Association of spirometry findings with AHR
FEV1 reflects mainly the functioning of the large and
medium airways(30), whereas FEF represents the functioning of the
medium-sized and small airways(30-32). There are several studies
observing the important role of FEV1 in predicting
AHR(12, 14, 33). After excluding children with an obstructive pattern,
FEF becomes more important, and FEV1 has been reported
to lose its significance(7, 32). Thus, FEF might have a possible role in
the prediction of AHR, particularly in patients with a normal
FEV1 and FEV1/FVC
ratio(31),(32). However, the predictive value of FEF
for AHR is controversial. While some authors found a significant
association of FEF values, especially of a forced mid-expiratory flow
between 25% and 75% of vital capacity (FEF25-75%),
with AHR in patients with normal FEV1(31, 32, 34),
others did not(35, 36). This inconsistency may be due, at least, to the
fact that some studies also included other diseases like cystic
fibrosis(35, 36). In our population, none of the spirometry variables
recorded at baseline were significantly associated with AHR. However,
after dichotomizing the FEF values at a cutoff of 65%, as proposed by
others(31),,(32), the role of FEF75< 65% in predicting AHR became significant.