Acclimatization and Adaptation to Chronic Hypoxia, Focusing on Changes in Pulmonary Blood Flow Distribution

点击翻译按钮获取中文摘要

Regional distribution of pulmonary blood flow (PBF) was studied at rest and during submaximal exercise in rats acclimatized to chronic hypoxia (10% O_2 for 3 weeks, A rats) and in nonacclimatized (NA) littermates. Both A and NA rats exercised in hypoxia (10% O_2) or in normoxia. Regional PBF distribution was determined using nonradioactive microspheres injected into the right atrium. The lungs were cut into 28 samples to determine the relative specific PBF of each sample.The NA rats exposed to normoxia showed a central-to-peripheral gradient of PBF distribution which was not modified by exercise. The PBF pattern was not altered by acute hypoxia during resting conditions ; however, the heterogeneity of PBF distribution showed a significant increase during exercise in acute hypoxia. In the A rats, the central-to-peripheral gradient observed at rest was attenuated with respect to that of the NA rats ; this was the case for both hypoxic and normoxic conditions. Normoxic exercise did not influence the distribution of PBF in the A rats ; however, as it happened in the NA rats, PBF distribution showed a significant increase in heterogeneity during hypoxic exercise. These data indicate that the relatively homogeneous distribution of PBF in the rat is altered by the combination of hypoxia and exercise, suggesting that both hypoxic pulmonary vasoconstriction and elevated blood flow are necessary to significantly increase the heterogeneity of PBF distribution. Pao_2 significantly increased during hypoxic exercise, suggesting a higher efficacy of pulmonary gas exchange. This could be because the changes in PBF distribution are matched by parallel changes in the ventilation distribution during hypoxic exercise.