Design and conduct of Caudwell Xtreme Everest: an observational cohort study of variation in human adaptation to progressive environmental hypoxia.
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 hypobaric hypoxia (EHH). The aim of this study was to describe the spectrum of adaptive responses in humans exposed to graded EHH and identify factors (physiological and genetic) associated with inter-individual variation in these responses.


METHODS



METHODS
Observational cohort study of progressive incremental exposure to EHH.


METHODS
University human physiology laboratory in London, UK (75 m) and 7 field laboratories in Nepal at 1300 m, 3500 m, 4250 m, 5300 m, 6400 m, 7950 m and 8400 m.


METHODS
198 healthy volunteers and 24 investigators trekking to Everest Base Camp (EBC) (5300 m). A subgroup of 14 investigators studied at altitudes up to 8400 m on Everest.


METHODS
Exercise capacity, exercise efficiency and economy, brain and muscle Near Infrared Spectroscopy, plasma biomarkers (including markers of inflammation), allele frequencies of known or suspected hypoxia responsive genes, spirometry, neurocognitive testing, retinal imaging, pupilometry. In nested subgroups: microcirculatory imaging, muscle biopsies with proteomic and transcriptomic tissue analysis, continuous cardiac output measurement, arterial blood gas measurement, trans-cranial Doppler, gastrointestinal tonometry, thromboelastography and ocular saccadometry.


RESULTS
Of 198 healthy volunteers leaving Kathmandu, 190 reached EBC (5300 m). All 24 investigators reached EBC. The completion rate for planned testing was more than 99% in the investigator group and more than 95% in the trekkers. Unique measurements were safely performed at extreme altitude, including the highest (altitude) field measurements of exercise capacity, cerebral blood flow velocity and microvascular blood flow at 7950 m and arterial blood gas measurement at 8400 m.


CONCLUSIONS
This study demonstrates the feasibility and safety of conducting a large healthy volunteer cohort study of human adaptation to hypoxia in this difficult environment. Systematic measurements of a large set of variables were achieved in 222 subjects and at altitudes up to 8400 m. The resulting dataset is a unique resource for the study of genotype:phenotype interactions in relation to hypoxic adaptation.
Centre for Altitude Space and Extreme Environment Medicine, UCL Institute of Human Health and Performance, First Floor, Charterhouse Building, UCL Archway Campus, Highgate Hill, London, N19 5LW, UK.
Denny Z H
DZ
Levett
Daniel S
DS
Martin
Mark H
MH
Wilson
Kay
K
Mitchell
Sundeep
S
Dhillon
Fabio
F
Rigat
Hugh E
HE
Montgomery
Monty G
MG
Mythen
Michael P W
MP
Grocott
D000222:Adaptation, Physiological / Q000502:physiology*; D000531:Altitude; D015331:Cohort Studies; D005080:Exercise Test; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D019370:Observation; D010807:Physical Endurance / Q000502:physiology