Role of carotid body activity responsible for hypoxic ventilatory decline in awake humans

Long, W. Q., G. G. Giesbrecht, and N. R. Anthonisen. Ventilatory response to moderate hypoxia in awakechemodenervated cats. J. Appl. Physiol. 74(2): 805-810, 1993.In humans and cats the ventilatory response to 30 min ofmoderate hypoxia (arterial PO₂ 40-55Torr) is biphasic: ventilation increases sharply for the first 5 minand then declines. In humans there is evidence that the decline isdependent on the initial increase. We therefore examined ventilatoryresponses to moderate isocapnic hypoxia in awake cats with and withoutcarotid body denervation. Cats underwent denervation or a shamoperation. Then they were studied in a Drorbaugh-Fenn plethysmographwhile ventilation, arterial PO₂, and end-tidal PO₂ and PCO₂ weremeasured. Three sham-operated and four denervated cats were studiedwith room air as the control. Sham animals demonstrated a biphasicresponse: ventilation rose to 211% of control at 5 min and fell to114% of control at 25 min. Denervated animals showed neither theinitial increase nor the subsequent decrease in ventilation. Threesham-operated and three denervated cats were studied with 2%CO₂ added to the inspirate. Results were similar: intactcats showed a biphasic response to hypoxia, whereas denervated catsshowed neither an increase nor a decrease in ventilation. Preliminaryexperiments showed that hypoxia was not associated with changes inCO₂ output or systemic blood pressure in either denervatedor intact animals. We conclude that depression of ventilation does notoccur in awake denervated cats in response to moderate hypoxiaand that the decline in ventilation that occurs in intact cats is insome way dependent on peripheral chemoreceptor output.