EFFECTS OF HYPOTENSION ON CUTANEOUS AND SUBCUTANEOUS BLOOD-FLOW IN ANESTHETIZED HUMANS

The aim of this study was to determine the effect of controlled hypotension on subcutaneous and cutaneous haemodynamics in humans. Moderate hypotension was achieved with nitroglycerin (NTG) and sodium nitroprusside (SNP) infusion during narconeuroleptanalgesia in seven patients. Subcutaneous and cutaneous blood flow were measured by a superficial and deep heat clearance (HC) technique. The mean arterial pressure (BP(a)BAR) decreased by 23%-30% and heart rate (f(c)) increased but only during NTG infusion (+22%; P < 0.02). Subcutaneous and cutaneous blood flows remained unchanged despite a significant decrease in calculated cutaneous resistance (NTG: -26%, P < 0.01; SNP: -34%, P < 0.02) and subcutaneous vascular resistance changed only with SNP (-31%, P < 0.02). After hypotension was discontinued the subcutaneous blood flow decreased (-13%, P = 0.05), whereas subcutaneous vascular resistance returned to its control values. An inverse relationship was found between f(c) and BP(a)BAR (NTG: r = -0.525, P < 0.01; SNP: r = -0.622, P < 0.01) as well as with subcutaneous blood flow (NTG: r = -0.653, P < 0.001; SNP: r = -0.573, P < 0.01). In addition, we found oscillatory changes in deep HC values which differed in magnitudes (NTG 0.22 (SEM 0.09) W.m-1.degrees-C-1 vs SNP 0.42 (SEM 0.1) W.m-1.degrees-C-1, P < 0.01) and frequencies (NTG 0.02 (SEM 0.006) Hz vs SNP 0.01 (SEM 0.002) Hz, P < 0.01). Despite unchanged blood flow, the effects of controlled hypotension on cutaneous and subcutaneous haemodynamics were different depending on the type of drug. These differences may have been related to counterregulatory responses and/or to direct vascular effects.