The effect of isradipine in acute altitude hypoxia on cerebral, renal, and splanchnic blood flow evaluated by Doppler measurements

Abstract

Recent studies have suggested that calcium antagonists may have a beneficial effect on high altitude pulmonary edema, but the effect on regional blood flow distribution is unknown. This study by transcranial and duplex Doppler evaluated the effect of the calcium antagonist isradipine on cerebral, renal, and splanchnic blood flows in acute altitude hypoxia. Twelve healthy subjects were investigated at sea level and repeatedly after 3–56 hours at high altitude (4350 m). Before the ascent, the subjects were randomized to treatment with isradipine 5 mg/day (n = 6) or placebo (n = 6). We measured flow velocities in middle cerebral arteries; flow rates in internal carotid arteries, portal vein, and right renal artery; and resistance indices in middle cerebral, internal carotid, renal, superior mesenteric, and hepatic arteries. Hypoxia increased middle cerebral artery flow velocity by 30% (placebo, p < 0.05) and 39% (isradipine, p < 0.01); increased internal carotid artery flow rate by 57% (placebo, p < 0.01) and 55% (isradipine, p < 0.05); and decreased middle cerebral and internal carotid artery resistance indices without differences between placebo and isradipine groups. Superior mesenteric artery resistance index was lower in hypoxia with isradipine compared with placebo (p < 0.05), suggesting a higher splanchnic blood flow. In conclusion, acute hypoxia induced an increase in cerebral blood flow. Besides decreasing superior mesenteric artery resistance index, prophylactic isradipine did not modulate the circulatory responses to acute hypoxia. The clinical significance of this increased splanchnic blood flow remains unclear.