  Asthma is one of the chronic inflammatory diseases of the airways, which
causes chest tightness, wheezing, breathlessness, and cough. Spirometry is an
effort-dependent test used to monitor and diagnose lung conditions like Asthma.
Vocal breath sound (VBS) based analysis can be an alternative to spirometry as
VBS characteristics change depending on the lung condition. VBS test consumes
less time, and it also requires less effort, unlike spirometry. In this work,
VBS characteristics are analyzed before and after administering bronchodilator
in a subject-dependent manner using linear discriminant analysis (LDA). We find
that features learned through LDA show a significant difference between VBS
recorded before and after administering bronchodilator in all 30 subjects
considered in this work, whereas the baseline features could achieve a
significant difference between VBS only for 26 subjects. We also observe that
all frequency ranges do not contribute equally to the discrimination between
pre and post bronchodilator conditions. From experiments, we find that two
frequency ranges, namely 400-500Hz and 1480-1900Hz, maximally contribute to the
discrimination of all the subjects. The study presented in this paper analyzes
the pre and post-bronchodilator effect on the inhalation sound recorded at the
mouth in a subject-dependent manner. The findings of this work suggest that,
inhalation sound recorded at mouth can be a good stimulus to discriminate pre
and post-bronchodilator conditions in asthmatic subjects. Inhale sound-based
pre and post-bronchodilator discrimination can be of potential use in clinical
settings.
