Effect of multiple denervations on the exercise hyperpnea in awake ponies. Pan, L. G., H. V. Forster, R. D. Wurster, A. G. Brice, and T. F. Lowry. Program in Physical Therapy, Marquette University, Milwaukee, WI 53233 and Department of Physiology, The Medical College of Wisconsin, Milwaukee, WI 53226 and Zablocki Veteran's Administration Medical Center, Milwaukee, WI 53226
APStracts 2:0107A, 1995.
In three previously reported studies, we had documented that the normal exercise hyperventilation in ponies is accentuated by carotid body denervation (CBD), not affected by hilar nerve pulmonary vagal denervation (HND), and mildly attenuated by spinal cord ablation of the dorsal lateral columns at L2 (SA). In the present study, we hypothesized that if redundancy of control existed in exercising ponies, then multiple denervations of theoretically important pathways in the same animal, might attenuate the ventilatory response to exercise in a way not predictable by the individual lesion experiments alone. There were three major findings in the various combinations of CBD, HND, and SA in ponies during treadmill exercise. First, the combination of CBD with HND or SA resulted generally in an accentuation of the hypocapnia during exercise that was predictable on the basis of CBD alone. However in one pony who showed a hypercapnic exercise response after SA alone, CBD subsequently caused a greater exercise hypercapnia. Second, HND in a CBD or SA pony did not affect the exercise PaCO2 response consistent with previous data showing the lack of an HND effect in otherwise intact ponies. Third, in ponies with all three denervations together, the predominant response was an increase not a decrease in the exercise hyperventilation; this increase was greater than that predicted from the individual lesions. We conclude that these data do not provide evidence of redundancy in mechanism for the exercise hyperpnea other than instances of carotid chemoreceptor error sensing when hypercapnia occurs during exercise. 

Received 2 August 1991; accepted in final form 16 February 1995.
APS Manuscript Number A788-1.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.