1. Inkendaal Rehabilitation Hospital, Neuromuscular Centre VUB-Inkendaal and Centre for Home Mechanical Ventilation, Inkendaalstraat, 1, B-1602 Vlezenbeek (Brussels) Belgium,
2. Sleep and Ventilation Unit, Royal Brompton Hospital, London, 6NP, UK
3. Inkendaal Rehabilitation Hospital, Neuromuscular Centre VUB-Inkendaal and Centre for Home Mechanical Ventilation, Inkendaalstraat, 1, B-1602 Vlezenbeek (Brussels) Belgium