Background: Asthma is characterized in part by small
airways dysfunction. Peak expiratory flow (PEF) measurement has been
suggested by all international guidelines as an important tool in
asthma management. The correlation between PEF and FEV1 but
not with forced expired flow at 50% of vital capacity
(FEF50) is well-established.
objective: To determine the value of PEF measurement as a
predictor of small airways status as expressed by
Design: Analysis of the association
between PEF and FEF50 in single and multiple
Patients: One hundred eleven asthmatic
children (mean age, 11.8 years), grouped in the following way according
to FEV1 values: within normal range (n = 46); mildly
reduced FEV1 (n = 44); and moderately/severely reduced
FEV1 (n = 21).
FEF50 and PEF were significantly correlated
(r = 0.49; p < 0.0001). However, in 41.6% of the
patients, the actual FEF50 differed by > 20% from the
calculated FEF50. PEF has a high specificity (82.4%) but a
poor sensitivity (51.7%) to detect FEF50 status. PEF was
better able to reflect abnormal FEF50 in the patients with
more severe asthma and to reflect normal FEF50 values in
the healthier patients. In patients with multiple measurements
(n = 40), the correlation between FEF50 and PEF was
significantly better than that derived from a single determination
(multiple measurements r = 0.77; single measurement,
r = 0.49).
Although PEF is an important tool in the management of asthmatic
patients, it does not yield a complete picture because it is not
sensitive in detecting small airways function. It is best used at home
along with regular spirometry measurements at the clinic. PEF may serve
as a better index of changes in small airways function once an
individual regression is determined.