Although spirometry (SPIRO) is the most common pulmonary function test, it has limitations. SPIRO can be difficult to obtain and reliably interpret in NMD, particularly as impairment progresses. OSC is a sophisticated yet easy to perform, reliable, and effort independent test of respiratory function. It appears well suited to NMD. Limited literature suggests minimal changes in OSC for NMD.
To characterize the relationship between SPIRO and OSC in a large adult NMD cohort.
SPIRO and OSC were performed in 71 NMD subjects (49 ± SEM 2 yrs). Diagnoses included, e.g., spinal muscular atrophy, myotonic dystrophy, and muscular dystrophies. For OSC, resistance (R5, R5-20) and reactance (X5, AX) values were obtained (tremoFlo, Thorasys, Canada).
Spirometry was abnormal. In 42 (group A), OSC was also abnormal. Results were generally attributable to restrictive and/or obstructive impairment due to underlying NMD, complications and/or comorbidities (e.g. severe scoliosis, atelectasis, obesity, airway disease). In 29 (group B), however, OSC was normal. Correlation between SPIRO and OSC parameters was variable and less significant than in other disorders with no relationship between FEV1/FVC and OSC.
SPIRO is abnormal in adult NMD. However, OSC can identify those with normal vs abnormal respiratory impedance (resistance, reactance). Utility of OSC in management of a broader range of NMD, particularly with disease progression, warrants further evaluation.