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Arterial Oxygen Pressure Drop at High Elevation Studied

Alveolar-arterial oxygen difference may be due to limitation in pulmonary diffusion, subclinical pulmonary edema

WEDNESDAY, Jan. 7 (HealthDay News) -- In extremely high altitudes, people experience an elevated difference in alveolar-arterial oxygen, suggesting a functional limitation in pulmonary diffusion or a degree of subclinical pulmonary edema, according to research published in the Jan. 8 issue of the New England Journal of Medicine.

Michael P.W. Grocott, of the University College London Institute of Human Health and Performance in the United Kingdom, and colleagues performed direct field measurements of the partial pressures of oxygen in the arterial blood (PaO2) of 10 humans during their ascents to and descents from the summit of Mount Everest, which is 29,029 feet high. From these measurements, the investigators calculated arterial oxygen saturation, and the alveolar-arterial oxygen difference.

As the PaO2 fell with increasing altitude, arterial oxygen saturation remained stable due to increased hemoglobin levels, until 23,294 feet, the report indicates. At a 27,559-foot elevation, the mean PaO2 in climbers was 24.6 mm Hg. At the same elevation, the mean arterial oxygen saturation was 26 percent lower than it had been at 23,294 feet (145.8 ml/L compared with 197.1 ml/L), resulting in a 5.4 mm Hg difference in alveolar-arterial oxygen.

"The calculated alveolar-arterial oxygen difference in these subjects suggests a degree of functional limitation in pulmonary diffusion or subclinical pulmonary edema, conditions that may explain why the values for the PaO2 are lower than expected," the authors write.

Several of the study authors report financial relationships with the pharmaceutical and health care industries, and the study was partially supported by Eli Lilly and other medical groups.

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