Diaphragmatic excursion and sternocleidomastoid muscle thickness correlate with exercise capacity and dynamic lung hyperinflation in patients with chronic obstructive pulmonary disease

<bold>Background:</bold> The diaphragm is the main muscle employed for respiration. Patients with chronic obstructive pulmonary disease (COPD) have difficulty inhaling as the diaphragm flattens and reduces mobility. Dynamic lung hyperinflation (DLH) is a key factor in pathophysiological pathways that leads to dyspnea and poor exercise tolerance. The activation threshold of the sternocleidomastoid (SCM) is high and activated during exercise if higher ventilation is required. However, the correlation between DEmax and SCM to exercise tolerance and DLH has not yet been reported. Therefore, this study aimed to determine the muscle function that has a stronger correlation to exercise tolerance and DLH. <bold>Methods:</bold> We included 50 patients with clinically stable COPD. DEmax and SCM were measured by ultrasonography. Symptom-limited cardiopulmonary exercise test (CPET) analyzed peak oxygen consumption (peak VO2) and change in IC (∆IC = lowest IC - IC at rest) during exercise as a surrogate marker of DLH. Multiple regression analysis was conducted to compute the final predictive model for peak VO2 and ∆IC using DEmax, SCM, FEV1, BMI, and quadriceps muscle strength (QMS) as independent variables. <bold>Results:</bold> The ventilation parameter during CPET, peak VO2 was found to have DEmax and SCM as explanatory variables, with DEmax having the stronger contribution (p<0.001). DEmax was found to be the most independent explanatory variable for ∆IC (p<0.0001). <bold>Conclusion:</bold> Reduced diaphragm mobility was related to decreased exercise capacity and DLH in patients with COPD.