Bronchial circulation during prolonged exercise in ponies

Summary Tracheal, bronchial, and renal blood flow were studied in 8 healthy ponies at rest and during exercise performed on a treadmill at a speed setting of 20.8 km/h and 7% grade (incline) for 30 minutes. Blood flow was determined with 15-μm-diameter radionuclide-labeled microspheres that were injected into the left ventricle when the ponies were at rest, and at 5, 15, and 26 minutes of exertion. Heart rate and mean aortic pressure increased from resting values (40 ± 2 beats/min and 124 ± 3 mm of Hg, respectively) to 152 ± 8 beats/min and 133 ± 4 mm of Hg at 5 minutes of exercise, to 169 ± 6 beats/min and 143 ± 5 mm of Hg at 15 minutes of exercise, and to 186 ± 8 beats/min, and 150 ± 5 mm of Hg at 26 minutes of exercise. Tracheal blood flow at rest and during exercise remained significantly (P < 0.05) less than bronchial blood flow. Tracheal blood flow increased only slightly with exercise. Vasodilation caused bronchial blood flow to increase throughout exercise. Pulmonary arterial blood temperature of ponies also increased significantly (P < 0.05) with exercise and a significant (P < 0.005) correlation was found between bronchial blood flow and pulmonary arterial blood temperature during exertion. At 5 minutes of exercise, renal blood flow was unchanged from the resting value; however, renal vasoconstriction was observed at 15 and 26 minutes of exercise. We concluded that bronchial circulation of ponies increased with exercise in close association with a rise in pulmonary arterial blood temperature. Also, increased thermal burden necessitated redistribution of blood flow away from kidneys late in exercise.