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Nitrogen narcosis (gettin' narked) is a fairly harmless phenomenon, if the diver is aware of its existence. The narcosis develops with an increasing Nitrogen partial pressure. Typically, it takes effect at depths greater than 30 meters, causing an anesthesia making the diver feel sleepy, drowsy and effecting memory of the dive. The diver may feel falsely secure, exercise poor judgment and become uncoordinated. Hallucinations and giddiness have been reported. The narcosis ceases quickly when reaching shallower depths. Though Nitrogen is the most known, other gases cause this 'inert gas narcosis'. Even Oxygen has narcotic properties. This appears to make enriched air (Nitrox) exhibit the same narcotic quality as air. Diving beyond the 52-54 meter limit common in commercial diving industry and the Navy requires other mixtures like Heliox and Trimix (Oxygen, Nitrogen and Helium), only to reduce the narcotic effects. These effects are the limiting factor, not decompression sickness. |
One of the most notorious illnesses is decompression sickness. During a dive the diver breathes air at the same pressure as the environment. At a depth of 30 m (90 feet) the pressure is 4 bar, whereas at the surface the pressure is 1 bar. Nitrogen is one of the main components of air (78%). When breathing Nitrogen is dissolved in the blood and body tissue. When a diver starts breathing air under pressure, more Nitrogen will dissolve until a new, higher Nitrogen level is established. At this level the partial Nitrogen pressure in the blood and tissue is the same as the partial Nitrogen pressure in the air. When a diver surfaces, the surrounding pressure and the pressure of the air he breathes drop. The surplus of Nitrogen in the blood and tissue has to be removed. Normally when a diver surfaces slowly, the Nitrogen is transported by the blood to the lungs and is expelled during exhaling. However, when there is too much Nitrogen surplus and the diver surfaces to quickly, Nitrogen is forming small bubbles in the blood and in the tissue. These small bubbles tend to stick together forming larger bubbles. These bubbles can block veins, depriving the body parts from the necessary Oxygen. The symptoms the diver feels ranges from itchy skin and fatigue to serious mental problems as numbness, inability to speak and even death.
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Hypercapnia (or hypercarbia) is a situation in which there is excess Carbon Dioxide. Most commonly this problem occurs when the diver fails to breathe slowly and deeply (due to work for example). Because of the enlarged dead air volume associated with diving, the diver inhales great part of the previous exhaled air, containing increasing levels of Carbon Dioxide. Because of this less Carbon dioxide can be expelled by the respiratory system. Elevated levels of Carbon Dioxide lead to headache, confusion and eventually to loss of consciousness. Since it is the Carbon Dioxide level that stimulates the respiratory system, the diver will breathe faster, resulting in even higher Carbon Dioxide levels. This vicious circle is broken if the diver ceases all activity and starts breathing deeply. Hypercapnia is sometimes associated with full-face masks, (semi) closed scuba (rebreather) and skip-breathing. In recreational diving hypercapnia is not very common. |
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Hypocapnia is a situation in which the Carbon Dioxide level is to low. It occurs during excessive hyperventilation (deep in- and exhaling). Hyperventilation can be voluntary or unintentionally. Symptom of hyperventilation is light-headedness and, in case of unintentional hyperventilation, can lead to loss of consciousness.
Hypocapnia during breath hold diving may lead to shallow water black out. When a diver hyperventilates excessively before a breath hold dive, Carbon Dioxide levels will become extremely low. Since it is this level which stimulates breathing (and not low Oxygen levels) this stimulus will not be present, even when Oxygen levels become to low. At depths the increased Oxygen partial pressure in the lungs of the diver allows the respiratory system to get some Oxygen from the air. However, when the diver surfaces (goes to shallow depths), the partial Oxygen pressure in his lungs will drop. The lungs no longer get Oxygen from the air, leading to blacking out due to hypoxia.
Breathing Oxygen at high partial pressures makes Oxygen toxic. In atmospheric air at sea level the partial pressure of Oxygen is 0.21 bar. There are two types of Oxygen toxicity:
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Most often Carbon Monoxide poisoning happens outside the realm of diving. However, a contaminated air supply may cause this problem. Carbon Monoxide (CO) is a tasteless and odorless gas, which usually originates from incomplete burning of fuel due to lack of sufficient Oxygen. Exhaust gas from engines contains Carbon monoxide. When breathing in, Carbon Monoxide binds to the hemoglobin in the blood, forming carboxyhemoglobin. Because Carbon monoxide binds much easier to hemoglobin than Oxygen and does not unbind as easily, the Carbon Monoxide sticks to the hemoglobin, making it useless for the transport of Oxygen. Continuing breathing Carbon Monoxide result in decreasing amount of active hemoglobin, resulting in hypoxia. Carbon Monoxide bound to hemoglobin (carboxyhemoglobin) is far more red than Oxygen bound hemoglobin. Hence Carbon Monoxide poisoning may color the lips and nail-beds of the victim red. However, during diving this may remain unobserved due to equipment and (red) color absorption at depth. |
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Carbon Monoxide poisoning during diving is more complicated: at depth more Oxygen is dissolved (due to higher partial Oxygen pressure) in the blood than at the surface. This dissolved Oxygen helps meeting the tissue Oxygen requirement, even if part of the hemoglobin is locked out by the Carbon Monoxide binding. When the Carbon Monoxide poisoning symptoms (headache, confusion, narrow vision) occur the diver ascends. Due to decreasing dissolved Oxygen levels in the blood the diver might black out from hypoxia at shallow depths.
Blood pressure is monitored by receptors called the carotid-sinus receptors, which are located in the carotid arteries. The carotid arteries branch up from each side of the neck, leading to the brain. If blood pressure is high, the carotid-sinus receptors signal the cardioinhibitory center in the brain, which slow down the heart rate and causes vasodilatation (widening of the blood vessels). Low blood pressure stops the signaling of the cardioinhibitory center and heart rate goes up again.
Problems may occur if a divers suit or other equipment is to tight around the neck. The resulting pressure may incorrectly be interpreted by the carotid-sinus receptors as high blood pressure, resulting in a stimulation of the cardioinhibitory centers and a lowering heart rate. Less blood flows to the brain. Since the pressure persists, less blood keeps flowing to the brain. Symptoms are discomfort, light-headedness and eventually loss of consciousness.