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At least 757 records · Page 42Linked to original sources
PubMed1992

In vitro hemolysis by mechanical heart valve prostheses with tilting disc.

Hemolytic and subhemolytic blood damage by mechanical heart valve prostheses have been observed in both clinical and in vitro investigations. A direct comparison between these studies is not possible. Nevertheless the transfer of some in vitro results to the behaviour of the valve in situ may be performed considering the similarity principle. This requires the use of dimensionless similarity numbers such as the plasma's hemoglobin concentration (PHb) or others, instead of dimensioned parameters. To evaluate the in vitro hemolysis of valve prosthesis a test chamber filled with human banked blood was used. An artificial ventricle ensuring an oscillatory flow through the valve was also used. The rise of PHb was evaluated in terms of a similarity number, called the lysis number. This number describes the probability of destroying a single red blood cell participating once in the hemolytic process under consideration. The lysis number, a Björk-Shiley valve (TAD 29), was found to be in the order of 2 x 10(-4). From this, the survival time of erythrocytes in patients with an artificial heart valve was estimated. It was found to be in the order of 20 d of T50 Cr in agreement with clinical results.

Erythrocyte Aging↗
PubMed1999

A new flow model for Doppler ultrasound study of prosthetic heart valves.

BACKGROUND AND AIM OF THE STUDY: Steady and pulsatile flow models used to assess the hydrodynamic aspects of prosthetic heart valves are generally made of Plexiglas and Lucite tubing. They often allow continuous-wave and pulsed-wave Doppler ultrasound velocity measurements to be made parallel to the flow, but cannot be used as such for ultrasound scanning of valve inflow and outflow velocities because of ultrasonic reverberation and refraction by the tubing. The aim of the study was to develop a new flow model which allowed ultrasonic scanning of the prosthetic valve flow for three-dimensional (3D) reconstruction of color Doppler flow distributions. METHODS: The flow model, designed with left ventricular and aortic chambers composed of agar gel which mimics the ultrasound characteristics of biological tissues, was developed and tested for comparative in vitro hydrodynamic and Doppler ultrasonic studies of aortic prosthetic valves. An electromagnetic flowmeter and a pressure monitor provided the flow and pressure signals for the hydrodynamic tests. The Doppler ultrasonic evaluation was performed with an Ultramark 9 HDI ultrasound system and a 3D ultrasound imaging system. The model was designed to enable assessment of prosthetic valve performance by pulsed-wave and continuous-wave Doppler velocity measurements, as well as by 3D color Doppler velocity measurements obtained by ultrasonic scanning of the left ventricle or aortic chamber with an ultrasound probe mounted on a motorized translation assembly. RESULTS: The study results showed that this new flow model can provide 3D color Doppler velocity distributions as well as accurate comparisons of hydrodynamic parameters of mechanical and bioprosthetic heart valves derived from Doppler and catheter measurements, both under steady and pulsatile flow conditions. CONCLUSION: This new flow model can be used to evaluate the usefulness of hydrodynamic parameters for the assessment of prosthetic heart valves using both conventional Doppler echocardiography, as currently used in patients, and 3D color Doppler ultrasonic imaging.

Blood Flow Velocity↗
PubMed2001

[Prognostication of the outcome of heart valve prosthesis implantation by the method of nonlinear chaos dynamics of the heart rate].

An examination of 39 patients with heart diseases was performed before and after operations by the method of geometrical analysis of the nonlinear chaos (fractal) variability of the cardiac rhythm on the basis of the apparatus-programmed complex "Poly-spectrum". Five-minute-long registrations of ECG were carried on. On the basis of the data of examination of 195 healthy volunteers the reference norm of this method parameters was determined. Reliably lower parameters were found in patients with the acquired valvular disease. A dynamic investigation of the geometrical nonlinear structure of the cardiac rhythm has shown the possibility to make a prognosis of early complications after prosthetics of the heart valves.

Adult↗
PubMed2005

Time-dependent analysis of leaflets in mechanical aortic bileaflet heart valves in closing phase using the finite strip method.

