Variability analysis of oscillatory airway resistance in children.

Testing pulmonary function in preschool children is problematic since individual cooperation is often insufficient to yield adequate results. This is especially the case when repetitive measurements are carried out, e.g., during provocation tests in order to diagnose bronchial hyperresponsiveness. We therefore sought to determine whether the variability of the oscillatory airway resistance, which can be measured with minimal patient cooperation, might serve as an approach to separate asymptomatic children with asthma from age-matched healthy controls. Monofrequent forced oscillation technique was used to measure the oscillatory resistance (Ros) continuously at a repetition rate of 10 Hz. Forty consecutive values of Ros at the end of expiration (Ros(pe)) and at the end of inspiration (Ros(pi)) were used to calculate variability measures [standard deviation (SD), averaged deviation (LD), root mean square successive differences (RMSSD)] known from heart rate variability analysis to describe the airway diameter variability in 36 asthmatics and 21 healthy controls. Airway diameter variability of Ros(pi) and Ros(pe) as expressed by SD from the mean (P = 0.01 and 0.05, respectively), from LD (P = 0.01 and 0.21, respectively) and from the RMSSD (P = 0.006 and 0.03, respectively) was greater in patients with asthma. Mean values of Ros(pi) and Ros(pe) were not different between groups. Airway diameter variability is higher in asymptomatic children with asthma than in healthy controls. Future research should evaluate whether the measurement of the variability of Ros(pi), which does not require the patient's cooperation, can give similar information as challenge tests with respect to bronchial hyperresponsiveness.