Hg) coincided with the late systolic peak in all patients, and in most patients (21 of 24) maximal systolic pressure in the radial artery (140 plus/minus 19 mm Hg) coincided with the early systolic peak. Maximal systolic pressure decreased more in the ascending aorta than in the radial artery (22 plus/minus 13 and 11 plus/minus 11 mm Hg, respectively; P < .001). However, the reduction in the shoulder of late systolic pressure in the radial artery (24 plus/minus 13 mm Hg) clearly indicated the reduction in maximal systolic pressure (late systolic peak) in the ascending aorta. The augmentation index of the ratio of the height of late systolic pressure to early systolic pressure fell proportionally (r = .74, P < .001) in the radial artery (from 0.88 plus/minus 0.13 to 0.60 plus/minus 0.11) and in the ascending aorta (from 1.57 plus/minus 0.25 to 1.26 plus/minus 0.24), which indicated the reduction in late systolic pressures. These data suggest that ordinary peripheral artery blood pressure measurement underestimates the vasodilation effects of nitroglycerin on the ascending aorta because without arterial pulse measurement it cannot show changes in late systolic pressure. (Hypertension. 1995;26:520-523.)