Reflections

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Reflections

• In the arterial system reflections of pressure
  and flow waves occur wherever there is a change
  in the local fluid impedance

• Decrease in diameter or increase in stiffness -gt
• positive reflection of pressure
• negative reflection of flow
• If no reflections pressure and flow waves are
  the same shape
• Arterial disease usually associated with
  increased reflections (except aneurysms)
• Energy is lost so cardiac output must increase to
  maintain a given flow

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Wave reflection
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Fourier analysis
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Q(t) q0 q1Cos(?t - ?1) q2Cos(?t - ?2)
q3Cos(?t - ?3) ...
P(t) p0 p1Cos(?t - ?1) p2Cos(?t - ? 2)
p3Cos(?t - ? 3) ...

Z pn/qnPressure/Flow F ?n - ?n
Pressure - Flow
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Vascular tree of rat kidney
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Rat Heart
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Dog
Vessel Diam. mm Number Total CSA mm2 Length mm Total Vol. mm3x103
Aorta 10.0 1 80 400 30
Large arteries 3.0 40 300 200 60
Main branches 1.0 600 500 100 50
Terminal 0.6 1800 500 1 25
Arterioles 0.02 4x107 12500 0.2 25
Capillaries 0.008 1.2x109 60000 0.1 60
Venules 0.03 8x107 57000 0.2 110
Terminal veins 1.5 1800 3000 1 30
Main branches 2.4 600 2700 10 270
Large veins 6.0 40 1100 20 220
Vena cava 12.5 1 120 40 50
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Blood distribution
8 - 11
10 - 12
Systemic Arteries
10 - 12
Lungs
Heart
4 - 5
Capillaries
Small venules
Systemic veins
Large
60 - 70
Total volume 5.5 litre
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Major components of large arteries
Component Stiffness kPa Amount Type Characterist
ics
Elastin E 0.1 30 Protein Rubber Collagen E
10 30 Protein Leather Muscle E 0.05 30
Cellular Liver Ground substance E 0 10 MPS
Gel Marmalade Endothelium E 0 lt 1 Cellular Wet
kleenex
Water 70
Stiffness depends on the ratio of collagen to
elastin
Bone 10 - 50 Wood 100 Steel 1000
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Size shape
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stanford-online.stanford.edu/ cardio2006/docs/Tayl
orLecture3Cardio06.pdf
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Elastin

• Randomly kinked, covalently cross-linked
  polypeptide chains
• Fibres of around 10 µm in diameter with variable
  lengths, found in lung, skin etc.
• Fenestrated lamellae (layers) around 3µm thick,
  found primarily in the tunica media of the
  arteries
• Found in all vertebrates with a closed (high
  pressure) circulatory system.
• Not hagfish and lampreys
• Equivalent rubbery materials in invertebrates
• Resilin, abductin, octopus arterial elastomer

http//www.nativefish.org/
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Elastin

• Synthesised by VSMC and VEC (perhaps)
• soluble tropoelastin
• excreted
• cross linked
• Undergoes large recoverable (elastic) stretch
• Elastic fibres are not fibres

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Elasticity of Elastin

• Entropy (typical elastomer)
• Hydrophobicity
• When relaxed, hydrophilic entities are in contact
  with interstitial water.
• When stretched, hydrophobic part of the molecule
  is brought into contact with the water, work is
  done against repulsion

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Elastin