Hypercapnia

Hypercapnia (from the Greekhyper = "above" and kapnos = "smoke") is a condition where there is too much carbon dioxide(CO₂) in the body. Carbon dioxide is a gaseousproduct of the body'smetabolismand is normally expelled through the lungs.

Hypercapnia is generally caused by hypoventilation, lungdisease, or diminished consciousness. It may also be caused by exposure to environments containing abnormally high concentrations of CO₂ (usually due to volcanic or geothermal causes), or by rebreathingexhaled carbon dioxide.

Symptoms of early hypercapnia (i.e. where arterial CO₂ pressure, PaCO₂, is elevated but not extremely so) include flushed skin, full pulse, extrasystoles, muscle twitches, hand flaps, and possibly a raised blood pressure. In severe hypercapnia (generally PaCO₂ greater than 10kPaor 75mmHg), symptomatology progresses to disorientation, panic, hyperventilation, convulsions, unconsciousness, and eventually death. In rebreatherdiving, this effect is sometimes called shallow water blackout.

In closed circuitSCUBA(rebreather) diving, exhaled carbon dioxide must be removed from the breathing system, usually by a scrubbercontaining a solid chemical compound with a high affinity for CO₂. If not removed from the system, it may be re-inhaled, causing an increase in the inhaled concentration.

Carbon dioxide poisoning during diving

There are a variety of reasons for CO₂ retentionwhere carbon dioxide is not being expelled completely when the diver exhales:

• The diver is exhaling into a vessel with inadequate ventilation, such as a long snorkel, full face diving mask, or diving helmet, and then re-inhaling from that vessel.
• The scrubber in the rebreatherthe diver is failing to remove sufficient carbon dioxide from the loop.
• The diver is overexerted, producing excess CO₂ due to elevated metabolic activity.
• The densityof the breathing gas is higher at depth, so the effort required to fully inhale and exhale has increased, making breathing more difficult and less efficient.
• The diver is deliberately hypoventilating, or "skip breathing," a technique which conserves breathing gaswith open-circuitscuba but should not be done with a rebreather. (On top of the risk of burst lung from holding the breath while ascending.)

See also

• Permissive hypercapnia
• hypocapnia, decreased level of carbon dioxide</br>
• Repiratory Physiology

References

• CO2 Effects on Humansde:Hyperkapnie

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It uses material from the http://en.wikipedia.org/wiki/Hypercapnia Wikipedia article Hypercapnia.