Fig 1.

Empirically-derived relationship between haemoglobin concentration (Hb) and arterial partial pressure of oxygen (Pao₂) in Andean men. From Villafuerte et al (2004) (used with permission). The average Hb of young high-altitude natives is represented by an empirical equation that expresses Hb as a function of Pao₂. This equation was derived using data collated from several studies, which investigated approximately 200 healthy men aged 18–45 years. Measurements were largely made in members of the native Quechua population at altitudes ranging from sea level to 4860 m, and Pao₂ was calculated from arterial haemoglobin oxygen saturation. Pao₂ is primarily determined by the altitude of residence, and for a given altitude, a Hb of more than two standard deviations above average is considered excessive (Villafuerte et al, 2004).