Clinical values of diaphragmatic movement in patients with chronic obstructive pulmonary disease

BACKGROUND: The limitation of activity due to dyspnea in chronic obstructive pulmonary disease (COPD) patients is affected by diaphragmatic dysfunction and reduced lung function. This study aimed to analyze the association between diaphragm function variables and forced expiratory volume in the first second (FEV1) and to estimate the clinical significance of diaphragm function in the correlation between COPD severity and lung function. METHODS: This prospective, single-center, cross-sectional observational study enrolled 60 COPD patients in a respiratory outpatient clinic. Data for baseline characteristics and the dyspnea scale were collected. Participants underwent a pulmonary function test (PFT), a 6-minute walk test (6MWT), and diaphragm function by ultrasonography. RESULTS: The right excursion at forced breathing showed the most significant correlation with FEV1 (r = 0.370, p = 0.004). The cutoff value was 6.7 cm of the right diaphragmatic excursion at forced breathing to identify the FEV1 above 50% group. In the group with a right diaphragmatic excursion at forced breathing < 6.7 cm, modified Medical Research Council (mMRC), St. George's Respiratory Questionnaire and the total distance of 6MWT showed no difference between groups with FEV1 under and above 50% (p > 0.05). In the group with ≥ 6.7 cm, mMRC and the total distance of 6MWT showed a significant difference between FEV1 under and above 50% (p = 0.014, 456.7 ± 69.7 m vs. 513.9 ± 60.3 m, p = 0.018, respectively). CONCLUSION: The right diaphragmatic forced excursion was closely related to FEV1, and analysis according to the right diaphragmatic forced excursion-based cut-off value showed a significant difference between both groups. When the diaphragm function was maintained, there was a lot of difference in the 6MWT’s factors according to the FEV1 value. Our data suggest that diaphragmatic function should be performed when interpreting PFT. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12890-022-02220-7.