Background: Lung hyperinflation contributes to dyspnea, morbidity and mortality in chronic obstructive pulmonary\ndisease (COPD). The inspiratory-to-total lung capacity (IC/TLC) ratio is a measure of lung hyperinflation and is\nassociated with exercise intolerance. However, knowledge of its effect on longitudinal change in the 6-min walk\ndistance (6MWD) in patients with COPD is scarce. We aimed to study whether the IC/TLC ratio predicts longitudinal\nchange in 6MWD in patients with COPD.\nMethods: This prospective cohort study included 389 patients aged 40â??75 years with clinically stable COPD in\nGlobal Initiative for Chronic Obstructive Lung Disease stages II-IV. The 6MWD was measured at baseline, and\nafter one and 3 years. We performed generalized estimating equation regression analyses to examine\npredictors for longitudinal change in 6MWD. Predictors at baseline were: IC/TLC ratio, age, gender, pack years,\nfat mass index (FMI), fat-free mass index (FFMI), number of exacerbations within 12 months prior to inclusion,\nCharlson index for comorbidities, forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and light\nand hard self-reported physical activity.\nResults: Reduced IC/TLC ratio (p < 0.001) was a statistically significant predictor for decline in 6MWD. With a\n0.1-unit decrease in baseline IC/TLC ratio, the annual decline in 6MWD was 12.7 m (p < 0.001). Study\nparticipants with an IC/TLC ratio in the upper quartiles maintained their 6MWD from baseline to year 3, while\nit was significantly reduced for the patients with an IC/TLC ratio in the lower quartiles. Absence of light and\nhard physical activity, increased age and FMI, decreased FEV1 and FVC, more frequent exacerbations and\nhigher Charlson comorbidity index were also predictors for lower 6MWD at any given time, but did not\npredict higher rate of decline over the timespan of the study.\nConclusion: Our findings demonstrated that patients with less lung hyperinflation at baseline maintained their\nfunctional exercise capacity during the follow-up period, and that it was significantly reduced for patients with increased\nlung hyperinflation.
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