The bulbus arteriosus, the fourth chamber of the teleost heart, is very similar in
structure and function to blood vessels. However, when the inflation properties of the
bulbus are compared with those of an artery, a striking difference appears. The pressurevolume
loops of arteries are J-shaped, indicating an increasing stiffness with increasing
distension. The bulbus pressure-volume curve can best be described as an r-J curve, with
an initial sharp rise followed by long plateau phase, and a final upturn following the
plateau. This suggests that the bulbus has a high initial stiffness that decreases as volume
increases before rising again at high distensions. To analyse the cause of this inflation
behaviour, 1 utilised light microscopy, electron microscopy, mechanical testing of bulbar
and arterial walls, and in vivo recordings of diameter and pressure changes of bulbi. The
results show that the answer to the bulbus question is multifaceted. The steep initial rise
in pressure is due to the geometry of the bulbus. When empty, the bulbus lumen is very
small. According to the Law of Laplace, a small radius requires a large pressure
increment in order for expansion to occur. As the lumen radius increases, the pressure
increments decrease in size. The extremely compliant plateau phase of the bulbar
inflation is due to the specialised material properties of the bulbar wall. The combination
of a high elastin/collagen ratio, lack of elastic lamellae and specialised elastin result in a
decreased elastic modulus (stiffness) within the bulbar wall. Once on the plateau phase of
the bulbar inflation, this decreased stiffness allows the bulbus to expand a tremendous
amount for small changes in pressure. The tensile tests show that the bulbar material
exhibits J-shaped changes in stiffness when stretched and, despite the low modulus, at
high extensions, the bulbar material can become quite stiff, resulting in the final rise in
stiffness seen in inflation. The inflation behaviour of the bulbus allows to it function as an
exceptional pressure and volume reservoir, mimicking the Windkessel effects o f a much
longer arterial tree.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/11643 |
| Date | 11 1900 |
| Creators | Braun, Marvin Herbert |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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