Repair Replacement Research Articles

A single unit system with preventive maintenance and repair subject to maximum operation and repair times

The purpose of the present study is to determine reliability measures of a single-unit system considering arbitrary distributions for the random variables associated with failure time, preventive maintenance and repair times, maximum operation time, maximum repair time and replacement time. The system fails completely either directly from normal mode or via partial failure. There is a single server who visits the system immediately to do repair activities. The partially failed operating unit is shutdown after pre-specific time (called maximum operation time) for preventive maintenance. However, repair of the unit is done after its complete failure. The completely failed unit is replaced by new one if server is unable to do its repair within a maximum repair time. The unit works as new after preventive maintenance and repair. The expressions for some important measures of system effectiveness are derived using semi-Markov process and regenerative point technique. The numerical results for a particular case are obtained to depict the behavior of MTSF, availability and profit function with respect to maximum operation time for fixed values of other parameters and costs.

Controversy in mitral valve repair, resection or chordal replacement?

Mitral valve plasty has superseded valve replacement as the standard technique for treating degenerative mitral valve prolapse. Quadrangular resection is considered the gold standard for posterior leaflet prolapse. Chordal replacement was first developed to treat the anterior leaflet and subsequently became widely used for the posterior leaflet, after which a new version of posterior leaflet resection was developed that did not involve local annular plication. In the era of the mini-thoracotomy, the premeasured loop technique is simple to adopt and is as durable as quadrangular resection. However, there is controversy surrounding whether resection or chordal replacement is the optimal technique. The resection technique is curative because it removes the main pathologic lesion. The disadvantage of the resection is that it can be complicated and often requires advanced surgical skills. In contrast, chordal replacement is not pathologically curative because it leaves behind a redundant leaflet. However, the long-term results appear to be equivalent in many reports. Functionally, chordal replacement retains greater posterior leaflet motion with a lower trans-mitral pressure gradient than quadrangular resection. Moreover, chordal replacement is simple and yields uniform results. The optimal technique depends on whether the anterior leaflet or posterior leaflet is involved, the Barlow or non-Barlow disease state, and whether a mini-thoracotomy or standard sternotomy approach is used. For mitral valve repair, the most superior and reliable technique for the posterior leaflet is resection using the newer resection technique with a sternotomy approach, which requires a skilled surgeon.

Geometric process model for a system with inspections and preventive repair

In this paper, the optimal repair–replacement problem is studied for a simple repairable system whose failures are detected only by periodic inspections. When a failure of the system is detected, it will be repaired by a repairman, and the lifetimes of the system after repair are geometrically decreasing. If the system is detected to be in working state, it will be preventively repaired, and the preventive repair brings the system to the state just as that of the beginning of the working cycle. A bivariate policy (T,N) is considered, where T is the time interval between inspections while N is the number of failures at which the system is replaced. The objective is to determine the optimal bivariate policy (T∗,N∗) such that the long-run average cost rate C(T,N) is minimized. Sufficient conditions for the existence and uniqueness of the optimal policies N∗ and T∗ are derived theoretically. An algorithm is also presented to find the optimal policy (T∗,N∗). Finally, a numerical example is given to validate the developed theoretical model. Some sensitivity analysis are provided to show the influence of the varying of some parameters on the optimal policy (T∗,N∗).

Multiple ruptures of left sinus of Valsalva aneurysm into main pulmonary artery

Sinus of Valsalva aneurysm is a rare congenital glitch. We report an extremely rare case of left sinus of Valsalva aneurysm compressing and rupturing into the main pulmonary artery with 2 communications. The 34-year-old man also had severe aortic regurgitation and severe tricuspid regurgitation. He underwent successful polytetrafluoroethylene patch repair and aortic valve replacement. The rarity of this case highlights the need for a precise preoperative diagnosis, the roles of transthoracic echocardiography, transesophageal echocardiography, and 3-dimensional echocardiography, and the importance of prompt surgical management.

