Table 1.
Demographic, Imaging, and Clinical Characteristics of the Subjects in Each of the Emphysema Distribution Clusters at Visit 1
| Characteristic | Minimal Emphysema Cluster (n = 1,312) | Upper Lobe-Predominant Cluster (n = 905) | Lower Lobe-Predominant Cluster (n = 796) | P Value (All Groups Omnibus Test) | P Value (Upper-Lobe Predominant vs Lower-Lobe Predominant) |
|---|---|---|---|---|---|
| Demographics | |||||
| Age, y | 53.20 (49.18-59.26) | 59.30 (52.50-66.30) | 64.00 (57.40-69.83) | < .001 | < .001 |
| Male sex, % | 36.36 | 53.37 | 58.92 | < .001 | .07 |
| Non-Hispanic whites, % | 48.63 | 61.44 | 83.67 | < .001 | < .001 |
| BMI | 29.69 (25.91-33.71) | 26.64 (23.17-30.33) | 28.03 (24.21-32.55) | < .001 | < .001 |
| Smoking history (pack-years) | 35.80 (24.08-47.10) | 43.90 (33.00-61.30) | 45.00 (32.68-63.00) | < .001 | 1.00 |
| Current smoking, % | 75.15 | 57.79 | 40.83 | < .001 | < .001 |
| CT measurements | |||||
| Total emphysema, % LAA- 950) | 0.24 (0.14-0.36) | 5.44 (2.43-13.76) | 5.52 (2.21-16.67) | < .001 | .85 |
| U/L ratio | 1.08 (0.78-1.51) | 4.60 (3.31-7.08) | 0.50 (0.39-0.62) | < .001 | < .001 |
| Airway wall thickening | 61.82 (59.73-64.20) | 61.76 (59.49-63.86) | 61.48 (59.46-63.91) | .14 | .75 |
| Pi10 | 3.72 (3.66-3.81) | 3.68 (3.61-3.76) | 3.68 (3.59-3.76) | < .001 | .41 |
| Percent gas trapping | 4.05 (1.97-8.10) | 24.58 (13.80-41.81) | 31.30 (12.37-55.29) | < .001 | .23 |
| Spirometry | |||||
| FEV1, % predicted | 86.45 (74.80-97.80) | 71.70 (52.90-87.00) | 65.80 (39.40-86.20) | < .001 | < .001 |
| FEV1/FVC | 0.79 (0.74-0.83) | 0.64 (0.51-0.72) | 0.59 (0.41-0.74) | < .001 | .73 |
| Bronchodilator, % responsiveness (%) | 16.86 | 24.81 | 27.33 | < .001 | .78 |
| Symptoms and exacerbations | |||||
| MMRC dyspnea score | 1.24 ± 1.41 | 1.67 ± 1.45 | 1.63 ± 1.45 | < .001 | 1.00 |
| SGRQ score | 30.55 ± 25.86 | 38.65 ± 26.15 | 36.72 ± 26.80 | < .001 | .39 |
| Chronic bronchitis, % | 17.84 | 22.65 | 22.36 | .007 | 1.00 |
| Exacerbation frequency, % | 14.94 | 28.18 | 28.89 | < .001 | 1.00 |
| Comorbidities, % | |||||
| Coronary artery disease | 4.50 | 6.63 | 10.68 | < .001 | .01 |
| Diabetes | 16.08 | 10.06 | 14.82 | < .001 | .01 |
| Dyslipidemia | 35.37 | 39.34 | 46.23 | < .001 | .01 |
| Metabolic syndrome | 19.28 | 13.04 | 18.84 | < .001 | .004 |
| Obesity | 47.64 | 27.62 | 35.80 | < .001 | .001 |
| Sleep apnea | 15.10 | 14.07 | 22.48 | < .001 | < .001 |
Variables are expressed as mean and SD for continuous normally distributed variables, median and interquartile range (25th to 75th percentile) for continuous nonnormally distributed variables, and percentages for categorical variables. Omnibus P values are obtained using analysis of variance for the continuous normally distributed variables, the Kruskal-Wallis test for the continuous nonnormally distributed variables, and the χ2 test for proportions. P values of upper-lobe predominance vs lower-lobe predominance are from pairwise t tests, Nemenyi tests, and χ2 post hoc tests for pairwise comparisons between upper lobe- predominant and lower lobe-predominant clusters for the continuous normally distributed variables, nonnormally distributed variables, and categorical variables, respectively. P values < .05 are in bold.
Emphysema is defined as percent of CT low-attenuation area < –950 Hounsfield units at end-inspiration using SLICER software. U/L ratio: ratio of % LAA-950 in both upper lobes to that in both lower lobes. Airway wall area percent is the percentage of the wall area compared with the total bronchial area for segmental airways. Exacerbation frequency is the percentage of subjects reporting at least 1 COPD exacerbation in the previous year. Metabolic syndrome = 3 of the following 4: BMI ≥ 30 (measured), diabetes mellitus, hypertension, and high cholesterol (all self-reported). Obesity = BMI ≥ 30.
MMRC = Modified Medical Research Council; % LAA-950 = percent of CT low attenuation area < –950 HU at end-inspiration; Pi10 = square root of the wall area of a hypothetical airway of 10-mm internal perimeter; SGRQ = St. George’s Respiratory Questionnaire; U/L ratio = ratio of % LAA-950 in both upper lobes to that in both lower lobes.