Alveoli are like small spherical clusters of grapes and are part of the primary lung lobules where the exchange of gas between air and blood takes place.
The state of breath-holding. Freedivers are apneic throughout the duration of their dive.
Arrhythmia: An irregular heartbeat caused by various disturbances such as drugs, breath-holding and forceful equalizations. Arrhythmias are not uncommon. In certain individuals they might prevent diving, depending upon professional medical evaluation.
A law of physics that explains the pressure and volume relationships of gases. It states that a volume of a gas is inversely proportional to the absolute pressure, while the density of that volume of gas is directly proportional. This principle explains how pressure affects air spaces within a diver’s body and gear.
The slowing of the heart beat. In divers, it’s triggered by immersion of ones’ face in cold water (see diving reflex).
A rapid slowing of the heart seen in all mammals just after the face is immersed in cold water. This oxygen-saving mechanism helps the freediver prolong their breath-hold time.
Hyper baric oxygen treatments
Medical treatments whereby oxygen is supplied under pressure in a recompression chamber to patients suffering from the bends (decompression illness) and other medical conditions. May be of some use for patients suffering brain injury after shallow-water blackout.
Increased amount of carbon dioxide in the blood. A diver who does not rest adequately between breath-hold dives will have elevated carbon dioxide levels. This can predispose him to carbon dioxide toxicity or blackout.
A condition characterized by the increased rate of urine output due to water pressure exerted on a diver’s body. It is one cause of divers becoming chilled and dehydrated.
A protective reflex that causes closing of the vocal cords to prevent passage of air or water into the lungs. This reflex occurs in unconscious persons or those slightly anaesthetized when an irritant such as water comes into contact with sensitive tissue near the vocal cords.
As the body goes into blackout, the arms and legs convulse, giving the appearance that the diver is dancing the samba.
Shallow water blackout (SWB)
Caused by a dramatic reduction in the partial pressure of oxygen during an ascent, leading to hypoxia. As a result, the free-diver experiences unconsciousness. There are no indicators to predict the onset of SWB.
A cavity found within the bones of the skull. The cavities are interconnected to the nasal passages and are lined with a mucus membrane and are subjected to blockage resulting in a squeeze when a diver descends.
For safety reasons, free-divers never train alone. Their buddy is referred to as a spotter and will step in to assist if there is any sign of a problem. The spotter is trained in the necessary first-aid techniques.
An organ in the body containing red blood cells. Trained divers experience a contraction of the spleen allowing extra red blood cells to enter the circulatory system.
A pressure imbalance on an air space that is found within the diver’s body or equipment. Such spaces include the ears, sinuses, mask, stomach and wetsuit. The “squeeze” results from a pressure imbalance between these air spaces and the water pressure surrounding the diver.
Static apnea blackout (SAB)
Like SWB, this also results in unconsciousness. However, this form of blackout is not due to any pressure changes. Very simply, the brain becomes starved of oxygen. It commonly occurs in swimming pools.