Journal of Applied Physiology, Vol 45, Issue 1 94-101, Copyright © 1978 by American Physiological Society
Cerebrospinal fluid acid-base balance during muscular exercise
G. E. Bisgard, H. V. Forster, B. Byrnes, K. Stanek, J. Klein and M. Manohar
Ventilation, metabolism, arterial blood gases, and blood and cerebrospinal
fluid (CSF) acid-base status were measured in exercise studies on seven
ponies during mild, moderate, and near-maximal treadmill exercise. CSF and
arterial blood were sampled via indwelling catheters. Generally
measurements were made during the 3rd, 6th, and 9th minute of steady-state
exercise, with CSF sampled only during the 9th minute. Alveolar ventilation
(VA) and metabolic rate (VO2) increased proportionately during exercise
below the anaerobic threshold, but above this threshold, VA increased at a
faster rate than VO2. The similarity of these response to those observed in
man suggests the pony is a suitable animal model for study of exercise
hyperpnea. No change in CSF acid-base balance occurred with
light-to-moderate work; however, with near-maximal work a fall in CSF
carbon dioxide partial pressure due to hyperventilation caused CSF to
become alkaline (pH = 7.380) relative to rest (pH = 7.330). CSF lactate
increased slightly with exercise but had no effect on CSF [HCO3-], which
remained constant from rest to severe exercise. We conclude that it is
unlikely the hyperpnea at any intensity of exercise results from an
increased H+ stimulation at the medullary chemoreceptor.
