Minimal Repair Research Articles

Prevalence of comorbidities in a surgical pectus excavatum population.

BackgroundPectus excavatum is the most common chest wall deformity and is associated to various connective tissue, cardiopulmonary, and skeletal abnormalities. Several conditions and syndromes have been associated to pectus excavatum, although the overall health implications of the pectus excavatum phenotype are unclear. Therefore, in this study we aimed to examine the health implications of the pectus excavatum phenotype by assessing all comorbidities and previous medical conditions in a cohort of patients undergoing pectus excavatum surgery.MethodsThis single-centre retrospective prevalence study included 1,046 patients undergoing minimal invasive repair of pectus excavatum from 2001 to 2012. Hospital medical charts were assessed and comorbidities and previous medical conditions were registered systematically and categorized according to the affected organ system.ResultsIn our study population of 1,046 patients, we registered 623 conditions. The median age was 17 years and the majority of patients (56%) had no previous or present conditions. Notable prevalence of asthma (8.8%), allergies (12.3%), previous hernia surgery (5.2%), and psychiatric conditions (4.9%) were found.ConclusionsThe majority of patients undergoing pectus excavatum surgery have no comorbidities or previous medical conditions. It seems that this patient category is comparable to the background population in this regard and our findings do not support screening this patient category for associated conditions.

Postoperative Outcomes of Minimally Invasive versus Conventional Mitral Valve Repair; A Randomized Study

Background: Minimally invasive mitral valve surgery (MIMVS) is associated with less surgical trauma. However, its advantages over the conventional approach are controversial. This study aims to compare the early postoperative pain, hospital stay, and pulmonary function between minimally invasive and conventional mitral repair.
 Methods: Fifty patients with non-ischemic mitral valve disease who had mitral valve repair between 2017 and 2019 were included in the study. Patients were randomly divided into two equal groups. Group A (n=25) included patients who had minimally invasive mitral valve repair via anterolateral mini-thoracotomy with video assistance, and Group B (n=25) included patients who had mitral valve repair via median sternotomy.
 Results: The cross-clamp (99.45±16.01 vs. 87. 5±19.16 min; p= 0.058) and the total bypass times (134.08±27.38 vs. 120.71±22.18 min; p= 0.35) were nonsignificantly longer in Group A. Operative time was significantly longer in Group A (207.08±44.31 vs. 173.54±28.25 min; p= 0.001). The ICU stay in Group (A) was 2.58±1.44 days, and in Group (B), the ICU stay was 3.75±1.77 days (p= 0.001). The hospital stay was 7.87±1.59 days in Group A, and 14.5 ±5.05 days in Group B (P<0.001). Postoperative FEV1 was 2.06±0.63 L in Group A and 1.39±0.43 L in Group B (p= 0.001). There was no difference in postoperative ejection fraction between both groups (p= 0.9).
 Conclusion: Minimal invasive mitral valve repair could reduce postoperative pain, length of ICU, and hospital stay and improve the postoperative respiratory function when compared to the conventional approach.

Optimal maintenance strategies for warranty products with limited repair time and limited repair number

Nowadays, to protect the interests of customers, many warranty policies take into account the limit of repair time and the limit of repair number. Under a rebate warranty policy, the seller has to give a refund to the customer according to the rebate warranty contract if the number of product failures or a single repair time for failure exceeds some certain limits. Minimal repair is conducted when the product fails, and the repair cost is charged to seller during the warranty period. After warranty expires, the product continues operating for a period of time before being replaced. The repair cost during the post-warranty period is undertaken by the customer. From the customer’s perspective, the expected life cycle cost rate of the warranty product is derived. By minimizing the expected cost rate, the existence and uniqueness of the optimal maintenance strategy for the warranty product are proven theoretically. Finally, as an example, the warranty car under the protection of “lemon laws” is studied to illustrate the proposed rebate warranty model.

Demand-driven condition-based maintenance planning under Markovian deterioration of machine condition

In this paper, single product single machine systems under Markovian deterioration of machine condition throughout a specified finite planning horizon are studied. It is assumed that the machine is subject to random failures and that any maintenance activities carried out in a period, reduces the system’s potential production capacity during that period. Furthermore, it is assumed that the machine is minimally repaired at failure, and PM is carried out, after inspection, to restore the machine to an ‘as-good-as-new’ status. The objective of the study is to find the optimal intervals for inspection and preventive maintenance (PM) activities in condition-based maintenance (CBM) planning with a discrete monitoring framework subject to minimize the sum of inspection, PM, minimal repair, and backlog costs. To achieve the goal, a stochastic dynamic programming model that enumerates demand is presented calling the demand-driven CBM model. The numerical results show that this model decreases the total cost significantly that depends on the demand and the unit backlog cost, which is an increasing and a concave function in the unit backlog cost regardless of the initial machine state.

