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Blood volume for different members of the expedition over time

Note that each individual has their own portion of the y-axis (on either the right or left side). The increase was about 1.5 liters and the peak corresponded to passing through tropical climes, when their vascular beds expanded (ie, from cutaneous vasodilation). The individual graphs have simply been staggered vertically. (Source: Barcroft J, Binger CA, Bock AV, et al. Observations upon the effect of high altitude on the physiological processes of the human body, carried out in the Peruvian Andes, chiefly at Cerro de Pasco. Philos Trans R Soc Lond B 1923;211:351-480. Public domain.)