Discriminating Measures and Normal Values for Expiratory Obstruction: Pattern Analysis of Current Smokers
We placed each of the currently smoking subjects into 1 of 16 (24) potential categories, depending on whether or not their FEVi, FVC, FEV/FVC, and FEV3/FVC values were below the LLN. This allowed us to decide whether each subject had normal spirometry findins, or had a pattern of obstruction, had probable restriction, or a combination, and whether or not the FEF25_75 values confirmed the diagnosis or were probably false-positive or false-negative findings.
Except where noted, values are reported as the mean ± SD and the 95th percentile as the LLN.
Several key spirometric values, with respect to ethnicity, gender, age, and height, are provided for the NHANES III never-smokers and current smokers in Table 1. The number of never-smokers (5,938) differs from that of Hankinson et al because of differences in age ranges and screening procedures. Table 2 gives the factors needed to derive the linear regression equations for FEV1/FVC and FEV3/FVC for never-smokers (eg, FEV1/FVC or FEV3/ FVC = mean constant — age constant X age). The mean absolute difference in FEV1/FVC between the formulas of Hankinson et al and our formula was only 0.28% for the 5,938 adults that we selected. This reflects the similarity between these two never-smoking series extracted from the same NHANES III database. buy-asthma-inhalers-online
Using LLN levels for FEV1/FVC, FEV3/FVC, and FEF25-75 in never-smokers, values of 4.4 to 5.1% were “abnormal” (ie, similar to the expected value of 5.0%). However, if one had improperly considered 80% of the mean predicted FEF25-75 value as the LLN, the conditions of an additional 20.8% of never-smoking NHANES III subjects would be considered to be abnormal. The relative variabilities of five spirometric measures are shown in Figure 1 for the largest group of never-smokers, white women. The LLN as a percentage of the mean predicted value was approximately 94% for FEV3/FVC and approximately 88% for FEV1/FVC with no significant effect with aging. In contrast, the LLN for FEV1, FVC, and FEF25-75 decreased from age 20 to 80 years, ranging from 82 to 72% for FEV1 and FVC, and 67 to 12% for FEF25-75. Similar patterns of variability (not presented) were seen for spirometric measures for all other never-smoking groups.
Table 1—Demographics of Selected Subject Populations
Variables | Men | Women | ||||
White | Black | Latin | White | Black | Latina | |
Never-smokers | ||||||
No. | 771 | 623 | 702 | 1,413 | 1,169 | 1,260 |
Age, yr | 46.6 ± 18.1 | 36.4 ± 14.6 | 36.9 ± 14.8 | 50.2 ± 17.7 | 40.1 ± 15.9 | 40.0 ± 15.7 |
Height, cm | 176.4 ± 6.6 | 176.3 ± 7.0 | 169.5 ± 6.8 | 162.9 ± 6.7 | 162.8 ± 6.4 | 156.4 ± 6.1 |
FVC, L | 4.96 ± 0.96 | 4.38 ± 0.79 | 4.76 ± 0.79 | 3.35 ± 0.73 | 3.06 ± 0.66 | 3.29 ± 0.64 |
FEVj, L | 3.91 ± 0.85 | 3.61 ± 0.71 | 3.89 ± 0.72 | 2.70 ± 0.66 | 2.55 ± 0.58 | 2.76 ± 0.59 |
FEVj/FVC, % | 78.7 ± 6.7 | 82.3 ± 6.5 | 81.7 ± 6.5 | 80.2 ± 6.9 | 83.4 ± 7.1 | 82.9 ± 6.8 |
FEV3/FVC, % | 92.8 ± 4.6 | 94.8 ± 3.9 | 94.4 ± 4.0 | 93.2 ± 4.5 | 94.8 ± 4.2 | 94.7 ± 4.2 |
FEF2/-7/%, L/s | 3.62 ± 1.36 | 3.78 ± 1.28 | 4.04 ± 1.31 | 2.37 ± 1.10 | 2.83 ± 1.10 | 3.04 ± 1.06 |
Current smokers | ||||||
No. | 684 | 705 | 551 | 701 | 612 | 262 |
Age, yr | 43.7 ± 15.4 | 41.5 ± 13.5 | 38.4 ± 14.3 | 42.1 ± 15.7 | 39.7 ± 12.8 | 38.4 ± 13.8 |
Height, cm | 176.5 ± 6.6 | 176.3 ± 6.9 | 169.4 ± 6.2 | 162.9 ± 6.4 | 163.9 ± 6.4 | 157.9 ± 6.4 |
FVC, L | 4.89 ± 0.96 | 4.29 ± 0.80 | 4.75 ± 0.80 | 3.44 ± 0.74 | 3.11 ± 0.62 | 3.41 ± 0.67 |
FEV1, L | 3.67 ± 0.89 | 3.37 ± 0.76 | 3.76 ± 0.76 | 2.68 ± 0.72 | 2.50 ± 0.57 | 2.79 ± 0.61 |
FEV1/FVC, % | 74.8 ± 8.8 | 78.4 ± 8.7 | 79.0 ± 7.6 | 77.4 ± 9.3 | 80.3 ± 8.0 | 81.5 ± 7.4 |
FEV/FVC, % | 90.4 ± 6.2 | 92.2 ± 5.8 | 92.9 ± 5.0 | 92.1 ± 6.3 | 93.2 ± 5.2 | 94.3 ± 4.5 |
FEF2/-7/%, Ls | 3.06 ± 1.46 | 3.21 ± 1.46 | 3.64 ± 1.39 | 2.50 ± 1.24 | 2.58 ± 1.08 | 2.94 ± 1.10 |
Table 2—FEV1/FVC and FEV3/FVC Formulas for Never-Smoking Adults
Group | Age Factor | Mean Constant | LLN Constant | SEE | r2 Value |
FEV1/FVC | |||||
White men | —0.1600 | 86.03 | 76.13 | 6.00 | 0.198 |
Black men | —0.2016 | 89.87 | 80.27 | 5.84 | 0.204 |
Latin men | —0.1947 | 89.09 | 80.25 | 5.38 | 0.222 |
All men | —0.1952 | 88.38 | 78.36 | 6.09 | 0.220 |
White women | —0.2116 | 90.84 | 81.29 | 5.81 | 0.295 |
Black women | — 0.1936 | 91.21 | 80.72 | 6.38 | 0.333 |
Latina women | —0.2029 | 91.24 | 81.94 | 5.65 | 0.240 |
All women | — 0.2030 | 91.11 | 80.98 | 6.16 | 0.288 |
FEV3/FVC | |||||
White men | — 0.1692 | 100.63 | 95.00 | 3.42 | 0.445 |
Black men | — 0.1699 | 100.99 | 96.03 | 3.02 | 0.405 |
Latin men | —0.1773 | 101.02 | 96.58 | 2.70 | 0.485 |
All men | —0.1756 | 100.86 | 95.56 | 3.22 | 0.449 |
White women | —0.1826 | 102.41 | 96.56 | 3.57 | 0.453 |
Black women | — 0.1568 | 100.86 | 95.16 | 3.46 | 0.323 |
Latina women | — 0.1740 | 101.74 | 96.78 | 3.01 | 0.449 |
All women | — 0.1782 | 101.83 | 96.02 | 3.53 | 0.436 |
Figure 1. LLN as a percentage of the mean predicted spiro-metric values. Values are derived for ages 20 to 80 years from 1,413 never-smoking white women, assuming that height remains constant. The pattern for men and other ethnic groups is similar. With changes in height, there are additional small increases in the variability of the LLN of FEV1 and FVC, and larger increases in the variability of the LLN of FEF25.