Rationale - Increased peripheral airway resistance and decreased reactance measured by forced oscillometry have been shown to predict loss of asthma control in children with asthma (Shi, Y. et al. J Allergy Clin Immunol 2013;131:718-23). Aim of the present study was to assess the capability of respiratory impedance indices to distinguish children with severe asthma from those with mild-moderate persistent asthma.
Methods - Children were recruited in 3 Centres. Severe asthma was defined according to Chung, K.F. et al. Eur Respir J 2014;43:343-73. For every case subject 1-2 age-matched controls with mild-moderate persistent asthma were recruited. Resistance (R8) and reactance (X8) at 8 Hz were measured using the "i2m" equipment (Cosmed, Rome, Italy) according to published guidelines. Spirometry was also performed (Cosmed). Z-scores were calculated using published reference equations.
Results - A total of 26 children with severe asthma (median age 10.6 yr, range 6.3-17.6 yr) and 43 controls (9.94 yr, 5.9-17.8 yr) were enrolled. Skin prick tests were positive in 92% of cases and 87% of controls. Mean (SD) lung function indices are reported in the table.
Severe Asthma, n=26
R8 hPa.s.L-1
Z-score
5.51 (1.86)
-0.13 (1.39)
5.29 (1.76)
-0.51 (1.13)
0.624
0.214
X8 hPa.s.L-1
-1.83 (1.46)
-0.33 (1.31)
-1.55 (1.06)
0.07 (0.88)
0.364
0.130
FEV1 L.s-1
2.04 (0.71)
-0.59 (1.17)
2.02 (0.82)
-0.10 (1.53)
0.905
0.179
Conclusions - Respiratory impedance indices were not significantly different in school-age children with severe asthma compared to age-matched controls with mild-moderate persistent asthma.