M-mode and two-dimensional echocardiography of heart valve prosthesis dysfunction

The diagnostic efficacy of M-Mode and 2-d echocardiography for the detection of malfunctioning prosthetic valves was studied in twenty-nine patients with prosthetic valves and clinical deterioration. Echocaradiographic abnormalities were found in 8 of 12 patients with confirmed valve dysfunction; 30.8% of the cases had false negative echo tracings. In 17 patients with normal echocardiographic pictures of the valves another cause of clinical deterioration was found (congestive heart failure, pericardial effusion, aneurysm of aortic root). In this study M-Mode and 2-d echocardiography had an excellent diagnostic accuracy rate in distinguishing congestive heart failure from valve dysfunction. Comparing the data of M-Mode and 2-d registration, both methods are found to be complementary. A major advantage of the 2-d echocardiography is its enhanced spatial orientation, whereas M-Mode echocardiography enables better evaluation of valve movements and corresponding time intervals and recognition of quick movements and fibrillations.     

Sustained-release naltrexone for alcoholism treatment: a preliminary study

OBJECTIVES: To evaluate midterm results of mechanical valves in pulmonary position in patients with pulmonary regurgitation and right ventricular dysfunction as an alternative to bioprostheses. PATIENTS: Mechanical valves (six tilting disc valves and two bileaflet valves) were implanted in eight patients previously operated on for tetralogy of Fallot (n = 7) and truncus arteriosus (n = 1), with severe right ventricular dysfunction caused by massive pulmonary regurgitation. RESULTS: All patients survived prosthesis implantation and are currently well. At follow-up (3 months to 9 years), they do not show signs of valve failure, and right ventricular function has dramatically improved in all but one, who still shows moderate ventricular hypokinesia. CONCLUSION: After operative correction of congenital heart defects in selected patients who show severe dysfunction of the right ventricle caused by pulmonary regurgitation/stenosis, mechanical valves may represent an alternative to bioprosthetic valves. The selection of the valve type is still a matter of debate. However, according to literature data, complications seem to have occurred only in patients with bileaflet mechanical valves in the pulmonary position, whereas no thromboembolic episodes or valve failure is reported in subjects with tilting disc valves in the right ventricular outflow. Tilting disc valves might perform better in the right ventricular outflow than bileaflet valves.     

A comparison of outcomes in men 11 years after heart-valve replacement with a mechanical valve or bioprosthesis. Veterans Affairs Cooperative Study on Valvular Heart Disease

BACKGROUND: Mechanical heart valves are durable but thrombogenic, and their use requires that the patient receive anticoagulants. In contrast, bioprosthetic valves are less thrombogenic, but they have limited durability because of tissue deterioration. METHODS: To compare the outcomes of patients who receive these two types of valves, we randomly assigned 575 men scheduled to undergo aortic-valve or mitral-valve replacement to receive either a mechanical or a bioprosthetic valve. The primary end points were death from any cause and any valve-related complication. RESULTS: During an average follow-up of 11 years, there was no difference between the two groups in the probability of death from any cause (11-year probability for mechanical valves, 0.57; for bioprostheses, 0.62; P = 0.57) or in the probability of any valve-related complication (0.65 and 0.69, respectively; P = 0.39). There was a much higher rate of structural valve failure among patients who received bioprosthetic valves (11-year probability, 0.15 for the aortic valves and 0.36 for the mitral valves) than among those who received mechanical valves (no valve failures; P < 0.001). However, this difference was offset by a higher rate of bleeding complications among patients with mechanical valves than among those with bioprosthetic valves (11-year probability, 0.42 and 0.26, respectively; P < 0.001) and by a greater frequency of peri-prosthetic valvular regurgitation among patients with mechanical mitral valves than among those with mitral bioprostheses (11-year probability, 0.17 and 0.09, respectively; P = 0.05). CONCLUSIONS: After 11 years, the rates of survival and freedom from all valve-related complications were similar for patients who received mechanical heart valves and those who received bioprosthetic heart valves. However, structural failure was observed only with the bioprosthetic valves, whereas bleeding complications were more frequent among patients who received mechanical valves.     

