Table 1. Characteristics of the participants.
| Current swimmers | Past swimmers | Non-swimmers | p | |
|---|---|---|---|---|
| N (males) | 205 (99) | 228 (115) | 342 (175) | - - |
| Age (years, mean ± sd) | 8.7 ±0.8 | 8.6 ±0.7 | 8.9 ±0.8 | 0.011¥ |
| Weight (kg) | 30.9 (26.6 to 36.9) | 32.1 (28.2 to 37.8) | 30.8 (26.9 to 37.3) | 0.048 |
| Height (cm) | 135 (130 to 139) | 136 (131 to 141) | 136 (131 to 141) | 0.196 |
| Sport practisers (%) | 100.0 | 98.3 | 98.2 | 0.965 |
| Lung function | ||||
| FVC (L) | 1.88 (1.71 to 2.15) | 1.91 (1.71 to 2.18) | 1.88 (1.66 to 2.10) | 0.125 |
| FEV1 (L) | 1.73 (1.58 to 1.95) | 1.78 (1.60 to 1.99) | 1.74 (1.55 to 1.92) | 0.081 |
| FEV1/FVC (%) | 92.8 (89.1 to 96.1) | 92.5 (89.0 to 96.6) | 92.7 (88.8 to 96.4) | 0.998 |
| FEF25-75 (L/s) | 2.23 (1.97 to 2.71) | 2.36 (1.93 to 2.71) | 2.27 (1.91 to 2.59) | 0.423 |
| PEF (L/s) | 3.77 (3.30 to 4.38) | 3.77 (3.38 to 4.21) | 3.69 (3.27 to 4.27) | 0.641 |
| FEV1 reversibility (mL) | 70 (20 to 130) | 60 (10 to 120) | 60 (-10 to 110) | 0.028 |
| FEV1 reversibility (%) | 4.0 (1.3 to 7.2) | 3.4 (0.6 to 6.7) | 3.1 (-0.7 to 6.2) | 0.040 |
| FVC reversibility (mL) | 40 (-30 to 100) | 30 (-30 to 80) | 20 (-40 to 90) | 0.219 |
| Exhaled NO (ppb) | 12 (7 to 20) | 11 (6 to 20) | 10 (5 to 19) | 0.086 |
| Asthmaβ | ||||
| Clinical criteria (n, %) | 11.7% | 8.3% | 9.4% | 0.459* |
| Functional criteria (n, %) | 6.3% | 7.0% | 6.4% | 0.957* |
| Treated asthma (n, %) | 6.3% | 4.0% | 6.1% | 0.441* |
| Ever asthma (n, %) | 7.3% | 4.8% | 7.3% | 0.438* |
| Atopic eczema (n, %) | 66.7% | 62.9% | 54.4% | 0.465* |
| Allergic rhinitis (n, %) | 33.3% | 33.8% | 31.1% | 0.907* |
| Allergic sensitization (%) | 32.8 | 39.5 | 34.2 | 0.302* |
| Otitis (n, %) | 27.0% | 21.0% | 32.4% | 0.043* |
| Pupillometry | ||||
| Maximum (mm, mean ± sd) | 5.2 ±0.9 | 5.3 ±1.0 | 5.3 ±0.8 | 0.278¥ |
| Minimum (mm, mean ± sd) | 3.4 ±0.6 | 3.4 ± 0.6 | 3.4 ±0.6 | 0.537¥ |
| CON (%, mean ± sd) | 35 ±5 | 36 ±5 | 36 ±5 | 0.203¥ |
| ACV (mm/s, mean ± sd) | 3.8 ±0.7 | 3.9 ±0.8 | 4.0 ±0.7 | 0.030¥ |
| MCV (mm/s, mean ± sd) | 5.1 ±1.0 | 5.3 ±1.0 | 5.4 ±0.9 | 0.010¥ |
| ADV (mm/s, mean ± sd) | 1.2 ±0.3 | 1.2 ±0.4 | 1.2 ±0.3 | 0.709¥ |
| T75 (s, mean ± sd) | 1.7 ±0.7 | 1.7 ±0.7 | 1.7 ±0.7 | 0.987¥ |
Data reported as median (P25 to P75) unless otherwise stated. BMI: body mass index; FEV1: forced expiratory volume in the first second of FVC; PEF: Peek expiratory flow; FVC: forced vital capacity; FEF25-75: forced expiratory flow middle portion of FVC; EBC: exhaled breath condensate; CON: percentage of pupil constriction; ACV: average constriction velocity; MCV: maximum conscription velocity; ADV: average dilation velocity. The p values signalling differences between the three groups were calculated using the Kruskal-Wallis test for non-parametric variables, with the exception of cases marked with (*) which were calculated using qui-square tests, and (¥), which were calculated using one-way ANOVA (for normal distributions).
βThe following operational asthma definitions were adopted: i) Clinical criteria–at least a 12% increase in FEV1 after bronchodilation and over 200mL and/or asthma diagnosed by a physician with reported symptoms (wheezing, dyspnoea or dry cough) occurring in the past 12 months; ii) Functional criteria–at least a 12% increase in FEV1 after bronchodilation and over 200mL; iii) Treated asthma criteria–asthma diagnosed by a physician and currently under inhaled corticosteroid treatment; and iv) Ever asthma–asthma diagnosed by a physician.