title: Residence at moderate altitude improves ventilatory response to high altitude.
abstract: BACKGROUND
  This study compared the distribution of arterial oxygen saturation (SaO2) and susceptibility to Acute Mountain Sickness (AMS) in moderate altitude residents (MAR) and low altitude residents (LAR) following rapid ascent to 4056 m.
  
  
  METHODS
  Resting PETCO2 and SaO2 were measured in 38 subjects residing for > 3 mo near Colorado Springs, CO (MAR group), at 1940 m (USAF Academy), and after approximately 1 h at 4056 m on the summit of Pikes Peak, CO, following ascent by car. SaO2 was also measured at 610-m elevation intervals during the ascent. Of the LAR (50 m) group, 39 subjects were exposed to a similar ascent profile in a hypobaric chamber.
  
  
  RESULTS
  At 1940 m the MAR SaO2 and PETCO2 were 94 +/- 1% (X +/- SD) and 33.6 +/- 2.8 mmHg, respectively. At 3048 m and higher, MAR SaO2 decreased, reaching 86 +/- 2% (p < 0.001) at 4056 m, and PETCO2 (32.1 +/- 4.5 mmHg) decreased (p < 0.05). At 50 m the LAR SaO2 and PETCO2 were 98 +/- 1% and 38.7 +/- 2.7 mmHg, respectively. At 1940 m and higher, LAR SaO2 decreased (p < 0.001), reaching 82 +/- 5% at 4056 m, and PETCO2 (36.4 +/- 3.5 mmHg) decreased (p < 0.05). Above 2438 m, the MAR SaO2 was higher (p < 0.001) than the LAR. Only one MAR subject, but nine LAR subjects reported AMS symptoms.
  
  
  CONCLUSIONS
  Ventilatory acclimatization developed during moderate altitude residence substantially enhances arterial oxygenation during rapid ascents to higher altitudes. Compared with prior studies, the level of ventilatory acclimatization achieved at moderate altitude is similar to residing at 4056 m for approximately 5-9 d.
authors.affiliation: Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760-5007, USA. Stephen.muza@us.army.mil
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Muza
authors.forename: Paul B
authors.initials: PB
authors.lastname: Rock
authors.forename: Michael F
authors.initials: MF
authors.lastname: Zupan
authors.forename: James C
authors.initials: JC
authors.lastname: Miller
authors.forename: William R
authors.initials: WR
authors.lastname: Thomas
authors.forename: Allen
authors.initials: A
authors.lastname: Cymerman
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000503:physiopathology*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D012119:Respiration; D013997:Time Factors
chemical_list: D010100:Oxygen