Journal of Applied Physiology, Vol 45, Issue 1 109-114, Copyright © 1978 by American Physiological Society
Respiratory responses to intravenous and intrapulmonary CO2 in awake dogs
E. C. Greco, W. E. Fordyce, F. Gonzalez, P. Reischl and F. S. Grodins
Ventilatory responses to CO2 inhalation and CO2 infusion were compared in
the awake dog. The CO2 was introduced directly into the systemic venous
blood via a membrane gas exchanger in a femoral arteriovenous shunt
circuit, and the extracorporeal blood flow, QX, was maintained constant at
one of two rates: low, 0.5 l/min; or high, 2.0 l/min. A total of 13
experiments was performed in four dogs comprising 50 control and 25
inhalation and infusion observations at each of the two flow rates.
Comparison of CO2-response curve slopes, S = delta V E/delta PaCO2, between
CO2 inhalation and infusion showed no significant difference either within
or between flow rates. The mean value of S for all conditions was 1.88
l/min per Torr with a 95% confidence interval of 1.66 -2.14. An independent
additive ventilatory drive amounting to 28% of low-flow control VE was
found at the highflow rate. We conclude that at constant blood flow the
responses to both CO2 inhalation and infusion are hypercapnic and not
significantly different.
