Exercise alters fractal dimension and spatial correlation of pulmonary blood flow in the horse

We determined the changes in fractal dimensions and spatial correlations of regional pulmonary blood flow with increasing exercise in race horses (n = 4) by using 15-mu m fluorescent microspheres. Fluorescence was measured to quantitate regional blood to 1.3-cm(3) samples (n = 1,621-2,503). Perfusio n distributions were characterized with fractal dimensions (a measure of sp atial variability) and spatial correlations. On average, the fractal dimens ion decreased with exercise (trot 1.216 to gallop 1.173; P < 0.05) despite a variable fractal dimension at rest. Spatial correlation of flow to neighb oring pieces increased with exercise (trot 0.57 +/- 0.074 to gallop 0.73 +/ - 0.051) and was inversely correlated with fractal dimension, indicating be tter spatial correlation as blood flow distribution becomes more uniform. T his is the first study to document a change in fractal dimension as a resul t of increasing pulmonary blood flow. Spatial differences in response to va soregulatory mediators may play a role in this phenomenon.