BACKGROUND AND AIMS OF THE STUDY: Mechanical heart valves (MHV) are widely used to replace dysfunctional and failed heart valves. The bileaflet MHV design is very popular due to its superior hemodynamics. Since their introduction in 1977, the hemodynamics of bileaflet prostheses has been extensively studied. In this study the dynamic behaviour during the closing phase of a bileaflet MHV under normal physiological conditions has been investigated. METHODS: Fluid analysis is based on the control volume with moving boundaries in the vicinity of the occluder. Unsteady continuity equation, unsteady momentum equation on the control volume and unsteady Bernoulli's equation have been used to calculate velocity of blood flow and force on the occluder tip. To solve the governing equations for the calculation of pressure and the related force, the finite strips method has been implemented. Only 32 strips are sufficient to calculate the force due to pressure on the leaflets. The equations of motion have been solved using the Runge-Kutta method in the fourth order. RESULTS: The maximum velocity of the leakage flow in the closing phase falls within the range of 3.5-4.4 m/s. The maximum velocity of the occluder tip is in the range of 2.4-3.2 m/s. The backflow also exhibits oscillation similar to that of the occluder with net backflow rate in the range of 9.7-12.3 ml/beat. The impact force between occluder and its housing is in the range of 80-140 N and impact occurs during 33.1-41.0 ms and the leaflets are completely settled at 108-115 ms in the closing phase. CONCLUSION: The finite strip method was implemented to study the closing phase of a bileaflet MHV. Results are consistent with the previous experimental data. This method is of general applicability to study dynamic behaviour of MHVs.

Aorta↗
PubMed1996

Embolic stroke in a pregnant patient with a mechanical heart valve on optimal heparin therapy.

A 28-year-old woman with a mechanical aortic heart valve experienced an embolic stroke in early pregnancy after her anticoagulation therapy was changed from warfarin to heparin. This occurred despite use of a subcutaneous heparin infusion pump and optimal anticoagulation. Thromboembolism can occur in pregnant patients with mechanical heart valves despite optimal heparin therapy.

Adult↗
PubMed2003

A novel bioreactor for the dynamic flexural stimulation of tissue engineered heart valve biomaterials.

Dynamic flexure is a major mode of deformation in the native heart valve cusp, and may effect the mechanical and biological development of tissue engineered heart valves (TEHV). To explore this hypothesis, a novel bioreactor was developed to study the effect of dynamic flexural stimulation on TEHV biomaterials. It was implemented in a study to compare the effect of uni-directional cyclic flexure on the effective stiffness of two candidate TEHV scaffolds: a non-woven mesh of polyglycolic acid (PGA) fibers, and a non-woven mesh of PGA and poly L-lactic acid (PLLA) fibers, both coated with poly 4-hydroxybutyrate (P4HB). The bioreactor has the capacity to dynamically flex 12 rectangular samples (25 x 7.5 x 2mm) under sterile conditions in a cell culture incubator. Sterility was maintained in the bioreactor for at least 5 weeks of incubation. Flexure tests to measure the effective stiffness in the "with-flexure" (WF) and opposing "against-flexure" (AF) directions indicated that dynamically flexed PGA/PLLA/P4HB scaffolds were approximately 72% (3 weeks) and 76% (5 weeks) less stiff than static controls (p<0.01), and that they developed directional anisotropy by 3 weeks of incubation (stiffer AF, p<0.01). In contrast, both dynamically flexed and static PGA/P4HB scaffolds exhibited a trend of decreased stiffness with incubation, with no development of directional anisotropy. Dynamically flexed PGA/P4HB scaffolds were significantly less stiff than static controls at 3 weeks (p<0.05). Scanning electron microscopy revealed signs of heterogeneous P4HB coating and fiber disruption, suggesting possible explanations for the observed mechanical properties. These results indicate that dynamic flexure can produce quantitative and qualitative changes in the mechanical properties of TEHV scaffolds, and suggest that these differences need to be accounted for when comparing the effects of mechanical stimulation on the development of cell-seeded TEHV constructs.

Absorbable Implants↗
PubMed2003

Early failure of the tissue engineered porcine heart valve SYNERGRAFT in pediatric patients.

