Journal of Applied Physiology, Vol 55, Issue 5 1426-1432, Copyright © 1983 by American Physiological Society
Effects of small changes in PaO2 on the ventilatory response to CO2 infusion
F. M. Bennett, R. D. Tallman Jr and F. S. Grodins
The steady-state ventilatory responses to CO2 inhalation and two levels of
intravenous CO2 infusion were examined in chronic awake dogs. Responses
were obtained for four treatments: 1) air breathing, in which arterial O2
tension (PaO2) increased during infusion; 2) normoxia, PaO2 maintained at
control levels; 3) hypoxia, PaO2 = 70 Torr; and 4) hyperoxia, PaO2 = 160
Torr. In three dogs, the ventilatory responses were obtained for treatments
1, 2, and 4 and in an additional three dogs for treatments 2, 3, and 4.
Analysis of the data by directional statistics indicates that the response
to infusion was hypercapnic for all treatments, and the slope of the
response (change in minute ventilation divided by change in arterial CO2
tension) was identical to that of CO2 inhalation. Also, the slopes of the
responses for the low infusion rate, CO2 output (VCO2) = 50%, and the high
infusion rate, VCO2 = 270%, were identical, which suggests that the CO2
response is not significantly curvilinear near the eucapnic region.
Finally, changing PaO2 between 70 and 160 Torr had no significant effect on
the response slopes. Thus the ventilatory response to CO2 infusion in the
awake dog is a hypercapnic hyperpnea that is not due to ventilatory
inhibition arising from an increase in PaO2.
