Effects of hypoxia on pulmonary microvascular volume

To determine the effects of alveolar hypoxia on pulmonary microvascular vol ume, X-ray microfocal angiographic images of isolated perfused dog lung lob es were obtained during passage of a bolus of radiopaque contrast medium du ring both normoxic (alveolar gas, 15% O-2, 6% CO2, and 79% N-2) and hypoxic (3% O-2,6% CO2, and 91% N-2) conditions. Regions of interest (ROIs) over t he lobar artery and vein at low magnification and a feeding artery (similar to 500 mu m diameter) and the nearby microvasculature (vessels smaller tha n similar to 50 mu m) at high magnification were identified, and X-ray abso rbance vs. time curves were acquired under both conditions from the same RO Is. The total pulmonary vascular volume was calculated from the flow and th e mean transit time for the contrast medium passage from the lobar artery t o lobar vein. The fractional changes in microvascular volume were determine d from the areas under the high-magnification X-ray absorbance curves. Hypo xia decreased lobar volume by 13 +/- 3% (SE) and regional microvascular vol ume by 26 +/- 4% (SE). Given the morphometry of the lung vasculature, these results suggest that capillary volume was decreased by hypoxia.