Journal of Applied Physiology, Vol 58, Issue 6 1942-1948, Copyright © 1985 by American Physiological Society
Ventilatory changes during exercise and arterial PCO2 oscillations in chronic airway obstruction patients
J. G. Prior, M. Powlson, G. M. Cochrane and C. B. Wolff
Ventilatory kinetics during exercise (30 W for 6 min) were studied in 3
asthmatics, 14 patients with chronic airway obstruction (11 with bronchial
or type B disease, 3 with emphysematous or type A disease), and in 5 normal
age-matched controls. The measure of ventilatory increase during early
exercise, alpha 1-3%, was calculated as (avg minute ventilation over
1st-3rd min of exercise--resting minute ventilation)/(avg minute
ventilation over 4th-6th min of exercise--resting minute ventilation) X
100. Arterial pH, PO2, and PCO2 (PaCO2) were measured in vitro at rest and
within 20 s of termination of exercise. Respiratory PaCO2 oscillations had
previously been monitored at rest in the patients (indirectly as in vivo
arterial pH, using a fast-response pH electrode) and quantified by upslope
(delta PaCO2/delta t). alpha 1-3% was normal in asthmatics (whose
respiratory oscillations as a group showed least attenuation) and in type A
patients (whose respiratory oscillations as a group were most attenuated).
In type B patients reduction in alpha 1-3% correlated with attenuation of
delta PaCO2/delta t (r = 0.75; P less than 0.01). There was no significant
correlation between delta PaCO2/delta t and change of in vitro PaCO2 from
rest to the immediate postexercise period. These findings are consistent
with the hypothesis that attenuation of delta PaCO2/delta t slows
ventilatory kinetics during exercise in type B but not type A patients.
Intact respiratory oscillations are not necessary for CO2 homeostasis after
the first few minutes of exercise.
