The carbon dioxide scrubber in the divers rebreather is failing to remove sufficient carbon dioxide from the loop (higher inspired CO2), or the breathing gas is contaminated with CO2. The diver is overexercising, producing excess carbon dioxide due to elevated metabolic activity and respiratory gas exchange cannot keep up with the metabolic production of carbon dioxide. Gas density limits ventilation at high ambient pressures. The density of the breathing gas is higher at depth, so the effort required to fully inhale and exhale increases, making breathing more difficult and less efficient (high work of breathing). Higher gas density also causes gas mixing within the lung to be less efficient, thus increasing the effective dead space. The diver is deliberately hypoventilating, known as "skip breathing". Skip breathing
Skip breathing is a controversial technique to conserve breathing gas when using open-circuit scuba, which consists of briefly holding ones breath between inhalation and exhalation (i.e., "skipping" a breath). It can lead to CO2 not being exhaled efficiently. The risk of burst lung (pulmonary barotrauma of ascent) is increased if the breath is held while ascending. It is particularly counterproductive with a rebreather, where the act of breathing pumps the gas around the "loop", pushing carbon dioxide through the scrubber and mixing freshly injected oxygen.In closed-circuit rebreather diving, exhaled carbon dioxide must be removed from the breathing system, usually by a scrubber containing a solid chemical compound with a high affinity for CO2, such as soda lime.
See also
Hypocapnia – State of reduced carbon dioxide in the blood, decreased level of carbon dioxide
Inert gas asphyxiation
Lake Nyos – Crater lake in the Northwest Region of Cameroon
Ocean acidification – Climate change-induced decline of pH levels in the ocean
Permissive hypercapnia
Waterboarding – Torture method simulating drowning

References


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