motion sickness

Sickness caused by contradiction between external data from the eyes and internal cues from the balance centre in the inner ear. For example, in seasickness the inner ear senses the ship's motion, but the eyes see the still cabin. This stimulates stress hormones and accelerates stomach muscle contraction, leading to dizziness, pallor, cold sweat, and nausea and vomiting. Minimizing changes of speed and direction may help, as may reclining, not turning the head, closing the eyes, or focusing on distant objects. Drugs can prevent or relieve motion sickness but may have side effects. Pressing an acupuncture point on the wrist helps some people.

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Protozoal disease transmitted by the bite of the tsetse fly. Two forms, caused by different species of the genus Trypanosoma, occur in separate regions in Africa. The parasite enters the bloodstream and invades the lymph nodes and spleen, which become swollen, soft, and tender. Irregular fever and delayed pain sensation develop. In the Rhodesian form, the patient soon dies of massive toxemia. The Gambian type progresses to brain and spinal cord invasion, causing severe headache, mental and physical fatigue, spastic or flaccid paralysis, chorea, and profound sleepiness, followed over two or three years by emaciation, coma, and death. Some patients develop a tolerance but still carry the trypanosomes. The earlier drug treatment begins, the greater the chance of recovery. Sleeping sickness is still prevalent in parts of Africa despite efforts to control it.

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or mountain sickness

Acute reaction to a change from low altitudes to altitudes above 8,000 ft (2,400 m). Most people gradually adapt, but some have a severe reaction that can be fatal unless they return to low altitude. Normal adaptations to the reduced oxygen at high altitude (e.g., breathlessness, racing heartbeat) are exaggerated; other manifestations include headache, gastrointestinal upsets, and weakness. Pulmonary edema is quickly reversed with oxygen and evacuation to a lower area.

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also called the bends or caisson disease

Harmful effects of rapid change from a higher- to a lower-pressure environment. Small amounts of the gases in air are dissolved in body tissues. When pilots of unpressurized aircraft go to high altitudes or when divers breathing compressed air return to the surface, external pressure on the body decreases and the gases come out of solution. Rising slowly allows the gases to enter the bloodstream and be taken to the lungs and exhaled; with a quicker ascent, the gases (mostly nitrogen) form bubbles in the tissues. In the nervous system, they can cause paralysis, convulsions, motor and sensory problems, and psychological changes; in the joints, severe pain and restricted mobility (the bends); in the respiratory system, coughing and difficulty breathing. Severe cases include shock. Recompression in a hyperbaric chamber followed by gradual decompression cannot always reverse tissue damage.

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