Characteristics of patients with COPD surveyed in the case cross-over study (n=168)
| Age, mean years (SD) | 70 (9.8) |
| Female, % (n) | 60 (101) |
| Race: | |
| White | 97% (163) |
| Black | 1% (2) |
| Other | 2% (3) |
| GOLD grade | |
| I (Mild) | 2% (3) |
| II (Moderate) | 23% (38) |
| III (Severe) | 50% (82) |
| IV (Very Severe) | 18% (30) |
| Normal FEV1/FVC with COPD symptoms | 7% (12) |
| Inadequate spirometry | 2% (3) |
| Reported doctor diagnosis of asthma | 43% (73) |
| Smoking status | |
| Current | 18% (30) |
| Ex | 78% (131) |
| Never | 4% (7) |
| Pack years (mean, SD) | 52 (31) |
| FEV1 improvement post-bronchodilator >15% | 20% (32) |
| Has ever worked full time (>30 hours per week) | 99% (166) |
| Worked for at least 1 week of study period | 14% (24) |
| Has worked for a year or more in dusty job | 50% (83) |
| Severity of dusty job | |
| Mild | 33% (27) |
| Moderate | 40% (33) |
| Severe | 28% (23) |
| Has ever been exposed to gas or chemical fumes in work | 41% (68) |
| Severity of gas or chemical fume exposure | |
| Mild | 37% (25) |
| Moderate | 44% (30) |
| Severe | 19% (13) |
*Two observations were missing.
COPD, chronic obstructive pulmonary disease.