Introduction: Progressive respiratory muscle weakness is the main factor in the development of life-threatening respiratory failure in Mytonic Dystrophy type 1 (DM1). Recently, benefits of lower limb exercises were described[1, 2].
Aims: To investigate if inspiratory muscle strength and endurance capacity can be improved by inspiratory muscle training (IMT).
Methods: Normocapnic DM1 patients at daytime, vital capacity (VC) and maximum inspiratory muscle strength (PImax) below 80% of pred. were eligible for this pilot study. Patients performed twice a day an IMT session of 30 inspirations at home during twelve weeks. A POWERbreathe KHP2 device is used, which tapers the inspiratory flow resistance electronically. Resistance started on 20% of PImax and was increased during a supervised training every two weeks. Spirometry, PImax, respiratory endurance capacity and a six minute walking distance (6MWD) were done at baseline and finish.
Results: Nine patients, mean age 39 years, completed the study. The exercises were well tolerated without occurrence of side effects. Training started on a mean resistance of 7.8 cmH2O and increased to a mean of 35 cmH2O (SD 17 cmH2O). Although VC remained stable, PImax increased with 97% from 2,94 kPa to 5,78 kPa (84% of pred.) and endurance capacity improved both in resistance and time (from 120 to 230 sec (SD 110 sec)). The 6MWD remained stable at 400m.
Conclusion: This study shows that IMT improves both inspiratory power and endurance capacity. Further studies are needed to confirm these findings and to investigate the optimal timing of initiating IMT and whether it could become a new therapy to delay the onset of respiratory failure in DM1.