Algorithm for Automatic Detection of Topological Changes in Water Distribution Networks

Topological and pressure-driven analyses are an integral part of reliability/risk considerations for a water distribution system. For example, it is often necessary to identify which parts of the distribution network are isolated from water sources after the valves have been closed in response to a mechanical pipe failure. Pressure-driven analysis is then necessary to ascertain the consequences of pipe failures in terms of the performance of the functioning subsystem while pipe breaks are being fixed in the isolated area. Therefore, it is extremely useful to have an algorithm for the automatic identification of nodes/pipes disconnected from the water source(s). However, this is a complex problem because valves sometimes significantly modify the network topology. Furthermore, the use of isolation valves can cause a demand shortage to some customers (due to pressure reduction) during the abnormal operating conditions in the system. Thus, pressure-driven simulation of the network behavior is required. For these reasons, a novel algorithm capable of automatic detection of topological network changes is coupled with a robust pressure-driven simulation model. This algorithm is tested on two case studies involving a small artificial water distribution system and a larger, real-life network. The results obtained clearly demonstrate the robustness of the algorithm developed.     

Porcine aortic leaflet arrangement may contribute to clinical xenograft failure

Clinical experience with the first generation porcine xenograft shows significant deterioration and mechanical failure after 7-8 years post-implantation. Although many mechanisms of valve failure have been identified, the inherent differences between porcine and human aortic valves have not been emphasized. To determine if these differences are significant, the authors studied the anatomy of the aortic valve in 10 post-mortem porcine hearts. The authors found that the non-coronary leaflet was the smallest and the right leaflet was the largest based on the dimensions of area, perimeter, weight, and attached edge length (p < 0.05). These results differ from reported analyses of human aortic valves, in which the smallest cusp is generally the right the largest is the non-coronary. The authors believe that these differences between the human and porcine aortic valves may result in atypical mechanical stresses and the disruption of blood flow patterns in the sinuses of Valsalva, and may decrease the long-term stability of the porcine bioprostheses. In other words, the failure found with porcine bioprostheses after 8 years of implantation might be expected from the inherent structure (and associated fluid dynamics) of the porcine aortic valve positioned in the human aortic root.     

Evaluation of prosthetic valve function and associated complications

Significant advances in imaging modalities have occurred to evaluate prosthetic valve function and associated complications. These developments involve predominantly the introduction of Doppler technology for the non-invasive determination of gradients and valve areas and TEE for an improved assessment of valve structure, function, and associated complications. The current role of cinefluoroscopy is mostly to complement TEE in the evaluation of motion of mechanical prosthetic valves in the aortic position. Cardiac catheterization is now rarely needed to assess valve function. Diagnosis of prosthetic valve obstruction can be performed in the majority of cases with transthoracic Doppler echocardiography. Differentiation of valve obstruction from normal valve function in small valves with high flow conditions, however, may be difficult. Because of this and the variability in normal valves among different prostheses, knowledge of the type and size of the implanted valve is essential. Patients and ultrasound laboratories are encouraged to seek and provide this information on a routine basis. Although transthoracic echocardiography is the main diagnostic modality for the serial evaluation of prosthetic valve function, it is important to recognize its limitations in assessing prosthetic mitral regurgitation and evaluating structural abnormalities of prosthetic valves. These are the situations in which TEE has the most impact. A summary of general indications of TEE in prosthetic valves is provided in Table 6. Finally, a baseline transthoracic Doppler study is essential in the overall follow-up and serial evaluation of valve function. For future comparisons, the best indices of valve functions are those obtained for patients as their own control, from a baseline Doppler echocardiographic study performed early after the operation.     

宝钢5m厚板厂精轧机伺服阀频繁更换原因分析及对策

目前伺服阀作为精密的电液转换元件,被广泛用于轧机上需要高控制精度和高响应速度的轧钢设备上。由于整个伺服系统包括液压执行元件、液压控制部分、电控和测量反馈部分等,所以出现故障时较难排查,特别是液压控制部分伺服阀出现问题难以判定,往往通过更换伺服阀备件解决,有时会产生误判。为此,针对宝钢厚板厂精轧机伺服阀出现故障的原因进行了分析,认为提高液压油的清洁度、增加伺服阀阀芯位置监控是延长伺服阀使用寿命、正确判定伺服阀性能的基础。通过落实改进措施,取得了良好的效果。     

