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Eur J Appl Physiol. 2003 Oct;90(3-4):351-9. Epub 2003 Sep 18.

Oxygen transport in blood at high altitude: role of the hemoglobin-oxygen affinity and impact of the phenomena related to hemoglobin allosterism and red cell function.

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Dipartimento di Medicina, Chirurgia e Odontoiatria, Ospedale San Paolo, Universita' Di Milano, via di Rudini' 8, 20142 Milan, Italy.


Altitude hypoxia is a major challenge to the blood O2 transport system, and adjustments of the blood-O2 affinity might contribute significantly to hypoxia adaptation. In principle, lowering the blood-O2 affinity is advantageous because it lowers the circulatory load required to assure adequate tissue oxygenation up to a threshold corresponding to about 5,000 m altitude, whereas at higher altitudes an increased blood-O2 affinity appears more advantageous. However, the rather contradictory experimental evidence raises the question whether other factors superimpose on the apparent changes of the blood-O2 affinity. The most important of these are as follows: (1) absolute temperature and temperature gradients within the body; (2) the intracapillary Bohr effect; (3) the red cell population heterogeneity in terms of O2 affinity; (4) control of altitude alkalosis; (5) the possible role of hemoglobin as a carrier of the vasodilator nitric oxide; (6) the effect of varied red cell transit times through the capillaries.

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