Definitions
Asthma is defined as a history of respiratory symptoms, such as wheezing, shortness of breath, chest tightness, and cough, that vary over time and in intensity, together with variable expiratory airflow limitation. Patients with characteristic asthma symptoms were diagnosed by means of spirometry and reversibility testing in accordance with the Global Initiative for Asthma (GINA) guideline. Patients younger than five were diagnosed on the basis of symptoms and inhaled corticosteroid responsiveness. All the patients had been under control with step 2-4 treatment for at least three months.20
Allergic rhinitis was defined as symptoms of nasal itching, congestion, rhinorrhea, and sneezing according to Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines. The condition was classified as intermittent or persistent depending on duration and as mild or moderate to severe according to severity.21
Skin prick test
Skin prick tests were performed using a prick test applicator (MedBlue One) on the flexural aspect of the forearm in line with standard guidelines, using standardized glycerinated extracts from LOFARMA (Milan, Italy) (1% weight/volume). Cat sensitization was defined as positive in children with a skin prick test induration diameter ≥3mm for cat epithelium solution.22 Detailed information about skin prick testing was given in supplementary data.
Exclusion criteria
The exclusion criteria for the study group were a history of chronic lung disease (except for asthma), first- and secondhand smoking exposure, chronic cardiac and neuromuscular disease, a history of low birth weight/premature birth/neonatal mechanical ventilation, malnutrition, obesity, malignancy, immune deficiencies, connective tissue disease, acute or chronic respiratory disease (adenoid hypertrophy or chronic sinusitis etc.) in the previous four weeks, or history of hospitalization or admission to intensive care unit in the previous year. Patients using inhaled short-acting beta agonists, systemic steroids, anticholinergics, and decongestants were also excluded from the study.
Exclusion criteria for the HC group were the presence of allergic respiratory diseases such as asthma and allergic rhinitis in addition to the criteria listed above.
Study design
When patients with asthma and/or allergic rhinitis presented to the pediatric allergy outpatient clinic for skin prick testing, those with cat sensitization were invited to take part in the study. Routine physical examinations were performed, and anthropometric measurements were recorded on the patients who agreed to participate in the study. Routine endoscopic authorhinolaryngological examinations were performed in the Ear-nose-throat (ENT) clinic in order to exclude any allergic rhinitis complications and/or comorbidities such adenoid hypertrophy or acute/chronic sinusitis. The patients were then referred to the respiratory function tests laboratory for IOS and spirometry.
Age- and sex-matched healthy subjects who had presented for routine health checks were randomly recruited from the general pediatric outpatient clinic and invited to participate in the study. Routine physical examinations were conducted, anthropometric measurements were recorded, and these were then referred to the respiratory function test laboratory.