TABLE 1

Characteristics of the study infants with successful impedance pneumography measurement (All) and in the subgroup who underwent a bronchial challenge test with methacholine (MIB)

AllMIB
Study children n4420
Boys28 (64)13 (65)
Gestational age weeks39 (29–42)39 (35–42)
Birth weight kg3.2 (0.9–5.2)3.3 (2.4–5.2)
Age months15.0 (5.0–28.0)18.0 (9.0–28.0)
Weight kg10.9 (6.2–15.6)11.0 (8.6–13.8)
Skin prick test positive7 (16)4 (20)
Atopic eczema18 (41)10 (50)
Parental smoking12 (27)5 (25)
Parental asthma14 (32)9 (45)
Dominant respiratory symptom
 Cough22 (50)12 (60)
 Wheeze10 (23)4 (20)
 Dyspnea5 (11)2 (10)
 Other16 (7)2 (10)
Physician-diagnosed wheeze25 (57)10 (50)
Medication during the last 2 months
 Bronchodilators40 (91)18 (90)
 Corticosteroids4 (9)2 (10)
FRC mL233 (125–380)237 (166–380)
FRC z-score0.4 (−2.0–6.5)0.6 (−0.6–4.1)
sGaw kPa−1·s−11.8 (0.5–5.9)2.3 (1.4–5.9)
sGaw z-score−1.7 (−5.7–8.9)−0.5 (−2.6–8.9)
V′maxFRC mL·s−1189 (18–465)260 (122–465)
V′maxFRC z-score−1.1 (−3.7–1.4)−0.8 (−2.0–1.4)
  • Data are presented as n (%) or median (range). FRC: functional residual capacity; sGaw: specific airway conductance; V′maxFRC: maximal flow at FRC.