Fig. 4. (a) Alveolar (VA) and dead space volume (VD) against ambient pressure (Pamb)
for various diving alveolar volumes (VA,o:VD,o). The balloon/pipe model is plotted for
comparison. Our model predicts that the trachea starts to collapse once the alveolar
volume reaches minimum air volume (MAV) and this causes VA to become
greater than predicted by the balloon/pipe model. (b) VD plotted against ambient
pressure (Pamb) for various diving alveolar volumes. Predicted tracheal volumes at
depth as recorded by radiography in a pressure chamber are plotted for comparison
(Kooyman et al., 1970). The experimental data show that the trachea of marine
mammals is compressible.