1. Introduction
Asthma is a heterogeneous disease and is defined as a chronic airway inflammation, leading to a variable airflow limitation, resulting in respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity [1]. The disease affects more than 334 million people worldwide and, according to the world health organization, 14% of children have ever suffered from any asthma symptom [1].
This high rate of asthma prevalence in children, as well as the rates of uncontrolled asthma and asthma exacerbation leads high rates of school absenteeism [2]. In addition, acute exacerbations remain one of the main causes of emergency department visits in childhood asthma [3]. In this context, innovative methods that could precisely detect the possibility of exacerbations is highly needed. Thus, impulse oscillometry system (IOS) had demonstrated to be useful technique to detect possible exacerbations, since IOS revealed to be much sensitive than traditional lung function test, spirometry [3]. In addition, some parameters measured by IOS, such as total airway resistance (R20Hz), proximal airway resistance (R5Hz), distal airway resistance (R5Hz – R20Hz) can reflect, when increased, some degree of airway remodeling, as compared with multidetector computed tomography (MDCT) imaging [4,5]. In fact, airway remodeling is a central feature of asthma and is directly related to disease control and progression [4].
Several inflammatory and fibrotic mediators such as Th2 cells related cytokines, eicosanoids and growth factors are released in the lungs as well as in the systemic circulation [6]. In this context, nitric oxide (NO) is a noninvasive biomarker which is most widely used in the assessment of airway inflammation. In the respiratory tract NO is released by different type of cells (epithelial cells, airway nervous, inflammatory cells and from vascular endothelium). A high concentration of NO is observed in asthmatics when compared with normal individuals [6]. In addition, high levels of NO have been associated with loss of control in asthma, hyperresponsiveness and airway remodeling [7]. Furthermore, high levels of NO are believed to trigger the release of pro-inflammatory mediators and growth factors, being related to more severe forms of asthma, such as corticosteroid resistant asthma [8]. Airway remodeling is known to be mediated by both pro-inflammatory and pro-fibrotic mediators [9].
Therefore, the present study investigated, for the first time, if asthmatic children present impaired lung mechanics associated with increased accumulation of pro-inflammatory and pro-fibrotic growth factors.