Hypoxia-induced bronchial responsiveness in awake sheep: role of carotid chemoreceptors.

Hypoxia enhances bronchial responsiveness in sheep and dogs and we recently reported a similar effect in asthmatic subjects. Activation of a reflex arc due to stimulation of peripheral chemoreceptors has been suggested to explain this finding. We evaluated the contribution of carotid body chemoreceptors to hypoxia-induced bronchial responsiveness in conscious sheep. Incremental concentrations of aerosolized methacholine were given to each of seven sheep ventilated successively (in a random order) with a normoxic and a hypoxic gas mixture (15% O2 in N2), both before and after peripheral surgical chemodenervation. Hypoxia alone did not affect lung mechanics in intact or chemodenervated animals. Bronchial responsiveness to methacholine was significantly increased by hypoxia in intact sheep, as compared to chemodenervated sheep. We conclude that hypoxia has a stimulating effect on bronchial responsiveness in awake sheep similar to that seen in human patients with asthma. This increased responsiveness may be mediated by hypoxic stimulation of carotid body chemoreceptors, which in turn may influence the nervous control of airway calibre.