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

The beneficial role of erythrocytosis for O-2 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 (v) over bar (O2)) 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 O-2 transport were also discussed, revealing the importance of P (v) over barO(2) in this model. Our theoretical analysis suggests that increasing [Hb] allows increase and maintenance of P (v) over barO(2) 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 O-2 content and O-2 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.