Table 1.
Characteristics of the Study Participants According to the Pattern of Lung-Function Growth and Decline.*
| Characteristic | Normal Growth (N = 170) |
Normal Growth and Early Decline (N = 178) |
Reduced Growth (N = 160) |
Reduced Growth and Early Decline (N = 176) |
P Value† |
|---|---|---|---|---|---|
| Maximum lung function attained — no. (%) | 45 (26) | 178 (100) | 30 (19) | 176 (100) | <0.001 |
| Age at maximum lung function — yr | 22.3±2.2 | 20.6±2.2 | 21.9±1.7 | 20.6±1.8 | <0.001 |
| Plateau phase | <0.001 | ||||
| Plateau not attained, maximum lung function not reached — no. (%) |
125 (74) | 0 | 130 (81) | 0 | |
| No plateau, immediate decline — no. (%) | 0 | 112 (63) | 0 | 106 (60) | |
| Maximum lung function reached, plateau attained — no. (%) |
45 (26) | 66 (37) | 30 (19) | 70 (40) | |
| Age when plateau attained — yr | 22.3±2.2 | 20.6±2.1 | 21.9±1.7 | 20.5±1.6 | <0.001 |
| Plateau phase completed — no. (%) | 1 (1)‡ | 66 (37) | — | 70 (40) | 0.60 |
| Duration of plateau — yr | 2.0‡ | 1.5±0.6 | — | 1.8±0.9 | 0.03 |
| Decline phase begun — no. (%) | 1 (1)‡ | 178 (100) | 0 | 176 (100) | |
| Had an early decline — no. (%) | 0 | 178 (100) | 0 | 176 (100) | |
| Age at start of any decline — yr | 24.0‡ | 21.1±2.3 | — | 21.3±2.0 | 0.46 |
| Demographic and physical characteristics | |||||
| Male sex — no. (%) | 82 (48) | 100 (56) | 114 (71) | 109 (62) | <0.001 |
| Age at randomization — yr | 9.3±1.7 | 9.7±1.7 | 9.3±1.8 | 9.9±1.7 | 0.006 |
| Prepubertal at randomization — no. (%)§ | 119 (70) | 106 (60) | 112 (70) | 106 (60) | 0.04 |
| Body-mass index at randomization — z score | 0.50±0.97 | 0.78±0.94 | 0.18±1.04 | 0.44±1.05 | <0.001 |
| Interval between diagnosis of asthma and enrollment — no. (%) |
0.003 | ||||
| <3 yr | 50 (29) | 45 (25) | 31 (19) | 28 (16) | |
| 3–6 yr | 85 (50) | 84 (47) | 81 (51) | 79 (45) | |
| ≥7 yr | 35 (21) | 49 (28) | 48 (30) | 69 (39) | |
| Maternal cigarette smoking during gestation — no. (%) | 17 (10) | 27 (15) | 20 (12) | 27 (15) | 0.40 |
| Lung function at randomization | |||||
| Prebronchodilator FEV1 — % of predicted value | 100.5±13.4 | 99.7±12.9 | 87.5±12.6 | 83.8±12.9 | <0.001 |
| Prebronchodilator FEV1:FVC — % of predicted value | 81.9±6.9 | 81.6±7.5 | 76.5±7.9 | 76.5±8.4 | <0.001 |
| Bronchodilator response — %¶ | 8.9±7.8 | 8.2±7.8 | 12.7±9.9 | 12.4±11.3 | <0.001 |
| Airway responsiveness — log mg/ml∥ | 0.3±1.2 | 0.4±1.1 | −0.2±1.1 | −0.2±1.1 | <0.001 |
| Lifetime smoking — pack-yr** | 0.5±1.5 | 0.4±1.4 | 0.4±1.1 | 0.5±1.5 | 0.97 |
| Age and spirometry at last visit | |||||
| Age — yr | 25.7±1.7 | 26.0±1.8 | 25.8±1.9 | 26.3±1.7 | 0.01 |
| Prebronchodilator FEV1 — % of predicted value | 104.3±7.6 | 97.7±9.5 | 87.1±7.9 | 79.7±10.0 | <0.001 |
| Prebronchodilator FEV1:FVC — % of predicted value | 80.4±6.4 | 78.1±7.2 | 73.0±8.0 | 71.2±9.6 | <0.001 |
Plus–minus values are means ±SD. FEV1 denotes forced expiratory volume in 1 second, and FVC forced vital capacity.
P values (two-sided) are for the comparison across pattern groups and are based on a chi-square test for nonordered categories (categorical variables) or analysis of variance (continuous variables).
One participant with a normal-growth pattern was determined to have a decline in lung function; however, the decline was not earlier than expected.
Prepubertal was defined as no Tanner components (pubic hair and either breast stage for girls or genital stage for boys) greater than stage 1.
Bronchodilator response was calculated as [(postbronchodilator FEV1 – prebronchodilator FEV1) ÷ prebronchodilator FEV1] × 100.
Airway responsiveness was defined as the concentration of methacholine that caused a 20% decrease in FEV1.
Data on smoking exposure were restricted to cigarette smoking. Smoking exposure was determined through the end of follow-up.