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

Departments of 1 Anesthesiology, 2 Physiology/Biophysics, and 3 Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120; 4 Department of Chest Medicine, Chiba University School of Medicine, Chiba 260, Japan; and 5 Departments of Medicine and Physiology/Biophysics, School of Medicine, University of Washington, Seattle, Washington 98195-0001 Pulmonary capillary perfusion was analyzed from videomicroscopic recordings to determine flow switching characteristics among capillary segments in isolated, blood-perfused canine lungs. Within each alveolus, the rapid switching pattern was repetitive and was, therefore, nonrandom (fractal dimensions near 1.0). This self-similarity over time was unexpected in a network widely considered to be passive. Among adjacent alveoli, the relationship among the switching patterns was even more surprising, for there was virtually no relationship between the perfusion patterns (coefficients of determination approaching zero). These findings demonstrated that the perfusion patterns in individual alveolar walls were independent of their next-door neighbors. The lack of dependence among neighboring networks suggests an interesting characteristic: the failure of one alveolar-capillary bed would leave its neighbors relatively unaffected, a feature of a robust design. pulmonary microcirculation; dogs