REGIONAL BLOOD-FLOW IN CANINE ATRIA DURING EXERCISE

Global and regional atrial blood flow was measured with radioisotope-l abeled microspheres in eight dogs during rest and two levels of exerci se. Both mean right and left atrial blood flow increased significantly (P < 0.05) to a similar degree with each level of exercise (right atr ia: 0.27 +/- 0.04, 0.89 +/- 0.11, and 1.57 +/- 0.21 ml.-min-1.g-1; lef t atria: 0.35 +/- 0.04, 0.90 +/- 0.09, and 1.61 +/- 0.17 ml.min-1.g-1) . Atrial blood flow during exercise is greater than anticipated if inc reased heart rate was the sole cause. In both right and left atria the ratio of appendage to nonappendage flow was significantly (P < 0.005) less than one during resting conditions (0.42 +/- 0.04 and 0.81 +/- 0 .05, respectively), not different from unity during mild exercise, and significantly (P < 0.02) greater than one during moderate exercise (1 .10 +/- 0.03 and 1.16 +/- 0.05, respectively). This disparity in the b lood flow to the appendage and nonappendage regions suggests that the appendage plays an augmented hemodynamic role during exercise, thus re quiring a larger proportion of the nutrient flow.