BREATHING AND BRAIN BLOOD-FLOW DURING SLEEP IN PATIENTS WITH CHRONIC MOUNTAIN-SICKNESS

Chronic mountain sickness (CMS) patients have lower arterial O-2 satur ation (Sa(O2)) during sleep compared with healthy high-altitude reside nts, but whether nocturnal arterial Oa content (Ca-O2) and brain O-2 d elivery are reduced is unknown. We measured Sa(O2), Ca-O2, sleep-disor dered breathing (SDB), and internal carotid artery flow velocity in 8 CMS patients, 8 age-matched healthy CMS controls, 11 healthy younger-a ged Han, and 11 healthy younger-aged Tibetan male residents of Lhasa, Tibet (3,658 m). CMS patients spent a greater portion of the night in SDB (total no. of episodes of apnea, hypopnea, and hypoventilation) th an did the CMS controls, young Han, or young Tibetans (15% vs. 5, 1, a nd 1%, respectively; P < 0.05) because of more frequent apnea and hypo ventilation episodes and longer duration of all types of episodes. SDB and unexplained arterial O-2 desaturation caused nocturnal Sa(O2) to be lower and more variable in CMS patients than in CMS controls or in younger-aged Han or Tibetan men. Average Ca-O2 was similar, but the CM S patients spent 29%, whereas the other groups spent <4%, of the night at values <18 ml O-2/100 ml whole blood. Internal carotid artery flow velocity during wakefulness was similar in CMS patients and CMS contr ols despite higher end-tidal Pco(2) values in the CMS patients. When c ontiguous sleep stages are compared, flow velocity rose from stage 2 t o rapid-eye-movement sleep in both groups. Whereas flow velocity remai ned elevated from awake to rapid-eye-movement sleep in the CMS control s, it fell in the CMS patients. During episodes of SDB, internal carot id flow velocity increased in CMS controls but did not change in the C MS patients such that values were lower in the CMS patients than in CM S controls at the end and after SDB episodes. We concluded that SDB an d episodes of unexplained desaturation lowered nocturnal Sa(O2) and Ca -O2, which, together with a lack of compensatory increase in internal carotid artery flow velocity, likely decreased brain O-2 delivery in C MS patients during a considerable portion of the night.