Abstract
Reduced partial pressures of inspired O2 may influence the bronchial circulation through a number of mechanisms (e.g. altered pulmonary and systemic vascular pressures, lung fluid regulation, airway cooling & drying from increased ventilation). The present study examined the impact of acute, graded hypoxia on bronchial blood flow (Qaw) in eight healthy adults (28 ± 9 years). Subjects were exposed to inspired O2 levels resulting in arterial O2 saturation (SaO2) values of 90% and 80% for 15 min each. To control for the mild hyperventilation that accompanies hypoxia, subjects then mimicked the 80% SaO2 ventilation (VE) rate with 21% FIO2 and again with CO2 added to the inspirate to maintain normocapnia. Qaw and cardiac output (CO) were measured using soluble gas techniques. Also measured were alveolar‐capillary conductance (Dm, index of lung fluid balance), pulmonary capillary blood volume (Vc), and systemic mean (MAP) and pulmonary arterial pressures (PAP). Hypoxia resulted in minimal change in MAP, a small rise in PAP, minimal change in CO and Vc, and a rise in Dm. There was also a non significant decrease in Qaw with hypoxia. Mild hyperventilation resulted in a significant fall in Qaw, but when normocapnia was maintained, Qaw returned to baseline values. These data suggest that acute, graded hypoxic exposure does not significantly impact Qaw, however, the hypocapnia associated with mild hyperventilation reduces Qaw.
Published Version
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