Carbon dioxide is a normal metabolic product but it accumulates in the body if it is produced faster than it is cleared. During strenuous exercise the production rate of carbon dioxide can increase more than tenfold over the production rate during rest. Carbon dioxide is dissolved in the blood and elimination is by gas exchange in the lungs during breathing.<unk>  is generally caused by hypoventilation, lung disease, or diminished consciousness. It may also be caused by exposure to environments containing abnormally high concentrations of carbon dioxide, such as from volcanic or geothermal activity, or by rebreathing exhaled carbon dioxide. In this situation the<unk>  can also be accompanied by respiratory acidosis. Acute<unk>  respiratory failure may occur in acute illness caused by chronic obstructive pulmonary disease (COPD), chest wall deformity, some forms of neuromuscular disease (such as myasthenia gravis, and obesity hypoventilation syndrome. AHRF may also develop in any form of respiratory failure where the breathing muscles become exhausted, such as severe pneumonia and acute severe asthma. It can also be a consequence of profound suppression of consciousness such as opioid overdose. During diving Normal respiration in divers results in alveolar hypoventilation resulting in inadequate CO2 elimination or<unk> . Lanphier's work at the US Navy Experimental Diving Unit answered the question, "Why don't divers breathe enough?": * Higher inspired oxygen () at accounted for not more than 25% of the elevation in end tidal CO2 (ETCO2) above values found at the same work rate when breathing air just below the surface. * Increased work of breathing accounted for most of the elevation of (alveolar gas equation) in exposures above , as indicated by the results when helium was substituted for nitrogen at . * Inadequate ventilatory response to exertion was indicated by the fact that, despite resting values in the normal range, rose markedly with exertion even when the divers breathed air at a depth of only a few feet. A variety of reasons exists for carbon dioxide not being expelled completely when the diver exhales: * The diver is exhaling into a vessel that does not allow all the CO2 to escape to the environment, such as a long snorkel, full-face diving mask, or diving helmet, and the diver then reinhales from that vessel, causing increased dead space. * The carbon dioxide scrubber in the diver's 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 one's 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. If not removed from the system, it may be reinhaled, causing an increase in the inhaled concentration. Under hyperbaric conditions,<unk>  contributes to nitrogen narcosis and oxygen toxicity by causing cerebral vasodilation which increases the dosage of oxygen to the brain.
Hypercapnia
Hypocapnia
Acidosis
Alkalosis
Metabolic alkalosis
Hypoxemia
Metabolic acidosis
Hypoventilation