Figure 1. Schematic illustration of the four steps in the oxygen transport chain (sometimes called the ‘oxygen cascade’) described in the text. (1) Gas exchange. (2) Diffusion into blood. (3) Blood transport of oxygen. (4) Diffusion into tissues. For illustrative purposes, body tissues are represented by three compartments containing mitochondria. In reality, many different tissue compartments are servised by the blood circulation.

Figure 2. Schematic representation of hypothetical blood columns, illustrating gradients of gravitational pressures depicted by arrows. The size of the arrows corresponds to the magnitude of the pressure vectors. In aquatic environments, pressure outside the blood column increases with depth approximately as do pressures within the blood column. Thus, transmural pressures across the vessel wall remain unchanged along the column length. In aerial environments, the arrows outside the blood column represent atmospheric pressure, which essentially does not change along the length of the column. The wall of the vessel containing the blood is distensible, and therefore increasing gradients of transmural pressure in air cause distension and blood pooling in the lower depths of the blood column. After Lillywhite (1996).

Figure 3. Relationship between rates of maximal oxygen consumption and altitude for persons who have temporarily adjusted to various altitudes. The data are from a scientific Himalayan expedition and reflect maximal exercise capacities. After Hlastala and Berger (1996).