Ramiro González Vera MD1, Alberto Vidal Grell MD2, Jose A. Castro-Rodríguez MD, PhD3, Alejandra Méndez Yarur RT2
  1. Department of Pediatric Pulmonology, Clínica Las Condes, Santiago Chile
  2. Department of Pediatric Pulmonology Clínica MEDS, Santiago Chile
  3. Department of Pediatric Pulmonology, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
To the Editor,
Recently Tsukahara et al. published a study of impulse oscillometry (IOS) in a cohort of 22 school‐age former preterm children at high risk of bronchopulmonary dysplasia in which reactance inversion (RI) was found in 7 (32%) children. And reported significant differences between inspiratory and expiratory resistance (R) and reactance (X) parameters in children with RI compared to those without RI. They postulated that RI may have a possible pathophysiological cause as tracheobronchomalacia or since it occurs at low oscillatory frequency it may be an artifactual component produced by high respiratory rates (1).
However, R and X are derived exclusively from the impulse test signal. If the technical standards for acceptability and reproducibility are met, ventilatory rate should not influence these parameters. Tsukahara et al. (1) showed only R and X at 10 Hz, but values at 5Hz and other IOS parameters reflecting peripheral airway function like reactance area (AX), resonance frequency (Fres), difference between respiratory R at 5 and 20 Hz (R5-R20), spirometry, and bronchodilator response (BDR) were not included. Therefore, information on lung function in these patients is limited. Notice that the R10 had highest values in the RI group, suggesting more obstructive compromise.
Our group, previously described that RI in children with moderate to severe persistent asthma (n=507, aged 3-18 years) was more frequent in younger children with greater peripheral airway obstruction. In those with RI, the X5 value was highest than expected, the correction X5c, done automatically by Sentry Suite software, correlated better with other IOS parameters reflecting peripheral small airways disfunction (2).
Therefore, to expand these findings, we performed a pilot study on RI in children with persistent moderate and severe asthma. Our hypothesis is that RI occurs mostly in children with narrow or prone to collapse airway as occurs in asthma and especially if they were premature or with low birth weight. The aim of this study was to compare pulmonary function among asthmatic children with and without RI, and between those in whom the RI disappeared versus persisted after the bronchodilator test.