| Popis: |
During short-term maximal exercise, horses have impaired pulmonary gas exchange, manifested by diffusion limitation and arterial hypoxemia, without marked ventilation-perfusion (V˙a/Q˙) inequality. Whether gas exchange deteriorates progressively during prolonged submaximal exercise has not been investigated. Six thoroughbred horses performed treadmill exercise at ∼60% of maximal oxygen uptake until exhaustion (28–39 min). Multiple inert gas, blood-gas, hemodynamic, metabolic rate, and ventilatory data were obtained at rest and 5-min intervals during exercise. Oxygen uptake, cardiac output, and alveolar-arterial[Formula: see text] gradient were unchanged after the first 5 min of exercise. Alveolar ventilation increased progressively during exercise, from increased tidal volume and respiratory frequency, resulting in an increase in arterial[Formula: see text] and decrease in arterial[Formula: see text]. At rest there was minimalV˙a/Q˙inequality, log SD of the perfusion distribution (log SDQ˙) = 0.20. This doubled by 5 min of exercise (log SDQ˙= 0.40) but did not increase further. There was no evidence of alveolar-end-capillary diffusion limitation during exercise. However, there was evidence for gas-phase diffusion limitation at all time points, and enflurane was preferentially overretained. Horses maintain excellent pulmonary gas exchange during exhaustive, submaximal exercise. AlthoughV˙a/Q˙inequality is greater than at rest, it is less than observed in most mammals and the effect on gas exchange is minimal. |
