O2 transport in ponies during treadmill exercise

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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)