76
Marine Mammal Physiology: Requisites for Ocean Living
Volume relative to starting
volume
0
0.2 0.4 0.6 0.8
1
Pressure (ATA)
1
2
3
4
5
6
7
8
9
10
(c)
(a)
(d)
Invasion rate (surface area × pressure)
0
0 .5
1
1 .5
Rigid
trachea
Tracheal
compression
(b)
Trachea
Total
Alveoli
Figure 4.2 (See color insert.) Compression of lung and thorax results in changes in invasion/diffusion
rate. (a) Chest compression of a bottlenose dolphin (Tuffy), photographed at 300 m depth, with experimental setup shown on the left. Thoracic collapse is visible behind the left flipper. (Image copyright U.S.
Navy; details published in Ridgway et al. 1969). (b) Graded lung compression showing illustrations of
two models: (i) rigid trachea (solid) and (ii) tracheal compression at depths less than alveolar collapse
(dotted). (c) Modeled relative volume changes of trachea and alveoli based on these models. Total volume
(trachea + alveoli = 1 l) reduces according to Boyle’s law (thick gray line). Volume changes are shown
based on a rigid trachea (solid black line, 0.1 l), and assuming that the tracheal volume decreases exponentially after 3 ATA (dotted black line), with resulting changes to the alveolar volume from 0.9 l at the
surface, decreasing more quickly with a rigid trachea (gray solid line) than with a compressing trachea
(dotted gray line). (d) The resulting invasion rate (alveolar surface area × pressure) (sensu Scholander
1940). The invasion rate is plotted from 1 at the surface breath-hold, to 0 at the depth of alveolar collapse.
Fick’s law states that the diffusion rate is proportional to surface area × pressure/membrane thickness,
thus the invasion rate divided by the membrane thickness would give the diffusion rate (i.e., this would
further reduce the invasion rate). It can be seen that near the surface, the invasion rate increases with a
pressure increase, but that at deeper depths this reduces to the depth of alveolar collapse. The effect of
tracheal compression at depths shallower than alveolar collapse effects deeper alveolar collapse and
increases the range of depths which have a high invasion (and diffusion) rate.
Marine Mammal Physiology: Requisites for Ocean Living
Volume relative to starting
volume
0
0.2 0.4 0.6 0.8
1
Pressure (ATA)
1
2
3
4
5
6
7
8
9
10
(c)
(a)
(d)
Invasion rate (surface area × pressure)
0
0 .5
1
1 .5
Rigid
trachea
Tracheal
compression
(b)
Trachea
Total
Alveoli
Figure 4.2 (See color insert.) Compression of lung and thorax results in changes in invasion/diffusion
rate. (a) Chest compression of a bottlenose dolphin (Tuffy), photographed at 300 m depth, with experimental setup shown on the left. Thoracic collapse is visible behind the left flipper. (Image copyright U.S.
Navy; details published in Ridgway et al. 1969). (b) Graded lung compression showing illustrations of
two models: (i) rigid trachea (solid) and (ii) tracheal compression at depths less than alveolar collapse
(dotted). (c) Modeled relative volume changes of trachea and alveoli based on these models. Total volume
(trachea + alveoli = 1 l) reduces according to Boyle’s law (thick gray line). Volume changes are shown
based on a rigid trachea (solid black line, 0.1 l), and assuming that the tracheal volume decreases exponentially after 3 ATA (dotted black line), with resulting changes to the alveolar volume from 0.9 l at the
surface, decreasing more quickly with a rigid trachea (gray solid line) than with a compressing trachea
(dotted gray line). (d) The resulting invasion rate (alveolar surface area × pressure) (sensu Scholander
1940). The invasion rate is plotted from 1 at the surface breath-hold, to 0 at the depth of alveolar collapse.
Fick’s law states that the diffusion rate is proportional to surface area × pressure/membrane thickness,
thus the invasion rate divided by the membrane thickness would give the diffusion rate (i.e., this would
further reduce the invasion rate). It can be seen that near the surface, the invasion rate increases with a
pressure increase, but that at deeper depths this reduces to the depth of alveolar collapse. The effect of
tracheal compression at depths shallower than alveolar collapse effects deeper alveolar collapse and
increases the range of depths which have a high invasion (and diffusion) rate.