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Transcranial Doppler is a widely used noninvasive technique for assessing cerebral artery blood flow. All previous high altitude studies assessing cerebral blood flow (CBF) in the field that have used Doppler to measure arterial blood velocity have assumed vessel diameter to not alter. Here, we report two studies that demonstrate this is not the case.(More)
Exposure to the underwater environment for recreational or occupational purposes is increasing. Approximately 7 million divers are active worldwide and 500,000 more are training every year. Diving related illnesses are consequently an increasingly common clinical problem with over 1000 cases of decompression illness reported annually in the USA alone.(More)
Many disease states are associated with regional or systemic hypoxia. The study of healthy individuals exposed to high-altitude hypoxia offers a way to explore hypoxic adaptation without the confounding effects of disease and therapeutic interventions. Using (31)P magnetic resonance spectroscopy and imaging, we investigated skeletal muscle energetics and(More)
Lowland residents adapt to the reduced oxygen availability at high altitude through a process known as acclimatisation, but the molecular changes underpinning these functional alterations are not well understood. Using an integrated biochemical/whole-body physiology approach we here show that plasma biomarkers of NO production (nitrite, nitrate) and(More)
We report the first direct observations of deranged microcirculatory blood flow at high altitude, using sidestream dark-field imaging. Images of the sublingual microcirculation were obtained from a group of 12 volunteers during a climbing expedition to Cho Oyu (8,201 m) in the Himalayas. Microcirculatory flow index (MFI) was calculated from the moving(More)
BACKGROUND The physiological responses to hypoxaemia and cellular hypoxia are poorly understood, and inter-individual differences in performance at altitude and outcome in critical illness remain unexplained. We propose a model for exploring adaptation to hypoxia in the critically ill: the study of healthy humans, progressively exposed to environmental(More)
The Caudwell Xtreme Everest (CXE) expedition involved the detailed study of 222 subjects ascending to 5300 m or higher during the first half of 2007. Following baseline measurements at sea level, 198 trekker-subjects trekked to Everest Base Camp (EBC) following an identical ascent profile. An additional group of 24 investigator-subjects followed a similar(More)
Xtreme Everest 2 (XE2) was part of an ongoing programme of field, laboratory and clinical research focused on human responses to hypoxaemia that was conducted by the Caudwell Xtreme Everest Hypoxia Research Consortium. The aim of XE2 was to characterise acclimatisation to environmental hypoxia during a standardised ascent to high altitude in order to(More)
BACKGROUND Cerebral blood flow velocity (CBFV) and sleep physiology in healthy children exposed to hypoxia and hypocarbia are under-researched. AIM To investigate associations between sleep variables, daytime end-tidal carbon dioxide (EtCO2) and CBFV in children during high-altitude ascent. METHODS Vital signs, overnight cardiorespiratory sleep studies(More)
INTRODUCTION We sought to quantify changes in skeletal muscle oxygenation during exercise using near-infrared spectroscopy (NIRS) in healthy volunteers ascending to high altitude. METHODS Using NIRS, skeletal muscle tissue oxygen saturation (StO2) was measured in the vastus lateralis of 24 subjects. Measurements were performed at sea level (SL; 75 m), at(More)