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

本文研究了慢性低氧习服大鼠(10%O2连续3周)和未习服仔鼠安静状态和亚极量运动时肺血流量的局部分布。A、NA大鼠在低氧(10%O_2)或常氧条件下进行运动。用右心房注射非放射性微球测定PBF的局部分布。将大鼠肺切成28个样本，测定每个样本的相对特异性PBF。常氧暴露下的NA大鼠的PBF分布呈现从中心到外周的梯度，运动不会改变这种梯度。安静状态下急性低氧不改变PBF分布模式，但急性低氧运动时PBF分布的不均一性显著增加。在A组大鼠中，静息时观察到的中心到外周的梯度相对于NA组大鼠的梯度有所减弱；这在低氧和正常氧条件下都是如此。常氧运动不影响PBF在A组大鼠体内的分布，但与NA组大鼠一样，在低氧运动过程中，PBF分布的异质性显著增加。这些数据表明，低氧和运动联合作用改变了PBF在大鼠体内的相对均匀分布，提示缺氧性肺血管收缩和血流量增加是显著增加PBF分布的异质性所必需的。低氧运动时PaO_2显著升高，提示肺内气体交换效率较高。这可能是因为PBF分布的变化与低氧运动期间通风分布的平行变化相匹配。

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.