28 INTRODUCTION M OUNTAINEERING AND TREKKING EXPEDITIONS at very high altitudes (5000 m) have be- come increasingly popular in the last 20 years. The possibility of persistent cerebral impair- ment from exposure to extreme hypoxia and resulting hypoxemia has been controversially HIGH ALTITUDE MEDICINE & BIOLOGY Volume 7, Number 1, 2006 © Mary Ann Liebert, Inc. Changes in Cerebral Glucose Metabolism after an Expedition to High Altitudes TOBIAS M. MERZ, 1 VALERIE TREYER, 2 URS HEFTI, 3 CHRISTINA M. SPENGLER, 4 URS SCHWARZ, 5 ALFRED BUCK, 2 and MARCO MAGGIORINI 1 ABSTRACT Merz, Tobias M., Valerie Treyer, Urs Hefti, Christina M. Spengler, Urs Schwarz, Alfred Buck, and Marco Maggiorini. Changes in cerebral glucose metabolism after an expedition to high al- titudes. High Alt. Med. & Biol. 7:28–38, 2006.—The possibility of persistent cerebral impairment due to exposure to extreme altitude and resulting hypoxic conditions is of great concern to both high altitude mountaineers and researchers. The aim of the present study was to investigate the effect of prolonged exposure to hypoxia on cerebral glucose metabolism, which probably pre- cedes structural and functional impairment. Positron emission tomography (PET) employing [18F]–2-deoxy-2-fluoro-D-glucose (FDG) was performed, and the normobaric hypoxic ventila- tory response (HVR) was assessed in 11 mountaineers before (pre) and after (post) climbing Mount Shisha Pangma (8048 m). During the climb, acute mountain sickness (AMS) symptoms were recorded and heart rate and oxygen saturation (Sa O 2 ) were measured daily. Neuropsy- chological evaluations were conducted at different heights. The difference FDG post - FDG pre was analyzed voxel by voxel using statistical parametric mapping (SPM) and volumes of interest (VOI). SPM revealed two areas of increased cerebral FDG uptake after the expedition, one lo- calized in the left cerebellum (+9.4%) and one in the white matter lateral of the left thalamus (+8.3%). The VOI analysis revealed increased postexpeditional metabolism in an area of the right cerebellum (+11%) and of the thalamus bilaterally (+3.7% on the left, +4.6% on the right). FDG–PET alterations did not correlate with changes in Sa O 2 , HVR, or AMS scores. All neu- ropsychological test results during the climb were unremarkable. We conclude that a prolonged stay at an extreme altitude leads to regional specific changes in the cerebral glucose metabolism without any signs of neuropsychological impairment during the climb. Key Words: high altitude; hypoxia; cerebral metabolism; cognitive function; FDG-PET 1 Intensive Care Unit of the Department of Internal Medicine, 2 Division of Nuclear Medicine, and 5 Department of Neurology, University Hospital Zurich, Switzerland. 3 Department of Surgery, Kantonsspital Aarau, Switzerland. 4 Institute for Human Movement Sciences, Swiss Federal Institute of Technology and Institute of Physiology, Uni- versity of Zurich, Switzerland.