Peripheral airway resistance and reactance are associated to symptom severity in asthmatic subjects

Forced Oscillation Technique (FOT) is increasingly used to measure the obstruction in the airways. We investigated central and peripheral airway obstruction, measured by FOT, in association to various questionnaires of symptoms.319 asthma patients were recruited during the BREATHE project. Analyses were performed between the questionnaires (ACT, ACQ-5, Nijmegen) as a) total score and b) separate questions and the FOT measurements estimating airway resistance (R5: total resistance, R19: central resistance, R5-R19[ET1] [GP2] : peripheral resistance) and reactance(X5) during inspiration (insp), expiration (exp) and as a total (tot). Cut-off points for symptom severity were examined.ACT score-based groups divided in well or poorly controlled disease, using a cut-off point at 20, differed significantly in only X5exp. When cut-off at 16, 20 and 25 was applied, differences between the groups in all FOT parameters became more evident (Figure 1). ACQ-5 cut-off at 0.75 and 1.5 captured differences in R5 and X5, while a Nijmegen cut-off at 25 showed differences in R5 and R19. Total scores from all questionnaires correlated with most FOT results. All questions in ACQ-5 correlated [ET1] with R5, R5-R19 and X5 whilst in ACT it was mainly the 2 first questions. Symptoms in asthma patients assessed by questionnaires correlate well with peripheral airway obstruction. A correlation appears to exist even for Nijmegen, which is a questionnaire not specific to asthma. Cut-off points used for defining asthma control may capture a dysfunction in peripheral airways, but not always.