Respiratory impedance and response to salbutamol in asthmatic Vietnamese children

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. Pediatr Pulmonol. 2010; 45:380–386. © 2010 Wiley‐Liss, Inc.