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Altitude Sickness at Sea Level: The Effects of Hypoxia in Daily Life

Few people ever go above 4,000 to 5,000 feet altitude, but almost all of us experience the symptoms of mountain sickness during our daily lives—though we often don’t realize it. There are many environmental, ventilatory, circulatory, and tissue conditions that cause signs, symptoms, and even death from hypoxia (lack of oxygen). A person can be very short on oxygen even at a low altitude, and the consequences can be as serious as they are on a very high mountain. Knowing common risk factors for sea-level hypoxia can prevent many damaging long-term effects and may even prove vital. The authors of Going Higher: Oxygen, Man, and Mountains, 2nd Edition offer some information on common causes of hypoxia and who is at risk.

Environmental Hypoxia—environmental changes that increase the effects of hypoxia

· Flying—Flying is by far the most frequent cause of brief everyday hypoxia. Although they might reach altitudes of 30,000-45,000 feet, the cabins of commercial aircraft are kept at a pressure equivalent to an altitude of between 5,000 and 7,500 feet. For the average passenger flying for a few hours at this altitude, the effects are rather mild. A sensitive person may notice slight shortness of breath; occasional irregular breathing; periodic breathing; and some feeling of uneasiness or discomfort. Those who have a tendency to hyperthyroidism, or those with a mild anemia or a pulmonary-cardiac condition may notice the altitude more. Individuals who are at risk for or have a sickle trait, such as sickle cell anemia, should consult a doctor before flying, as lack of oxygen makes red blood cells more fragile.
· Common Gases and Air pollutants—Each year in the United States, some 1,500 people die from carbon monoxide (CO) poisoning. Stoves, automobiles, space heaters, and especially combustion in confined places like shacks, parking garages, fishing shanties, and tightly woven tents cause problems from carbon monoxide hypoxia. For commuters with early or mild coronary artery disease, exposure to exhaust fumes on congested highways is enough to cause angina. Other gases and pollutants, such as carbon dioxide, methane, and gaseous or liquid nitrogen are also environmental causes of hypoxia. The most effective—and most preventable—way to introduce pollutants into your lungs is by smoking

Ventilatory Hypoxia—caused by any illness or damage that interferes with the flow of outside air through airways into the lungs, or with the diffusion of oxygen from the alveoli into blood.

· COPD (Chronic Obstructive Pulmonary Disease)—The term COPD usually refers to the common combination of chronic bronchitis and emphysema. About 16 million people in the United States have COPD, and many die every year of associated pneumonia, respiratory failure, and other complications. Smoking causes roughly 80 to 90 percent of COPD cases.
· Disturbed Breathing During Sleep and Sleep Apnea—Many people tend to breath unevenly during sleep and notice it little if at all. However, in the extreme cases this may become a problem. In these cases, sleep is disturbed by the struggle to breathe, and the hapless victim is sleepy all day. When sleep is frequently interrupted, judgment, decision making, and even reflex actions are impaired the next day (sleep apnea has been blamed for a good many automobile accidents). In severe cases of snoring, preventive measures should be considered to avoid eventual pulmonary hypertension and failure. Treatment options include using a device that produces a steady flow of air though a small tube in the nose, wearing a mask, and surgery. Sleep apnea causes brief but repeated periods of mild arterial oxygen desaturation, which over time can cause pulmonary hypertension and even right heart failure.
· Sudden Infant Death Syndrome (SIDS)—There is increasing evidence that SIDS is often due to an abnormality in the part of the brain that senses oxygen and carbon dioxide and controls breathing and waking during sleep. Babies with this abnormality are susceptible to sudden death, which could be triggered by an event such as lack of oxygen, excessive carbon dioxide intake, overheating, or infection. An important factor to seems to be the sleeping position: Infants who sleep on their backs are less susceptible, although this is not the whole answer.
· Asthma—Asthma is a frequent cause of intermittent episodes of hypoxia with many of its symptoms. Because the air is cleaner and thinner, some patients with mild asthma actually do better at moderate altitudes.

Circulatory Hypoxia—any interference with the carriage or delivery of oxygen

· Toxic Substances—Like CO, certain chemicals combine with hemoglobin to cause hypoxia. Substances that can cause circulatory hypoxia include topical anesthetics, silver nitrate, sulfonamide antibiotics, cyanide, and aniline compounds (found in inks, polishes, and paints).
· Heart Problems—When heart muscle is damaged because arteriosclerosis has reduced circulation to one or several parts of the heart muscle, it cannot pump enough oxygen-carrying blood to the body to meet demands. Rare congenital defects also jeopardize the heart as a pump.
· Mutant Hemoglobins—When individuals with sickle trait become hypoxic, the abnormal cells are distorted into shapes that cannot take on as much oxygen as normally; this reduces the oxygen-carrying capacity of blood and decreases supply to the tissues.

Histotoxic Hypoxia—when tissues are unable to use oxygen, despite normal oxygen delivery

· Excessive oxygen demand due, for example, to strenuous exertion, high fever, or an overactive thyroid—in short, anything that increases tissue demand without an adequate compensatory increase in oxygen supply—may result in hypoxia severe enough to cause signs or symptoms.

- Adapted from Going Higher: Oxygen, Man, and Mountains, 2nd Edition by Charles S. Houston, M.D., David E. Harris, Ph.D., and Elllen J. Zeman, Ph.D. (The Mountaineers Books, $22.95 paperback)

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