Table 6

Effect of air trapping on exercise capacity through mediators

Mediators	Mediation analysis of effect of RV/TLC to
	Watts_Peak			Work_Total			VO_2Peak
	N	% mediated (95% CI)	P value	N	% mediated (95% CI)	P value	N	% mediated (95% CI)	P value
Cardiovascular outputs
Peaks
O₂-Pulse_Peak	235	35.9 (–6.1 to 69.3)	0.078	230	39.3 (3.3 to 82.7)	0.036		N/A *
HR_Peak	235	20.7 (0.7 to 54.7)	0.044	230	27.6 (2.7 to 74.4)	0.034	235	27.7 (–0.7 to 79.8)	0.052
SBP_Peak	220	5.3 (–7.0 to 30.3)	0.390	219	6.8 (–9.0 to 41.9)	0.396	220	5.0 (–6.7 to 31.7)	0.388
DBP_Peak	220	0.3 (–4.5 to 10.2)	0.804	219	0.02 (–5.5 to 8.2)	0.978	220	0.04 (–4.6 to 8.0)	0.934
Slopes
O₂-Pulse_Slope	229	11.5 (–5.7 to 32.4)	0.192	229	10.3 (–5.1 to 34.0)	0.194		N/A *
HR_Slope	229	2.4 (–13.3 to 32.4)	0.794	229	1.4 (–10.6 to 23.0)	0.794	229	1.2 (–9.7 to 19.6)	0.792
SBP_Slope	221	6.9 (–4.9 to 24.1)	0.248	220	3.6 (–4.6 to 19.4)	0.340	221	4.9 (–3.4 to 21.7)	0.278
DBP_Slope	221	0.3 (–18.6 to 13.9)	0.970	220	0.2 (–17.6 to 13.0)	0.968	221	0.3 (–20.1 to 15.1)	0.968
Pulmonary outputs
RR_Peak	225	1.3 (–17.1 to 30.8)	0.882	224	2.2 (–22.9 to 48.2)	0.858	225	2.3 (–25.5 to 64.7)	0.882
VE_Peak	235	75.1 (42.7 to 137.8)	0.002	230	85.9 (49.4 to 173.5)	0.002	235	98.0 (64.2 to 204.2)	<0.001
VT_Peak	229	44.9 (21.2 to 93.6)	<0.001	228	43.1 (17.6 to 107.8)	0.004	229	37.5 (15.0 to 91.4)	0.002

To see if the association of air trapping (independent variable) with exercise capacity (dependent variable) was mediated through the cardiovascular or pulmonary outputs, mediation analyses were performed with adjustment for age, sex, height and body mass index and inclusion of one mediator at a time. Statistically significant values are shown in bold.
*The associations of VO_2Peak with O2-Pulse_Peak and O2-Pulse_Slope were not computed due to existence of “mathematical coupling” between VO₂ and O₂-Pulse, which depends on VO₂ for its calculation (O₂-Pulse=VO₂/HR).
DBP, diastolic blood pressure; HR, heart rate; O₂-Pulse_Peak, oxygen uptake per heartbeat at peak exercise; RR_Peak, peak respiratory rate; RV, residual volume; SBP, systolic blood pressure; SHS, secondhand smoke; TLC, total lung capacity; VE_Peak, peak minute ventilation value; VO_2Peak, peak oxygen uptake; VT_Peak, peak tidal volume.