Tracheobronchial perfusion during exercise in ponies

Tracheobronchial circulation during exercise has previously not been examined. Therefore blood flow to the trachea and bronchi (up to 7th generation of branching) was studied in seven healthy adult ponies at rest and during the 3rd and 10th min of exercise performed at a treadmill speed setting of 25 km/h. The ambient air temperature varied from 19 to 20 degrees C and humidity from 35 to 45%. To determine blood flow radionuclide-labeled 15-microns-diameter microspheres were injected into the left ventricle via a catheter advanced from the left carotid artery (exposed using local anesthesia), and a reference sample was obtained from the aorta. Adequate mixing of microspheres with blood was demonstrated by similar perfusion values for left and right kidneys. Exercise increased heart rate (194 +/- 9 and 200 +/- 7 beats/min) and mean aortic pressure (169 +/- 8 and 156 +/- 4 mmHg) of ponies at 3rd and 10th min. Tracheal blood flow (6.7 +/- 0.5 ml.min-1 x 100 g-1) of resting ponies was only one-third of the bronchial blood flow (21.6 +/- 4.9 ml.min-1 x 100 g-1) Significant changes in tracheal perfusion did not occur at 3rd or 10th min of exercise. Although bronchial perfusion also did not change at the 3rd min of exercise, it rose dramatically to 202.8 +/- 30.3 ml.min-1 x 100 g-1 during the 10th min. Concomitantly, renal blood flow decreased at 10th min of exertion. The large increase in bronchial blood flow at 10th min of exertion may have been necessitated by the need to help dissipate body heat.