Exercise-induced bronchospasm or dyspnoea in obese children?

Exercise-induced bronchospasm (EIB) is usually defined as one of the more common causes of exercise-induced dyspnoea (EID), causing difficult breathing during physical activity by obstruction of the airways, which is a hallmark of asthma. However, dyspnoea is a complex psycho-physiological symptom characterized by sensation of an increase in the perceived work of breathing which may manifest during physical activity and resulting from many different causes. In clinical practice, most of the diagnoses of asthma induced by physical activity are based on the evaluation of symptoms reported by children or parents. This is often proved to be misleading because a link between the symptoms reported and the results of tests during physical activity, such as standardised exercise test, has not been demonstrated. Overweight and obesity may contribute to dyspnoea during the physical activity and moreover, in recent years, several studies have investigated the correlation between obesity and chronic respiratory diseases such as asthma and EIB. CastroRodriguez et al. have identified five possible biological mechanisms which can explain the relationship between asthma and obesity: mechanical effects of obesity on respiratory function, altered immune response and inflammatory activation of specific gene regions, hormonal influences related to gender, and influence of diet and physical activity. The excessive accumulation of adipose tissue at the chest wall may alter the pulmonary respiratory mechanisms favouring an increase in the response of bronchial smooth muscle. Both asthma and obesity can cause excessive reduction of small airways diameter and increase gas trapping. Overweight patients have a decreased tidal air volume and functional residual capacity, with consequently more difficulties to stand physical activity. The risk of asthma developing in overweight children is higher in females than in males, and higher in those girls who have an early menarche. Indeed, obese asthmatic patients require a greater number of medications for asthma; emergency visits; hospital admissions; and accesses to emergency care, more than asthmatic children who are not overweight. In the present issue of Allergologia et Immunopathologia, Lopes et al. report the results of a study assessing the frequency and severity of EIB in obese adolescents. Eighty adolescents of both genders, aged 10–16 years old, were divided into four groups: asthmatic obese, asthmatic nonobese, obese non-asthmatic, and healthy individuals, analysing how obesity can influence EIB. Every patient performed an exercise test and changes in the pulmonary function (FEV1) have been evaluated. The study showed that obese asthmatic children have no greater risk frequency of EIB than non-obese asthmatic children (50% vs. 38%, respectively). However, maximum percent fall in FEV1 and area above the curve, calculated to evaluate EIB severity and recovery, were significantly greater in the asthmatic obese group compared to the asthmatic non-obese group. The authors concluded that although obesity does not increase the prevalence of EIB, being overweight can indeed contribute to increase EIB severity and to delay recovery among asthmatics. All these evidences lead to consider that obese asthmatics can present difficulties in the recovery of normal pulmonary function with a consequent limitation of their participation in physical and sporting activities. Therefore, dyspnoea during exercise in obese patients should not always be considered a manifestation of EIB, but should be placed in the differential diagnosis with other causes for EID, which include normal physiologic exercise limitation, vocal cord dysfunction, exercise-induced laryngomalacia and hyperventilation syndrome. Physical deconditioning, common in sedentary, obese children, is one common cause of EID, particularly in school-age children who do not have asthma, although some of these children are mistakenly diagnosed as having asthma. The person with excess weight is most prone to the development of EID for physical characteristics which alter the lung mechanism and bronchial responsiveness. Obesity also affects the perception of symptoms of asthma and asthma severity change through co-morbidities associated with asthma; such as gastro-oesophageal reflux, obstructive sleep apnoea and obesity hypoventilation syndrome. Epidemiological data from Glazebrook et al. have shown that most of the children with severe asthma are obese and are much less active than children in the control group. Although obesity per se seems not to be a risk factor for bronchial obstruction, obese patients have an increased risk for dyspnoea, and often obese asthmatic children require a ARTICLE IN PRESS