Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


The purpose of experiment one was to develop and validate an open circuit technique (OCT) employing a mixing-chamber for measurement of gas exchange during non-steady-state exercise in humans and ponies. Serial measurements of oxygen uptake ((')VO(,2)) using human subjects and ponies were made during rest to exercise transitions using the OCT incorporating a time delay to match mixed expired gas concentrations with the appropriate ventilatory volume. Oxygen uptake calculated by the OCT did not differ significantly (P > 0.05) from (')VO(,2) obtained by Douglas bag procedures. These data demonstrate that an OCT analysis system is a sensitive means of (')VO(,2) measurement in the non-steady-state. Experiment two analyzed arterial carbon dioxide tension (PaCO(,2)) dynamics at the onset and offset of exercise in ponies. PaCO(,2) decreased (P < 0.05) below resting values within 1-min after commencement of exercise and remained lower than resting values through min-4 of exercise. At the termination of exercise PaCO(,2) increased significantly (P < 0.05) above rest within min 2-3 of recovery. These data suggest that alveolar ventilation and CO(,2) flow to the lung are not tightly matched at the onset and offset of exercise and thus do not support the CO(,2) hypothesis of ventilatory control in this species. Experiment three examined the O(,2) deficit-O(,2) debt relationship in ponies at two levels of treadmill exercise. The O(,2) deficit was significantly lower (P < 0.05) than the O(,2) debt at each of the two work rates. Further, the size of O(,2) deficit and O(,2) debt increased significantly (P < 0.05) with an increase in work rate. These data suggest a human/pony species difference in the O(,2) deficit-O(,2) debt relationship. The purposes of experiment four were to examine gas exchange kinetics in the pony from rest to exercise and during a work-to-work transition. The kinetic responses of expired ventilation, expired carbon dioxide, and heart rate were unaffected (P > 0.05) by exercise intensity or recent exercise history. Further, with similar metabolic increments, the rate of oxygen uptake ((')VO(,2)) adaptation from rest to exercise was not significantly different (P > 0.05) from the (')VO(,2) time course during work-work transitions. In contrast, the (')VO(,2) half-times were significantly greater (P < 0.05) during the transition from rest to exercise at a moderate work rate when compared to a lower work load.