T. HAQUE ET AL.
Copyright © 2013 SciRes. OJRD
67
tween FEV1 and PEF, that are forced expiratory maneu-
vers, was excellent, with some 2/3 of the variance in one
explained by the other.
It is important to bear in mind that the various meas-
ures of pulmonary function actually measure different
aspects of respiratory mechanics. FEV1 and PEF are cer-
tainly responsive to changes in airways resistance; how-
ever, they are also very dependent on patient effort. Raw,
measured in the body plethysmograph, is sensitive to
changes in flow-resistance of the airways, but excludes
lung and chest wall tissue resistance. The APD measures
total respiratory resistance, and includes a large compo-
nent of upper airways resistance (see [8]). The most
practical use for the APD would likely be to follow pa-
tients with lung disease serially at home given the ease of
use and low cost of this device. We had hoped that the
measurement of serial function before and after bron-
chodilator would simulate serial measurements for stan-
dard spirometry compared with APD. Unfortunately, few
patients had bronchodilator studies ordered, and the
overall change in FEV1 with bronchodilator was small
(approximately 100 cc). Finally, in a recent study [15],
the intrasubject variability of APD measurements was
assessed. It was found that the largest portion of the
variability of measurements was in fact due to changes
within the subject and not to changes within the APD,
strengthening our argument that the device would be
most useful for serial measurements in patients with lung
disease.
In sum, there are significant correlations between APD
derived measures of respiratory resistance and measures
derived from standard pulmonary function testing. The
variance explained was less than that between commonly
used measures of pulmonary function. Studies should be
directed at the evaluation of efficacy of serial measure-
ments over time in patients with respiratory disease.
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