Results
Seventy-two asthmatics (44 boys) and 29 healthy children (13 boys), aged
8 to 11 years, were included in this study. 49(68%) asthmatic children
had no symptoms during the last 3 months while 23 patients (32%) had
symptoms as chronic dry cough in 14(61%) or cough/wheezing on exertion
in 9(39%). Thirty-two patients (44%) had no anti-asthmatic treatment
while 40(56%) were treated by inhaled steroids alone in 10 (14%), or
associated with leukotriene antagonist in 2 (3%), with long-acting BD
agent in 9 (13%), or both in 9 (13%). 10 (14%) asthmatics had
leukotriene antagonist alone.
Patients’ characteristics and spirometric parameters at baseline,
expressed as absolute value or z-score, and their BD responses expressed
as Δ%, are presented in table 1 . The two populations were
similar for age, height, weight and body mass index. FVC and zFVC were
not different between the two groups. Asthmatics had significantly
smaller absolute values and z-scores for FEV1 (p=0.003 ,
respectively p=0.04 ), FEV1/FVC (p=0.002 for both ),
FEF25-75% (p=0.0003, respectively, p=0.004 ), FEF50/PEF
(p=0.01 , respectively p=0.007 ) and β-angle
(p=0.009 , respectively p=0.006 ) than healthy children.
More asthmatics, 32 (44%), than controls, 7 (24%), had β-angle
<180° or FEF50/PEF <0.05 that define a concave shape
of FVL but without statistical significance. 10 (14%) asthmatic
children had zFEV1/FVC <-1.64 associated with zFEV
<-1.64 in 6 (8%) of them.
Spirometric parameters after BD inhalation, expressed in z-score, were
lower in asthmatics than controls but without statistical significance,
except for zFEV1/FVC-bd (p=0.02 ) (supplementary table).
BD responses showed no difference for Δ%FEV1 between asthmatic and
control children. Asthmatics presented higher BD responses compared to
controls statistically significant for Δ%FEV1/FVC (p=0.04 ) and
Δ%FEF50/PEF (p=0.02 ), but not for Δ%β-angle (p=0.07).
The comparison between the 23 (32%) asthmatic children presenting
respiratory symptoms during the last 3 months and the 49 (68%)
asymptomatic patients is presented in table 2 . Age, weight and
height were comparable in both groups. zFEV1 was similar and zFEV1/FVC,
zFEF25-75%, zFEF50/PEF and zβ-angle were lower in the group of children
with symptoms vs no-symptoms but without statistical
significance. BD change was not different between the 2 groups for
Δ%FEV1 and Δ%FEV1/FVC but it was significantly higher in asthmatics
with symptoms for Δ%FEF50/PEF and Δ%β-angle, reported to the
asymptomatic group (p=0.02 ).
ROC curves are represented for the different parameters at baseline in
z-score in figure 2 and for their BD reversibility infigure 3 . AUC (95CI), sensitivity, specificity and respective
cut-offs are presented in table 3 for the parameters at baseline
in z-score, for their BD reversibility expressed as Δ%, and their
combination.
At baseline, zFEV1/FVC, zβ-angle or zFEF50/PEF presented similar AUC’s,
slightly more elevated than zFEV1’s AUC (figure 2 ). The
spirometric parameters exhibited different patterns of sensitivity and
specificity, i.e. zFEF50/PEF and zβ-angle showed the best
sensitivity while specificity was similar for zFEV1, zβ-angle or
z-FEF50/PEF (table 3 ). When combining the spirometric parameters,
the AUC’s improved and best sensitivity was obtained when considering
zFEV1+zβ-angle or zFEV1+z-FEF50/PEF, at the respective thresholds, while
best specificity was obtained for zFEV1/FVC+zFEF50/PEF (table 3 ).
ROC curves for BD reversibility showed larger AUC for Δ%FEF50/PEF,
followed by Δ%FEV1/FVC and Δ%β-angle (figure 3 and table
3 ). Sensitivity was best for Δ%β-angle or Δ%FEF50/PEF and very low
for Δ%FEV1 (table 3 ). Specificity was best for Δ%FEV1 and low
for Δ%β-angle. The association of parameters improved the AUC’s but not
the sensitivity – specificity.