EFFECTS OF TRAINING ON THE DEVELOPMENT OF EXERCISE-INDUCED ARTERIAL HYPOXEMIA IN HORSES

Objectives-To compare the development of exercise-induced arterial hyp oxemia in horses before and after training, and to determine whether i ncreases in maximum oxygen uptake ((V) over dot(O2max)) following trai ning results in a greater degree of exercise-induced arterial hypoxemi a. Animals-13 three- to five-year-old Standardbred geldings without cl inical signs of respiratory or cardiovascular disorders. Procedure-Hor ses were rested for 4 months prior to commencing a 16-week training pr ogram. Arterial blood was collected from the transverse facial artery during standardized exercise tests performed before and after 8 and 16 weeks of training. Variables measured during exercise tests included arterial blood gas tensions and (V) over dot(O2max). Training and test ing was performed on a treadmill set at a 10% slope. Results-Minimum a rterial partial pressures of oxygen (Pa-o2) during exercise decreased from 83.3 +/- 1.5 mm of Hg before training to 77.8 +/- 1.0 mm of Hg af ter 16 weeks of training. Maximum arterial oxygen content increased fr om 239.2 +/- 3.1 to 257.9 +/- 3.8 ml/L, which resulted from an increas e in hemoglobin concentration. The (V) over dot(O2max) increased by 19 % following training. Minimum values of PaO2 and arterial oxygen satur ation were significantly correlated with when data from each stage of training were pooled. Calculated values for minimum alveolar oxygen te nsion decreased after 8 weeks of training, and alveolar ventilation in creased at the end of training. Alveolar-arterial oxygen tension diffe rence increased by 4 mm of Hg following training. Conclusions-in train ed horses, an increase in (V) over dot(O2max) is associated with a dec rease in minimum Pa-O2 during intense exercise and is mostly attributa ble to an increase in the alveolar-arterial oxygen tension difference. Therefore, interpretation of blood gas data from exercising horses sh ould take into consideration (V) over dot(O2max).