is 50–85% of the maximum dive depth. It is interesting to note that
they do not exhale immediately on ascent and the reason for this
can be explained by our model. The point where the trachea starts
to collapse is the point where the pressure gradient between the
outside and inside of the rib cage switches from negative to positive
(Pamb −Pint > 0), i.e., the structure of the alveoli are starting to
oppose Pamb. If the glottis was opened when there is this positive
pressure gradient, sea water would enter the respiratory system
since the alveoli and trachea would tend to expand. Conversely,
if the glottis was opened when Pamb −Pint < 0 the respiratory system
would tend to collapse and air would escape. If an animal has
dived to a depth where VA MAV without releasing any bubbles. After this
point exhalation occurs passively because Pint > Pamb.