Discriminating Measures and Normal Values for Expiratory Obstruction: Subjects
Utilizing data from the same NHANES III source, we did the following: (1) calculated the mean and LLN values for FEV3/FVC in these never-smoking and currently smoking groups; (2) compared the variability of FEV1/FVC, FEV3/FVC, and FEF25-75 values in never-smokers and current smokers; and (3) assessed changes associated with aging and smoking. We hypothesized that the fraction of the FVC that had not been expired during the first 3 s of the FVC (1 — FEV3/FVC) measures the increase in long-time-constant lung units that is associated with aging and smoking, and thus adding value to the spirometric assessment of airflow limitation. We further hypothesized that FEV3/FVC complements FEV1/FVC and that both are superior to FEF25-75 in identifying and characterizing expiratory airway obstruction, add comment
Data from NHANES III were extracted for men and women > 20 years of age for the following ethnic-racial groups: white (white); African-American (black); and Mexican-American (Latin or Latina). These data, from unidentified subjects, had been ethically obtained with Institutional Review Board approval. The term never-smokers included individuals those who had not smoked pipes, cigars, or > 100 cigarettes in a lifetime, and excluded those with known respiratory, skeletal, or neurologic disorders. The term current smokers included all currently smoking adults without known skeletal or neuromuscular disorders. All spirometric tests met ATS standards with at least three reproducible forced expirations and maximal scores for quality and reproducibility. Age was recorded in months, height in 0.1-cm increments, weight in 0.1-kg increments, volumes in milliliters, and flows in milliliters per second. The following calculations were made: (1) the mean, slope, intercept, SE of the estimate, LLN values, and correlation coefficients for FEV1/FVC and FEV3/FVC were derived by linear regression for black, Latin, and white men and women 20 to 80 years old who had never smoked; (2) the formulas of Hankinson et al and our formulas for FEV1/FVC were compared; (3) the LLN as a percentage of the mean predicted values were calculated for FVC, FEV1s FEV1/FVC, FEV3/FVC, and FEF25-75 for each never-smoking group; (4) for all subjects, deviations from the mean predicted values were plotted, and individuals with values below those for the LLN were identified; and (5) age coefficients for FEV1/FVC and 1 — FEV3/FVC were calculated for never-smokers and current smokers.