AltitudeOmics: cerebral autoregulation during ascent, acclimatization, and re-exposure to high altitude and its relation with acute mountain sickness

Abstract

Cerebral autoregulation (CA) acts to maintain brain blood flow despite fluctuations in perfusion pressure. Acute hypoxia is thought to impair CA, but it is unclear if CA is affected by acclimatization or related to the development of acute mountain sickness (AMS). We assessed changes in CA using transfer function analysis of spontaneous fluctuations in radial artery blood pressure (indwelling catheter) and resulting changes in middle cerebral artery blood flow velocity (transcranial Doppler) in 21 active individuals at sea level upon arrival at 5,260 m (ALT1), after 16 days of acclimatization (ALT16), and upon re-exposure to 5,260 m after 7 days at 1,525 m (POST7). The Lake Louise Questionnaire was used to evaluate AMS symptom severity. CA was impaired upon arrival at ALT1 (P < 0.001) and did not change with acclimatization at ALT16 or upon re-exposure at POST7. CA was not associated with AMS symptoms (all R < 0.50, P > 0.05). These findings suggest that alterations in CA are an intrinsic consequence of hypoxia and are not directly related to the occurrence or severity of AMS.

The Leicester cerebral haemodynamics database: normative values and the influence of age and sex

“…1), a threshold of ARI < 4 could still be considered appropriate in situations where investigators want to favour sensitivity, in detriment of specificity, to identify patients that might be at risk of secondary damage due to weakening of CA. This threshold correlates well with studies that have reported abnormality of dCA in patients with severe head injury (Panerai et al 2004), carotid artery disease (Panerai et al 1998b), stroke (Salinet, Panerai & Robinson 2014, Saeed et al 2013), high altitude depression of CA (Subudhi et al 2014) and other conditions (Panerai 2008). …”

The Contribution of Arterial Blood Gases in Cerebral Blood Flow Regulation and Fuel Utilization in Man at High Altitude

“…Many studies have concluded that autoregulation is impaired at HA (e.g., ref. 25), although this is not a universal finding and surely relates to lack of a consensual metric for the quantification of CA. 26 A number of studies have found an important function of the sympathetic nervous system in attenuating surges in CBF (reviewed in ref.…”

Acute high-altitude sickness

“…Disturbed autoregulation may occur in AMS [35,46] and could enhance pressure transduction to the brain, although findings are controversial [47]. Repeated transient increases of ICP may sensitise trigeminal nociception [48] and decrease compliance of the CNS to a variable degree, since the capacity for spatial compensation varies considerably between individuals [49].…”