Acute hypoxia does not alter inter-alveolar perfusion distribution in unanesthetized rats

Effects of hypoxic vasoconstriction on inter-alveolar perfusion distribution (≤1000 alveoli) have not been studied. To address this, we measured inter-alveolar perfusion distribution in the lungs of unanesthetized rats breathing 10% O2. Perfusion distributions were measured by analyzing the trapping patterns of 4 μm diameter fluorescent latex particles infused into the pulmonary circulation. The trapping patterns were statistically quantified in confocal images of the dried lungs. Trapping patterns were measured in lung volumes that ranged between less than 1 and 1300 alveoli, and were expressed as the log of the dispersion index (log DI). A uniform (statistically random) perfusion distribution corresponds to a log DI value of zero. The more this value exceeds zero, the more the distribution is clustered (non-random). At the largest tissue volume (1300 alveoli) log DI reached a maximum value of 0.68 ± 0.42 (mean ± s.d.) in hypoxic rats (n = 6), 0.50 ± 0.38 in hypercapnic rats (n.s.) and 0.48 ± 0.25 in air-breathing controls (n.s.). Our results suggest that acute hypoxia did not cause significant changes in inter-alveolar perfusion distribution in unanesthetized, spontaneously breathing rats.