OBJECTIVES: The first tissue engineered decellularized porcine heart valve, Synergraft (Cryolife Inc., USA) was introduced in Europe as an alternative to conventional biological valves. This is the first report of the rapid failure of these new grafts in a small series. MATERIALS AND METHODS: In 2001, 2 model 500 and 2 model 700 Synergraft valves were implanted in four male children (age 2.5-11 years) in the right ventricular outflow tract as a root. Two patients had a Ross operation and two had a homograft replacement. RESULTS: The cryopreserved Synergraft valves appeared macroscopically unremarkable at implantation. Recovery from surgery was uneventful and good valve function was demonstrated postoperatively. Three children died, two suddenly with severely degenerated Synergraft valves 6 weeks and 1 year after implantation. The third child died on the 7th day due to Synergraft rupture. Subsequently the fourth graft was explanted prophylactically 2 days after implantation. Macroscopically all four grafts showed severe inflammation starting on the outside (day 2 explant) leading to structural failure (day 7 explant) and severe degeneration of the leaflets and wall (6 weeks and 1 year explant). Histology demonstrated severe foreign body type reaction dominated by neutrophil granulocytes and macrophages in the early explants and a lymphocytic reaction at 1 year. In addition significant calcific deposits were demonstrated at all stages. Surprisingly pre-implant samples of the Synergraft revealed incomplete decellularization and calcific deposits. No cell repopulation of the porcine matrix occurred. CONCLUSION: The xenogenic collagen matrix of the Synergraft valve elicits a strong inflammatory response in humans which is non-specific early on and is followed by a lymphocyte response. Structural failure or rapid degeneration of the graft occurred within 1 year. Calcific deposits before implantation and incomplete decellularization may indicate manufacturing problems. The porcine Synergraft treated heart valves should not be implanted at this stage and has been stopped.

Animals↗
PubMed2000

Different modes of degeneration in autologous and heterologous heart valve prostheses.

BACKGROUND AND AIM OF THE STUDY: This study was performed to elucidate the mechanism of primary tissue failure of bioprosthetic heart valves, which were fabricated from autologous pericardium (Autogenics). Results were compared with the degeneration pattern of heterologous pericardial bioprostheses. METHODS: Between March 1994 and December 1996, 87 Autogenics heart valves were implanted in the aortic position. Since then, 15 valves had to be explanted due to structural deterioration. The average implant period was 33+/-8 months. All explants were examined by gross morphological evaluation and X-ray analysis to identify the failure mode of these devices. In eight explanted autologous tissue valves and six explanted heterologous pericardial bioprostheses, exact morphological evaluation was performed by scanning electron microscopy, microscopic and immunohistochemical techniques. RESULTS: All autologous tissue valves failed due to cuspal tears localized at the commissures. Nocalcification could be detected by X-ray analysis and microscopic methods. Endothelial cell coverage was evident at the outflow surface of all autologous bioprostheses. Histological examination showed severe disintegration of the collagen fibers by insudated plasma proteins and erythrocytes, and the absence of the original fibroblasts. Collagen fibers were vigorously altered between the inner and outer stent of the Autogenics valve. In contrast, heterologous pericardial valves failed due to severe calcification of the cusps. Histological evaluation displayed invasion of macrophages and calcific deposits. The collagenous texture of the pericardial tissue was significantly better preserved compared with autologous tissue. CONCLUSION: High biocompatibility of autologous tissue valves is indicated by the absence of calcium deposits, macrophages and foreign body giant cells, and the presence of endothelial cell ingrowth. Severe disintegration of autologous tissue suggests that brief immersion in glutaraldehyde generates inadequate mechanical stability of bioprosthetic heart valve material. Heterologous valves exhibit low biocompatibility but superior preservation of the collagenous biomaterial.

Aged↗
PubMed1975

[Proceedings: Studies on mechanically induced hemolysis following prosthetic heart valve replacement].

Investigations into the problem of mechanical hemolysis were carried out in 28 patients with one or more prosthetic heart valve replacements. Signs of compensated intravascular hemolysis were demonstrated in all cases by determination of lactic dehydrogenase activity and free hemoglobin in the serum. We found no correlation between the type and number of prosthetic heart valves and the incidence of hemolysis.

Adult↗
PubMed1975

Studies on the pathogenesis of rheumatic heart disease. An immunological relationship between the polysaccharide of group A streptococcus and the glycoprotein of heart valve.

The immunization of rabbits with bovine heart valve homogenates induced the formation of antibody which reacted with CTC soluble extracts and also proteolytic enzyme treated fractions. Analysis by fractionation of materials revealed 2 peaks and both peaks contain monosaccharides. The first peak was more antigenic to anti-valvular sera. The cross-reactivity between the valvular glycoprotein and group A streptococcal polysaccharides was confirmed by the immunological inhibition tests. Widespread deposits of gamma globin were observed in valve of patients with recurrent rheumatic valvulitis who has valve replacement. This work was performed under scientific-grants-in-aid from the Ministry of Education. Portions of this study were presented at the 38th annual meeting of the Japanese Circulation Society, Yamaguchi, April, 1974.

Adult↗
PubMed1989

[Comparative study of hemolysis in patients after implantation of Soviet-made artificial heart valves and spherical and angle-opening disc closing devices].

