The bronchomotor effects of a deep inhalation (DI) may provide relevant information about the mechanisms of exercise-induced airway obstruction in children and may be assessed by respiratory conductance (Grs) measured using the forced oscillation technique. The aims of the present study were to assess the effect of DI on Grs after exercise in relationship to the lung function response to exercise.Grs at 12 Hz using a head generator and spirometric data were measured in 62 children suspected of asthma before and 5 min after a 6-min free run.After exercise, Grs was significantly increased by DI in 38 subjects, who also showed larger Grs and forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) responses to exercise than the 24 nonresponders. Stepwise regression indicated significant correlation between the response of Grs to DI and both Grs and FEV1/FVC responses to exercise.The data are consistent with exercise-induced bronchoconstriction being reversed by deep inhalation.
Respiratory mechanical impedance measured at a single frequency is of great interest to describe change in airways dimensions with time in young children with asthma. Adequate filtering is mandatory in order to eliminate spurious values at rapid flow transient or during glottis closure. The aim of the study was to test a new filtering procedure. Respiratory impedance was measured at 12 Hz using the head generator technique in 33 asthmatic children aged 3.5-7.5 years. Two separate measurements were obtained at baseline and one 10 min after salbutamol inhalation. Assuming corrupted data would correspond to major distortion in flow oscillation, the tested procedure calculated an index expressing departure of each flow oscillation from an ideal sinusoid (flow shape index filter (FSIF)). Cut-offs ranging from 5 to 20% were compared to the visual identification and 'by hand' elimination of corrupted data (visual filtering). Sensitivity and specificity of FSIF versus visual filtering indicated an optimal range of cut-off values between 10 and 15% (FSIF10 and FSIF15). Compared with visual filtering, respiratory conductance in inspiration (Grs) was marginally but significantly lower with FSIF10 (p < 0.01) but not FSIF15 and had slightly larger (within measurement) coefficient of variation with either FSIF10 or FSIF15 (p < 0.01). Between-measurement repeatability of Grs and Grs change induced by salbutamol were similarly estimated by FSIF10, FSIF15 or visual filtering. It is concluded that FSIF appears as a valid alternative to visual filtering. The 10% cut-off is a good compromise considering sensitivity (72%), amount of rejected data (<20%) and effect on Grs and variability.
There is a high incidence of pediatric asthma in Vietnam, but little lung function data are available. The aim of the study was to compare respiratory resistance (Rrs), reactance (Xrs), and responses to salbutamol between asthmatic and healthy primary school children in Hanoi. Because respiratory mechanics vary along the breathing cycle, measurements were assessed separately in inspiration (Rrsi, Xrsi) and expiration (Rrse, Xrse).Inpatients with doctor-diagnosed asthma were measured 2-3 days following admission using the forced oscillation technique (FOT) at a single frequency (8 Hz). Z-scores and responses to salbutamol were compared between 102 asthmatics and 98 controls, and accuracy of group classification by FOT parameters was assessed by Youden index, an indicator to the proportion of subjects correctly classified in each group.In asthmatics versus controls, Rrsi-but not Rrse-was significantly larger and both Xrsi and Xrse were significantly more negative (P < 0.01). Both Rrs and Xrs responses to salbutamol were significantly larger in asthmatics than controls (P < 0.001). Youden indexes indicated response to salbutamol generally had better diagnostic values than Z-scores and was best discriminative first with Rrsi, then with Xrse.It is concluded that different FOT characteristics may be described in asthmatic and healthy Vietnamese children. The diagnostic value of each parameter depends upon the breathing cycle. Most useful in practice probably is the response to salbutamol measured by Rrsi.
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