Effect of non-invasive ventilation on respiratory muscle loading and endurance in patients with Duchenne muscular dystrophy.

BACKGROUND

Respiratory muscle weakness in patients with Duchenne muscular dystrophy (DMD) leads to respiratory failure for which non-invasive positive pressure ventilation (NIPPV) is an effective treatment. This is used initially at night (n-NIPPV) but, as the disease progresses, diurnal use (d-NIPPV) is often necessary. The connection between NIPPV and relief of respiratory muscle fatigue remains unclear. A study was undertaken to determine the extent to which n-NIPPV and d-NIPPV unload the respiratory muscles and improve respiratory endurance in patients with DMD.

METHODS

Fifty patients with DMD were assessed at 20.00 and 08.00 h. More severely affected patients with nocturnal hypoventilation received n-NIPPV; those with daytime dyspnoea also received d-NIPPV via a mouthpiece (14.00-16.00 h). Lung function, modified Borg dyspnoea score, spontaneous breathing pattern, tension-time index (TT(0.1) = occlusion pressure (P(0.1))/maximum inspiratory pressure (MIP) x duty cycle (Ti/Ttot)) and respiratory muscle endurance time (Tlim) against a threshold load of 35% MIP were measured.

RESULTS

More severe respiratory muscle weakness was associated with a higher TT(0.1) and lower Tlim. In contrast to non-dyspnoeic patients, patients with dyspnoea (Borg score > 2.5/10) showed an increase in Tlim and decrease in TT(0.1) after n-NIPPV. At 16.00 h, immediately after d-NIPPV, patients with dyspnoea had lower TT(0.1) and Borg scores with unchanged Tlim. Compared with the control day without d-NIPPV, TT(0.1), Borg scores and Tlim were all improved at 20.00 h.

CONCLUSIONS

In patients with dyspnoea with DMD, the load on respiratory muscles increases and endurance capacity decreases with increasing breathlessness during the day, and this is reversed by n-NIPPV. An additional 2 h of d-NIPPV unloads respiratory muscles and reverses breathlessness more effectively than n-NIPPV alone.