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.