Probabilistic Assessment of CO<sub>2</sub> due to Concrete Repairs for Crack-Free Condition of Marine Concrete Structures

An approach which combines the Latin Hypercube technique with Crank-Nicolson based finite difference approach is developed for probabilistic assessment of chloride diffusion in concrete structures with repairs. Two random variables, i.e., surface chloride and diffusion coefficient, are considered. Four repair strategies are proposed by varying the diffusion coefficient of repair concrete and the repair depth. A repair by cover replacement is applied at a critical time which the chloride content at a threshold depth reaches its critical value for concrete cracking. The critical time is defined as the repair time, which the CO2 due to repair concrete production and replacement processing occurs. By this method, the median of repair time and the probabilistic time-dependent CO2 can be assessed. The mean and the percentiles of cumulative total CO2 are compared.

Left ventricular pseudoaneurysm following balloon mitral valvuloplasty

Balloon mitral valvotomy is a commonly performed procedure for mitral stenosis. This procedure can lead to complications such as left ventricular perforation with tamponade, mitral regurgitation and stroke. Here we report a case of left ventricular pseudoaneurysm following balloon mitral valvotomy. It was a consequence of adherent pericardium secondary to open mitral valvotomy performed earlier. It was surgically corrected by pseudoaneurysm repair and mitral valve replacement. We believe that this is the first such reported case.

Assessment of Corrosion Damage in a Finger-Type Slug Catcher

Corrosion pits of up to 6 mm depth, associated with areas of high solid deposition were discovered in the finger-type slug catcher and glycol sump during routine inspection (first in 2005 and then in 2013) following lengthy periods of below-threshold CI injection and partial implementation of the corrosion management plan. Corrosion rates were predicted to have increased from 0.46 mm/year in 2005 to 0.71 mm/year in 2007 and then decreased to 0.41 mm/year in 2008. Subsequent integrity assessments concluded that the slug catcher was not fit for continued operation at the current rate of pitting and was therefore shut down to prevent potential loss of containment. Results of API 579 fitness for service assessments of the corroded areas justified the subsequent decision to de-rate the system and that no further corrosion can be tolerated at the original design pressure, at least until the rates of corrosion and its mechanisms were fully understood. Based on the damage morphology, chemical and monitoring data and theoretical concepts, a synergy of mechanisms (under deposit corrosion, CO2 corrosion, preferential weld corrosion and microbial-induced corrosion) is identified as being responsible for the observed damage. The short-term mitigation plan is to routinely inspect the damaged locations (by UT wall thickness checks) while simultaneously implementing a corrosion management and control plan which consists of: continuous inhibitor dosing, pH stabilisation (with MEA/DEA) to above pH 6, batch biociding, sampling of residuals, chlorides, iron, SRB/GHB count, water cut, water content and pH of lean glycol, glycol content of pipeline fluid and online monitoring. The inspection, sampling and monitoring results should then be reviewed initially monthly, subsequently quarterly by the corrosion and integrity team in order to assess the rate of pitting. If the target (<0.125 mm/year) is being breached frequently, then alternative but more costly mitigation should be considered such as repair or outright replacement of the finger-type by vessel-type slug catchers which have built-in sand jetting systems designed to deal with high deposition rates and are therefore considered less prone to associated corrosion damage.

Oxidative stress and nitric oxide pathway in adult patients who are candidates for cardiac surgery: patterns and differences

We investigated whether oxidative stress and the arginine/nitric oxide pathway differ in control subjects and in adult patients who are candidates for the three most common cardiac surgical operations: coronary bypass surgery, aortic valve replacement for calcific non-rheumatic aortic stenosis or mitral valve repair for degenerative mitral insufficiency. In this prospective observational study, we studied 165 consecutive patients undergoing surgery from January to June 2011 (coronary bypass surgery, n = 63; aortic valve replacement for calcific non-rheumatic aortic stenosis, n = 51; mitral valve repair for degenerative mitral insufficiency, n = 51). Thirty-three healthy subjects with cardiovascular risk factors similar to surgery patients were also studied (Controls). Oxidative stress (the ratio of reduced and oxidized glutathione and urinary isoprostane), antioxidants (alpha- and gamma tocopherol) and factors involved in nitric oxide synthesis (arginine, symmetric and asymmetric dimethylarginine) were measured before surgery. Analysis of variance general linear models and principal component analysis were used for statistical analysis. Surgical patients had increased levels of oxidative stress and decreased levels of antioxidants. Increased levels of nitric oxide inhibitor asymmetric dimethylarginine were detected in surgical candidates, suggesting arginine/nitric oxide pathway impairment. Concerning the differences among surgical procedures, higher oxidative stress and a major imbalance of the ratio between substrate and inhibitors of nitric oxide synthesis were evidenced in patients who were candidates for mitral valve repair with respect to coronary bypass surgery patients and patients with calcific non-rheumatic aortic stenosis. Patients undergoing cardiac surgery have increased oxidative stress and a trend towards an impaired arginine/nitric oxide pathway with respect to Controls. Patients affected by mitral valve regurgitation show more pronounced perturbations in these pathways. The clinical implications of these findings need to be investigated.

