Effect of progressive normobaric hypoxia on dynamic cerebral autoregulation

Area of Science:

• Physiology
• Neurology
• Environmental Medicine

Background:

• Cerebral autoregulation (CA) maintains stable cerebral blood flow despite fluctuating perfusion pressures.
• Acute hypoxia is known to impair dynamic CA (dCA), but the specific oxygen threshold is not well-defined.

Purpose of the Study:

• To investigate the impact of progressive normobaric hypoxia on dCA.
• To determine the relationship between dCA impairment and acute mountain sickness (AMS) symptoms.

Main Methods:

• Eleven healthy young men underwent progressive normobaric hypoxia (21%, 18%, 15%, 12% O2).
• Dynamic CA was assessed using duplex ultrasonography to measure common carotid artery blood flow and the thigh-cuff method.
• AMS symptoms were evaluated using the Lake Louise Questionnaire during prolonged hypoxia (14.1% O2).

Main Results:

• Dynamic CA progressively decreased as inspired oxygen levels were reduced (P < 0.001).
• A linear relationship was observed between decreasing oxygen levels and dCA reduction.
• AMS symptoms were significantly correlated with changes in dCA at lower oxygen concentrations (15% and 12% O2).

Conclusions:

• Dynamic cerebral autoregulation is impaired progressively with increasing severity of hypoxia.
• Reduced dCA, particularly at moderate to severe hypoxia (<15% O2), is linked to the severity of acute mountain sickness.
• These findings suggest dCA assessment could serve as a sensitive clinical indicator for AMS risk.