Stratified distribution of blood flow in secondary lobule of the rat lung

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Abstract
Radiolodlnated macro-aggregated albumin (1131 MAA) of particle size less than 20 [mu] was injected intravenously in 4 rats breathing air, as a marker of pulmonary blood flow distribution. Counterstained radioautographs were prepared from 100-[mu] frozen sections of their fixed, inflated lung lobes. Counting of radioactive particle distribution was carried out in the subpleural 3 mm of lung tissue and In more central parts of the lobes, using counting fields based on the anatomy of the secondary lung lobule. There was a gradient of diminishing particle counts from apex to base of the secondary lobule. Analysis in terms of an anatomically reasonable and internally consistent model indicated a gradient of blood flow per unit of lung volume of about 4:1 from apex to base of the lobule. The gradient was only slightly modified in 2 other rats breathing O2 for 10 min. before I131 MAA Injection. The gradient of stratified blood flow distribution is In the same direction as the ventilation gradient imposed by arrangement of alveolar spaces in series, and will reduce the potential Va/Qc gradient along the gas exchange axis.