Biomedical Engineering Reference
In-Depth Information
Fig. 2.1 Schematic
representation of the
respiratory system and its
main components
diffusion takes place. Diffusion allows the oxygen from the alveoli to pass through
the alveolar walls into the blood and the carbon dioxide to pass through the capillary
walls into the alveoli.
In order to move air in and out of the lungs, the volume of the thoracic cavity is
increased (or decreased). The lungs do not contract but increase or decrease in vol-
ume. Muscles like intercostals or diaphragm contract during inspiration. Normally,
the expiration is passive, the inspiration is active (
contraction of muscles). By
increasing the thoracic cavity, the pressure around the lungs decreases, the lungs
expand, and air is sucked in.
=
2.2 Morphology
In the literature, there are two representative sets of airway morphological values:
the symmetric case and the asymmetric case of the respiratory tree, schematically
depicted in Fig. 2.2 .The symmetric case assumes a dichotomously equivalent bifur-
cation of the airways in subsequent levels and is agreed by a group of authors e.g.
[ 97 , 135 , 164 ] as in Table 2.1 .The asymmetric case is when the bifurcations are
still dichotomous, but they occur in non-sequent levels, as given in Table 2.2 .The
parameter Δ denotes the asymmetry index. In this case, a parent airway will split
into two daughters: one of subsequent level m
+
1 and one of level m
+
1
+
Δ .This
latter anatomical context is agreed by another group of authors: [ 54 , 65 ].
2.3 Specific Pulmonary Abnormalities
Chronic Pulmonary Emphysema refers to a class of respiratory disorders which im-
plies the existence of excess air in the lungs [ 6 , 53 , 64 ]. It results from three major
pathophysiological events in the lungs:
chronic infection, caused by inhaling smoke or other substances that irritate the
bronchi and bronchioles;
the infection, the excess of mucus, and inflammatory edema of the bronchiolar
epithelium together cause chronic obstruction of smaller airways;
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