Table 2.

Multivariable Linear Regression Model to Test Independent Association, and Interaction, Between Smoking Rate and Sleep Duration on 6-Min Walk Test Distance Covered^a

Study Variable	Slope Estimate	95% CI	P Value
Smoking rate	–5.37	10.37 to –0.38	.04
Sleep duration	–0.14	–0.33 to 0.06	.18
FVC	0.32	–0.01 to 0.64	.05
Heart rate at 1 min of recovery	1.02	0.22 to 1.82	.01
Oxygen saturation	6.76	1.90 to 11.62	.01
Apnea-hypopnea index	–1.61	–3.79 to 1.48	.39
Smoking rate × sleep duration	0.02	0.00 to 0.03	.04

^aModel adjusted for age, biological sex, educational attainment (at least 8 y of schooling or not), BMI, Center for Epidemiologic Studies-Depression Scale, use of antihypertensives, use of nodal blockers, use of statins, use of COPD medication (long-acting muscarinic antagonist, long-acting β-agonist, or inhaled corticosteroid), use of diabetes medication, evidence of diabetes, oxygen saturation, FVC, apnea-hypopnea index, and 1-min resting heart rate.