First published online August 25, 2003
Form and function of the bulbus arteriosus in yellowfin tuna (Thunnus albacares): dynamic properties
Marvin H. Braun1,*,
Richard W. Brill2,
John M. Gosline3 and
David R. Jones4
1 Department of Zoology, Cambridge University, Downing Street, Cambridge,
UK, CB2 3EJ,
2 Cooperative Marine Education and Research Program, Virginia Institute of
Marine Science, PO Box 1208, Greate Rd, Gloucester Point, Virginia 23062,
USA,
3 Department of Zoology, University of British Columbia, Vancouver, BC,
Canada, V6T 1Z4
4 Zoology Animal Care, 6199 South Campus Road, University of British
Columbia, Vancouver, BC, Canada, V6T 1W5
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Fig. 1. A yellowfin tuna used in the video dimensional analysis (VDA) study showing
the bulbus in relation to the ventricle within the pericardial cavity during
diastole and systole. The catheter used to record pressure entered the bulbus
ventrally. The VDA window was aligned with the bulbus so that from diastole to
systole the black portion of the window followed the edges of the bulbus
during a heartbeat. Length, as well as width, changed with each beat of the
heart.
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Fig. 2. (A) Recordings of bulbar blood pressure and diameter from a yellowfin tuna.
(B) Comparison of static and dynamic pressure-diameter (P-D) loops. The
dynamic trace (green) was created by plotting pressure against diameter for
the heartbeat in A and is superimposed on a P-D curve (black) created by a
bulbar inflation from a syringe, post mortem. Arrows indicate the
clockwise or anticlockwise cycling of the loop. (Diameter ratio is the
diameter divided by the initial diameter.)
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Fig. 3. Comparison of dynamic and static inflations over a wide pressure range. (A)
Pressure-volume (P-V) loop from static inflation of a yellowfin tuna bulbus
arteriosus. (B) A dynamic pressure-diameter (P-D) loop for the pressure range
4-8 kPa. (C) A dynamic P-D loop for the pressure range 10.6-12.6 kPa. (D) A
dynamic P-D loop for the pressure range 16-22 kPa. Arrows link the pressure
ranges in B, C and D to the static loop in A.
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Fig. 4. Recordings of bulbar blood pressure and diameter from yellowfin tuna. (A)
Following a long cardiac interval, the smallest stroke volume (*)
generated the largest pulse pressure. (B) At mean systolic pressure, large
changes in diameter result in small changes in pressure (arrows). See text for
explanation of diamond. (C) At very high pressures, small changes in diameter
result in large fluctuations in pressure (triangles).
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Fig. 5. (A) Pressure-volume (P-V) loops from static, in situ inflations of
bulbi from yellowfin tuna. Anterior and posterior refer to where on the bulbus
the video dimensional analysis (VDA) window was centred. (B) Pressure-diameter
strain loop for the same bulbi as in A. The diameter strain was calculated
using diameter data from the VDA. (C) Diameter plotted against volume for the
bulbus measured at the anterior end. A linear regression was run on this plot
and the solution is shown. (D) Diameter plotted against volume for the bulbus
measured at the posterior end. A linear regression was run on this plot and
the solution is shown.
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Fig. 6. (A) Recordings of bulbar blood pressure and diameter from a yellowfin tuna
during normal beating. (B) The volume changes within the bulbus during the
beating in A.
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Fig. 7. (A) Recordings of bulbar blood pressure and diameter from a yellowfin tuna
during a marked fall in pressure and heart rate. (B) Volume changes within the
bulbus from A. (C) Pressure and diameter from a tuna after Saffan injection.
(D) Volume changes within the bulbus from C.
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© The Company of Biologists Ltd 2003
V) experienced by the bulbus arteriosus and
ventral aorta over a physiological pressure range. The thick vertical lines
indicate the bulbar volume changes, and the thin vertical lines indicate the
ventral aortic changes. Volume was normalized to maximal internal volume. (B)
Dimensional changes that a bulbus and a ventral aorta of the same external
diameter would undergo from zero to diastolic and then to systolic pressure.
Zero to diastolic pressure. At zero pressure, the bulbus' lumen is
smaller than the artery's lumen, resulting in a much lower tension during
inflation. The low tension in the bulbar wall results in a requirement for a
large pressure to allow expansion. As shown in A, the small strain change in
the bulbus generates a large pressure for a small volume. Diastolic to
systolic pressure. During inflation from diastole to systole, the bulbus
undergoes a large strain (35%) due to the large volume changes seen in A at
systolic pressure. The artery undergoes a strain of 5%, due to the low
compliance seen in A at systolic pressure. D, external diameter;
d, lumen diameter. Values of strain for the bulbus were calculated
using video dimensional analysis (VDA). Values of strain for the proximal
aorta came from McDonald
(1974