Physiological responses during ascent to high altitude and the incidence of acute mountain sickness.

Acute mountain sickness (AMS) occurs when there is failure of acclimatisation to high altitude. The aim of this study was to describe the relationship between physiological variables and the incidence of AMS during ascent to 5300 m. A total of 332 lowland-dwelling volunteers followed an identical ascent profile on staggered treks. Self-reported symptoms of AMS were recorded daily using the Lake Louise score (mild 3-4; moderate-severe ≥5), alongside measurements of physiological variables (heart rate, respiratory rate (RR), peripheral oxygen saturation (SpO2 ) and blood pressure) before and after a standardised Xtreme Everest Step-Test (XEST). The overall occurrence of AMS among participants was 73.5% (23.2% mild, 50.3% moderate-severe). There was no difference in gender, age, previous AMS, weight or body mass index between participants who developed AMS and those who did not. Participants who had not previously ascended >5000 m were more likely to get moderate-to-severe AMS. Participants who suffered moderate-to-severe AMS had a lower resting SpO2 at 3500 m (88.5 vs. 89.6%, p = 0.02), while participants who suffered mild or moderate-to-severe AMS had a lower end-exercise SpO2 at 3500 m (82.2 vs. 83.8%, p = 0.027; 81.5 vs. 83.8%, p 5000 m (OR 2.740, p-value 0.003) predicted the development of moderate-to-severe AMS. The Xtreme Everest Step-Test offers a simple, reproducible field test to help predict AMS, albeit with relatively limited predictive precision

Caudwell Xtreme Everest: A prospective study of the effects of environmental hypoxia on cognitive functioning.

BACKGROUND: The neuropsychological consequences of exposure to environmental hypobaric hypoxia (EHH) remain unclear. We thus investigated them in a large group of healthy volunteers who trekked to Mount Everest base camp (5,300 m). METHODS: A neuropsychological (NP) test battery assessing memory, language, attention, and executive function was administered to 198 participants (age 44.5±13.7 years; 60% male). These were studied at baseline (sea level), 3,500 m (Namche Bazaar), 5,300 m (Everest Base Camp) and on return to 1,300 m (Kathmandu) (attrition rate 23.7%). A comparable control group (n = 25; age 44.5±14.1 years; 60% male) for comparison with trekkers was tested at/or near sea level over an equivalent timeframe so as to account for learning effects associated with repeat testing. The Reliable Change Index (RCI) was used to calculate changes in cognition and neuropsychological function during and after exposure to EHH relative to controls. RESULTS: Overall, attention, verbal ability and executive function declined in those exposed to EHH when the performance of the control group was taken into account (RCI .05 to -.95) with decline persisting at descent. Memory and psychomotor function showed decline at highest ascent only (RCI -.08 to -.56). However, there was inter-individual variability in response: whilst NP performance declined in most, this improved in some trekkers. Cognitive decline was greater amongst older people (r = .42; p < .0001), but was otherwise not consistently associated with socio-demographic, mood, or physiological variables. CONCLUSIONS: After correcting for learning effects, attention, verbal abilities and executive functioning declined with exposure to EHH. There was considerable individual variability in the response of brain function to sustained hypoxia with some participants not showing any effects of hypoxia. This might have implications for those facing sustained hypoxia as a result of any disease

Caudwell Xtreme Everest expedition

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 ascent to EBC and remained there for the duration of the expedition, with a subgroup of 14 collecting data higher on Everest. This article focuses on published data obtained by the investigator-subjects at extreme altitude (&gt;5500 m). Unique measurements of peak oxygen consumption, middle cerebral artery diameter and blood velocity, and microcirculatory blood flow were made on the South Col (7950 m). Unique arterial blood gas values were obtained from 4 subjects at 8400 m during descent from the summit of Everest. Arterial blood gas and microcirculatory blood flow data are discussed in detail

A novel ambulatory closed circuit breathing system for use during exercise

We describe a unique ambulatory closed circuit for delivering high fractions of inspired oxygen to an exercising user who does not require isolation from their environment. We describe the major components and their function and suggest potential applications for such a circuit. This circuit may benefit patients who are chronically dependant on oxygen, are unable to exercise due to hypoxia, or require oxygen supplementation at high altitude