Editing Apnea (section)

==Hyperventilation==
Voluntary [[hyperventilation]] before beginning voluntary apnea is commonly believed to allow the person involved to safely hold their breath for a longer period. In reality, it will give the impression that one does not need to breathe, while the body is actually experiencing a blood-oxygen level that would normally, and indirectly, invoke a strong [[dyspnea]] and eventually involuntary breathing. Some have incorrectly attributed the effect of hyperventilation to increased oxygen in the blood, not realizing that it is actually due to a decrease in {{CO2}} in the blood and lungs. Blood leaving the lungs is normally fully saturated with oxygen, so hyperventilation of normal air cannot increase the amount of oxygen available, as oxygen in blood is the direct factor. Lowering the {{CO2}} concentration increases the pH of the blood, thus increasing the time before blood becomes acidic enough so the respiratory center becomes stimulated, as described above. While hyperventilation will yield slightly longer breath-holding times, any small time increase is at the expense of possible [[Hypoxia (medicine)|hypoxia]], though it might not be felt as easily.<ref>{{cite journal |last=Given |first=Mac F. |title=The Effect of Hyperventilation on the Ability to Hold One's Breath: Testing the Influence of Beliefs versus Physiology |journal=The American Biology Teacher |date=1 April 1997 |volume=59 |issue=4 |pages=229–231 |doi=10.2307/4450291|jstor=4450291 }}</ref> One using this method can suddenly lose consciousness unnoticed—a [[Freediving blackout#Shallow water blackout|shallow water blackout]]—as a result. If a person loses consciousness underwater, there is considerable danger that they will [[Drowning|drown]]. An alert diving partner or nearby lifeguard would be in the best position to rescue such a person. Static apnea blackout occurs at the surface when a motionless diver holds their breath long enough for the circulating oxygen in blood to fall below that required for the brain to maintain consciousness. It involves no pressure changes in the body and is usually performed to enhance breath-hold time. It should never be practiced alone, but under strict safety protocols with a safety guard or equipment beside the diver.