Postural vital capacity difference with aging in duchenne muscular dystrophy.

Introduction: A change in vital capacity (VC) from standing to supine can be an index of diaphragm paralysis if it exceeds 25%. We aimed to verify whether the postural VC difference increases with age and reflects diaphragm weakness in DMD.

Methods: VCs were measured in DMD. Postural VC difference and percentage were calculated from the VC data. Maximal inspiratory pressure (MIP) and MIP percentage were measured as an indirect index of diaphragm weakness.

Results: A total of 220 patients and 544 measurements were collected. MIP and MIP percentage decreased significantly with age (P < 0.001 for both). Estimated postural VC difference and percentage also decreased (P < 0.001, P = 0.006, respectively). Age group comparisons showed a significant decrease in younger, but not older subjects.

Conclusions: This study shows that the postural VC difference tended to decrease with age and might not reflect diaphragmatic weakness in DMD; however, this should be interpreted cautiously.