| Abstract: | We assessed cardiovascular variables and blood O2 contents in order to characterize O2 transport in ponies during treadmill exercise. In normal ponies at 1.8, 3, and 6 mph, respectively, cardiac output (Qc) increased from 12 l/min at rest to maximum levels of 19.7, 28.7, and 39.9 l/min between 30 and 60 s. Qc then decreased to steady-state levels of 18.2, 24.6, and 32.7 l/min by 4 min. Heart rate (HR) showed a similar biphasic response in the 1st min of exercise. Systolic and diastolic arterial blood pressure (BP) decreased at the onset of exercise by 20-25 Torr (P less than 0.05) and then increased to a steady-state by 60 s. Mean right ventricular pressures (MRVBP) increased from approximately 9.7 Torr at rest to 15.9 (1.8 mph), 15.2 (3 mph), and 23.6 Torr (6 mph) by 1 min and then decreased throughout the remainder of the 8 min of exercise (P less than 0.05). At 3 and 6 mph, respectively, arterial O2 content (CaO2) increased from 11.6 vol% at rest to 12.7 and 15.0 vol% by 45 s and 13.1 and 16.6 vol% by 7 min. At 7 min of 9.3 mph exercise, it increased to 20.34 vol%. Hemoglobin (Hb) at 3 mph increased from 9.6 g/100 ml at rest to 10.5 g/100 ml by 45 s and 11.7 g/100 ml by 7 min. At 6 mph, Hb increased to 12 g/100 ml at 45 s and 13.0 g/100 ml by 7 min of exercise. These data demonstrate that the rapid, work load-dependent increase in CaO2 represents an important mechanism to increase O2 transport in exercising ponies.(ABSTRACT TRUNCATED AT 250 WORDS) |
