Body mass and fat-free mass indices in COPD - Relation with variables expressing disease severity

Background: COPD primarily affects the lungs but also produces systemic consequences that are not reflected by the recent staging according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines. Body mass index (BMI) and fat-free mass index (FFMI) represent different aspects of nutrition abnormalities in COPD. We investigated whether BMI and FFMI could be related to parameters expressing airflow obstruction and limitation, exercise capacity, airway inflammation, and quality of life, and whether they would reflect the GOLD staging of the disease. Methods: One hundred patients with clinically stable COPD equally classified into the five stages of the disease were evaluated for BMI, FFMI (measured by bioelectrical impedance analysis), airway obstruction and hyperinflation (FEV1, FEV1/FVC, inspiratory capacity), exercise capacity (6-min walk distance [6MWD], Borg scale before and after 6MWD]), chronic dyspnea using the Medical Research Council (MRC) scale, airway inflammation (sputum differential cell counts, leukotriene B, in supernatant), and quality of life (emotional part of the chronic respiratory disease questionnaire). Results: 6MWD was significantly associated with both BMI and FFMI values, while FFMI additionally presented significant correlations with MRC scale, percentage of predicted FEV1 and FEV1/FVC ratio. No association was observed between the two nutritional indexes. BMI was not statistically different among patients in the five stages of COPD, while FFMI reflected the staging of the disease, presenting the highest values in stage 0. Conclusions: Nutritional status is mainly related to exercise capacity. FFMI seems to be more accurate in expressing variables of disease severity, as well as the current staging compared to BMI.