Journal of Applied Physiology, Vol 62, Issue 1 141-148, Copyright © 1987 by American Physiological Society
Ventilatory and blood gas dynamics at onset and offset of exercise in the pony
S. K. Powers, R. E. Beadle, D. Thompson and J. Lawler
The purpose of these experiments was to examine the temporal pattern of
arterial carbon dioxide tension (PaCO2) to assess the relationship between
alveolar ventilation (VA) and CO2 return to the lung at the onset and
offset of submaximal treadmill exercise. Five healthy ponies exercised for
8 min at two work rates: 50 m/min 6% grade and 70 m/min 12% grade. PaCO2
decreased (P less than 0.05) below resting values within 1 min after
commencement of exercise at both work rates and reached a nadir at 90 s.
PaCO2 decreased maximally by 2.5 and 3.5 Torr at the low and moderate rate,
respectively. After the nadir, PaCO2 increased across time during both work
rates and reached values that were not significantly different (P greater
than 0.05) from rest at minute 4 of exercise. Partial pressure of O2 in
arterial blood and arterial pH reflected hyperventilation during the first
3 min of exercise. At the termination of exercise PaCO2 increased (1.5
Torr) above rest (P less than 0.05), reaching a zenith at 2-3 min of
recovery. These data suggest that VA and CO2 flow to the lung are not
tightly matched at the onset and offset of exercise in the pony and thus
challenges the traditional concept of blood gas homeostasis during muscular
exercise.
