Quantitative assessment of the airway response to bronchial tests based
on a spirometric curve shift
Abstract
Objective: Although spirometry is the most common pulmonary
function test, there is no method to quantitatively infer about airway
resistance or other properties from the flow-volume curves. Recently, an
identifiable inverse model for forced expiration was proposed, as well
as the idea to deduce changes in airway resistances and compliances from
spirometric curve evolution. The aim of this work was to combine the
above advances in a method for assessing the airway response to
bronchial tests from a spirometric curve shift. Methods: The
approach is based on the differential measurement of the degree, site of
maximal effect and width of changes, further recalculated into relative
changes in the distribution of airway resistances
(δRg) and compliances
(δCg) along the bronchial tree. To this end,
appropriate models were identified using the pre- and post-test
spirometry data. The accuracy was validated using sets of data simulated
by the anatomy and physiology based models. Finally, the method was used
to analyze the bronchodilation tests of three asthmatic subjects.
Results: The expected errors in assessing the degree, site and
width of changes in the zone of conducting airways were 6.3%, 2.4
generations and 22%, respectively, and for δRg
and δCg were 5-10% and 13-16%, respectively.
The analyses of clinical data indicated a significant reduction in
resistances and an increase in compliances of airway generations 8-12,
consistent with clinical knowledge. Conclusion: An unprecedented
method to plausibly transforming the spirometry data into the site and
degree of changes in airway properties has been proposed.
Significance: The method can be used to deduce about the effects
of bronchial tests, as well as to monitor changes in the airways between
visits or to investigate how inhaled pharmaceuticals affect the bronchi.