REGIONAL PULMONARY BLOOD-FLOW DURING REST, TILT, AND EXERCISE IN UNANESTHETIZED DOGS

We assessed the heterogeneity of regional pulmonary blood flow (PBFr), using radioactive microspheres in five unanesthetized dogs standing a t rest (Rest), standing at a 45 degrees upward tilt (Tilt), and during moderate treadmill exercise (Exer). The excised lungs were cut into 1 -cm(3) pieces along transverse, horizontal, and longitudinal planes. M ean PBFr increased from 23.3 ml . min(-1). g(-1) at Rest to 57.4 ml . min(-1). g(-1) during Exer, but the relative dispersions were not stat istically different between states (47.3-51.9%). A small but significa nt gravity-dependent gradient in PBFr of less than or equal to 4.7%/cm (r(2) less than or equal to 0.118) as well as a PBFr decreasing radia l gradient from the lung midpoint of less than or equal to 7.2%/cm (r( 2) less than or equal to 0.108) were present in all states. PBFr at Re st was highly correlated with those at Tilt (r(2) = 0.773) and Exer (r (2) = 0.888), and a variable PBFr gradient of less than or equal to 2. 5%/cm from base to apex was observed. Fractal dimensions calculated us ing relative dispersion as a function of aggregated sample size were n ot significantly different between states and were 1.132 (r(2) = 0.987 ) at Rest, 1.121 (r(2) = 0.973) at Tilt, and 1.149 (r(2) = 0.986) duri ng Exer. Thus, gravity and centripetal gradients consistently accounte d for a maximal difference of only about twofold in PBFr and <11% of o verall PBFr heterogeneity in 1-cm(3) samples. Recursive anatomic branc hing of pulmonary arteries and local mechanical factors apparently acc ount for most of the blood flow heterogeneity in small pieces of lung.