Effects of hypoxia on the pulmonary microvascular permeability in adult rabbit lung

Within the last 30 years, researchers have explored what role hypoxia might play in causing permeability changes in the pulmonary microvasculature. Since the data accumulated thus far are unclear, the effects of hypoxia on microvascular transport in the isolated, Ringer's perfused adult rabbit lung was observed and the following parameters were measured or computed for both oxygenated and hypoxic perfusates: pulmonary arterial (r_a) and pulmonary venous (r_v) resistances, pulmonary capillary filtration coefficients (K_f), and pulmonary capillary endothelial reflection coefficients () for NaCl and inulin. Separate reservoir bottles were used to create the desired oxygenated (aeration of solution with 95% O₂-5% CO₂) gas mixture or hypoxic (aeration of solution with 95% N₂-5% CO₂) gas mixture. A higher, but not significant, resistance value was found during the oxygenated state. A significant increase in the pulmonary capillary filtration coefficient during hypoxia (10.72 × 10^–4±0.446 × 10^–4 cm³/s cm H₂O for the hypoxic perfusate and 8.80 × 10^–4±0.384 × 10^–4 cm³/s cm H₂O for the oxygenated perfusate) was found and a significant difference between oxygenated and hypoxic pulmonary capillary reflection coefficients for inulin was computed (oxygenated solution revealed a finding of 0.120±0.003 and the hypoxic solution revealed 0.105±0.002). These findings imply a change in the microvascular permeability during hypoxia. According to the pore theory, a change in pore number, pore size, or both could have occurred. However, from the reflection coefficient data, a change in pore radius seems most likely.