Single Versus Double Ended High Frequency Pressurization of Mock Arteries: Symmetry of Expansion
Biomedical Science Instrumentation, 42, pp. 446-451, (2006)

Ramesh, R1, Conti JC2, Strope ER1

1 Dynatek dalta Scientific Instruments, 105 E Fourth St, Galena, MO 65656

2 Department of Physics, Astronomy and Material Sciences, Southwest Missouri State University, Springfield, MO, 65803



Introduction:

Frequency response characteristics of mock arteries play a very significant role in high frequency durability testing of medical devices such as grafts and stents. In vitro durability testing of stents depends on cyclic load applied by the mock artery on the medical device.



• This study analyzes distension of mock arteries at different locations with single
   and double ended mode of pressurization at various frequencies.

• Single Ended Pressurization: Pressurizing mock arteries by forcing fluid from
   one end.

• Double Ended Pressurization: Pressurizing mock arteries by forcing fluid from
   both ends.


Methods:

• Six 10cm long silicone mock arteries with internal diameter 27.75 ±0.2mm.

• Length chosen represents the most common length used for testing stents.

• Radial compliance of 6.55 % per 100mm Hg @ 72bpm between 80 and 120mm Hg.

• Large Vascular Prosthesis (LVP) tester was used to test mock arteries
   between frequencies of 0 to 100 Hz.

• LVP is equipped with Ling Dynamic Shaker (V408 –PA 100 E) with peak force of
   22 lbf and maximum peak to peak displacement of 14mm.

• Dynamic Shaker in turn compresses the bellow drive system.


Figure 1: Large Vascular Prosthesis with Ling Dynamic Shaker.

• High speed photography (Fast Cam PCI 1280 with Photron Motion Tools
   1.0.5 software) was used to measure the distension of mock arteries.


Technique used for measurement:




Figure 2: Schematic representation of mock artery.




Testing:

• All six mock arteries were connected to proximal and distal manifolds of the
   LVP tester.

• Manifolds contains a reservoir connecting all mock arteries in common.

• Mock arteries filled with distilled water and a pressure transducer fixed to the
   distal manifold.

• Two points on the uppermost mock artery were marked 16mm apart at three
   different locations.

• High speed photographic camera was fixed vertically above such that all three
   points are monitored simultaneously.



Figure 3: Schematic representation of experimental setup.




Figure 4: Schematic representation of silicone mock artery.



Single ended pressurization:

• Fluid is forced into mock arteries from proximal end by the bellows.

• Experiment was conducted at different frequencies between 5 to 100 Hz.

• Pressure measured at distal manifold cycled between 160 and 80mm Hg.

• At each testing frequency, respective movements of the markings were recorded
   with sinusoidal pressure variation.

• After each recording, the position changes of each of the markings were tracked
   by an automated tracking function.

• Strain in the chord length was determined at all three locations.


Double ended pressurization:

• A rigid hollow central tube of 1.5 inches diameter was attached between
   the manifolds.


Figure 5: Schematic representation of distal manifolds.

• Central tube had higher rigidity, hence its compliance is negligible compared to
   mock arteries.

• During forward stroke of bellows, fluid passes through the central tube and
   enters mock arteries from both distal and proximal end.

• Experiment was conducted at different frequencies between 5 to 100 Hz.


Results:





Figure 6: Graphical representation of % strain versus frequency for single ended pressurization.



Figure 7: Graphical representation of % strain versus frequency for double ended pressurization.


Discussion:

• Complexity of relation between distension (% E) and frequency at different
   locations is partially understandable.

• Experimental considerations such as harmonics and asymmetric pressurization
   are possible sources of frequency dependent variations.

• Frequency dependent compliance of mock arteries and experimental
   apparatus explain some of the changes.

• End effects could have a possible influence on the data.

• Further experiments in longer tubes are ongoing.


Acknowledgements:

Special thanks to all the employees of Dynatek dalta Scientific Instruments.


References:

1) Conti, J.C. and Strope, E.R., Radial Compliance of Natural and Mock Arteries:
    How this Property Defines the Cyclic Loading of Deployed Vascular
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2) Conti, J.C., Strope, E.R., Rohde, D.J. and Spence, L.D., Frequency
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3) Conti, J.C., Strope, E.R., Price K.S, Sources of Error in Monitoring High
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4) Gonza, E.R., Mason, W.F., Marble, A.E., and others, Necessity for
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5) AAMI/ISO standard ISO/CD- V-1 25539-01:2003 and ANSI/AAMI VP-20, (1994)

6) Ramesh R., Strope E.R., Price K.S., Conti J.C., Frequency Dependent
    Hysteresis of Silicone and Latex Mock Arteries Used in Stent Testing.
    Biomedical Sciences Instrumentation, 41, 163-168, (2005)

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