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Chapter 4- Diving Physiology Diving Physiology 141 munity about the kind and frequency of tests that divers need. Nervous System Disorders In some forms of epilepsy, seizures occur that cause loss of consciousness or control. A seizure under water could lead to drowning or embolizing. There is debate over how long a period following a single seizure episode constitutes a reasonable prediction that it is not likely to recur. Several states in the United States allow driving after six months without recurrence. Others require a year or more. Many in diving feel that any seizure activity must lead to an absolute contraindication against diving, and they do not distinguish between active, uncontrolled seizures and a single episode. Others state that the decision of risk in diving varies and is up to the diver and the diver’s physician to decide. Diabetes There is debate whether diabetes mellitus is an absolute contraindication to diving. A person who is heavily insulin-dependent with a history of severe hypoglycemic episodes is considered to be at increased risk of loss of consciousness or ability to act effectively underwater. Some authorities categorically state that diabetes mellitus must be an absolute contraindication. Others state that diabetes encompasses a wide range of severity, with some forms constituting a negligible risk, particularly in someone who closely monitors and controls their blood sugar and activity levels. Ear and Sinus Disorders Ear and sinus abnormalities may make it difficult or impossible to equalize pressure on descent. Attempting to dive may result in pain, damage to the ears or sinuses, complications from resulting infection, and/or hearing loss. Perforated eardrum rules out diving. Chronic inflammation of the ear and sinus passages may rule out diving. Seasonal inflammations such as hay fever and head colds may involve postponing diving during episodes. Smoking, Drugs, and Alcohol Smoking. Cigarette smoking increases your risk of bronchitis, emphysema, lung cancer, cardiovascular disease, high blood pressure, and other conditions that reduce quality and length of your life. The ill effects of cigarettes are so pronounced, that breathing smoke that someone else exhales is bad for your health. The Environmental Protection Agency estimates 3,000 deaths a year in American nonsmokers from lung cancer from secondhand smoke. The effects of pressure change and cold exposure on your respiratory and cardiovascular systems may make cigarette-related long term diseases more hazardous for you as a diver than for the population in general. Immediate effects of smoking also concern divers. Smoking even one cigarette irritates your airways, increases mucous secretion, airway spasm, and resistance to airflow. These are thought to increase risk of air trapping and lung overexpansion injuries. Smoking raises your blood carbon monoxide levels to the point of limiting oxygen delivery and exercise tolerance. When combined with the coronary-artery narrowing effects of nicotine, risk of heart attack rises. The risk is particularly real under conditions of cold exposure common to diving. If you don’t smoke, don’t start. Avoid secondhand smoke. If you smoke, see your physician for information on cutting back and stopping. While you are quitting, refrain from smoking for several hours before diving. Drugs. A commonsense guideline is that any drug that should not be used when driving a motor vehicle or operating machinery should not be used when diving. For example, a variety of seasickness and some antihistamine medications can make you too sleepy to function well. Another commonsense decision is whether you should be diving if you are ill enough to need medication. There is the possibility that diving may cause a drug to have a different effect underwater than on land, some of which is speculation at this point. Drugs that decrease mental functioning and depress physical functioning on land, have a greater effect under pressure. It also seems to be the case that if a drug affects judgment or ability to function rationally or quickly, it will be more dangerous at depth because demands are greater. A few common drugs are briefly


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