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Updated: May 23, 2026

Investigation into Deep Breathing through Measurement of Ventilatory Parameters and Observation of Breathing Patterns
Published on: September 16, 2019
Closed and open breathing circuit function in healthy volunteers during exercise at Mount Everest base camp (5300 m)
R C N McMorrow1, J S Windsor, N D Hart
1UCL Centre for Altitude Space and Extreme Environment Medicine, UCL Institute of Child Health, University College London, London, UK. mcmorrow.roger@gmail.com
Abstract:
We present a randomised, controlled, crossover trial of the Caudwell Xtreme Everest (CXE) closed circuit breathing system vs an open circuit and ambient air control in six healthy, hypoxic volunteers at rest and exercise at Everest Base Camp, at 5300 m. Compared with control, arterial oxygen saturations were improved at rest with both circuits. There was no difference in the magnitude of this improvement as both circuits restored median (IQR [range]) saturation from 75%, (69.5-78.9 [68-80]%) to > 99.8% (p = 0.028). During exercise, the CXE closed circuit improved median (IQR [range]) saturation from a baseline of 70.8% (63.8-74.5 [57-76]%) to 98.8% (96.5-100 [95-100]%) vs the open circuit improvement to 87.5%, (84.1-88.6 [82-89]%; p = 0.028). These data demonstrate the inverse relationship between supply and demand with open circuits and suggest that ambulatory closed circuits may offer twin advantages of supplying higher inspired oxygen concentrations and/or economy of gas use for exercising hypoxic adults.
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