Introduction

Exercise-induced respiratory symptoms (EIRS) are frequently reported by asthmatics, with rates ranging from 33% in the Asia-Pacific area to 59% in Central Eastern Europe1. In Latin America, this condition has been observed in 37% of such individuals2. Many children and adolescents believe their asthma is a factor that prevents them from participating in physical activities and that this is an inherent feature of the disease. This often brings with it the stigma of being less able and thus restricts peer group activities and participation in sports and games3,4,5.
Although various conditions, including poor pulmonary function, poor physical conditioning, exercise-induced laryngeal obstruction and dysfunctional breathing 6,7, may be associated with EIRS in children and adolescents with asthma, exercise induced bronchospasm (EIB) is probably the most frequent and occurs in approximately 50%8 of them. EIB is defined as the acute narrowing of the lower airways after exercise and may also contribute significantly to avoidance of participation in physical activities in children and young people with asthma9,10.
Diagnosis of EIB cannot be made solely on the basis of self-reported respiratory symptoms, as it has poor predictive value compared to objective tests11,12. To avoid under- and over-diagnosis and to enable correct treatment strategies to be adopted, EIB must be established by measuring changes in lung function provoked by exercise or a surrogate stimulus. The most common technique is serial measurement of forced expiratory volume in the first second (FEV1) before and after treadmill running. The criterion for EIB diagnosis is a > 10% drop in FEV1 after the exercise challenge compared to the baseline13.
Eucapnic voluntary hyperventilation (EVH) has been recommended as a surrogate stimulus for EIB diagnosis.13 It is considered safe, enables better control of ventilation rates and inspired air conditions, and dispenses with the need for physical effort14,15,16,17. The procedure follows the same physiopathological pathways for EIB as treadmill running, namely dehydration of the airway surface liquid of the bronchial mucosa13. In this method, the patient voluntarily hyperventilates by breathing dry air enriched with 5% CO2 (to avoid respiratory alkalosis) at a pre-specified target ventilation rate13.
One important property of a diagnostic test is reproducibility and knowledge of the inherent variability (agreement and repeatability) has practical implications for evaluation of its clinical usefulness18. Anderson et al.19found a general agreement for EIB diagnosis of 76% between two exercise challenge tests carried out 1 to 4 days apart in 373 individuals reporting signs or symptoms suggestive of asthma. Lower agreement (30%) between two tests separated by 1 to >35 days for EIB diagnosis was found in a study of asthmatic adults when the diagnostic cutoff was a 15% drop in FEV120.
The few studies that examined the reproducibility of EVH for EIB diagnosis were conducted in adult athletes and included a small number of individuals with asthma21,22 or compared different EVH provocation protocols23. One study reported the results of repeated EVH tests in a small number of non-athlete adult males with asthma (eight individuals) and found a 100% agreement between challenge responses, obtained seven days apart or with an interval of 35 days24. We were not able to find studies of the short-term reproducibility of FEV1response in asthmatic children and adolescents after EVH challenge.
The aim of the present study was to evaluate the short-term test-retest agreement and reproducibility (repeatability) of FEV1changes after EVH in children and adolescents with medically diagnosed asthma.