DISCUSSION
To the best of our knowledge, this is the first study to evaluate the respiratory functions of children with cat sensitization and respiratory allergic diseases (asthma and/or allergic rhinitis) using the IOS and also spirometry. The results revealed an increase in airway resistance and a decrease in reactance parameters of the entire and peripheral airways measured using IOS, while no difference was determined using spirometry, in CS group compared to the HC’s. Peripheral airway resistance and reactance were more impaired in asthma group compared to allergic rhinitis, but it was insignificant to coexistent asthma and allergic rhinitis. Our findings are particularly valuable since they show that respiratory functions are unrelated to domestic cat contact in the home and peripheral airway resistance and main airway reactance were worse in pre-school age patients than in older children. No difference was observed between the Step 2 and Step 3-4 treatment asthma groups in terms of IOS or spirometry parameters. The study results are important because they show that cat allergy begins in the entire and/or peripheral airways in early childhood, even if respiratory function tests with spirometry are normal, in the absence of cat contact at home and in various asthma severity.
In terms of resistance, higher zR5 showed an increase in entire airway resistance, while the higher R5-20 parameter revealed an increase in peripheral airway resistance. In terms of reactance, the decreases in zX5 and zX20 indicate reactance impairment in the total airway and the increase in Fres and AX in the peripheral airway.24 We claim that early stages of lung function deterioration could not be detected by traditional spirometry, and it may be unable to reveal the respiratory functions of peripheral airways. In contrast, an earlier cohort study performed respiratory function tests using IOS and evaluated specific IgE for aeroallergens in 486 randomly selected children aged 11 years, and found that these parameters were not significantly affected in participants with cat sensitization.30 In this population based study, the low number of participants with cat sensitivity and asthma, the high number of patients who could not undergo IOS, and the fact that IOS parameters were given as crude values may have affected the results.
Cat allergen sensitivity varies depending on the individual’s atopy status, environment and the duration of exposure.10Interestingly, only 10% of the children with cat sensitization in this study were exposed to cats in their homes. Although the rate of exposure to domestic cats was low, we may nevertheless speculate that cat allergen concentrations may have risen in recent years due to global warming, their being easily spread, small in size, and more suspended in the air, and since they spread more easily in social environments, especially in closed areas such as schools.31 It is well known that cat allergen is frequently detected in house dust in shopping malls, classrooms, and examination rooms, being carried on people’s clothing and hair, even if there are no cats in the immediate environment.32 Probably due to this reason, we could not detect any difference between the respiratory function tests of groups Do+ and group Do-. In Simoneti’s cohort, the frequency of asthma increased among individuals with cats at home, although their spirometry values were not different from those of the other groups (who kept dogs at home or who never had pets).15 In Leung’s study, the presence of cat allergen in the home significantly increased the level of Feld1 in house dust, although no correlation was observed between the household cat allergen level and FeNO or spirometry values.14 In Langley’s study from 2003, high exposure among sensitive patients to cat allergen in the home was associated with decrease in FEV1, and increase in FeNO, and more severe bronchial hyperreactivity.33 Zeidler et al. studied the respiratory function tests of cat-allergic asthmatic patients with natural cat exposure. No significant change was observed in FEV1 during tests performed before and at the 6th and 23rd hours after exposure, while a significant decrease in FEF25-75 and FVC was observed at the 6th hour. Moreover, increased air trapping at HRCT and bronchial hyper-reactivity were observed at the 6th and 23rd hours after cat exposure. Small airway obstruction and bronchial hyper-reactivity may therefore have persisted until the 23rd hour with natural cat exposure.34
Surprisingly, we observed no difference between the Step 2 and Step 3-4 treatment asthma groups in terms of IOS or spirometry parameters as all participants were under regular medication and disease control for at least three months. However, Konradsen et al.’s study showed that cat and dog allergies were associated with more severe childhood asthma.11 Another study comparing the clinical and laboratory characteristics of patients with cat allergy and asthma in terms of domestic cat exposure reported no difference in respiratory function tests, nasal-ocular symptoms, or asthma control tests, although the group with domestic cat exposure required higher potency steroids and longer-acting beta agonists. The authors also showed that living with a cat in the home despite allergies necessitated the use of more preventive medications.16
The principal strengths of this study include the fact that allergic rhinitis and asthma were diagnosed by pediatric allergy specialists working in a tertiary referral center, all lung function measurements being performed by the same physician and nurse to the same standards. IOS and spirometry, respectively, were performed to eliminate conflicting test results. All children were evaluated by ENT physicians before recruitment in order to exclude diseases that might affect pulmonary functions. Particular care was taken to ensure that all patients’ asthma was under control, that they had no active infection, and that they received Step 2-4 ICS therapy at least three months. Additionally, patients with pollen allergy were included in the study during a period outside the pollen season.
The principal limitation of this study is that the results cannot be generalized to the entire population due to its single-center and cross-sectional nature. Another limitation involves the lack of mono-sensitized cat-allergic children. More than 90% of the patients with cat sensitization in this population had poly-sensitization. However, based on our current data, it was not possible to predict the effects of poly-sensitization in most of our patients or the effects of other allergens on respiratory function tests. As there is no z score of Fres and a higher expected crude value for young children, might impact our results. Another limitation of the study was the presence of participants who could not perform spirometry, particularly those under five years of age due to their inability to comply with the test. Moreover, cross-sectional evaluation of the children during a single time period measurement limited our data concerning the change in lung functions according to cat allergen exposure or treatment response. We were also unable to measure indoor Feld1 concentrations in the patients’ homes for the purpose of investigating the causal association between deterioration of lung functions and exposure to allergen concentrations.
CONCLUSION
This study shows, for the first time in the literature, that children with respiratory allergic diseases and cat sensitization exhibited increased entire and peripheral airway resistance and decreased reactance compared to age- and sex-matched healthy controls. Domestic cat exposure was not related to increased respiratory function deterioration, and may therefore be more associated with cat allergens being small in size and with their ability to spread easily in social areas. In addition, the present study will contribute significantly to the existing literature as the first to show commencement of early airway obstruction at early ages in children with cat sensitization irrespective of spirometric lung function tests being normal, the presence or absence of exposure to domestic cats in the home, the condition being under control with regular medication, and asthma severity. We suggest that further, multi-center cohort studies with larger populations are now needed to strengthen our preliminary results. Further research is now required in order to elucidate the molecular and clinical aspects of cat allergy in childhood, and to identify its effect on respiratory functions, as we are clearly still looking at the mere tip of a whole iceberg of unknown factors.