Lung function decline and incidence of chronic obstructive pulmonary disease in participants with spirometry-defined small airway dysfunction: a 15-year prospective cohort study in China

Table 3 Annual rate of decline in lung function in COPD patients with pre-bronchodilator small airway dysfunction and those without small airway dysfunction*

Variable	Pre-BD COPD with SAD (N = 795)	Pre-BD COPD without SAD (N = 50)	Pre-BD COPD with SAD vs. Pre-BD COPD without SAD
			Unadjusted		Adjusted
			Mean Difference (95% CI)	P Value	Mean Difference (95% CI) †	P Value †
Pre-BD lung function
FEV₁ (ml/year)	31.9 ± 2.0	8.0 ± 7.8	23.9 (8.0 to 39.7)	0.003	30.9 (16.5 to 45.3)	< 0.001
FEV₁ of predicted value (%/year)	0.62 ± 0.08	−0.58 ± 0.33	1.19 (0.52 to 1.87)	< 0.001	1.51 (0.90 to 2.11)	< 0.001
FEV₁ Z-score	0.056 ± 0.008	−0.062 ± 0.033	0.118 (0.050 to 0.185)	< 0.001	0.147 (0.086 to 0.208)	< 0.001
FVC (ml/year)	47.2 ± 3.0	50.3 ± 11.8	−3.2 (−27.1 to 21.8)	0.796	1.9 (−26.3 to 30.0)	0.897
FVC of predicted value (%/year)	0.95 ± 0.10	0.89 ± 0.38	0.06 (−0.72 to 0.84)	0.879	0.23 (−0.68 to 1.14)	0.617
FVC Z-score	0.080 ± 0.009	0.070 ± 0.035	0.010 (−0.060 to 0.080)	0.774	0.027 (−0.046 to 0.100)	0.466

Plus–minus values are means ± standard error
BD = bronchodilator; SAD = small airway dysfunction; COPD = chronic obstructive pulmonary disease; CI = confidence interval; FEV₁ = forced expiratory volume in one second; FVC = forced vital capacity
^* A random-effects model was adopted to evaluate the annual decline in lung function
^† Adjusted by age, sex, body mass index, smoking status, smoking index, family history of respiratory diseases, biomass exposure, occupational exposure history, and individual pre-bronchodilator spirometric values at baseline (FEV₁, FEV₁ of predicted value, FEV₁ Z-score, FVC, FVC of predicted value, and FVC Z-score)

ISSN: 1465-993X