A mixed integer nonlinear programming model for the optimal repair–replacement in the firm

Optimal repair–replacement problem is an important aspect of economic decision making at the firm and aggregate levels. In this paper, we extend the continuous time optimal replacement model in the firm under technological progress by considering the possibility of repairing/replacing the machines during their lifetime period. In our model, two possible decisions can be recognized by the managers in which the machines are repaired under the efficiency condition or replaced under the availability of technological progress in the firm. As a special case, we restrict the model to the more real case in which all the growth, purchase price and repair cost functions are assumed to be in the exponential form. The solvability of the model in this case is also discussed.

Surgery promotes early postoperative changes in left atrial volume and function in non-ischemic symptomatic mitral regurgitation: a three-dimensional echocardiography study

Background: Left Atrial (LA) dilation is associated with a worse prognosis in various clinical situations, including chronic Non-Ischemic Mitral Regurgitation (NIMR). Real time Three-Dimensional Echocardiography (3DE) has allowed a better assessment of LA volume and function. Although LA reverse remodeling has been observed in long-term outcome after surgery in NIMR, little is known about the behavior of LA structure and function in an early post-operative period. We aimed to analyze these aspects with 3DE. Methods: We prospectively studied 43 patients with symptomatic chronic NIMR who underwent valve repair or bioprosthetic valve replacement. LA volumes and function were analyzed before and 30 days after surgery by means of 3DE in all patients, and in a control group of 20 healthy subjects. We studied maximum, minimum and pre-atrial contraction volumes, and calculated total, passive and active LA emptying fractions. Results: Before surgery patients had higher LA volumes (p<0.001), but smaller LA emptying fractions than controls (p<0.01). After surgery, all three LA volumes reduced in both groups. Postoperative increase in active LA emptying fraction also occurred in both groups. Independent predictors of early postoperative LA reverse remodeling were diastolic blood pressure before surgery (Coefficient= - 0.004; p= 0.02), lateral mitral annulus early diastolic velocity (e') (Coefficient=0.02; p=0.008), and a mean transmitral diastolic gradient increment (Coefficient= - 0.035; p < 0.001), but not the surgical technique. Besides, e' was the only variable independently associated with the early recovery of active LA emptying fraction (OR= 1.664, P=0.027). Conclusion: LA reverse remodeling and functional improvement occur soon after surgery of symptomatic chronic NIMR patients, regardless of the surgical technique. Those changes are related to preoperative diastolic blood pressure and an echocardiographic marker of left ventricular diastolic function.

Optimisation of PM scheduling for multi-component systems – a simulated annealing approach

Proper planning of preventive maintenance (PM) is crucial in many industries such as oil transmission pipelines, automotive and food industries. A critical decision in the PM plans is to determine frequencies and types of maintenance actions in order to achieve a certain level of system availability with a minimum total cost. In this paper, we consider the problem of obtaining availability-based non-periodic optimal PM planning for systems with deteriorating components. The objective is to sustain a certain level of availability with the minimal total maintenance-related costs. In the proposed approach, the planning horizon is divided into some inspection periods of equal intervals. For any given interval, a decision must be made to perform one of the three actions on each component; inspection, preventive repair and preventive replacement. Any of these activities has different effects on the reliability of the components and the corresponding distinct costs based on the required recourses. The cost function includes the cost for repair, replacement, system downtime and random failures. System availability and PM resources are the main constraints considered. Since the proposed model is combinatorial in nature involving non-linear decision variables, a simulated annealing algorithm is employed to provide good solutions within a reasonable time.

