Inspiratory Muscle Training in Patients With Duchenne Muscular Dystrophy
T. Wanke, K. Toifl, M. Merkle, D. Formanek, H. Lahrmann, H. Zwick - Chest 1994; 105;2:475-482

The aim of this study was to assess the usefulness of a specific inspiratory muscle training in Duchenne muscular dystropy (DMD). Fifteen patients with DMD started 6 months of training the inspiratory muscles and 15 patients served as a control group. Maximal sniff assessed esophageal and transdiaphragmatic pressure values served as indices for global inspiratory muscle strength and diaphragmatic strength, respectively. Inspiratory muscle endurance was assessed by the length of time a certain inspiratory task could be maintained. Additionally, serum creatine kinase measurements were done to detect possible muscular damage caused by training.
Results: In 10 of the 15 patients, respiratory muscle function paramaters improved significantly after 1 month of training. Further improvements were to be seen after 3 and after 6 months. Even 6 months after the end of training, those effects remained to a large extent. In the other five patients, there was no such improvement after 1 month of training which was therefore discontinued. All these five patients had vital capacity values of less than 25 percent predicted and/or PaCO2 values of more than 45 mm Hg. The 15 control patients had no significant change in their respiratory muscle function parameters.
Conclusion: We conclude that a specific inspiratory muscle training is useful in the early stage of DMD.

Points of Interest: The training apparatus enabled the patient to do resistive breathing maneuvers against a variable inspiratory resistance. The inspiratory resistive breathing training consisted of ten loaded breathing cycles of 1 minute duraction each, with 20 second intervals between them, twice daily.
At the beginning of the study the Pesmax (maximal sniff assessed esophageal pressure) and Pdimax (maximal sniff assessed transdiaphragmatic pressure) were not significantly different in the two groups. After the 6 month training period, however, the ten patients who completed the training had significantly higher Pesmax and Pdimax values than the 12 control subjects without severe functional impairment. And, in the ten patients who completed the training, the endurance time increased significantly. It should also be noted that in the ten patients who completed the training, their target pressure during the resistive breathing tests increased during the training period. Our study shows the following results: (1) In patients with DMD, respiratory muscles and in particular the diaphragm, are trainable in terms of strength and endurance, provided that their ventilatory function is not severely restricted. (2) In patients with VC values less that 25% predicted and/or PaCO2 of more than 45 mmHg, a specific training of the inspiratory muscles does not produce any benefit. On the other hand, a damaging effect could be excluded, at least for a training period of 1 month.
In our study, training not only improved diaphragmatic and global inspiratory muscle function, but nearly all of the adaptation gained from training was also retained 6 months after the cessation of the training. Healthy young subjects who had 4 or 5 weeks of training lost at least 50 percent of the gain after 8 to 15 weeks of no training.1 Belman and Gaesser2 have shown in normal elderly subjects that almost all the adaptations gained from 8 weeks of training were retained 2 months after its cessation. It is therefore very likely that the adaptations in ventilatory muscles become greater with increased training periods.