Diving
Humans are poorly adapted to the underwater environment. Breath-hold diving is limited by limits on the capacity of the thorax to compress during descent, and ability to withstand hyperoxia and hypercapnia. Using compressed gas technology humans can breathe underwater, although with effects on pulmonary statics, dynamics, and gas exchange. Breathing compressed gas causes an increase in density, leading to impairment of both inspiratory and expiratory flow, and hence a reduction in maximum exercise ventilation. In addition, there is an increased Bohr dead space, which can further lower alveolar ventilation. Hypercapnia is common during diving. Immersion causes blood redistribution from the periphery into the lung, and a decrease in compliance. Gaseous compounds exert their physiological effects in proportion to their partial pressures. Thus, gases that are in concentrations that are safe to breathe at 1 ATA can become toxic during diving, including oxygen. Pulmonary O
