Decline in Lung Volume With Duchenne Muscular Dystrophy Is Associated With Ventilation Inhomogeneity.

BACKGROUND

Advanced stages of Duchenne muscular dystrophy (DMD) result in severe lung volume decline and are associated with high respiratory morbidity and mortality. The aim of this study was to investigate whether lung volume decline in subjects with DMD is associated with ventilation inhomogeneity measured with the multiple-breath washout technique.

METHODS

This cross-sectional study of lung function included 45 subjects with DMD and 16 healthy controls using multiple-breath washout, spirometry, and cough peak flow.

RESULTS

Subjects with DMD exhibited an elevated lung clearance index (> 7.0) defined as the cumulative exhaled volume divided by the functional residual capacity to lower the sulfur hexafluoride concentration below 2.5% compared with controls (8.16 ± 2.55 vs 6.23 ± 0.46, P < .001). Lung clearance index elevation was negatively correlated with vital capacity (% predicted: r = -0.79, P < .001) and cough peak flow (L/min: r = -0.41, P = .005). Furthermore, dead-space ventilation (dead-space-to-tidal-volume ratio) and functional residual capacity showed a positive correlation with lung clearance index elevation (r = 0.81 and 0.48, P < .001). An FVC of < 24% predicted lung clearance index elevation with a sensitivity of 96% and a specificity of 80%.

CONCLUSIONS

Moderate-to-severe lung volume decline in subjects with DMD is associated with ventilation inhomogeneity. Lung clearance index elevation may be the result of altered ventilation geometry or retention of airway secretions in the infection-free DMD subject.