Abstract
OBJECTIVE:
To establish the upper limits for changes in FEV1, slow vital capacity
(SVC), FVC, and inspiratory capacity (IC) after placebo administration in patients
with airflow obstruction.
METHODS:
One hundred and two adults with airflow obstruction (FEV1 = 62 ± 19%
of predicted) were included in the study. All of the participants performed SVC
and FVC maneuvers before and after the administration of placebo spray. The
changes in FEV1, SVC, FVC, and IC were expressed as absolute values,
percentage of change from baseline values, and percentage of predicted values, 95%
CIs and 95th percentiles being calculated. Factor analysis was performed in order
to determine how those changes clustered.
RESULTS:
Considering the 95% CIs and 95th percentiles and after rounding the values, we
found that the upper limits for a significant response were as follows:
FEV1 = 0.20 L, FVC = 0.20 L, SVC = 0.25 L, and IC = 0.30 L
(expressed as absolute values); FEV1 = 12%, FVC = 7%, SVC = 10%, and IC
= 15% (expressed as percentage of change from baseline values); and
FEV1 = 7%, FVC = 6%, SVC = 7%, and IC = 12% (expressed as percentage
of predicted values).
CONCLUSIONS:
In patients with airflow obstruction, IC varies more widely than do FVC and SVC.
For IC, values greater than 0.30 L and 15% of change from the baseline value can
be considered significant. For FVC, values greater than 0.20 L and 7% of change
from the baseline value are significant. Alternatively, changes exceeding 0.20 L
and 7% of the predicted value can be considered significant for FEV1
and FVC. On factor analysis, spirometric parameters clustered into three
dimensions, expressing changes in flows, volumes, and dynamic hyperinflation.
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