Oxygen Delivery
Anthropologists and evolutionary biologists, physiologists and biomedical scientists share an intense interest in the biology of high-altitude populations. Anthropologists and evolutionary biologists are curious about the processes of evolution and adaptation to an extreme, unavoidable environmental stress. Physiologists and biomedical scientists want to understand the processes engaged to maintain homeostasis under an extreme stress and hope to find clues to improve the treatment of patients at all altitudes.
Oxygen Transport
Oxygen comprises roughly 21% of the atmosphere at all altitudes. The partial pressure of oxygen decreases with increasing altitude because the barometric pressure decreases. This plot illustrates the relative decrease in the partial pressure of oxygen with altitude and was provided by courtesy of Ray Huey at the University of Washington (below).
The result is few oxygen molecules are inspired in each breath of air and there are fewer oxygen molecules at all stages of the oxygen transport process as illustrated. The figure illustrates the decrease in the partial pressure of oxygen from teh outside air through the body and tho the mitochondrial and back to the heart.
The graph illustrates, quantitatively, the difference in the partial pressure of oxygen at sea level and at about 15,000′. Based on information in a classic 1964 publication by the respected Peruvian physiologist, Alberto Hurtado, it illustrates the markedly lower levels of oxygen at all stages of the oxygen cascade, as it is often called. For instance, at 15,000′ the inspired partial pressure of oxygen is about the same as arterial levels at sea level and the alveolar partial pressure is about the same as venous levels at sea level!
B. 2
O2 Cascade at High and Low Altitudes
At high altitude, the cascade starts at a lower partial pressure of oxygen and there is less oxygen available at each stage of the cascade. People must make biological adjustments to ensure that enough oxygen reaches the cells and the mitochondria, despite the shortage.
This figure is based on a classic study of Andean highlanders conducted by the great Peruvian physiologist and physician, Carlos Monge.