Right Temporal Cerebral Dysfunction Heralds Symptoms of Acute Mountain Sickness

Background: We prospectively investigated the effects of high altitude mountain trekking on brain function measured by electroencephalography (EEG) and transcranial doppler sonography (TCD) in relation to endexpiratory CO2 (EtCO2) peripheral O2 saturation (SaO2) and symptoms of acute mountain sickness (AMS). Methods: The studiy was performed during a common trekking route at the Khumbu Himal, Nepal, from Lukla (2865m) to the Silver Pyramid (5050m) near the Everest Base Camp. EEG and TCD were performed at baseline (100m), and at altitudes of 3440m and 5050m. SaO2, EtO2 and Lake-Louise-AMS Score was evaluated daily twice. Of 26 mountaineers who reached 5050m, we excluded four, who developed symptoms of AMS prior to reaching or at 3440m and those, whose EEGs showed excessive artefacts. Results: The 12 individuals, who developed later symptoms of AMS (Lake-Louise-AMS Score ≥3) showed a significant increase of right temporal delta activity (powerspectral analysis) between 100m and 3440m compared with the 10 healthy subjects (p<0.05). In addition, the symptomatic climbers showed an increase of mean cerebral blood flow velocity of the right medial cerebral artery (depth 55mm) between 3440m and 5050m compared to the asymptomatic climbers (P<0.05). The increase of right temporal delta activity between 100m and 5050m in EEG power spectrum correlated negatively (r=-0.650, P<0.05) with a EtCO2 decrease (-28%) in the symptomatic group. Conclusion: The alteration of right temporal brain function as documented by EEG precedes the appearance of symptoms of AMS. Increase of cerebral blood flow in this area might reflect a compensatory mechanism due to the increased demand of oxygen. The negative correlation between EtCO2 and the EEG changes may reflect insufficient compensatory hyperventilation. Acknowledgements: This study was supported by grants from the Austrian Society of Alpine and High Altitude Medicine (ÖGAHM), Bayrische Sparkassenstiftung and Münchner Zeitungsverlag. We thank RONAST, Comitato Ev-K2-CNR Bergamo for free use of the Pyramid Laboratory, High Country Trekking and all participants.