Comparative study of in vitro flow characteristics between a human aortic valve and a designed aortic valve and six corresponding types of prosthetic heart valves

A model of a pulsatile cardiovascular system is described including an electronic control, a hydraulic driving unit, a volume storage, a peripheral resistance and measuring equipment. Six different artificial heart valves, a designed aortic valve (Aachen pockett valve II) and a human aortic valve have been tested in the outflow position of the pump. Three of them are presently being used in clinical applications. Measurements of pressure and volume flow have been obtained for different frequencies n, pump volumes Vp and time ratios between pressure and suction phase. From the experimental results a comparative evaluation was deducted for different working conditions. In comparison to natural human aortic valve (NK) large volume flow is verified by the Aachen pocket valve II (AT), the Gott-Dagget value (GD), the Starr-Edwards valve (SE) and the Lillehei-Kaster valve (LK). The Gott-Daggett valve has the smallest back flow volume. The Smeloff-Cutter and in particular the Wada-Cutter valve have the largest regurgitation. This is to be expected since the Cutter valves are purposely so designed that they do not close tightly in order to avoid blood sedimentation. The human aortic valve, the Gott-Daggett valve and the Aachen pocket valve demonstrate the most favourable opening-closing characteristics. The human aortic valve achieves a negligible pressure loss, followed by the Bj?rk-Shiley and the Lillehei-Kaster valve.     

A videofluoroscopic comparison of straw and cup drinking: the potential influence on dental erosion

Tracheostoma valves are often required in the rehabilitation process of speech after total laryngectomy. Patients are thus able to speak without using their hands to close the tracheostoma. The improved Groningen tracheostoma valve consists of a "cough" valve with an integrated ("speech") valve, which closes for phonation. The cough valve opens as the result of pressure produced by the lungs during a cough. The speech valve closes by the airflow produced by the lungs, thus directing air from the lungs into the esophagus at a deliberately chosen moment. An experimental setup with a computer-based acquisition program was developed to measure the pressure at which the cough valve opened and the flow at which the speech valve closed. In addition, the airflow resistance coefficient of the tracheostoma valve was defined and measured with an open speech valve. Both dry air from a cylinder and humid expired air were used. Results showed a pressure range of 1-7 kPa to open the cough valve and a flow range of 1.2-2.7 l/s to close the speech valve. These values were readily attained during speech, while the flow range occurred above values reached in quiet breathing. The device appeared to function well in physiological ranges and was optimally adjustable to an individual setting. No significant differences were measured between air from a cylinder and humid expired air. Findings showed that methods used to obtain results could be employed as a reference method for comparing aerodynamic characteristics of tracheostoma valves.     

Risk of reoperative valve replacement for failed mitral and aortic bioprostheses

BACKGROUND: One factor influencing the choice of mechanical versus bioprosthetic valves is reoperation for bioprosthetic valve failure. To define its operative risk, we reviewed our results with valve reoperation for bioprosthetic valve failure. METHODS: Records of 400 consecutive patients having reoperative mitral, aortic, or mitral and aortic bioprosthetic valve replacement from January 1985 to March 1997 were reviewed. RESULTS: Reoperations were for failed bioprosthetic mitral valves in 219 patients, failed aortic valves in 153 patients, and failed aortic and mitral valves in 28 patients. Including 26 operations (6%) for acute endocarditis, 153 operations (38%) were nonelective. One hundred nine patients (27%) had other valves repaired or replaced, and 72 (18%) had coronary bypass grafting. The incidence of death in the mitral, aortic, and double-valve groups was respectively, 15 (6.8%), 12 (7.8%), and 4 (14.3%); and the incidence of prolonged postoperative hospital stay (>14 days) was, respectively, 57 (26.0%), 41 (26.8%), and 8 (28.6%). Only 7 of 147 patients (4.8%) having elective, isolated, first-time valve reoperation died. Multivariable predictors (p < 0.05) of hospital death were age greater than 65 years, male sex, renal insufficiency, and nonelective operation; and predictors of prolonged stay were acute endocarditis, renal insufficiency, any concurrent cardiac operation, and elevated pulmonary artery systolic pressure. CONCLUSIONS: Reoperative bioprosthetic valve replacement can be performed with acceptable mortality and hospital stay. The best results are achieved with elective valve replacement, without concurrent cardiac procedures.     

