Nocturnal periodic breathing during acclimatization at very high altitude at Mount Muztagh Ata (7,546 m).
BACKGROUND
Quantitative data on ventilation during acclimatization at very high altitude are scant. Therefore, we monitored nocturnal ventilation and oxygen saturation in mountaineers ascending Mt. Muztagh Ata (7,546 m).


OBJECTIVE
To investigate whether periodic breathing persists during prolonged stay at very high altitude.


METHODS
A total of 34 mountaineers (median age, 46 yr; 7 women) climbed from 3,750 m within 19-20 days to the summit at 7,546 m. During ascent, repeated nocturnal recordings of calibrated respiratory inductive plethysmography, pulse oximetry, and scores of acute mountain sickness were obtained.


RESULTS
Nocturnal oxygen saturation decreased, whereas minute ventilation and the number of periodic breathing cycles increased with increasing altitude. At the highest camp (6,850 m), median nocturnal oxygen saturation, minute ventilation, and the number of periodic breathing cycles were 64%, 11.3 L/min, and 132.3 cycles/h. Repeated recordings within 5-8 days at 4,497 m and 5,533 m, respectively, revealed increased oxygen saturation, but no decrease in periodic breathing. The number of periodic breathing cycles was positively correlated with days of acclimatization, even when controlled for altitude, oxygen saturation, and other potential confounders, whereas symptoms of acute mountain sickness had no independent effect on periodic breathing.


CONCLUSIONS
Our field study provides novel data on nocturnal oxygen saturation, breathing patterns, and ventilation at very high altitude. It demonstrates that periodic breathing increases during acclimatization over 2 weeks at altitudes greater than 3,730 m, despite improved oxygen saturation consistent with a progressive increase in loop gain of the respiratory control system. Clinical trial registered with www.clinicaltrials.gov (NCT00514826).
Bloch
Konrad E
KE
Department of Internal Medicine, University Hospital of Zurich, Zurich Centre for Integrative Human Physiology, University of Zurich, Switzerland. konrad.bloch@usz.ch
Latshang
Tsogyal D
TD
Turk
Alexander J
AJ
Hess
Thomas
T
Hefti
Urs
U
Merz
Tobias M
TM
Bosch
Martina M
MM
Barthelmes
Daniel
D
Hefti
Jacqueline Pichler
JP
Maggiorini
Marco
M
Schoch
Otto D
OD
D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000368:Aged; D000532:Altitude Sickness / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology; D002681:China; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009051:Mountaineering / Q000502:physiology*; D010092:Oximetry / Q000379:methods; D010101:Oxygen Consumption / Q000502:physiology; D010991:Plethysmography / Q000379:methods / Q000706:statistics & numerical data; D017286:Polysomnography / Q000379:methods / Q000706:statistics & numerical data; D012119:Respiration; D020182:Sleep Apnea, Central / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology