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.