Tidal breathing parameters measured using structured light plethysmography in healthy children and those with asthma before and after bronchodilator

Structured light plethysmography (SLP) is a light‐based, noncontact technique that measures tidal breathing by monitoring displacements of the thoracoabdominal (TA) wall. We used SLP to measure tidal breathing parameters and their within‐subject variability (v) in 30 children aged 7–16 years with asthma and abnormal spirometry (forced expiratory volume in 1 sec [FEV1] <80% predicted) during a routine clinic appointment. As part of standard care, the reversibility of airway obstruction was assessed by repeating spirometry after administration of an inhaled bronchodilator. In this study, SLP was performed before and after bronchodilator administration, and also once in 41 age‐matched controls. In the asthma group, there was a significant increase in spirometry‐assessed mean FEV1 after administration of bronchodilator. Of all measured tidal breathing parameters, the most informative was the inspiratory to expiratory TA displacement ratio (IE50(SLP), calculated as TIF50(SLP)/TEF50(SLP), where TIF50(SLP) is tidal inspiratory TA displacement rate at 50% of inspiratory displacement and TEF50(SLP) is tidal expiratory TA displacement rate at 50% of expiratory displacement). Median (m) IE50(SLP) and its variability (vIE50(SLP)) were both higher in children with asthma (prebronchodilator) compared with healthy children (mIE50(SLP): 1.53 vs. 1.22, P < 0.001; vIE50(SLP): 0.63 vs. 0.47, P < 0.001). After administration of bronchodilators to the asthma group, mIE50(SLP) decreased from 1.53 to 1.45 (P = 0.01) and vIE50(SLP) decreased from 0.63 to 0.60 (P = 0.04). SLP‐measured tidal breathing parameters could differentiate between children with and without asthma and indicate a response to bronchodilator.