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Few data are available on the bronchodilator response in preschool children. This study was set up to study baseline lung function and bronchodilator responses in healthy and asthmatic children younger than 7 yrs old. In 281 preschool children attending kindergarten (age range 2.7-6.6 yrs old) respiratory system resistance (Rrs) and reactance (Xrs) by impulse oscillation system at 5, 10, 15, 20, 25 and 35 Hz as well as resonance frequency (f0) were measured before and 20 min after 200 microg inhaled salbutamol by a metered-dose inhaler connected to a spacer device. Thirty-four of them were diagnosed as asthmatics based on a validated standardized questionnaire. The mean Rrs (+/-SD) at 5 Hz (Rrs,5) was 1.03 (+/-0.24) kPa x L(-1) x s for healthy children and 1.09 (+/-0.26) kPa x L(-1) x s for stable asthmatics. The mean change in Rrs,5 after salbutamol was -0.13 (+/-0.20) kPa x L(-1) x s for the healthy children and -0.09 (+/-0.25) kPa x L(-1) x s for the asthmatic group. The scatter for the measurements was striking. Neither baseline values of impulse oscillation nor its changes after bronchodilator administration was significantly different between healthy and stable asthmatic children. A change in respiratory system resistance at 5 Hz of 40% is to be considered the cut-off for a " positive" bronchodilator response.
Hellinckx et al. (Sat,) studied this question.