Relationship between expiratory activity of the lateral abdominal muscle and exercise tolerance in chronic obstructive pulmonary disease

[Purpose] The purpose of this study was to investigate the relationship between the expiratory activity of the lateral abdominal muscle during quiet breathing and exercise tolerance in COPD patients. [Subjects] The participants were 15 moderate and severe male COPD patients (FEV1 = 42.5 +/- 15.9% predicted) and 15 sex- and age-matched healthy subjects. [Methods] The expiratory activity of the lateral abdominal muscle and exercise tolerance were measured. The expiratory activity was estimated from the thickness difference (Tdif) of the lateral abdominal muscle during quiet breathing using ultrasonography. Exercise tolerance was assessed by the incremental shuttle walking test (ISWT). Pearson's correlation coefficient was used to study the correlation between Tdif and the distance walked in ISWT, and FEV1 [Results] Tdif was higher in COPD patients than in healthy subjects, and a moderate significant negative correlation was found between Tdif and the distance walked. However, there was no significant correlation between Tdif and FEV1. [Conclusion] The results indicate that exercise intolerance may be more important factors than airflow limitation in expiratory muscle activity during quiet breathing in advanced COPD patients.