Table 5

Test of possible mediation effect of airflow measures on association of maximum exercise capacity with air trapping

Mediating variable	Effect of RV/TLC on VO_2max (mL/min)
Mediating variable	Airflow-mediated effect (%)	P values	Non-mediated effect (%)	P values
FEV₁/FVC	6.9	0.286	93.1	0.020
FEV₁	15.2	0.237	84.8	0.042
FEF_25–75	1.6	0.609	98.4	0.011
FEF₇₅	2.0	0.655	98.0	0.014

To see if the association of hyperinflation (RV/TLC) with maximum exercise capacity (VO_2max) was mediated through airflow indices, mediation analyses were performed with adjustment for age, sex, height, and weight and inclusion of one airflow index at a time based on the model: Work=β₀+β₁(age)+β₂(sex)+β₃(height)+β₄(weight)+β₅(RV/TLC)+β₆(airflow index). n=179. Significant p-values are shown in bold.
FEF_25–75, maximum airflow at mid-lung volume; FEF₇₅, maximum airflow at low-lung volume; FEV₁, forced expiratory volume in 1 s; FVC, forced vital capacity; RV, residual volume; TLC, total lung capacity; VO_2max, maximum oxygen uptake.