Time course of the human pulmonary vascular response to 8 hours of isocapnic hypoxia.
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.
Dorrington
K L
KL
University Laboratory of Physiology, Oxford, United Kingdom.
Clar
C
C
Young
J D
JD
Jonas
M
M
Tansley
J G
JG
Robbins
P A
PA
D000328:Adult; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output; D003971:Diastole; D006339:Heart Rate; D006439:Hemodynamics; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D011650:Pulmonary Alveoli / Q000502:physiology / Q000503:physiopathology; D011651:Pulmonary Artery / Q000502:physiology / Q000503:physiopathology*; D011652:Pulmonary Circulation / Q000502:physiology*; D012044:Regression Analysis; D013318:Stroke Volume; D013599:Systole; D013997:Time Factors; D014655:Vascular Resistance
D002245:Carbon Dioxide; D010100:Oxygen