INTRODUCTION
Chronic respiratory diseases (CRD) are associated with abnormalities in
the airways and other structures of the lung, with asthma being the most
common CRD in the pediatric age range, and cystic fibrosis (CF) being
the most frequent genetic disease in Caucasians 1.
Asthma is a chronic inflammatory disease characterized by variable
airway obstruction, leading to hyperresponsiveness, inflammation, and
respiratory symptoms, representing a major cause of pediatric
hospitalization worldwide 2. On the other hand, CF is
a hereditary, autosomal recessive disease, caused by the mutation of a
gene that encodes the transmembrane conductance regulator protein
(CFTR). The absence or dysfunction of the protein leads to a multisystem
disease, inducing obstruction in secretory glands and a pro-inflammatory
state, especially in the lungs 3.
In patients with CRD, exercise intolerance is common and is usually
considered as the inability of individuals to perform exercise at the
same levels that would be expected for an age-matched control4. Patients with asthma use to report
exercise‐associated symptoms which are related to multiple factors,
including the degree of airway obstruction, decreased ventilatory
capacity, a greater sensation of dyspnea, exercise-induced
bronchoconstriction (EIB), or low exercise capacity 5.
Despite this, there is no clear consensus on their exercise capacity.
Some studies reported no differences between healthy and asthmatic
patients 6,7, while others showed lower respiratory
capacity in those with a diagnosis of asthma 8–10.
For children and adolescents with CF, evidence reports a reduction in
exercise capacity compared to healthy controls 11.
The forced expiratory volume in the first second (FEV1)
is one of the most used clinical parameters for monitoring CRD,
including asthma 2 and CF 3.
Evidence indicates that FEV1 correlates with clinical
worsening and EIB in children and adolescents with asthma12, but implications of lung function on reduced
exercise capacity are still unclear 13,14. In patients
with CF, evidence suggests that only a part of the variability in
exercise capacity can be explained by FEV115. In general, the mechanisms responsible for
exercise limitation in CRD are still poorly understood. In individuals
with asthma, exercise intolerance may result from a combination of
complex interactions between mechanical, physiological, and
psychological mechanisms, including bronchial smooth muscle contraction
due to increased breathing, loss of heat, and moisture in the
respiratory tract 5. On the other hand, there are
controversial data on mechanisms underlying low exercise capacity in CF,
which may be related to poor nutritional status, peripheral muscle
dysfunction, dysfunctional gas exchange, and exercise-induced
ventilatory dysfunction 15.
During progressive exercise, minute ventilation (VE) must increase
through a combination of a rapid increase in tidal volume to a maximum
of approximately 50% of forced vital capacity (FVC) and a progressive
but steady increase in respiratory rate 16. The most
typical feature of CRD is progressive expiratory airflow obstruction and
the development of expiratory flow limitation. As exercise ventilatory
demands increase, the combination of high respiratory rates and
decreased expiratory flows may result in an insufficient expiratory time
to completely exhale the inspired breath 17.
Ventilatory limitation in CRD can be reflected in different parameters
during CPET, such as ventilatory efficiency or breathing reserve (BR).
Ventilatory efficiency is represented by ventilatory equivalents for
oxygen consumption (VE/VO2), and for
carbon dioxide production (VE/VCO2)18. The increase in ventilatory demand due to abnormal
ventilatory control in CRD can lead to poor ventilatory efficiency, with
a need for greater minute ventilation (VE) to eliminate
the same amount of carbon dioxide as compared to healthy children7,19. On the other hand, BR compares how closely
VE achieved in peak exercise approaches the maximal
voluntary ventilation (MVV) 20. The ratio of peak
exercise minute ventilation to MVV (BRI), ranges from 0.40 to 0.75 in
untrained healthy individuals 21. In patients with CRD
the BRI is elevated, suggesting reduced BR at peak exercise11,22. BR has been considered a powerful predictor of
mortality in CF patients awaiting lung transplantation23, although it has not been reported in patients with
asthma 24.
A better understanding of how CRD may affect aerobic fitness and the
identification of the main mechanisms leading to exercise intolerance
may help researchers and health professionals to better monitor and
treat those patients. Thus, the aim of this study was to evaluate
exercise capacity and its association with lung function, ventilatory
limitation, and ventilatory efficiency in children and adolescents with
mild‐to‐moderate CF and asthma when compared to healthy controls.