Muscle mass and function are related to respiratory function in chronic obstructive pulmonary disease

Background: Chronic obstructive pulmonary disease (COPD), as an airway limitation condition, is accompanied by alteration of muscle mass and function. We aimed to determine the relationship between disease severity and body composition, muscle function, and nutritional status in COPD patients. Methods: This cross-sectional study was conducted on 129 COPD participants. Muscle strength, body composition, and calf circumference (CC) were measured using a hydraulic hand dynamometer, bioelectrical impedance analysis (BIA), and a tape measure, respectively. Furthermore, fat-free mass index (FFMI), body mass index (BMI) and muscle mass value were calculated by equations. Forced expiratory volume in one second (FEV1) was assessed as well. Nutritional status was also evaluated by subjective global assessment (SGA) questionnaire. SPSS software (version 21 ) was used, chi-square, fisher's exact test, univariate and multivariate linear regression models were used for statistical analysis. P-values less than 0.05 were considered significant. Results: Based on FEV1 classification, 52.7% of the patients had severe conditions. The reports indicated that the prevalence of low CC was 54.2%, low muscle mass 38.7%, low FFMI 34.8%, low right handgrip strength 61.2% and low left handgrip strength 64.3%. Furthermore, there was an increasing trend based on FEV1 in low CC (p=0.032), low muscle mass (p=0.005), low FFMI (p=0.002), low right handgrip strength (p=0.004) and low left handgrip strength (p=0.014). The results of univariate analysis showed muscle mass (p=0.036), total protein (p=0.043), FFM (p=0.047), FFMI (p=0.007), SGA (p=0.029), right handgrip strength (p=0.004) and left hand grip strength (p=0.023) were associated with FEV1. In addition, the results of multivariate analysis demonstrated low values of FFMI (p=0.005) and right handgrip strength (p=0.042) were the main detrimental factors for FEV1. The results of multivariate analysis were confirmed by stepwise model. Conclusion: Low values of muscle mass and function are prevalent among COPD patients. The present study revealed that low FFMI and handgrip strength were closely related to disease severity.