Pulmonary vascular response to air-breathing exercise in humans following an 8-h exposure to hypoxia

This study is concerned with the pulmonary vasculature in euoxia after preconditioning with 8 h of hypoxia. The particular question we ask is whether the pulmonary vasculature will dilate normally with exercise or retain some degree of vasoconstriction, as has previously been reported in studies involving longer exposures to the hypoxia of high altitude. Ten subjects were studied on two separate days. On one day, subjects were exposed to 8 h of isocapnic hypoxia (end-tidal P-O2 55 Torr) and on the other day to 8 h of euoxia as a control. Before and after each exposure, subjects undertook 20 min of exercise at an intensity to elevate heart rate (HR) by similar to 30 bpm. During this period, Doppler echocardiography was used to assess the maximum pressure gradient during systole across the tricuspid valve (Delta P-max) as an index of pulmonary arterial pressure. Following 8-h hypoxia, but not control, Delta P-max increased by similar to 2 mmHg with the subjects breathing air at rest (ANOVA, P<0.02). Under control conditions, exercise at similar to 30 bpm above resting HR increased Delta P-max by 9.9 +/- 1.3 mmHg (mean +/- SE). Following 8-h hypoxia, but not control, this sensitivity of Delta P-max to exercise increased by similar to 35% to 13.4 +/- 2.1 mmHg (P<0.05). We conclude that prior conditioning with 8 h of hypoxia impairs the ability of the pulmonary vasculature to dilate normally during exercise. (C) 2009 Elsevier B.V. All rights reserved.