information:filtering
Breathing under pressure

Provision of breathing gas at ambient pressure can greatly prolong the duration of a dive, but there are other problems that may result from this technological solution. Absorption of metabolically inert gases is increased as a function of time and pressure, and these may both produce undesirable effects immediately, as a consequence of their presence in the tissues in the dissolved state, such as nitrogen narcosis and high pressure nervous syndrome, or cause problems when coming out of solution within the tissues during decompression.

Other problems arise when the concentration of metabolically active gases is increased. These range from the toxic effects of oxygen at high partial pressure, through buildup of carbon dioxide due to excessive work of breathing, increased dead space, or inefficient removal, to the exacerbation of the toxic effects of contaminants in the breathing gas due to the increased concentration at high pressures. Hydrostatic pressure differences between the interior of the lung and the breathing gas delivery, increased breathing gas density due to ambient pressure, and increased flow resistance due to higher breathing rates may all cause increased work of breathing, fatigue of the respiratory muscles, and a physiological limit to effective ventilation.