3D‐FE Modelling and Simulation of Multi‐way Loading Process for Multi‐ported Valves

Multi‐ported valves are widely used in the marine, sanitary, petrochemical and power industry. Multi‐way loading forming technology provides an efficient approach for integral forming of high strength multi‐ported valves, such as tee pipe coupling, high‐pressure cross valves, large‐scale complex valves, and so on. Since the multi‐way loading process is a very complicated plastic forming process due to the complexity of loading path, finite element numerical simulation is adopted to investigate the multi‐way loading process in order to predict and control the multi‐ported valve forming process. A reasonable model of the process is developed under DFEORM‐3D environment based on the coupled thermo‐mechanical finite element method. Then the reliability of the model is validated with respect to geometry development and forming defects. Numerical simulations of multi‐way loading forming for a tee valve and a cross valve have been carried out via using the developed model. Further, the forming processes of tee valve and cross valve have been compared. Moreover, the modelling method is also suitable for multi‐way loading processes of other complex components.     

Allograft heart valve viability and valve-processing variables

BACKGROUND: The impact of allograft valve viability on valve durability remains controversial. Analyses of our clinical results have demonstrated the superiority of the cryopreserved valve viable at the time of implantation over the 4 degrees C stored valve nonviable at the time of implantation. In this study, we quantitatively assessed the effects on viability of current and past valve-processing protocols at The Prince Charles Hospital. METHODS: The viability of pulmonary valves was quantitatively analyzed by thin-layer autoradiography to assess the effects of donor type, antibiotics, and valve storage. RESULTS: Control valve segments obtained from beating-heart donor valves had a higher initial viability (0.92+/-0.02) than nonbeating-heart donor valves (0.66+/-0.03). Cryopreservation after low-dose antibiotic sterilization significantly reduced viability to 50% to 60% of the control, and in the presence of amphotericin B, viability dropped further to 10% to 36% of the control. After 7 days' storage at 4 degrees C, viability was reduced to 2% of control and to 0% viability after 21 days. CONCLUSIONS: For maximal preimplantation viability, valves should be procured as soon as possible after cessation of heart beat and should be cryopreserved if they are not to be clinically implanted within 1 to 2 days. Amphotericin B should not be used in conjunction with cryopreservation if viability is to be maximized.     

Prospects of glutamate antagonists in the therapy of Parkinson''s disease

BACKGROUND AND AIMS OF THE STUDY: Several different biological, bioprosthetic and mechanical devices are available for heart valve replacement. We present a quantitative methodology to estimate the (event-free) life-expectancy and lifetime risk of valve-related events for individual patients after implantation of any one of these valve types. METHODS: We modelled the age-dependent prognosis of a patient after aortic valve replacement with a discrete-time Markov model and Monte-Carlo simulation to estimate (event-free) life-expectancy and life-time risk of valve-related events, respectively. Quantitative estimates to parameterize these models used hypothetical devices and presumed data were based on a limited review of published literature. RESULTS: This decision-analytical approach allowed an estimation of the overall and event-free life-expectancy as well as the lifetime risk of valve-related events after implantation of different types of prosthetic heart valve in the aortic position. In the current, hypothetical model, one valve type excelled for all age groups in terms of life expectancy and life-time risk of valve-related events. The choice of the second-best alternative varied according to patient age and comorbidity. Sensitivity analyses showed results to be especially dependent on the durability of the replacement valve and surgical risk. CONCLUSIONS: This methodological approach is very flexible, and its quantitative results may guide decision making, if increasing quantitative information on heart valve prosthesis performance becomes available in future. Markov models and Monte Carlo simulation may be used to obtain a better understanding of the effect that different types of prosthetic heart valves have on patient prognosis, while quantitative results may help cardiologists and cardiac surgeons to choose a specific valve type for an individual patient.     

