Abdominal volume contribution to tidal volume as an early indicator of respiratory impairment in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is characterised by progressive loss of muscular strength that leads to an increasingly restrictive pulmonary syndrome. However, it is still not clear whether this determines alterations in the breathing pattern. We studied: 66 DMD patients at different stages of the disease (mean±sem age 12.6±0.6 yrs, range 5–22 yrs of age), subdivided into four groups according to age; and 21 age-matched healthy male controls. Spirometry, lung volumes and nocturnal oxygen saturation were measured in all DMD patients. Ventilatory pattern and chest wall volume variations were assessed by optoelectronic plethysmography during spontaneous breathing both in seated and supine positions. Whilst in a seated position, no significant differences were found between patients and controls or between different age groups. In the supine position, the average contribution of abdominal volume change (ΔVAB) to tidal volume progressively decreased with age (p<0.001). The patients who showed nocturnal hypoxaemia showed significantly lower ΔVAB. In conclusion, chest wall motion during spontaneous breathing in awake conditions and in supine position is an important indicator of the degree of respiratory muscle impairment in DMD. ΔVAB is not only an important marker of the progression of the disease but is also an early indicator of nocturnal hypoxaemia.