Exercise‐induced changes in respiratory impedance in young wheezy children and nonatopic controls

Abstract

Exercise-induced bronchoconstriction (EIB) is a specific sign of active asthma, but its assessment in young children may be difficult with lung function techniques requiring active cooperation. The aim of the study was to assess the normal pattern of exercise-induced responses of respiratory impedance by using impulse oscillometry (IOS), and to investigate how these responses discriminate wheezy children from control subjects. IOS measurements were performed in a consecutive sample of wheezy children aged 3-7 years (n = 130) and in an aged matched control group of nonatopic children without respiratory symptoms (n = 79) before and after a free running test. After exercise, wheezy children showed significantly larger responses in respiratory resistance (Rrs5), reactance (Xrs5), and the resonance frequency (Fr) than the control subjects. In the control group, the upper 95% confidence limit of the maximal change was 32.5% for Rrs5, 85.7% for Xrs5, and 53.1% for Fr. By using analysis of receiver operating characteristics, the change in Rrs5 distinguished the wheezy children from the control subjects more effectively than change in Xrs5 or Fr. In wheezy children, the response was significantly effected by the outdoor temperature and exercise intensity in terms of maximum heart rate. In conclusion, an increase of 35% in Rrs5 after a free running test can be regarded as an abnormal response. Wheezy children show an enhanced airway response, which is clearly distinguishable from the control subjects. IOS is a feasible method to detect EIB in young children.

Airway Response to Exercise by Forced Oscillations in Asthmatic Children

“…The RRS was measured by the impulse oscillation technique in preschool children submitted to an outdoor free run (ambient temperature Ϫ15°C to ϩ 20°C) and retested 2 min and later after exercise (29). The reported optimal decision level, a 30% increase in mean RRS at 5 Hz, was associated with a sensitivity of 0.62 at specificity Ͼ0.90 (29), both values being larger than in this report. Notable protocol variances could have explained this difference such as type of challenge and thermohygrometric environment (2,26).…”

“…Indeed, the bronchodilation after the DI in asthma is supported by the significantly more negative ⌬RRS DI versus controls 5 min after exercise (Table 3). Furthermore, the repetition of DIs after exercise could possibly have damped amplitude of both spirometry and FOT estimates of the bronchoconstriction in asthmatics, with little effect in controls, contributing to lower the sensitivity compared with reports from the literature (3,29).…”

Monitoring asthma in children

“…Methods used in children <5 years of age Interrupter resistance (Rint), IOS and FOT measure respiratory resistance as a proxy of airway obstruction and as such, may be used in the diagnosis and in the assessment of treatment response in wheezing children [102][103][104][105][106][107]. Moreover, tidal flow-volume loops may reflect abnormal breathing patterns and bronchial obstruction.…”

The safety and feasibility of the inhaled mannitol challenge test in young children: Table 1–

“…Previous studies using FOT with an inhaled challenge test used cut-off levels ranging from a 25% to 50% increase in Rrs [5][6][7]. If a 25% increase in Rrs8 is used to define a positive response the response rate in the EIS group would remain unchanged, with three of the healthy children being classified as having a positive response.…”

“…This preliminary study did not attempt to compare the mannitol challenge test with a free-running exercise challenge test [7], examine the reproducibility of the mannitol test in young children or explore methods for shortening the challenge test, and studies of this nature are required.…”