DELAYED-ONSET HYPERTENSION WITH INFRARENAL AORTIC CROSS-CLAMPING IN DOGS

The time course and mechanism of systemic hypertension associated with infrarenal aortic cross-clamping were investigated in 31 chloralose-a nesthetized dogs after ligating the tail artery, the paired infrarenal lumbar arteries, and the circumflex iliac arteries bilaterally. Cardi ac output, renal blood flow, and suprarenal and infrarenal mean arteri al blood pressure were continuously monitored. Infrarenal aortic clamp ing (90 min) in the standard group (n = 6) consistently decreased infr arenal blood pressure from 90+/- 6 to 13 +/-1 mm Hg within 1 min, whil e suprarenal blood pressure gradually increased over 20-30 min from 88 +/- 7 to 144 +/- 8 mm Hg, where it remained until declamp. The SHAM g roup (identical operation and instrumentation, without aortic clamping ) (n = 5) showed no statistically significant changes. After 90 min of clamp total peripheral and renal resistance nearly doubled but no sta tistically significant changes in cardiac output, heart rate, central venous pressure, renal blood flow, renin, or glomerular filtration rat e were detected. Upon declamping, pressures returned to control levels within 20 min. Groups with bilateral nephrectomy (n = 9) or unilatera l iliac artery clamping (n = 7) produced similar time courses and patt erns of hemodynamic change. Ablation of afferent nerves from the left hind limb (n = 4) eliminated the hypertension produced by left iliac a rtery clamping. The substantial delay (20-30 min) to the onset and ful l development of suprarenal hypertension, with near immediate infraren al hypotension, is not consistent with a direct mechanical impedance e ffect. Hypertension in the presence of a bilateral nephrectomy or unil ateral iliac artery clamping combined with its full reversal by nerve section strongly suggests that this is a reflex hypertension. This ref lex mechanism of hypertension development has implications for intra- or perioperative events associated with hypertension management. (C) 1 994 Academic Press, Inc.