Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
(e)
Fig. 4.5.
If the two global modes are active in the right
phase, the labia gain energy from the airflow. This series of
snapshots illustrates the final labial motion in such a situa-
tion (modified after [Gardner et al. 2001])
To understand the origin of these movements in an airflow is not trivial,
but we are going to suppose that these movements can exist. Moreover, we
are going to suppose that they are coordinated in such a way that the labia
have a convergent profile while they are moving away from each other, and
a divergent profile when they are approaching each other. We shall see that
under these assumptions, it is easy to understand the origin of the force
responsible for overcoming the dissipation [Titze 1988, Gardner et al. 2001,
Laje et al. 2002a]. It is appropriate to point out that this mode structure
is compatible with direct endoscopic observations [Goller and Larsen 2002,
Fee et al. 1998].
4.3.2 Self-Sustained Oscillations
Let us see now how the combination of movements described above allows
the establishment of oscillations. We begin with the bird expiring, meaning
that it generates a high bronchial pressure, responsible for the airflow. In this
situation, the pressure below the labia is higher than atmospheric pressure,
while the pressure above them is essentially equal to atmospheric pressure
[Titze 1988, Gardner et al. 2001]. When the labia form a convergent profile
(see Fig. 4.6), the value of the pressure between them is nearly the bronchial
pressure. On the other hand, when the labia form a divergent profile, the
pressure between them is approximately atmospheric pressure. Therefore,
