Biomedical Engineering Reference
In-Depth Information
Some measurements are performed during forced inspirations and forced expi-
rations, that is, the spirometry lung function test. A person's vital capacity can be
measured by a spirometer. In combination with other physiological measurements,
the vital capacity (
VC
) can help making a diagnosis of the underlying lung disease.
Vital capacity is the maximum amount of air a person can expel from the lungs after
a maximum inspiration. It is equal to the inspiratory reserve volume plus the tidal
volume plus the expiratory reserve volume. Force vital capacity (
FVC
) is the max-
imum volume of air that a person can exhale after maximum inhalation. Another
important measure during spirometry is the forced expired volume in one second
(
FEV
1
). The
FEV
1
/FVC
ratio is used in the diagnosis of obstructive and restrictive
lung disease, and normal values are approximately 80 %. In obstructive lung dis-
ease, the
FEV
1
is reduced due to obstruction to air escape. Thus, the
FEV
1
/FVC
ratio will be reduced. In restrictive lung disease, the
FEV
1
and
FVC
are equally re-
duced due to fibrosis or other lung pathology (not obstructive pathology). Thus, the
FEV
1
/FVC
ratio should be approximately normal. From the above, we observe that
the spirometric values of the adults and children given in tables from Chap.
7
are in
agreement.
From Fig.
8.13
we notice that the decision of using one or another distance form
is important for the mapping representation. With the sum given by (
8.15
) the sep-
aration between groups is possible, whereas using (
8.16
) it becomes impossible to
strictly separate between groups. One can clearly distinguish separated high den-
sity nuclei for each of the three groups: healthy, COPD, and KS. This means that it
is possible to classify between these groups by means of MDS, given the suitable
distance measure. Some COPD outliers are present, denoting marked progress of
the obstructive disease, whereas majority of the KS objects lie fairly close to the
nuclei of COPD. The reason for this similitude is that, although being a restrictive
disease, KS affects in a similar manner the airway resistance. In spite of having
different origins, airway resistance increases in both COPD and KS. In a similar
manner, the compliance is lower in both COPD and KS. Nevertheless, different bal-
ance between these mechanical properties will place an object in the MDS map
closer or further from the nucleus of the group. This is usually the case with signifi-
cant pathologic restrictions, hence a more pronounced manifestation of the disease.
Our results suggest that MDS is able to distinguish between restrictive (KS) and
obstructive (COPD) pathologies, for clinical classification purposes. Moreover, the
corresponding dendrogram tree from Fig.
8.16
supports this conclusion, by similar
clustering.
In children, from Figs.
8.14
-
8.15
we can observe that some of the asthma patients
were fairly close to the healthy subjects nucleus. The underlying reason for this
result is that these asthma patients were controlled with specific medication, with
intake prior to the lung function test. Hence, no significant differences from the
healthy group can be seen, i.e. false 'healthy points'. The other asthma patients,
who had exacerbations and a pronounced respiratory restriction, are either partially
controlled, or did not take the medication prior to the exam. As far as cystic fibrosis
is concerned, due to the nature of the disease, which affects in general the organism
and not only the respiratory system, a clear separation could not be made from
