[Abnormal respiratory regulation in myotonic dystrophy].

The abnormal respiratory regulation as well as respiratory muscle degeneration are thought to be involved in the pathogenesis of alveolar hypoventilation in myotonic dystrophy (MD). In the present study we recorded changes in oxygen saturation resulting from exercise and hyperventilation in MD, Duchenne muscular dystrophy (DMD) patients and healthy volunteers by pulse oxymetry. Following are the results obtained in this study. (1) In DMD individuals showing preexisting mild desaturation around 90-95%, mild muscle exercise such as drawing a picture always caused further desaturation, which is presumably due to an increase in oxygen demand. On the other hand the MD patients with the same level of desaturation often showed paradoxical improvement in oxygen saturation up to 95-97% after a similar mild exercise, however, they showed obvious desaturation by a harder exercise such as propelling wheelchair. (2) There was a fluctuation of oxygen saturation at rest in MD, while this was not apparent in DMD patients and normal volunteers. (3) In MD and normal individuals, a strenuous hyperventilation is always followed by an oxygen desaturation through ventilatory suppression probably caused by hypocapnea resulting from the hyperventilation. This desaturation phase is much more prolonged in MD patients than in normal control subjects. The above data indicate further evidence of abnormal ventilatory regulation in MD.