| Summary: | To examine the hypothesis that the human pulmonary vascular response to hypoxia has a component with a slow time course, we measured pulmonary vascular resistance (PVR) in six healthy adult males during 8 h of isocapnic hypoxia. A balloon-tipped pulmonary artery catheter with thermistor was introduced via a forearm vein and used to derive PVR. The subjects were seated in a chamber in which the oxygen and carbon dioxide concentrations were adjusted to maintain an end-tidal Po2 of 50 Torr and an end-tidal Pco2 equal to the subject's normal prehypoxic value. PVR was measured before and at 0.5-h intervals during 8 h of hypoxia, the following 3 h of isocapnic euoxia (end-tidal Po2 100 Torr),and a subsequent 1-h reexposure to hypoxia. PVR rose from 1.23 ±0.26 (SE) Torr-min-I'1 under euoxia [time (0 = 0] to 1.77 ±0.21 Torr -min -l"1 at t = 0.5 h, reached a maximum at 2 h (2.91 ±0.33 Torr-min-T1), and remained fairly constant between 2 and 8 h. Restoration of euoxia at 8 h led to a reduction in PVR with a slow component. Reexposure to hypoxia at 11 h resulted in a greater increase in PVR than at 1 h. Systemic vascular resistance had a similar slow component to its response, falling from 18.6 ±1.3 Torr-min-T1 at t = 0 to 17.3 ±1.4 Torr-min-1-1 at t = 0.5 h, 14.4 ±0.6 Torr-min-1-1 at t = 4 h, and 13.8 ±O.STorr-mhvlatf = 8 h. The human pulmonary and systemic vascular responses to hypoxia extend over at least several hours. hypoxic pulmonary vasoconstriction; cardiac output; pulmonary ventilation; systemic vascular resistance Copyright © 1997 the American Physiological Society.
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