According to conventional wisdom, a left shift of the ODC permits greater saturation of the hemoglobin at a lowered PO2, therefore making it possible for more oxygen to be carried. Such an adaptation, however, also requires a lower PO2 at the tissue level for the hemoglobin to unload its oxygen. Although some high altitude species do this (e.g. llama, alpaca, and vicuna), not all take this approach.
Adult humans at moderate altitude, for example, undergo a right shift of the ODC which increases the ease of oxygen unloading at the tissue level. Because the hemoglobin is loading on the wide "shoulder" region of the ODC, only a small degree of desaturation of the arterial blood is experienced by the maneuver.
To review oxygen dissociation curve
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