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

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 (Pv̄_O22) and arterial O ₂ 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 Pv̄_O2 in this model. Our theoretical analysis suggests that increasing [Hb] allows increase and maintenance of Pv̄_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.