TEMPORAL HETEROGENEITY OF REGIONAL PULMONARY PERFUSION IS SPATIALLY CLUSTERED

This study investigates temporal changes in regional pulmonary perfusi on. Five dogs were studied with five or six different radiolabeled mic rospheres being injected via a central vein over 30 s every 20 min. Th e lungs of each animal were cubed into 1.9 cm(3) pieces with spatial c oordinates noted for each piece. Within individual pieces, the coeffic ient of variation of regional perfusion over time was 17.2 +/- 6.8% (S D) and across dogs accounted for 7.26 +/- 5.7% of total perfusion hete rogeneity. Temporal variability or ''twinkling'' was not random. When lung pieces with similar temporal flow patterns were grouped together (regardless of spatial location), groups were more tightly clustered i n space than expected by chance. Statistical clustering methods reveal ed regulation of blood flow on a large scale (lobar arteries), and fra ctal analyses suggested regulation existed on a smaller scale (arterio les). We conclude that regional pulmonary perfusion is heterogeneous o ver time in a nonrandom pattern and that pieces clustered by temporal patterns of perfusion are neighbors in the spatial domain.