AJP - Heart and Circulatory Physiology, Vol 273, Issue 3 1126-H1134, Copyright © 1997 by American Physiological Society

ARTICLES

Time course of the human pulmonary vascular response to 8 hours of isocapnic hypoxia

K. L. Dorrington, C. Clar, J. D. Young, M. Jonas, J. G. Tansley and P. A. Robbins
University Laboratory of Physiology, Oxford, United Kingdom.

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.1(-1) under euoxia [time (t) = 0] to 1.77 +/- 0.21 Torr.min.1(-1) at t = 0.5 h, reached a maximum at 2 h (2.91 +/- 0.33 Torr.min.1(-1)), 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.1(-1) 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 +/- 0.8 Torr.min.1(-1) at t = 8 h. The human pulmonary and systemic vascular responses to hypoxia extend over at least several hours.

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