Temporal pattern of pulmonary gas exchange during exercise in ponies

We characterized the temporal patterns of pulmonary O2 consumption (VO2) and CO2 excretion (VCO2) in exercising ponies. We also assessed the cardiac, ventilatory, and hematologic contributions to the VO2-VCO2 changes during exercise. At five moderate treadmill work loads in normal ponies, VO2 and VCO2 generally increased progressively throughout the 1st min reaching, respectively, approximately 95 and 80% of steady state by 45-60 s. Between 1 and 1.5 min, Vo2 and Vco2 were either stable or they decreased 300-500 ml, but then each increased slightly, reaching steady-state levels between 3 and 5 min. The increases to steady-state VO2 and VCO2 were clearly not monoexponential. Arterial O2 content (CaO2) increased during exercise, presumably because of mobilization of stored splenic erythrocytes. For example, after 1 and 6 min at 6 mph 3% grade, CaO2 had increased above rest by 3.2 and 4.9 vol%, respectively (P less than 0.05). Hyperventilation during exercise decreased arterial CO2 content (CaCO2) below rest. For example, after 1 and 6 min at 6 mph 3% grade, CaCO2 had decreased below rest by 2.8 and 1 vol%, respectively (P less than 0.05). At all work loads, heart rate (HR) and presumably cardiac output increased rapidly during the 1st min, reaching a maximum by approximately 45 s. HR then decreased (P less than 0.05), reaching a steady state by 3 min of exercise. During the first 1.5 min of exercise in carotid body-denervated (CBD) ponies, the changes in VO2, HR, and CaO2 were temporally delayed relative to the normals, whereas the changes in VCO2 and CaCO2 were relatively augmented.(ABSTRACT TRUNCATED AT 250 WORDS)