TABLE 1

Demographics of study groups at baseline

ParameterSmokers with normal spirometryp-value
Normal DLCOLow DLCO
Individuals5946
Males/females43/1631/15>0.6
Age years45±846±8>0.5
Ethnicity AA/E/H41/10/837/5/4>0.6
BMI kg·m−228±525±5<0.002
Smoking history#
 Pack-years24±1330±15>0.05
 Packs per day1.0±0.51.1±0.6>0.5
 Age of smoking initiation years17±517±4>0.9
 Urine nicotine ng·mL−11102±1290951±1285>0.6
 Urine cotinine ng·mL−11276±9271298±894>0.9
Cough score1.2±1.31.7±1.5>0.06
Sputum score1.1±1.31.3±1.3>0.3
MMRC score0.4±0.60.5 ±0.6>0.2
Emphysema+ %2.0±0.022.2±0.04>0.8
Serology§
 α1-antitrypsin mg·dL−1152±24145±21>0.1
 ESR mm·h−113±1112±10>0.7
 IgE IU·m−1129±208169±259>0.4
 CRP mg·dL−10.2±0.20.3±0.2<0.005
 Hepatitis C negative/positiveƒ46/939/6>0.8
Lung function##
 VC % predicted114±14108±14<0.05
 FVC % predicted111±14104±14>0.1
 FEV1 % predicted111±15104±14<0.03
 FEV1/FVC % observed81±479±5<0.03
 TLC % predicted99±1394±14<0.03
 RV % predicted90±2589±37>0.8
 RV/TLC % predicted28±731±11>0.1
DLCO % predicted93±1068±9<10−4
DLCO/VA mL·mHg−1·min−1·L−14.4±0.63.6±0.7<10−6
Assessment over time mean±sd (range)
 Duration of follow-up months46±21 (5–113)41±31 (5–146)>0.4
 Number of PFTs2±1 (2–6)3±2 (2–8)<10−3
 Interval between PFTs months33±18 (5–73)18±20 (1–127)<10−6
  • Data are presented as n or mean±sd, unless otherwise stated. A total of 105 active smokers was enrolled in the study, including 46 individuals with normal history, and physical and general laboratory tests, normal posterior–anterior and lateral chest radiography, and normal spirometry and lung volumes, but low diffusing capacity of the lung for carbon monoxide (DLCO), and 59 with normal spirometry, lung volumes and DLCO. All were followed over time with full lung function studies. AA: African-American; E: European; H: Hispanic; BMI: body mass index; MMRC: Modified Medical Research Council dyspnoea scale [14]; ESR: erythrocyte sedimentation rate; CRP: C-reactive protein; VC: vital capacity; FVC: forced vital capacity; FEV1: forced expiratory volume in 1 s; TLC: total lung capacity; RV: residual volume; VA: alveolar volume; PFT: pulmonary function test. #: current smoking was verified at baseline by urine nicotine and its derivative cotinine; at subsequent visits for lung function testing, active smoking status was verified by questionnaire. : cough and sputum scores were each evaluated on a scale of 0–4, where 0 represented “not at all”, 1 “only with chest infections”, 2 “a few days a month”, 3 “several days a week” and 4 “most days a week” [15]. +: chest high-resolution computed tomography % emphysema at −950 Hounsfield units. §: all individuals tested negative for HIV and had normal levels of α1-antitrypsin. ƒ: data available for 55 out of 59 smokers with normal spirometry and DLCO, and 45 out of 46 smokers with normal spirometry but low DLCO. ##: DLCO corrected for haemoglobin and carboxyhaemoglobin [11].