Drowning - Why it's not that bad.
Submerging the face into water causes the mammalian diving reflex, which is found in all mammals, and especially in marine mammals such as whales and seals. This reflex puts the body into energy saving modus to maximize the time an organism can stay under water. The effect of this reflex is greater in cold water than in warm water, and includes three factors:
Bradycardia, a reduction in the heart rate of up to 50% in humans.
Peripheral Vasoconstriction, the restriction of the blood flow to the extremities to increase the blood and oxygen supply to the vital organs, especially the brain.
Blood Shift, the shifting of blood to the thoracic cavity (region of the chest between the diaphragm and the neck) to avoid the collapse of the lungs under higher pressure during deeper dives.
Thus both a conscious and an unconscious person can survive longer without oxygen under water than in a comparable situation on dry land.
A conscious victim will hold their breath (see Apnea), and will try to access air, often resulting in panic, including rapid body movement. This uses up more oxygen in the blood stream and reduces the time to unconsciousness.
The victim can voluntarily hold their breath for some time, but the breathing reflex will increase until the victim will try to breathe, even when submerged. The breathing reflex in the human body is related not to the amount of oxygen in the blood but the amount of carbon dioxide. During apnea, the oxygen in the blood is used by the cells, and converted into carbon dioxide. Thus, the level of oxygen in the blood decreases, and the level of carbon dioxide increases. Increasing carbon dioxide levels lead to a stronger and stronger breathing reflex, up to the breath-hold breakpoint, at which the victim can no longer hold their breath. This typically occurs at a partial pressure of carbon dioxide of 55mm Hg, but may differ significantly from individual to individual and can be increased through training. Decreasing oxygen levels, however, lead to a sudden loss of consciousness without warning, usually around a partial pressure of 25 to 30mm Hg. This condition of inadequate oxygen is called hypoxia. Trained apnea divers can hold their breath and resist the breathing reflex until they pass out. The loss of consciousness due to hypoxia is called shallow water blackout when it occurs as the victim is ascending from a dive; the decreasing water pressure around the victim causes the partial pressure of oxygen in the blood to also decrease. The loss of consciousness due to hypoxia is more likely when rapid breathing before apnea decreased the level of carbon dioxide in the blood without increasing the level of oxygen, as the blood is usually saturated with oxygen. Therefore, blackout may occur without warning before a breathing reflex is felt. Breath holding in water should never be preceded by rapid breathing to store oxygen, and should always be supervised by a second person.
Bradycardia, a reduction in the heart rate of up to 50% in humans.
Peripheral Vasoconstriction, the restriction of the blood flow to the extremities to increase the blood and oxygen supply to the vital organs, especially the brain.
Blood Shift, the shifting of blood to the thoracic cavity (region of the chest between the diaphragm and the neck) to avoid the collapse of the lungs under higher pressure during deeper dives.
Thus both a conscious and an unconscious person can survive longer without oxygen under water than in a comparable situation on dry land.
A conscious victim will hold their breath (see Apnea), and will try to access air, often resulting in panic, including rapid body movement. This uses up more oxygen in the blood stream and reduces the time to unconsciousness.
The victim can voluntarily hold their breath for some time, but the breathing reflex will increase until the victim will try to breathe, even when submerged. The breathing reflex in the human body is related not to the amount of oxygen in the blood but the amount of carbon dioxide. During apnea, the oxygen in the blood is used by the cells, and converted into carbon dioxide. Thus, the level of oxygen in the blood decreases, and the level of carbon dioxide increases. Increasing carbon dioxide levels lead to a stronger and stronger breathing reflex, up to the breath-hold breakpoint, at which the victim can no longer hold their breath. This typically occurs at a partial pressure of carbon dioxide of 55mm Hg, but may differ significantly from individual to individual and can be increased through training. Decreasing oxygen levels, however, lead to a sudden loss of consciousness without warning, usually around a partial pressure of 25 to 30mm Hg. This condition of inadequate oxygen is called hypoxia. Trained apnea divers can hold their breath and resist the breathing reflex until they pass out. The loss of consciousness due to hypoxia is called shallow water blackout when it occurs as the victim is ascending from a dive; the decreasing water pressure around the victim causes the partial pressure of oxygen in the blood to also decrease. The loss of consciousness due to hypoxia is more likely when rapid breathing before apnea decreased the level of carbon dioxide in the blood without increasing the level of oxygen, as the blood is usually saturated with oxygen. Therefore, blackout may occur without warning before a breathing reflex is felt. Breath holding in water should never be preceded by rapid breathing to store oxygen, and should always be supervised by a second person.