Pulmonary capillary perfusion: intra-alveolar fractal patterns and interalveolar independence

Pulmonary capillary perfusion was analyzed from videomicroscopic recordings to determine flow switching characteristics among capillary segments in is olated, blood-perfused canine lungs. Within each alveolus, the rapid switch ing pattern was repetitive and was, therefore, nonrandom (fractal dimension s near 1.0). This self-similarity over time was unexpected in a network wid ely considered to be passive. Among adjacent alveoli, the relationship amon g the switching patterns was even more surprising, for there was virtually no relationship between the perfusion patterns (coefficients of determinati on approaching zero). These findings demonstrated that the perfusion patter ns in individual alveolar walls were independent of their next-door neighbo rs. The lack of dependence among neighboring networks suggests an interesti ng characteristic: the failure of one alveolar-capillary bed would leave it s neighbors relatively unaffected, a feature of a robust design.