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.