Disordered respiration in dystrophia myotonica
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The purpose of this investigation is to endeavour to find an explanation for the high morbidity and mortality that occurs in patients suffering from dystrophia myotonica, in relation to anaesthesia, and to ascertain whether there exists a specific hyper- sensitivity to thiopentone.The natural history of the disease is reviewed in some detail, surveying many of its features, including the muscular wasting and myotonia, which might well affect the muscles of respiration.10 cases of the disease and a series of controls are investigated.Some tests of lung function are performed, and the effects of thiopentone on respiration are studied under various conditions. The earlier experiments make use of a simple recording spirometer for studying the possible respiratory depressant effects of the drug on ventilation; but later, with the aid of a Jerkin plethysmograph, it is also possible to inspect the pattern of respiration.Five of the 10 cases of dystrophia myotonica display profound and prolonged respiratory depression, after injection of 50 - 100 mg. thiopentone, and irregular respiration is induced or accentuated in three of these cases. The drug has little effect on the remaining patients and controls.The maximum expiratory pressure in all cases is reduced to a level that is significantly lower than the controls, while other tests such as the maximum breathing capacity is within the normal range in 90% of the patients. It is concluded that there exists in dystrophia myotonica, respiratory dysfunction which varies with the severity of the disease, and which may not be evident until a respiratory depressant drug is given.The prolonged and profound respiratory depressant effect of thiopentone depends on the presence of pre-existing respiratory insufficiency, which appears to be due to muscular wasting and not myotonia.The reduction in maximum expiratory pressure implies a decreased ability to cough, which in the presence of pharyngeal and laryngeal weakness may lead to the inhalation of secretions into the bronchial tree.The response to thiopentone is not specific, but can be produced by other respiratory depressant drugs. It is impossible to predict the effect on respiration by the use of simple tests of lung function.The morbidity and mortality appears to be related not specifically to anaesthesia but to sedation of these patients, which accentuates any respiratory depression already present. With the reduced ability to cough, these features represent a condition similar to that of bulbo-spinal poliomyelitis, with its attendant disabilities.