MECHANICAL VENTILATION

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

M Toussaint¹, P Soudon¹, W Kinnear²

¹ Centre for Home Mechanical Ventilation, Ziekenhuis Inkendaal, Vlezenbeek, Belgium
² Department of Respiratory Medicine, University Hospital, Nottingham, UK

Dr M Toussaint, ZH Inkendaal, Inkendaalstraat 1, 1602 Vlezenbeek, Belgium; michel.toussaint{at}inkendaal.be

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.

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