The relationship between fat-free mass index and pulmonary hyperinflation in COPD patients

Reduced fat-free mass (FFM), a common finding in chronic obstructive pulmonary disease (COPD), may indirectly impact peak exercise capacity through a greater level of pulmonary hyperinflation. We aimed to investigate if FFM index (FFM/squared height) impacts exercise induced dynamic hyperinflation in COPD patients.

Fifty-four patients with moderate-to-very severe COPD performed a symptom limited incremental cardiopulmonary exercise tests with serial measurements of inspiratory capacity (IC). FFM was measured by whole-body bioelectrical impedance.

Patients were 66.7 ± 7.7 years old with mean forced expiratory volume in 1 s (FEV₁) of 1.08 ± 0.41 L (42 ± 15% of predicted). Peak exercise IC was significantly (P < 0.05) correlated with IC at rest (r = 0.78), FEV₁(r = 0.66), FVC (r = 0.59), FFM (r = 0.38) and FFM index (r = 0.29). However, only FEV₁ and rest IC predict peak IC (r = 0.86; P < 0.01) in a multivariate linear regression analysis.

FFM index was weakly associated with peak exercise IC in COPD patients. However, it ceased to be an independent predictor when corrected for expiratory airflow limitation (FEV₁) and lung hyperinflation at rest (rest IC).