Abstract
Horses have high mean pulmonary artery pressure (Ppa) both at rest and during exercise (≈30 and ≥ 80 mmHg, respectively). The mechanisms are unknown. To see if hypoxic pulmonary vasoconstriction (HPV) plays a role, we compared pulmonary artery pressure-flow (Ppa-Q) curves when inspired O 2 fraction (F i O 2 ) was 0.16, 0.21, and 0.30, in 5 noraml Thoroughbred horses standing quitely and while galloping at 10 and 14 m/sec on a level treadmill. We calculated O 2 consumption (V̇ O 2 ) from measurements of respired gas composition and flow, and calculated Q̇ from V̇ O 2 and measurements of oxygen content in arterial and mixed venous blood (Ca O 2 and C v̄ O 2 ). V̇ O 2 was 3.8, 74 and 128 ml·mim −1·kg −1, at rest and at 10 and 14 m/sec, and did not vary with F i O 2 at any speed. At 14 m/sec only, when F i O 2 was lowered to 0.16, Ca O 2 fell (to 14.7 from 20 ml/dl on air), Q̇ increased (to 0.86 from 0.66 L·min −1·kg −1 on air), and stroke volume increased (to 4.1 from 3.2 ml·kg −1 on air). Slopes and intercepts of Ppa-Q̇ curves did not vary with F i O 2 . We concled that HPV does not contribute to the high Ppa of exercising horses breathing air near sea level.
Published Version
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