摘要:

Defining and assessing the performance of heart valve replacement devices is difficult. This article is a brief discussion of the problems and present state of the art.

ISSN:0309-1902    

DOI:10.3109/03091909209021949

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Since 1981, the Department of Medical Physics and Clinical Engineering at the University of Sheffield has been responsible for the organization, management and data collection associated with the largest multicentre heart valve implant patient follow up study in the Western world. At the present time, the database comprises information on over 16,000 valve implants, which have been provided by 57 surgeons working at 22 centres in the UK. All this data is available for in-depth statistical analysis. Over 30 individual valve models presently are included in the Study and these can be categorized into five main types: ball, disc, porcine, pericardial and homograft. Analysis includes descriptive statistics as well as valuable information on the various performances of the different valves. Survival and event-free survival graphs are obtained by actuarial methods and individual valve types can be studied in depth in terms of freedom from thromboembolic complications and valve dysfunction. Whilst this approach provides interesting and valuable survival data, it does not take account of the wide variation in prognostic factors which occur within large groups of patients. This latter problem can be addressed by the use of proportional hazards analysis and this paper provides details of this approach and typical results obtained from the use of this method. These include the comparative performances of the major types of valves currently in use in terms of the event-free survival of the patients.

ISSN:0309-1902    

DOI:10.3109/03091909209021950

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

The Laboratory of Biomedical Engineering (of the National Health Institute, technical body of the Italian Health Service) performsin vitro testing of prosthetic heart valves for mechanical characteristics of materials, fatigue life, and fluidodynamic performance. Testing of materials is directed towards the physico mechanical characterization of the structural components of the valves, e.g. elasticity and resistance to stress of biological tissues and stents. Long-term fatigue life tests are conducted by means of systems which make valves beat at more than 1200 cycles/min. These tests are preceded and followed by geometrical characterization and by steady flow testing in order to obtain information about stenosis and leakage. Special attention is devoted to pulsatile flow testing which is performed on two pulse duplicators: the Dynalek system and the system developed by the University of Sheffield. The same valve was tested with these systems according to their different possible set-ups within the general requirements established by ISO-DIS 5840. This paper presents significant measurements, taking into account their dependence on the systems adopted. Results show (a) the difficulties in comparing test results because of different operating conditions, and (b) the systems' sensitivity with regards to some parameters which affect measurements under comparable set-up conditions (FDA Interlaboratory Comparison Testing Protocol).

ISSN:0309-1902    

DOI:10.3109/03091909209021951

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

The advent of high-quality ultrasound technology has made the assessment of prosthetic valve function quicker, easier, and more accurate than ever before. By using cross-sectional imaging, colour flow mapping, and spectral Doppler techniques from both the precordium and the oesophagus, it is possible to assess a prosthetic valve fully. Cardiac catheterization with its attendant risks can be avoided. Echocardiography gives detailed morphological information, and it can be used for routine serial follow-up of individual patients. Using the patient as his or her own control avoids the problems caused by poorly-defined‘normal ranges’for prosthetic function.

ISSN:0309-1902    

DOI:10.3109/03091909209021952

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

It is essential that the factors leading to bioprosthelic valve dysfunction are fully understood if a more durable bioprosthesis is to be developed and the incidence of premature failure reduced. Studies of explanted bioprostheses yield important information on both the aetiology of valve failure and influence of valve/host interactions. Details are given of the Sheffield Explant Study which holds data on 570 explants and 34 different models. Advantages and disadvantages of this type of study are discussed.

ISSN:0309-1902    

DOI:10.3109/03091909209021953

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

To increase durability and decrease calcification tendencies, the reduction of mechanical leaflet stress is of prime importance. In order to achieve this for a three-leaflet valve, the leaflets of a new design of prosthesis (the J-3) are manufacutred in a medium open, almost flat shaped position, whereby the stent posts are expanded by a cone-shaped mold. Owing to this design, the leaflets have stable closed and open positions, the transition succeeds with low opening pressure. Valves are manufactured by dip-coating in polyurethane. Hydrodynamic evaluation of this polyurethane valve shows minimum pressure drop and very low energy losses compared with other commercially available valves. Very low shear stresses in the flow field downstream of the valve are observed by laser-Doppler-anemometry. In durability tests, prototypes have reached lifetimes equivalent to 17 years. For comparative testing of durability and biocompatibility, six bioprostheses and seven J-3 valves were implanted in mitral position of growing Jersey calves. While animal tests are encouraging, they also reveal necessary manufacturing improvements.

ISSN:0309-1902    

DOI:10.3109/03091909209021954

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Allograft heart valves have been used for over 30 years. During the first decades of use, the research and clinical objectives were to find a means for long-stem storage of tissue. Methods such as irradiation, glutaraldehyde fixation, long-term antibiotic storage at 4°C and other methods were common. These methods, however, were found to give reduced long-term clinical performance when compared with viable fresh tissue or tissue which had been cryopreserved. Recognizing this fact, more recent emphasis has been to address issues surrounding means by which allografts can be cryopreserved and thawed to retain maximum viability. An additional concern was to find a means to maximize donor retrieval by salvaging tissue which normally would be discarded because of bacterial contamination. This study demonstrates that when a proper cryopreservation technique is used, with stringent antibiotic treatments, biomechanical parameters remain normal with only a slight decrease in cell viability.

ISSN:0309-1902    

DOI:10.3109/03091909209021955

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0309-1902    

DOI:10.3109/03091909209021956

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0309-1902    

DOI:10.3109/03091909209021957

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0309-1902    

DOI:10.3109/03091909209021958

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor