Chronic intermittent hypoxia in obstructive sleep apnea: a narrative review from pathophysiological pathways to a precision clinical approach

Obstructive sleep apnea syndrome (OSAS) is a prevalent condition caused by dynamic upper airway collapse during sleep. The pathological impact and consequences are due to chronic intermittent hypoxia (CIH). Hypoxia increases the expression of several inflammatory stress markers and endothelial dysfunction. Recent studies suggest that patients with a similar AHI but with severe nocturnal hypoxia using oximetric parameters, such as the lowest saturation of oxygen during the night (min SaO2), percentage of total sleep time with oxygen saturation < 90% (T90) or the oxygen desaturation index (ODI-3%), commonly reported during the sleep study, are indicative of the increased expression of inflammatory markers due to severe nocturnal hypoxia and CIH during the night compared to subjects with moderate-severe OSAS without severe nocturnal hypoxia. The aim of this review is to describe physiological pathways involved in OSAS and their clinical consequences, focused in CIH and oximetric parameters showed in sleep study and their potential utility as inflammatory markers.