Composite Three‐Dimensional Woven Scaffolds with Interpenetrating Network Hydrogels to Create Functional Synthetic Articular Cartilage

The development of synthetic biomaterials that possess mechanical properties that mimic those of native tissues remains an important challenge to the field of materials. In particular, articular cartilage is a complex nonlinear, viscoelastic, and anisotropic material that exhibits a very low coefficient of friction, allowing it to withstand millions of cycles of joint loading over decades of wear. Here we show that a three-dimensionally woven fiber scaffold that is infiltrated with an interpenetrating network hydrogel can provide a functional biomaterial that provides the load-bearing and tribological properties of native cartilage. An interpenetrating dual-network "tough-gel" consisting of alginate and polyacrylamide was infused into a porous three-dimensionally woven poly(ε-caprolactone) fiber scaffold, providing a versatile fiber-reinforced composite structure as a potential acellular or cell-based replacement for cartilage repair.

Left ventricular outflow tract obstruction after mitral valve repair treated with alcohol septal ablation

Left ventricular outflow tract (LVOT) obstruction due to systolic anterior motion of the mitral valve (SAM) occurs in 4-5% of patients after mitral valve repair. If conservative treatment is unsuccessful, reoperation is indicated. Treatment options include repeated mitral valve repair or valve replacement and septal myectomy if hypertrophy is present. We report a case of a patient with pre-operatively undiagnosed hypertrophic cardiomyopathy who suffered from progressive dyspnea post-operation due to severe LVOT obstruction with SAM. This case was successfully treated with catheter-based alcohol septal ablation.

Prognostic value of preoperative B-type natriuretic peptide in aortic valve replacement, mitral valve repair and mitral valve replacement

Prognostic value of preoperative B-type natriuretic peptide in aortic valve replacement, mitral valve repair and mitral valve replacement

Large aortic root pseudoaneurysm occurring late after aortic root repair and valve replacement for endocarditis

A 68-year-old male presented with Group B Streptococcus aortic valve (AV) endocarditis with aortic root abscess and refractory sepsis. An emergency cardiac surgery was performed with root abscess drainage, excision and debridement of necrotic tissue, reconstruction of annulus, and AV replacement. Fifteen months later he presented with a huge aortic root pseudoaneurysm (PA). This case illustrates late occurrence of aortic root PA following AV surgery for endocarditis.

Tracheal tissue engineering: building on a strong foundation

Evaluation of: Elliott MJ, De Coppi P, Speggiorin S et al. Stem-cell-based, tissue engineered tracheal replacement in a child: a 2-year follow-up study. Lancet 380 (9846) 994–1000 (2012).Tissue-engineered tracheal transplants may offer a treatment strategy to address advanced structural disorders of the large airway. The approach aims to offer an alternative to the typically applied slide tracheoplasty, which can lead to stent erosion or even death. Laryngotracheal agenesis or severe stenosis can be fatal for developing fetuses and often leads to the decision to terminate the pregnancy. A tissue-engineered, autologous (stem) cell-seeded construct might be a promising option for children, as this alternative surgical replacement strategy has been successfully used in clinics for bladder repair and tracheal replacement in adults. In the reviewed 2-year follow-up study, Elliott and colleagues implanted an allogeneic, decellularized trachea that was supported with an absorbable polydioxanone stent, which was saturated with an autologous, bone marrow-derived stem cell mixture prior to implantation into a pediatric patient.

