Systemic pressor response during hindlimb ischemia is inversely related to femoral artery pressure and fractional inspired oxygen.

Abstract

Delayed-onset reflex increases in mean arterial pressure (MAP) occur during clamping of the infrarenal aorta. This study investigated the afferent limb of the reflex by independently altering femoral artery blood pressure (FBP) or fractional concentration of inspired oxygen (FIO2) while monitoring systemic arterial blood pressure. The infrarenal aorta was divided, and an occlusive roller pump delivered incremental flow to the distal aorta thus controlling FBP. In six dogs the FBP was reduced in random order to 50, 40, 30, 20, and 10 mm Hg and held constant for 30 minutes. In another six dogs the FBP was held at 20 mm Hg, whereas the FIO2 was randomly varied among 0.13, 0.21, and 1.0 for 30-minute intervals. Under these conditions MAP was significantly and inversely correlated with FBP (MAP was 172 +/- 8 mm Hg when FBP was 10 mm Hg, p < 0.0001; MAP was 158 +/- 8 mm Hg when FBP was 20 mm Hg, p = 0.0001; MAP was 138 +/- 7 mm Hg when FBP was 30 mm Hg, p = 0.0048; and MAP was 130 +/- 7 mm Hg when FBP was 40 mm Hg, p = 0.0045). MAP was significantly and inversely related to the FIO2 value when FBP was fixed at 20 mm Hg (MAP of 186 +/- 9 mm Hg at FIO2 of 0.13 and was significantly higher than MAP of 163 +/- 11 mm Hg at FIO2 of 0.21, p = 0.01; and MAP of 157 +/- 10 mm Hg at FIO2 of 1.0, p = 0.0001). The magnitude of the delayed systemic pressor response is inversely proportional to the FBP. We suggest that this pressor response is also particularly sensitive, in part, to arterial blood oxygen tension when hindlimb perfusion pressure is low.