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It's important to avoid the side effects of hypoventilation when diving because it can result in an excessive buildup of carbon dioxide.
This help guide explains how the direct consequences of inadequate breathing and ventilation may cause sedation and shortness of breath.
Every time scuba divers or snorkelers exhale air they will be releasing carbon dioxide from the body.
However, too much exposure to high levels of CO2 in body tissues and blood can be dangerous.
Here's the thing:
During exertion in water, failing to breathe efficiently can make carbon dioxide become poisonous.
It can also happen because of a voluntary reduction in breathing rate.
Scuba divers in particular are more susceptible to carbon dioxide toxicity when breathing compressed air at depth because of its density. Thus, they need to use more effort to move it through "dead air spaces" (e.g. the breathing apparatus).
Pro Tip: The risk for scuba divers to get carbon dioxide poisoning increases when they are using a closed or semi closed rebreather if it malfunctions.
For the most part, the signal for the human body to breathe comes from sustained elevations of carbon dioxide in the bloodstream.
When divers learn how to freedive they use a maneuver known as "intentional hyperventilation". As such, vigorous exhalation (breathing deeply in and out) before making a breath-hold skin dive gets rid of (expels) large amounts of CO2.
Despite it being a 'potentially' hazardous exercise, low levels of carbon dioxide allow divers to hold their breath for long periods underwater.
Even so, if a diver runs low on oxygen they can suffer a hypoxic blackout (lose consciousness). It happens because the carbon dioxide fails to reach a level high enough to stimulate the need to breathe (e.g. return to the surface).
As a result, scuba divers, freedivers, skin divers, and spearfishers need to avoid inadequate ventilation. Other risk factors of hypocapnia - carbon dioxide poisoning due to high breathing resistance - include:
From a training standpoint, divers who suffer frequent headaches or low rates of air consumption after diving may be suffering mild cases of carbon dioxide sickness. Other severe manifestations include:
Pro Tip: An arterial blood gas (ABG) test following a dive will not usually detect any significant increase in carbon dioxide levels.
In general, the recommended treatment for CO2 poisoning during a dive is to end the dive without delay and make a gradual ascent to the surface.
Important: Beginners who have regular headaches after surfacing from dives should review the industry standard relating to scuba diving breathing techniques and make modifications where necessary.
Important: The tutorial video [16:21 seconds] presented by DAN explains how gas toxicities and pressure affect the human body during a dive.