Complement activation is involved in the structural deterioration of bovine pericardial bioprosthetic heart valves

Disintegrated collagen fibers surrounded with protein deposits are a morphologic feature in torn, folded, and disrupted cusps of pericardial prostheses explanted for clinical dysfunction. New technologies for valve bioprostheses with improved durability require further investigation of molecular mechanisms initiating the deterioration of bioprosthetic valves. The authors' aim was to obtain experimental evidence of biologic factors contributing to the degradation of the bioprosthetic matrix. Clinically failed Mitroflow (22), Hancock (3), Ionescu-Shiley (2), and Sorin (1) valves were explanted after 69-170 months. Non calcific deterioration of the prosthetic matrix was studied with labeled antibodies to plasma proteins and cells. IgG, and complement proteins C1q, C3, and C4 were accumulated close to dissociated collagen bundles (26/28) throughout the prostheses. Fibrin was identified on the cuspal surface and in the deep disrupted areas. The fibrin peptides and proteolytic breakdown products of the complement components, the latter consistent with complement activation and chemotaxis for monocytes, were shown by immunoenzymic assay on Western blots from the valve extracts. The complement activation triggered by the IgG aggregates generates bioactive peptide signals that can activate macrophages (22/28) and neutrophil granulocyte elastase (22/24) able to cooperate with the mechanical stress in the breakdown of the chemically processed, non hemocompatible, and non-self macromolecular matrix.     

Outcome analysis of 245 CarboMedics and St. Jude valves implanted at the same institution

BACKGROUND: Thromboembolism and valve-related death are major complications associated with prosthetic valve implants, but it is difficult to evaluate the relative incidence of these complications based on studies in which the implantation of only one valve is reported from any given institution. We therefore report the outcome of patients implanted at our institution during the same time period with either the recently released CarboMedics (CM) or the St. Jude Medical (SJ) valve prostheses. METHODS: Between October 1994 and January 1996, 245 consecutive patients received either SJ (116 patients) or CM (129 patients) valves at our institution. Follow up of these patients was 99.6% complete, for a total of 318.5 cumulative patient-years (median follow-up, 1.4 years). RESULTS: The 30-day mortality rates for SJ and CM implants were 3.4% and 3.1%, respectively. Actuarial survival and freedom from valve related mortality rates at 1.5 years for SJ and CM valves were 94%+/-2% versus 86%+/-3% (p = 0.03) and 100% versus 94%+/-2% (p = 0.005), respectively. There was no structural valve failure for either implant, but there were five thrombosed valves in the CM group and none in the SJ group (p = 0.04). All thrombosed valves were mitral (four mitral valve replacement, one aortic and mitral valve replacement). Two of the thrombosed valves were successfully explanted, whereas the three remaining patients died. Freedom from a thromboembolic event in the mitral position at 1.5 years, including thrombosed valves was 97%+/-3% and 83%+/-5% for SJ and CM valves, respectively (p = 0.04). CONCLUSIONS: The results of this study suggest that further evaluation of thromboembolic outcomes after CM compared with SJ valve implantation is warranted.     

Prosthetic heart valve thrombosis: a 3-year experience

A series of 12 patients with 16 episodes of prosthetic heart-valve thrombosis over 3 years is presented. Most episodes affected mitral or tricuspid bileaflet prostheses. All patients were inadequately anticoagulated at the time of thrombosis. The clinical presentation was acute and severe in 6 patients, and subacute or chronic in the rest. Physical examination was suggestive of stuck valves in most cases. Transthoracic echocardiography revealed increased transvalvular gradients in most. However, clearer evidence of valve thrombosis was obtained from transesophageal echocardiography or fluoroscopy. 9 patients eventually had their valves re-replaced successfully, and the preoperative diagnosis was confirmed in all. 5 patients were operated as soon as the diagnosis was established. and an additional 4 were operated after failure of anticoagulation. In 4 patients the valve leaflets became completely mobile after a course of thrombolysis. Prosthetic valve thrombosis is a severe and potentially fatal complication in patients with mechanical heart valves. Alertness of physicians at all levels- the general practitioner, the internist and the cardiologist- to the possibility of valve thrombosis and to its clinical presentation may lead to prompt and earlier diagnosis and to comprehensive therapy.     

