[Effects of the addition of carbon dioxide on manifestations of acute hypoxia in rats].

In pentobarbitalized rats, hypoxia induced by inhalation of O2 8%-N2 92%, produces a transient hyperventilation which is followed by a respiratory depression and an apnea. A cardiovascular collapse is then observed. Correction of the hypocapnia depending on the initial hyperventilation, by inhalation of a gas mixture containing 4% CO2 maintains the hyperventilation and suppresses the cardiovascular collapse. Carbon dioxide activity is both a direct one by stimulation of respiratory centers and an indirect one by increasing the sensitivity of the peripheral arterial chemoreceptors to hypoxia. Four percent carbon dioxide just compensating hypocapnia are sufficient to prevent apnea and vascular collapse. The increase of this concentration up to hypercapnia complicates the interpretation of the results by addition of hypoxic and hypercapnic effects.