Table 2– Correlation between high-resolution computed tomography (HRCT) airway wall thickening, HRCT air trapping and pulmonary function

HRCT variables	PFTs
	FVC % pred	FEV₁ % pred	MMEF % pred	FEV₁/FVC %	RV/TLC %
Air trapping
Visual score	-0.446^#	-0.639^#	-0.404^#	-0.356^#	0.293
AT_HU-850	-0.034	-0.197	-0.310^#	-0.257	0.146
AT₁₅	0.030	0.153	0.255	0.203	-0.176
AT_HU-850 corrected for ground glass	-0.017	-0.233	-0.402^#	-0.297	0.078
AT₁₅ corrected for ground glass	0.018	0.183	0.333^#	0.213	-0.114
Airway wall thickening
Visual score	-0.077	-0.113	-0.67	-0.33	0.112
Wall area	0.178	0.257	0.088	0.002	-0.396^¶
Wall area %	-0.29	-0.04	-0.032	0.043	0.124
WA_BSA	0.217	0.369^¶	0.343^¶	0.160	-0.162
WA_{lung area}	0.157	0.214	0.109	0.022	-0.318^¶
WA_%age	-0.10	0.077	0.132	0.159	0.180
WA_Pi10	0.11	0.07	-0.18	-0.06	-0.11

Data are presented as Spearman rank correlation coefficients. PFT: pulmonary function test; FVC: forced vital capacity; % pred: % predicted; FEV₁: forced expiratory volume in 1 s; MMEF: maximum mid-expiratory flow at 25–75% of FVC; RV: residual volume; TLC: total lung capacity; HU: Hounsfield units; AT_HU-850: number of voxels < -850 HU as percentage of total number of voxels; AT₁₅: HU at 15th percentile; WA_BSA: wall area normalised to body size; WA_{lung area}: wall area normalised to right lung area at right upper lobe apical bronchus level; WA_%age: wall area percentage corrected for age; WA_Pi10: wall area at a perimeter of the inner airway lumen of 10 mm. ^#: significant correlation in expected direction; ^¶: significant correlation in opposite direction.