| Summary: | Maximal expiratory flows (MEF) are dependent on gas density, lung volume, subject effort and airway characteristics. Variable changes in MEF occur after ascent to altitude which may represent an interaction between gas density changes, catecholamine stimulation and mild interstitial edema. Hypoxia induced catecholamine up‐regulation has also been associated with acute mountain sickness (AMS). This study examined the association between MEF variability and AMS symptoms in United States Antarctic Program personnel (n=198, age 37±1 yrs, 3% asthma) rapidly transported to the South Pole (SP, 9302 ft). Spirometric parameters, epinephrine (Epi), norepinepherine (NE) and SaO2 levels were recorded at sea level (SL, McMurdo Station) and after the 2 nd night at SP. AMS was assessed using Lake Louise questionnaires (score ≥ 3). FVC, FEV 1 , FEF 25 , FEF 75 and FEF 25–75 increased by 0, 3, 17, 10 and 14% from SL to SP, respectively. On day 2, AMS incidence was 31% and Epi and NE increased by 44 and 71%. Changes in MEF ranged from −64 to +93% in FEF 25–75 and −63 to +70% in FEF 75 . Subjects with the greatest increase in MEF had higher incidence of AMS (24 vs 41%) and higher NE levels, while the subjects with the greatest decrease in MEF had lower SaO2 values (88 vs 90%). Subjects with increased MEF had increased AMS and bronchodilation while subjects with decreased MEF displayed values consistent with mild interstitial edema.
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