Table 2.

Factor Loadings for a 5-Factor Model Based on the Combined Data Set (n = 8,157), Genetic Epidemiology of Chronic Obstructive Pulmonary Disease Study, United States, 2008–2011

Variable	Emphysema Disease Axis	Airway Disease Axis	Gas Trapping	CT Intensity Variability	TLC and FRC	Proportion of Variance Explaineda
Pulmonary function
FEV1/FVC	−0.63b	−0.61b	−0.23	0.12	0.05	0.83
FEV1% predictedc	−0.41	−0.89b	−0.1	0.03	−0.08	0.98
FVC% predictedc	−0.06	−0.82b	0.06	−0.05	−0.19	0.72
Peak expiratory flow	−0.4	−0.7b	−0.19	0.08	0.16	0.72
Forced expiratory flow 25%–75%	−0.51b	−0.7b	−0.22	0.07	0.11	0.81
TLC (predicted-race adjusted)	−0.04	−0.08	−0.03	0.01	0.95b	0.9
FRC (predicted-race adjusted)	0.05	−0.02	0.04	0.03	0.94b	0.88
Inspiratory CT
Less than −856 HU	0.86b	−0.18	0.03	−0.44	0.01	0.96
Less than −910 HU	0.96b	−0.05	0.11	−0.2	0	0.98
Less than −950 HU	0.96b	0.08	0.18	0.1	0	0.96
Inspiration histogram, 15th percentile	−0.94b	−0.01	−0.12	0.19	0.01	0.93
Emphysema, lower one-third, %	0.92b	0.04	0.12	0.02	0.05	0.87
Emphysema, upper one-third, %	0.91b	0.09	0.19	0.15	−0.04	0.89
Inspiration intensity, mean	−0.88b	0.06	−0.06	0.41	−0.01	0.94
Inspiration intensity, SD	−0.03	0.26	0.12	0.66b	−0.01	0.52
Exp/insp attenuation ratio	0.31	0.41	0.81b	−0.24	−0.01	0.99
Expiratory CT
Less than −910 HU	0.75b	0.33	0.54b	0.15	0.03	0.98
Less than −950 HU	0.73b	0.33	0.48	0.3	0.04	0.97
Gas trapping, %	0.68b	0.23	0.65b	−0.05	0.03	0.95
Expiration histogram, 15th percentile	−0.66b	−0.25	−0.58b	0.1	−0.01	0.84
Expiration intensity, mean	−0.62b	−0.27	−0.64b	0.36	0	0.99
Expiration intensity, SD	0.1	−0.1	−0.19	0.82b	0.05	0.74
Airway measurements
Wall area, % segmental	−0.07	0.57b	0.13	0.07	−0.08	0.36
Pi 10	−0.16	0.51b	0.13	0.16	−0.1	0.34
Pi 15	−0.21	0.51b	0.1	0.14	−0.02	0.33
BMI	−0.26	0.07	−0.13	0.50b	0.01	0.33
Proportion of variance explained	0.37	0.17	0.1	0.09	0.07
Cumulative variance explained	0.37	0.53	0.64	0.72	0.8

Abbreviations; BMI, body mass index; CT, computed tomography; Exp, expiration; FEV₁/FVC, ratio of forced expiratory volume at 1 second to forced vital capacity; FEV₁%, percentage of forced expiratory volume at 1 second; FRC, functional residual capacity; FVC%, percentage of forced vital capacity; HU, Hounsfield unit; Insp, inspiration; Pi 10, airway wall thickness at an internal perimeter of 10 mm; Pi 15, airway wall thickness at an internal perimeter of 15 mm ; SD, standard deviation; TLC, total lung capacity.

^a Proportion of variance in the row variable explained by the 5 factors.

^b Factors loading ≥│0.5│.

^c Based on Third National Health and Nutrition Examination Survey reference values (9).