Forced expiratory volume in 1 s (FEV 1 ) detection of exercise-induced bronchoconstriction (EIB) to identify asthma has good specificity but rather low sensitivity. The aim was to test whether sensitivity may be improved by measuring respiratory resistance (RRS) by the forced oscillation technique (FOT). Forty-seven asthmatic and 50 control children (5-12 y) were studied before and after running 6 min on a treadmill. RRS in inspiration (RRSi) and expiration (RRSe), FEV 1 and RRSi response to a deep inhalation (DI) were measured before and after exercise. In asthmatics versus controls, exercise induced significantly larger increases in RRSi (p Ͻ 0.001) and larger decreases in FEV 1 (p ϭ 0.004). Asthmatics but not controls showed more bronchodilation by DI after exercise (p ϭ 0.02). At specificity Ͼ0.90, sensitivity was 0.53 with 25% increase RRSi and 0.45 with 27% increase RRSe or 5% decrease FEV 1 . It is concluded that the FOT improves sensitivity of exercise challenge, and the RRSi response to DI may prove useful in identifying the mechanism of airway obstruction. (Pediatr Res 68: 537-541, 2010) E xercise-induced bronchoconstriction (EIB) is closely linked to airway inflammation and unlikely to develop in healthy children (1), so that detecting airway hyperresponsiveness to exercise in the lung function laboratory is considered highly specific of asthma, i.e. it is associated with low rate of false-positive responses. A limitation is the rather low sensitivity of the test (2,3). EIB has been identified in primary school children by changes in forced expiratory volume in 1 s (FEV 1 ) or peak expiratory flow, and decision levels were mostly based on the former parameter (3). Respiratory resistance (RRS) measured by the forced oscillation technique (FOT) offers an alternative assessment of airway caliber, the time variations of which may be characterized for instance using a single excitation frequency (4). Computing RRS separately in inspiration and expiration (RRSi and RRSe, respectively) rather than over the whole breathing cycle may be of interest because the upper airways, which may represent a confounding factor in assessing the intrathoracic airways, are known to contribute differently to airway mechanics in inspiration and expiration (5,6). Furthermore, the RRS change in relation to volume history, more specifically the bronchomotor alteration that follows a deep inhalation (DI), has potential relevance in identifying the mechanism of EIB (7-9). Indeed, stretching the acutely contracted bronchial smooth muscle promotes bronchial wall relaxation, which in turn could be taken as an indicator of the magnitude of the airway response (10). To the best of our knowledge, a systematic analysis of diagnostic value of single-frequency RRS has not been performed during case-control identification of EIB in the lung function laboratory at school age.Therefore, the aim of this study was to assess the value of the FOT in identifying EIB in asthmatic children. More specifically, RRSi and RRSe and the change in...

Changes in lung function after exercise in healthy primary school children have mostly been described in field studies. More complete description and insight into relevant mechanisms may be provided in lung function laboratory. The aim was to describe airway caliber and response to deep inhalation (DI) after exercise in healthy primary school children. Respiratory resistance (Rrs) by the forced oscillation technique and spirometry were measured before and after exercise in 50 healthy primary school children. The Rrs response to DI was assessed in 31 subjects, assuming a significantly larger decrease in Rrs after exercise would attest relief of exerciseinduced airway smooth muscle contraction. Measurements were taken before, 5 min (E5) and 15 min (E15) after exercise. Significantly larger Rrs and lower forced expiratory volume in 0.5 s were observed at E5 versus baseline or E15 (p Ͻ 0.05). DI induced significant decrease in Rrs (p ϭ 0.01) that was not different between E5 and baseline. Healthy primary school children exhibit changes in Rrs and spirometry after exercise indicating small but significant airway narrowing. The response to DI similar at baseline and E5 suggests airway narrowing from hyperemia in the bronchial wall rather than airway smooth muscle constriction. T here is considerable interest in assessing the airway response to exercise in children because of the clinical impact of exercise triggered asthma attacks (1,2). Field studies in unselected primary school children have described the distribution of lung function changes after exercise (3,4) or tested prevalence of exercise induced bronchoconstriction (EIB) in relation with respiratory symptoms (5,6). In these studies, the response was expressed as largest fall in forced expiratory volume in 1 s (FEV1) within 10 -15 min of exercise cessation (3,4) or considered positive when peak expiratory flow decreased 15% or more (5,6). To the best of our knowledge, whether significant change in airway caliber occurs in healthy children during the recovery from exercise has not been documented. In the context of a lung function laboratory, the airway response to exercise may be characterized more thoroughly and indications obtained relative to potential mechanisms. The respiratory resistance (Rrs) measured by the forced oscillation technique (FOT) is considered a good proxy to airway caliber above a few herz (7). It is particularly relevant to pediatric studies, as it requires minimal cooperation. Forced expiratory volume in 0.5 s (FEV0.5) has been suggested more sensitive than FEV1 to airway caliber in young children because of their high rate of lung emptying (8). FEV0.5 could also prove useful in school children who are known to have higher FEV1 to forced vital capacity ratio than adults. In addition, the tracking of time variations of Rrs has the potential to identifying mechanisms of bronchoconstriction by assessing change induced by a deep inhalation (DI) (9,10). When acute bronchoconstriction has been pharmacologically induced in a context ...