Table 3

Associations of exercise capacity with each of the cardiopulmonary exercise outputs or SHS exposure

Independent variables	Dependent variables
	Peak workload (watt) (Watts_Peak)			Cumulative work (watt-minute) (Work_Total)			Peak volume of O₂ consumption (mL/min) (VO_2Peak)
	N	PE ±SEM 95% CI	P value	N	OR ±SEM 95% CI	P value	N	OR ±SEM 95% CI	P value
Cardiovascular outputs
Peaks
O₂-Pulse_Peak	245	10.3±0.7 (8.8 to 11.7)	<0.001	239	53.9±4.6 (44.9 to 62.9)	<0.001		N/A *
HR_Peak	245	0.7±0.1 (0.4 to 0.9)	<0.001	239	4.4±0.7 (3.1 to 5.6)	<0.001	245	8.0±1.1 (5.7 to 10.2)	<0.001
SBP_Peak	226	0.3±0.1 (0.1 to 0.5)	0.004	224	2.2±0.6 (1.0 to 3.5)	<0.001	226	3.1±1.1 (0.9 to 5.4)	0.006
DBP_Peak	226	0.1±0.2 (−0.3 to 0.5)	0.621	224	0.1±1.2 (−2.4 to 2.5)	0.945	226	0.2±2.2 (−4.2 to 4.6)	0.923
Slopes
O₂-Pulse_Slope	238	−64.5±18.1 (−100.1 to −28.9)	<0.001	238	−251.9±109.5 (−467.6 to −36.2)	0.022		N/A *
HR_Slope	238	−11.7±1.9 (−15.5 to −8.0)	<0.001	238	−40.9±11.7 (−63.9 to −17.8)	<0.001	238	−64.1±20.9 (−105.2 to −23.0)	0.002
SBP_Slope	227	−7.0±1.5 (−10.1 to −4.0)	<0.001	225	−22.3±9.3 (−40.7 to −4.0)	0.017	227	−44.1±16.6 (−76.8 to −11.4)	0.008
DBP_Slope	227	−12.7±3.0 (−18.6 to −6.9)	<0.001	225	−50.0±17.7 (−84.9 to −15.1)	0.005	227	−113.7±31.3 (−175.5 to −52.0)	<0.001
Pulmonary outputs
RR_Peak	235	1.1±0.2 (0.6 to 1.5)	<0.001	233	7.9±1.3 (5.4 to 10.4)	<0.001	235	17.9±2.1 (13.8 to 22.1)	<0.001
VE_Peak	245	1.4±0.1 (1.2 to 1.7)	<0.001	239	8.4±0.6 (7.2 to 9.6)	<0.001	245	17.5±0.9 (15.7 to 19.3)	<0.001
VT_Peak	239	37.2±5.6 (26.1 to 48.3)	<0.001	237	177.6±33.5 (111.5 to 243.6)	<0.001	239	307.8±59.2 (191.1 to 424.5)	<0.001
VO_2AT	202	57.8±7.7 (42.6 to 73.0)	<0.001	200	287.1±47.4 (193.6 to 380.5)	<0.001	202	799.3±71.3 (658.8 to 939.9)	<0.001
VE/VCO_2Peak	245	−1.2±0.6 (−2.3 to −0.02)	0.046	239	−0.4±3.4 (−7.2 to 6.4)	0.906	245	−7.9±6.1 (−19.9 to 4.0)	0.191
RV/TLC	235	−1.6±0.5 (−2.5 to −0.6)	0.001	230	−8.6±2.8 (−14.1 to −3.1)	0.002	235	−14.3±5.0 (−24.2 to −4.4)	0.004
FRC/TLC	220	−0.3±0.4 (−1.1 to 0.4)	0.363	219	−2.1±2.2 (−6.5 to 2.2)	0.337	220	−5.0±4.0 (−12.8 to 2.8)	0.210
SHS exposure
Airline SHS exposure (years)	241	−0.8±0.2 (−1.2 to −0.3)	<0.001	235	−2.3±1.4 (−5.1 to 0.4)	0.092	241	−5.0±2.4 (−9.7 to −0.2)	0.040
Childhood home SHS exposure (Y/N)	245	−0.5±4.1 (−8.7 to 7.6)	0.895	239	4.7±24.3 (−43.1 to 52.5)	0.845	245	−17.7±42.5 (−101.4 to 65.9)	0.676
Adult home SHS exposure (Y/N)	245	−5.1±4.9 (−14.7 to 4.5)	0.292	239	−19.0±28.8 (−75.7 to 37.6)	0.509	245	−50.9±50.2 (−149.7 to 47.9)	0.311

The association between exercise capacity (dependent variable) and each of the cardiopulmonary exercise measures, pulmonary outputs or SHS exposure (independent variable) were individually assessed by multivariable linear regression modeling with adjustment for age, sex, height, body mass index and corresponding baseline values (for slope variables). 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; FRC, functional residual capacity; 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; VCO_2Peak, peak carbon dioxide production; VE_Peak, peak minute ventilation value; VO_2AT, oxygen uptake at anaerobic threshold; VO_2Peak, peak oxygen uptake; VT_Peak, peak tidal volume.