The clinical use of impulse oscillometry in neuromuscular diseases

Background: The patients with neuromuscular diseases (NMD) are very fragile and it is hard to evaluate respiratory involvement of the primary disease in this group. Therefore, our study aimed to reveal the relationship between pulmonary function tests (PFT) and impulse oscillometry (IOS) and their correlation with respiratory clinical findings in NMD.

Material and methods: A total of 86 consecutive patients with NMD were included. The clinical findings of respiratory involvement, PFT, and IOS results of the patients were analyzed.

Results: Forty patients out of 86 were female. There were 29 patients with amyotrophic lateral sclerosis, four patients with myasthenia gravis, and 53 patients with muscular dystrophies/myopathies. According to the PFT results, 47 patients had restrictive PFT. However, there was no difference in IOS parameters when we compared the patients according to restrictions in PFT. A positive correlation was found with FVC %pred and X₅. PEF %pred values were positively correlated with X₁₀, X₁₅, and X₂₀, and negatively correlated with A_X and R_5-20. The patients with worse swallowing capability had increased R_rs levels, and more negative X_rs levels. The shortness of breath led to lower FEV₁ %pred., higher R₅, A_X and R_5-20, and also more negative X₁₀, X₁₅, and X₃₅.

Conclusion: Clinically reported dysphagia, a decreased capability of coughing, and shortness of breath in patients with NMD make R_rs increase in general, but X_rs parameters, which mainly express rib cage elasticity, turn more negative. In patients with NMD, IOS monitoring may help in evaluating the regression in respiratory functions, however, future studies are needed to understand more.