Carotid body potentiation induced by intermittent hypoxia: implications for cardiorespiratory changes induced by sleep apnoea.

1. The most usual form of chronic hypoxia in humans is the intermittent hypoxia resulting from obstructive sleep apnoea (OSA). The OSA syndrome is a highly prevalent sleep breathing disorder that is considered an independent risk factor for hypertension and cardiovascular diseases. Endothelial dysfunction, oxidative stress, inflammation and sympathetic activation have been proposed as potential mechanisms involved in the onset of the hypertension. However, evidence for a unique pathogenic mechanism has been difficult to establish in OSA patients because of concomitant comorbidities. Thus, animal models have been developed to study the pathological consequences of exposure to chronic intermittent hypoxia (CIH). 2. Because OSA patients and animals exposed to CIH show augmented ventilatory, sympathetic and cardiovascular responses to acute hypoxia, it has been proposed that enhanced carotid body responsiveness to hypoxia is involved in the autonomic changes induced by OSA and in the development of the hypertension. Recently, this proposal has received further support from recordings of carotid body chemosensory neural discharges in situ and in vitro showing that exposure of animals to CIH increases basal carotid body chemosensory discharges and enhances the chemosensory response to hypoxia. 3. In the present brief review, we discuss the evidence supporting an important role for the carotid body in the progression of cardiorespiratory changes induced by OSA and the contribution of oxidative stress, endothelin-1 and pro-inflammatory molecules in the potentiation of the carotid body chemosensory function induced by CIH.