Table 3– Pearson's correlation coefficients between computed tomography indexes and pulmonary function variables measured in the learning set of 100 patients

	D_LCO %	FEV₁ %	FEV₁/VC	TLC %	RV %	FRC %	FVC %
CT1 (phenotype)	-0.48**	-0.19*	-0.33**	0.25*	0.20*	0.29**	-0.04
CT2 (severity)	-0.37**	-0.55**	-0.61**	0.44**	0.55**	0.58**	-0.30**

CT1, CT2: numeric indexes resulting from the application of principal component analysis to the relationship of relative lung area with X-ray attenuation < -950 HU and average wall thickness of an arbitrary airway with an internal perimeter of 10 mm. D_LCO: single breath diffusion capacity of the lung for carbon monoxide; FEV₁: forced expiratory volume in 1 s; VC: vital capacity; TLC: total lung capacity; RV: residual volume; FRC: functional residual capacity; FVC: forced vital capacity. *: p<0.05; **: p<0.01.