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Optimal hemoglobin concentration and high altitude: a theoretical approach for Andean men at rest

Laboratorio de Transporte de Oxígeno, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima 31, Peru

Submitted 3 April 2003 ; accepted in final form 1 December 2003

The beneficial role of erythrocytosis for O₂ transport has been questioned by evidence from bloodletting and hemodilution research as well as by studies suggesting the existence of an "optimal" hematocrit (Hct) or hemoglobin concentration ([Hb]) value. To assess to what extent erythrocytosis is beneficial in Andean men at high altitude, we examined and discussed optimal [Hb] using a mathematical approach by modeling the mixed (mean) venous PO₂ (P_O2) and arterial O₂ content, considering for both the relation between [Hb] and arterial PO₂. Relations of [Hb] to other physiological variables such as cardiac output and convective arterial O₂ transport were also discussed, revealing the importance of P_O2 in this model. Our theoretical analysis suggests that increasing [Hb] allows increase and maintenance of P_O2 with only moderate declines in arterial PO₂ as a consequence of moderate increases in altitude, reaching its maximum at the optimal [Hb] of 14.7 g/dl. Our analysis also shows that [Hb] corresponding to high arterial O₂ content and O₂ transport values is apparently not quite advantageous for improvement of oxygenation. Furthermore, chronic mountain sickness is discussed as an insightful example of the effects of excessive erythrocytosis at high altitude.

oxygen transport; hypoxia; theoretical model; mixed venous partial pressure of oxygen

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