Mitral Regurgitation and Coronary Artery Bypass Surgery: Comparison of Mitral Valve Repair and Replacement

Background : The aim of this retrospective study was to determine if there is a statistically significant difference (p < 0.05) between mitral valve repair (MVRp) with concomitant surgical revascularization of the myocardium (CABG) and mitral valve replacement (MVR) with concomitant CABG, considering the duration of surgery, early postoperative morbidity, in-hospital mortality, length of stay in the Intensive Care Unit (ICU) and overall in-hospital stay. Methods : Between January 1st 2006 and December 31st 2008, 75 patients underwent surgery for mitral regurgitation and ischemic heart disease. Patients were divided in two groups determined by the procedure that was performed on the mitral valve (MVRp + CABG group had 34 patients, MVR + CABG group had 41 patients). All the patients were operated by the same surgical team and received the usual anaesthesia protocol.Results : Patients in the MVR + CABG group had statistically significant higher EuroSCORE risk levels, higher NYHA status and higher incidence of postoperative low cardiac output syndrome (LCOS). Neurological complications showed statistically significant higher incidence in the MVRp + CABG group. There was no statistically significant difference in regard to in-hospital mortality between these two groups. Patients in the MVR + CABG group had statistically significant longer in-hospital stay.Conclusions : Mitral valve repair and mitral valve replacement are complementary methods considering early postoperative morbidity and mortality. Higher incidence of LCOS and in-hospital stay in the MVR + CABG group was to be expected on behalf of poorer preoperative status.

Optimal repair–replacement policies for a system with two types of failures

In this paper, the optimal replacement problem is investigated for a system with two types of failures. One type of failure is repairable, which is conducted by a repairman when it occurs, and the other is unrepairable, which leads to a replacement of the system at once. The repair of the system is not “as good as new”. The consecutive operating times of the system after repair form a decreasing geometric process, while the repair times after failure are assumed to be independent and identically distributed. Replacement policy N is adopted, where N is the number of repairable failures. The system will be replaced at the Nth repairable failure or at the unrepairable failure, whichever occurs first. Two replacement models are considered, one is based on the limiting availability and the other based on the long-run average cost rate of the system. We give the explicit expressions for the limiting availability and the long-run average cost rate of the system under policy N, respectively. By maximizing the limiting availability A(N) and minimizing the long-run average cost rate C(N), we theoretically obtain the optimal replacement policies N∗ in both cases. Finally, some numerical simulations are presented to verify the theoretical results.

Optimal post-warranty maintenance policy with repair time threshold for minimal repair

In this paper, we consider a renewable minimal repair–replacement warranty policy and propose an optimal maintenance model after the warranty is expired. Such model adopts the repair time threshold during the warranty period and follows with a certain type of system maintenance policy during the post-warranty period. As for the criteria for optimality, we utilize the expected cost rate per unit time during the life cycle of the system, which has been frequently used in many existing maintenance models. Based on the cost structure defined for each failure of the system, we formulate the expected cost rate during the life cycle of the system, assuming that a renewable minimal repair–replacement warranty policy with the repair time threshold is provided to the user during the warranty period. Once the warranty is expired, the maintenance of the system is the user's sole responsibility. The life cycle of the system is defined on the perspective of the user and the expected cost rate per unit time is derived in this context. We obtain the optimal maintenance policy during the maintenance period following the expiration of the warranty period by minimizing such a cost rate. Numerical examples using actual failure data are presented to exemplify the applicability of the methodologies proposed in this paper.

Ruptured sinus of Valsalva aneurysm: 10-year Indian surgical experience

Sinus of Valsalva aneurysm is a rare anomaly with a higher incidence in Eastern than Western populations. Recent improvements in diagnostic techniques have resulted in more patients undergoing surgical repair. Uncorrected, the intracardiac shunts and frequently associated cardiac lesions cause a preventable deterioration in heart function. We retrospectively analyzed the data of 33 patients who underwent repair of ruptured sinus of Valsalva aneurysm from May 2000 to January 2010. The aneurysms originated from the right coronary sinus in 24 patients and from the noncoronary sinus in 9, and ruptured into the right ventricle in 21, right atrium in 10, and left ventricle in 2. Operative procedures included simple plication (1), patch repair (32), and aortic valve replacement (10). There were 3 early deaths. The 30 survivors were followed up for 5.4 ± 2.6 years; all had an improvement in functional class, with superior results in those with no aortic regurgitation. Surgical treatment of ruptured sinus of Valsalva aneurysm has an acceptably low operative risk and good long-term symptom-freedom survival. An early aggressive approach is recommended to prevent worsening symptoms and more extensive disease.