A good read for those of you who wants to know more about Apnea/Freediving.
It will explain the physiology aspect of it and the effects it will have on our body and the way we dive.
Also mention is the dangers and how to avoid them.
Taken from
http://library.thinkquest.orgThere are two outstanding factors which characterize the free diver – the process of breath-holding and the changes that occur in the lungs and the chest as a result of the increased water pressure.
Apnea or Holding Your Breath The apnea is a state in which one voluntarily or involuntarily “ceases to breathe”. The diver takes a deep breath and descends under water. While he is submerged, he does not inhale air from the atmosphere which does not mean that he doesn’t breathe at all. As a result of physical activity, cooling and raised pressure, the tow processes of cellular and pulmonary respiration accelerate which shortens the apnea. The length of the apnea depends not only on an individual’s lung capacity but also on the speed of CO2 release in the organism. For example, while at rest the apnea lasts 60 seconds but it is only 20 seconds during heavy physical exercise. This is due to the increased release of carbon dioxide and the reduced amount of oxygen in the blood.
Impulse of Breathing and Critical Line We inhale oxygen and exhale carbon dioxide. In a state of apnea (when the breath is held), the release of CO2 temporarily stops which results in the accumulation of carbon dioxide in the cells, blood and lungs. Simultaneously, carbon dioxide starts irritating the respiratory center. In a particular moment, the irritation becomes so unbearable that the person is not able to hold his breath anymore. There occurs an irresistible will to exhale and release the large amount of CO2 called an impulse of breathing, which discontinues the apnea. The concentration of CO2 in the blood, which forces the impulse of breathing is called the critical line. The critical line cannot be strictly determined because of individual differences. The high level of the critical line might be due to the richer concentration of O2, better training of the apnea or simply holding the breath after maximum inhalation.
Usually, a healthy person has an apnea of one minute. If he, despite his abilities, manages somehow to overcome the impulse of breathing, the amount of CO2 exceeds the critical line and might cause blackout or suffocation.
Hyperventilation Certainly, people are not satisfied with an apnea of one minute and search for other methods to prolong their stay and distance themselves from the impulse of breathing. In fact, this is done by hyperventilation – the practice of excessive breathing. There are two ways of hyperventilation:
Using atmospheric air: First, take about 10 deep breaths. This way, the usual level of CO2 in the blood is artificially reduced so that the diver can have longer apnea (there will be larger space for CO2 to accumulate). The inhalations should be quick, periodical and not exceeding 12–15 because a very low level of CO2 is abnormal and might cause disturbances such as dizziness, nausea or convulsions. Hyperventilation can prolong the apnea on land for up to 1.5–2 minutes and the training of hyperventilation – up to 2–2.5 minutes.
WARNING: After hyperventilation, do slow and easy movements under water. This will reduce quick oxygen consumption and avoid the rapid increase of carbon dioxide.
Using pure oxygen: After the regular hyperventilation, take several breaths of pure oxygen or start hyperventilation with pure oxygen from the very beginning. This type may prolong the apnea for about 7–8 minutes. Even records of 15 minutes were set with careful practice of this kind of hyperventilation.
