Impulse Oscillometry
A Jaeger MasterScreen IOS system (Jäeger, Wurzburg, Germany) was used to measure the input impedance of the respiratory system. This was performed in line with American Thoracic Society/ European Respiratory Society guidelines.23 The IOS technique is used to measure pulmonary resistance (R) and reactance (X). The flow signals were evaluated for 30s in a frequency range of 5 to 20Hz for amplitude differences to determine R and X values. The main parameters of IOS include resistances [R5, R20 R5‐20 (resistance at 5 Hz minus resistance at 20Hz)] and reactance [X5, X20, resonant frequency (Fres) and reactance area (AX)].18 Higher frequencies of R (~20Hz), reflecting the larger airways, were regarded as representing resistance in central airways. Lower frequencies of R (~5Hz) provided information about the totality of airways (both small and large). Peripheral (small) airway resistance was defined as R5-20. Acceptable variability was 15%. The coherence thresholds were set to ≥0.6 at 5Hz and ≥0.8 at 20Hz.24,25 R5, R20, X5, and X20 were transformed into z-scores from reference data to adjust the values for age and gender. R5-20, Fres, and AX were used as measured crude values because of the lack of references.26
Spirometry
The spirometry test was performed using a Jaeger MasterScreen IOS system (Erich Jaeger, Hochberg, Germany). The precise technique employed for this study was based on the recommendation in the American Thoracic Society official statement on the standardization of spirometry.27 The acceptable coefficient of variation was <10%. Lung function parameters were expressed as percentage values (%) predicted using Hankinson’s formula.28 Z-scores for spirometric parameters (zFVC, zFEV1, zFEV1/FVC, zFEF25-75) were elicited using Global Lung Initiative equations.29
Ethics
The study was approved by our institution’s local research ethics committee (2022/121). All participants took part voluntarily, and written informed consent was obtained from the parents of all children and also personally from children older than 12.
Sample Size
For statistical power analysis, due to the lack of previous studies evaluating lung functions with IOS in children with cat sensitization and respiratory allergic diseases; sample size was measured according to the effect size (Cohen’s d) as 0.5. Analysis using G*Power 3.1.9.7 revealed that at an effect rate of 0.71, a margin of error of 0.05, and a critical t value of 1.65 at an effect power of 85%, least 59 patients would be required in each group. In the light of potential losses of 10% that might occur during the lung function measurements, we planned to include at least 65 patients in both groups, yielding a total of 130 participants.
Statistical Analysis
SPSS version21.0 statistical software (SPSS for Windows 21.0, IBM SPSS Inc., Chicago, IL, USA) was used for statistical analysis. Categorical variables are presented as numbers (%) and continuous variables as mean±SD and median values (interquartile range-IQR). Univariate analyses involving categorical data were performed using thex2 test. Data from pulmonary function tests exhibiting parametric variables according to the Shapiro-Wilk normality test, were analyzed using Student’s t-test, and nonparametric variables using the Mann-Whitney U test (comparison between the patient and healthy groups and Groups Do+ and Do-). Kruskal-Wallis test was applied to compare differences among groups asthma, allergic rhinitis and coexistent of both as they were nonparametric data. Spearman’s correlation analysis was applied to non-parametric continuous variables. A value of p<0.05 were considered statistically significant.