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Instantaneous back flow through peripheral clearance of medtronic hall tilting disc valve at the moment of closure (1994)

Lee, C. S. ; Chandran, K. B.

Springer

Annals of biomedical engineering 22 (1994), S. 371-380

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ISSN: 1573-9686

Keywords: Valve closure ; Tilting disc valve ; Peripheral clearance ; Instantaneous back flow ; Computational fluid dynamic analysis ; Wall shear stress ; Pressure ; Cavitation

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: Abstract An investigation of the flow dynamics through the peripheral clearance (the gap formed between the occluder tip and the metal housing in the closed position) of a tilting disc heart valve at the moment of valve closure is presented. A Medtronic Hall valve in the mitral position of anin vitro experimental set up is employed to measure the transient pressure pulses near the entrance (ventricular side) and exit (atrial side) of the peripheral clearance at valve closure. Flow within the peripheral clearance is analyzed employing a two-dimensional quasisteady computational fluid dynamics model with the measured peak pressures specified as the boundary conditions inducing the flow. The valve is visualized from its inflow (atrial) side using a stroboscopic lighting technique to investigate the presence of cavitation bubbles within the clearance. The pressure measurements showed that a relatively large pressure drop exists between the entrance and the exit to the clearance for about 0.5 msec at the moment of valve closure. The numerical simulation resulted in relatively large magnitudes of wall shear stress and pressure reduction within the clearance due to the flow established by the large pressure drop between the entrance and the exit. Cavitation bubbles visualized within the peripheral clearance at higher loading rates for valve closure correlated with the presence of large pressure reduction within the clearance. Analysis of the results of this study indicates that the back flow through the clearance at the instant of valve closure may contribute toward injury to formed elements in blood in spite of the short duration of the flow.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02368243

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Polymerization behavior of 2,2,6,6-tetramethylpiperidinyl methacrylate: A monomer carrying a hindered amine group (1992)

Lee, C. S. ; Lau, Wayne W. Y. ; Lee, S. Y. ; [et al.]

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 983-988

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ISSN: 0887-624X

Keywords: copolymerization ; 2,2,6,6-tetramethylpiperidinyl methacrylate ; HALS ; copolymer structure ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Copolymers of 2,2,6,6-tetramethylpiperidinyl methacrylate (TPMA) with styrene (S) and with methyl methacrylate (MMA) were synthesized using AIBN as initiator. S-TPMA copolymers from feed ranging from 0.10-0.80 mole fractions TPMA and MMA-TPMA copolymers from feed of 0.04-0.85 mole fractions TPMA were used in the determination of monomer reactivity ratios r1, r2. Four different methods were employed in the calculations of r1 and r2 and all calculated results were in good agreement with each other. The structure of S-TPMA copolymers was inferred to be of an alternating nature while that of MMA-TPMA copolymers was random. Both copolymers are potential hindered amine light stabilizers (HALS) and are expected to be less extractable from, and more compatible with, polystyrene and poly(methyl methacrylate) base polymers.

Additional Material: 3 Ill.