Ventilatory and metabolic responses to ambient hypoxia or hypercapnia in rats exposed to CO hypoxia

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Abstract
Gautier, Henry, Cristina Murariu, and Monique Bonora.Ventilatory and metabolic responses to ambient hypoxia or hypercapnia in rats exposed to CO hypoxia. J. Appl. Physiol.83(1): 253–261, 1997.—We have investigated at ambient temperatures (Tam) of 25 and 5°C the effects of ambient hypoxia (Hxam; fractional inspired O2 = 0.14) and hypercapnia (fractional inspired CO2 = 0.04) on ventilation (V˙), O2 uptake (V˙o 2), and colonic temperature (Tc) in 12 conscious rats before and after carotid body denervation (CBD). The rats were concomitantly exposed to CO hypoxia (HxCO; fractional inspired CO = 0.03–0.05%), which decreases arterial O2 saturation by ∼25–40%. The results demonstrate the following. 1) At Tam of 5°C, in both intact and CBD rats,V˙/V˙o 2 is larger when Hxam or CO2 is associated with HxCO than with normoxia. At Tam of 25°C, this is also the case except for CO2 in CBD rats. 2) At Tam of 5°C, the changes inV˙o 2 and Tc seem to result from additive effects of the separate changes induced by Hxam, CO2, and HxCO. It is concluded that, in conscious rats, central hypoxia does not depress respiratory activity. On the contrary, particularly whenV˙o 2 is augmented during a cold stress, bothV˙/V˙o 2during HxCO and the ventilatory responses to Hxam and CO2 are increased. The mechanisms involved in this relative hyperventilation are likely to involve diencephalic integrative structures.