n. an X-ray device used in radiotherapy to localize accurately the exact position of the radiation fields before treatment begins.
(OSA, obstructive sleep apnoea syndrome, OSAS) a serious condition in which airflow from the nose and mouth to the lungs is restricted during sleep, also called sleep apnoea syndrome (SAS). It is defined by the presence of more than five episodes of *apnoea per hour of sleep associated with significant daytime sleepiness. Snoring is a feature of the condition but it is not universal. There are significant medical complications of prolonged OSA, including heart failure and high blood pressure. Patients perform poorly on driving simulators, and driving licence authorities may impose limitations on possession of a driving licence. There are associated conditions in adults, the *hypopnoea syndrome and the upper airways resistance syndrome, with less apnoea but with daytime somnolence and prominent snoring. In children the cause is usually enlargement of the tonsils and adenoids and treatment is by removing these structures. In adults the tonsils may be implicated but there are often other abnormalities of the pharynx, and patients are often obese. Treatment may include weight reduction or nasal *continuous positive airways pressure (nCPAP) devices, *mandibular advancement splints, or noninvasive ventilation. Alternatively *tonsillectomy, *uvulopalatopharyngoplasty, *laser-assisted uvulopalatoplasty, or *tracheostomy may be required.... obstructive sleep apnoea
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