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At least 361 records · Page 20Linked to original sources
PubMed2000

Tissue engineering of heart valves: in vitro experiences.

BACKGROUND: Tissue engineering is a new approach, whereby techniques are being developed to transplant autologous cells onto biodegradable scaffolds to ultimately form new functional tissue in vitro and in vivo. Our laboratory has focused on the tissue engineering of heart valves, and we have fabricated a trileaflet heart valve scaffold from a biodegradable polymer, a polyhydroxyalkanoate. In this experiment we evaluated the suitability of this scaffold material as well as in vitro conditioning to create viable tissue for tissue engineering of a trileaflet heart valve. METHODS: We constructed a biodegradable and biocompatible trileaflet heart valve scaffold from a porous polyhydroxyalkanoate (Meatabolix Inc, Cambridge, MA). The scaffold consisted of a cylindrical stent (1 x 15 x 20 mm inner diameter) and leaflets (0.3 mm thick), which were attached to the stent by thermal processing techniques. The porous heart valve scaffold (pore size 100 to 240 microm) was seeded with vascular cells grown and expanded from an ovine carotid artery and placed into a pulsatile flow bioreactor for 1, 4, and 8 days. Analysis of the engineered tissue included biochemical examination, enviromental scanning electron microscopy, and histology. RESULTS: It was possible to create a trileaflet heart valve scaffold from polyhydroxyalkanoate, which opened and closed synchronously in a pulsatile flow bioreactor. The cells grew into the pores and formed a confluent layer after incubation and pulsatile flow exposure. The cells were mostly viable and formed connective tissue between the inside and the outside of the porous heart valve scaffold. Additionally, we demonstrated cell proliferation (DNA assay) and the capacity to generate collagen as measured by hydroxyproline assay and movat-stained glycosaminoglycans under in vitro pulsatile flow conditions. CONCLUSIONS: Polyhydroxyalkanoates can be used to fabricate a porous, biodegradable heart valve scaffold. The cells appear to be viable and extracellular matrix formation was induced after pulsatile flow exposure.

Animals↗
PubMed1999

Are older patients with mechanical heart valves at increased risk?

BACKGROUND: Controversy exists regarding the use of mechanical valves in older patients. Many authorities believe that the use of anticoagulants in the elderly is associated with an increased risk of warfarin-related complications. Therefore, we compared the results with mechanical valves in older patients to a cohort of younger patients. METHODS: Aortic (AVR) or mitral valve replacement (MVR) with a mechanical valve was performed in 1,245 consecutive patients who were followed prospectively. They were grouped by age (group 1, < or = 65 years; group 2, > 65 years). The study groups consisted of AVR (group 1, 459 patients; group 2, 323 patients) MVR (group 1, 313 patients; group 2, 150 patients). RESULTS: The average age for the groups was: AVR (group 1, 51 years; group 2, 70 years; p = 0.03) and MVR (group 1, 53 years; group 2, 70 years; p = 0.03). For AVR the incidence of thromboembolism was 0.050 (group 1) and 0.038 (group 2) (p = 0.37) and the actuarial freedom from thromboembolism was 83.0%+/-3.0% and 86.5%+/-1.0%, respectively (p = 0.13). The incidence of bleeding after AVR was 0.021 for group 1 and 0.028 for group 2 (p = 0.49). For MVR the incidence of thromboembolism was 0.059 for group 1 and 0.051 for group 2 (p = 0.75) and the actuarial freedom from thromboembolism was 78.8%+/-3.0% and 75.4%+/-8.7%, respectively (p = 0.71). The incidence of bleeding after MVR was 0.020 for group 1 and 0.027 for group 2 (p = 0.62). CONCLUSIONS: Mechanical valves perform well in selected older patients with no increased risk of bleeding or thromboembolism.

Age Factors↗
PubMed1983

In-vitro fluid dynamic characteristics of the abiomed trileaflet heart valve prosthesis.

The need for better and longer lasting trileaflet valves has led to the design and development of the Abiomed polymeric trileaflet valve prosthesis. In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use. The pressure drop studies yielded effective orifice areas of 1.99 and 1.54 cm2, and performance indices of 0.41 and 0.45 for the Nos. 25 and 21 valves, respectively. Leaflet photography studies indicated that the two valve sizes had maximum opening areas of 225 and 145 mm2, respectively, at a normal resting cardiac output. Steady and pulsatile flow velocity measurements with a laser-Doppler anemometer (LDA) system indicate that the flow field downstream of the Abiomed valve is jetlike and turbulent. Maximum mean square axial velocity fluctuations of 55 and 83 cm/s, and turbulent shear stresses of 220 and 450 N/m2 were measured in the immediate vicinity of the nos. 25 and 21 valves, respectively. The Abiomed valves studied had been originally configured for use in valved conduits, and it is therefore our opinion that further improvements can be made to the valve and stent design, which would enhance its fluid dynamic performance.

Aortic Valve↗
PubMed1982

The Björk-Shiley heart valve prosthesis. Flow characteristics of the new 70 degrees model.

Thrombus formation on the outflow face and tissue overgrowth along the sewing ring adjacent to the minor outflow region are major clinical pathologic problems observed with the Björk-Shiley tilting disc valve. In the hope of reducing these pathologic conditions the convexo-concave Björk-Shiley valve was designed. A new modification to the convexo-concave model has further improved most of the fluid dynamic characteristics of the valve. In vitro flow studies indicate an average improvement in pressure drop characteristics of about 20 to 30%. Velocity measurements made with a laser-Doppler anemometer in the immediate downstream vicinity of the modified convexo-concave valve indicate that the design changes have further reduced the size of the stagnation zone near the outflow face of disc. It was observed, however, that the regurgitation across the valve increased by about one to two percentage points.

Aortic Valve↗
PubMed2001

[Turbulence and high intensity transient signals (HITS) as a parameter for optimum orientation of mechanical heart valves].

BACKGROUND: In previous studies, the impact of valve orientation on the hemodynamic performance of mechanical aortic valves has been demonstrated. This study investigates Turbulence (RNS values) and High Intensity Transient Signals (HITS) as a new and objective parameter for hemodynamics in various orientations of Medtronic Hall (MH) and St. Jude Medical (SJM) aortic valves. METHODS: Rotation devices carrying a MH or SJM valve were implanted into four pigs. The device allowed valve rotation without reopening the aorta. In various orientations, turbulent shear stresses (RNS values) and HITS were measured. RESULTS: RNS and HITS changed for both valve designs in the different orientations, with superior results for the MH in the hemodynamically best orientation. Downstream turbulence (RNS) and HITS varied in the same direction, but a one to one correlation was not observed. CONCLUSIONS: RNS and HITS vary with respect to valve orientation and design with superior results for the tilting disc valve. Both MH and SJM valves showed lower turbulence and HITS counts in their hemodynamically best orientations. HITS were related to downstream turbulence and the hemodynamic performance of the mechanical aortic valves.

Animals↗