Marine mammals solve the problems associated with lung
collapse and middle ear squeeze by specialized adaptations
in the thoracic cavity and in the middle ear. Most marine
mammals have compliant chest walls that allow for complete
lung collapse and possess specialized structures in
their lungs that allow the alveoli to collapse first, followed
by the terminal airways (Figure 2). These structures may
also aid in reinflation of the lung. Recent studies show that
marine mammals have specialized surfactants in their
lungs that aid in postdive reinflation of the lung. With
respect to middle ear squeeze, marine mammals have specialized
cavernous sinuses in the middle ear that presumably
engorge with blood as the animal dives and thus fills
the air space.