Changes of hematocrit and hemoglobin concentration in the cold Himalayan environment in dependence on total body fluid

The organism is exposed to a considerable hypoxic stress at high altitude, and the well-known polyglobulia is an effective strategy to sustain oxygen delivery to the tissue at reduced saturation of hemoglobin. In general, an increasing erythropoiesis is thought to be the reason, although this increase of red blood count can be observed after a short time of altitude exposure and the parameters are expressed as water-depending concentrations. Therefore, the influence of water distribution on hemoglobin (Hb) and hematocrit (Hct) values during a long-term exposure at high altitude was investigated. Measurements were performed in 12 mountaineers before, during, and either 7/8 or 11/12 days after a Himalaya expedition (26-29 days at 4,850 to 7,600 m altitude). Arriving at 4,850 m an initial increase of Hb and Hct was followed by a short decrease during the first week and a continuous increase during the further stay. In maximum, 131.3% (Hb) and 117.4% (Hct) of the starting point were reached during the fourth week at altitude after the attempt to reach the summit of Broad Peak (8,047 m). Parallel the dehydration in the beginning turned to a hyperhydration at the end of the stay (D(2)O method). Erythropoietin rose only temporarily at altitude (max. +11 +1 mU/ml serum). Upon return, Hb and Hct normalized within a few days whereas hemoglobin mass (initially 881+ 44 g, CO-Hb method) was still increased by 13% (p < 0.01). In conclusion, a hemoconcentration effect (dehydration) is the reason of the initial peak of Hb and Hct. The further increase can only partially be explained by an absolute increase of Hb and Hct caused by stimulated erythropoiesis. A shift of intravasal fluid to the interstitial space is the other main reason of the observed changes in red blood count.