Regional blood flow in canine atria during exercise

Global and regional atrial blood flow was measured with radioisotope-labeled microspheres in eight dogs during rest and two levels of exercise. Both mean right and left atrial blood flow increased significantly (P < 0.05) to a similar degree with each level of exercise (right atria: 0.27 +/- 0.04, 0.89 +/- 0.11, and 1.57 +/- 0.21 ml.min-1 x g-1; left atria: 0.35 +/- 0.04, 0.90 +/- 0.09, and 1.61 +/- 0.17 ml.min-1 x g-1). Atrial blood flow during exercise is greater than anticipated if increased 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 blood flow to the appendage and nonappendage regions suggests that the appendage plays an augmented hemodynamic role during exercise, thus requiring a larger proportion of the nutrient flow.