Objectives of high blood pressure treatment: left ventricular hypertrophy, diastolic function, and coronary reserve

The authors report the cases of two patients admitted to hospital for investigation of haemolytic anaemia. Both had undergone, 10 and 12 years previously, mitral valve replacement with a Ionescu-Shiley bioprosthesis. In both cases, in the absence of signs of cardiac failure, Doppler echocardiography showed mitral regurgitation. The association of haemolytic anaemia and dysfunction of the bioprosthesis led to redux valve replacement and correction of the anaemia. Haemolytic anaemia was the presenting sign of bioprosthetic valve dysfunction requiring replacement of the prosthesis. This complication is common with mechanical valve prostheses but much more rare in bioprosthetic valves.     

轧钢加热炉故障检测与诊断方法研究

基于多元统计投影技术(如主元分析、PCA)，连续生产过程故障检测与诊断研究已经得到了学术界和工业界的广泛重视。针对轧钢加热炉这类典型的工业生产过程，运用多元统计投影技术进行了故障检测与诊断的研究。在建立过程主元模型的基础上，对单故障源和多故障源两类问题进行了研究。结果表明，该方法对过程故障能实现有效的检测与诊断。     

Randomized trial of cerebrospinal fluid shunt valve design in pediatric hydrocephalus

OBJECTIVE: Forty percent of standard cerebrospinal fluid shunts implanted for the treatment of pediatric hydrocephalus fail within the first year. Two new shunt valves designed to limit excess flow, particularly in upright positions, were studied to compare treatment failure rates with those for standard differential-pressure valves. METHODS: Three hundred-forty-four hydrocephalic children (age, birth to 18 yr) undergoing their first cerebrospinal fluid shunt insertion were randomized at 12 North American or European pediatric neurosurgical centers. Patients received one of three valves, i.e., a standard differential-pressure valve; a Delta valve (Medtronic PS Medical, Goleta, CA), which contains a siphon-control component designed to reduce siphoning in upright positions; or an Orbis-Sigma valve (Cordis, Miami, FL), with a variable-resistance, flow-limiting component. Patients were monitored for a minimum of 1 year. Endpoints were defined as shunt failure resulting from shunt obstruction, overdrainage, loculations of the cerebral ventricles, or infection. Outcome events were assessed by blinded independent case review. RESULTS: One hundred-fifty patients reached an endpoint; shunt obstruction occurred in 108 (31.4%), overdrainage in 12 (3.5%), loculated ventricles in 2 (0.6%), and infection in 28 (8.1%). Sixty-one percent were shunt failure-free at 1 year and 47% at 2 years, with a median shunt failure-free duration of 656 days. There was no difference in shunt failure-free duration among the three valves (P = 0.24). CONCLUSION: Cerebrospinal fluid shunt failure, predominantly from shunt obstruction and infection, remains a persistent problem in pediatric hydrocephalus. Two new valve designs did not significantly affect shunt failure rates.     

Results of heart valve replacement: especially on the selection criteria for valve prostheses and on a new anticoagulation regimen

Since March 1981 till the end of 1987, a total of 76 artificial heart valves were implanted in 72 patients. Heart valve prostheses were selected individually according to the patient's needs rather than assigning a single model to every patient. Postoperatively patients were placed on an anticoagulation therapy regimen consisting of reduced-dose warfarin (prothrombin time maintained at 30% of the control) and a small dose (81 mg/day) aspirin. During this period no bioprosthesis was implanted. For aortic valves, Starr-Edwards caged-ball valves were used in 53.1% and St. Jude Medical (SJM) valves in 37.5%. For mitral valves, SJM valves were used in 68%. No mechanical valve failure and no thrombosed valve was encountered. There was one patient-prosthesis missmatch. The incidence of thromboembolism for the entire series was 5/181.2 patient-years. There was 1-2/181.2 patient-years incidence of hemorrhagic complications. These figures were comparable to the ones with conventional warfarin therapy. No intracranial hemorrhage was encountered. Our selection criteria for artificial heart valves and our method of anticoagulation were discussed in detail. We conclude that at present there is no single prosthesis which satisfies all the varying needs of every patient, and the prosthesis which is best suited to that particular patient should be selected. We are generally happy with our current method of postoperative anticoagulation and will continue with this regimen.