Intravascular hemolytic parameters were studied in 40 patients after implantation of Soviet-made cardiac values with a ball versus angle-opening disc closing device. It was found that with the angle-opening disc closing cardiac valves "LIKS" and "EMIKS", hemolysis developed considerably more infrequently and was less marked than with ball valves. A significant difference was found between the activity of lactate dehydrogenase and the levels of haptoglobin in the compared groups of patients (p less than 0.05).

Adult↗
PubMed1989

An in vitro study of prosthetic heart valve sound.

Patients with an implanted mechanical heart valve sometimes experience the closing sounds of the valve as disturbing. To study the generation of valve sounds in general, a pulse duplicator study was carried out, testing eight commonly used types of prosthetic valves in the aortic position. Pulse rate was set at 70 beats/min, stroke volume at 70 ml and mean 'aortic' pressure at 100 mmHg. Despite the controlled conditions, there was great variability of the closing sound, in both intensity and spectral composition, making noise comparisons and spectral characterization ('sonoprint') difficult. In general, bileaflet mechanical valves produced less noise than did tilting disc valves, particularly those with large opening angles. One small-size (23 mm) tilting disc valve produced 50% less noise than large types. The plastic ball valve, the porcine and the polyurethane trileaflet valve all were very quiet.

Heart Valve Prosthesis↗
PubMed1991

Choosing a prosthetic heart valve.

Although most of the available prosthetic heart valves function remarkably well, the variety of available designs attests to the inability of any single one to fulfill the requirements of the ideal valve substitute. The mechanical prostheses include the caged-ball, tilting-disc, and bileaflet valves. Tissue valves available in the United States are the Carpentier-Edwards and Hancock porcine heterograph valves. Review of several large comparative studies on valve performance reveals that the overall results with tissue and mechanical valves are about equal at the end of 10 years. The characteristics of each type of valve substitute dictates the selection of one prosthesis in preference to others for a particular patient. Mechanical prostheses are recommended for patients without contraindications for anticoagulants. Tissue valves are reserved for patients over 70 years of age or for patients in whom anticoagulation is contraindicated. Multiple other patient-related factors need to be considered in selecting the appropriate valve, including the psychosocial situation and patient preference.

Bioprosthesis↗
PubMedDate not supplied

Influence of anisotropy on the mechanical behaviour of bioprosthetic heart valves.

Chemically modified pericardium is commonly used in the fabrication of bioprosthetic heart valves. This material exhibits non-linear elastic behaviour and, as for most other biological soft tissues, it is orthotropic in its extensibility. The influence of the natural orthotropy of pericardium on the mechanical behaviour of pericardial heart valves during the whole cardiac cycle has been studied, using the finite element method. A model of the leaflet of a bicuspid valve has been created, defining the material of the tissue as orthotropic non-linear elastic. Two preferential orthogonal orientations of the tissue have been analysed (axial and circumferential). The results show that even a small amount of orthotropy (an orthotropy index of 1.5 has been used) can significantly affect the mechanical behaviour of the valve, and that an appropriate orientation of the fibres can contribute to optimizing the stress distribution in the leaflets.

Anisotropy↗
PubMed2001

Mechanisms of mechanical heart valve cavitation: investigation using a tilting disk valve model.

BACKGROUND AND AIM OF THE STUDY: The induction of mechanical heart valve (MHV) cavitation was investigated using a 27 mm Medtronic Hall (MH27) tilting disk valve. METHODS: The MH27 valve was mounted in the mitral position of a simulating pulse flow system, and stroboscopic lighting used to visualize cavitation bubbles on the occluder inflow surface at the instant of valve closure. MHV cavitation was monitored using a digital camera with 0.04 mm/pixel resolution sufficient to render the tiny bubbles clearly visible on the computer monitor screen. RESULTS: Cavitation on MH27 valve was classified as five types according to the time, site and shape of the cavitation bubbles. Valve cavitation occurred at the instant of occluder impact with the valve seat at closing. The impact motion was subdivided into three temporal phases: (i) squeezing flow; (ii) elastic collision; and (iii) leaflet rebound. MHV cavitation caused by vortices was found to be initiated by the squeezing jet and/or by the transvalvular leakage jets. By using a tension wave which swept across the occluder surface immediately upon elastic impact, nuclei in the vortex core were expanded to form cavitation bubbles. CONCLUSION: Analysis of the shape and location of the cavitation bubbles permitted a better understanding of MHV cavitation mechanisms, based on the fluid dynamics of jet vortex and tension wave propagations.

Biomechanical Phenomena↗