The Analysis of Weibull Lifetime Data Subject to Imperfect Repair

A repairable system with two types of failures is studied. Type I failure (minor failure) is removed by a minimal repair, whereas type II failure (catastrophic failure) is modified by an unplanned replacement. The first failure of the system follows a Weibull probability distribution and two maintenance policies are considered. In the first policy, the system is replaced at time T or the first type II failure, and in the second policy, the system is replaced at the nth type I failure, the first type II failure or at time T, whichever takes place first. This paper aims to derive a general representation for the likelihood function of the proposed models. The likelihood-ratio test statistic, maximum likelihood estimators and asymptotic confidence intervals for the parameters are also found. Finally, a Monte Carlo simulation is conducted to illustrate the results.

Joint optimization of lot sizing and condition-based maintenance for a production system using the proportional hazards model

This paper optimizes economic production quantity (EPQ) and condition-based maintenance (CBM) simultaneously for a production system subject to aging and deterioration. Different from previous models jointly determining EPQ and CBM, the proposed model is developed based on the proportional hazards model with a continuous-state covariate process, and on a CBM policy with multiple maintenance actions and dynamic control limits. Taking advantage of the opportunity of the downtime when a production run completes, condition monitoring is performed to reveal the system deterioration and then a suitable action is selected from preventive replacement, preventive repair, and no maintenance. Random failures during a production phase can be fixed by corrective replacement, corrective repair, or minimal repair. Considering that in many practical situations condition monitoring cannot be conducted at failure, corrective maintenance actions are determined based on (1) the system age at failure and the deterioration at the beginning of the production run (Scenario 1); or (2) both the system age and deterioration at the beginning of the production run (Scenario 2). The objective is to jointly optimize the production lot size and the CBM policy by minimizing the long-run average cost rate. The optimization problem is solved based on the policy-iteration algorithm in the semi-Markov decision process (SMDP) framework. A numerical example is provided to illustrate the proposed approach. The results show that Scenario 1 produces a more cost-effective but more complex maintenance strategy than Scenario 2 does.

Internal Mammary Artery Compression After Pectus Excavatum Repair Does Not Increase Risk of Hemorrhagic Complications in Pediatric Patients.

Objectives: Minimal invasive repair of pectus excavatum (MIRPE) described by Nuss is the most popular correction nowadays of this deformity. During the introduction of the bars, they can hurt or compress the internal mammary arteries (IMA). The aim of this study was to observe the prevalence of IMA compression in children after MIRPE. Also, we examined if IMA obstruction increases the risk of complications at bar removal, and if these vascular changes are reversible.Materials and Methods: All patients operated on pectus excavatum in our tertiary pediatric surgical center between 2013 and 2019 were involved in the study. Data of age, sex, number of bars and characteristics of the deformity were examined. IMA flow was checked by Doppler ultrasound (DUS) after MIRPE and after bar removal, too.Results: Among 41 patients with mean age of 15.2 years there were 18 asymmetrical deformities, 23 sternal rotations. Mean pectus index was 4.01. After the Nuss procedure 7(9%) stenoses and 10(12%) occlusions of IMA were found on DUS. After bar removal 3 of 4 stenoses have resolved, but all examined occlusions (3/3) persisted. There were no complications during bar removals.Conclusion: IMA compression after MIRPE in children is uncommon, and is not influenced by severity of deformity. Obstruction of these vessels does not increase the risk of hemorrhagic complications at bar removal. Data of larger cohort are needed to determine reversibility of these changes.

Optimal replacement policy with replacement last under cumulative damage models

−In this study, we discuss a preventive replacement policy under cumulative damage models that include the concept of replacement last. The system is subject to two types of shocks (represented by type 1 shock and type 2 shock) whose probabilities depend on age. Each type 1 shock leads to an amount of additive damage to the system and also causes a minor failure of the system, which can be rectified by a minimal repair. The system will have a catastrophic failure as long as the accumulated damage exceeds a failure level threshold L. Meanwhile, type 2 shock will cause catastrophic failure of the system. The system is replaced preventively at age τ or the n-th type 1 shock or the time instant when the accumulated damage exceeds a pre-specified level k (but less than L), whichever occurs last, and is replaced correctively at the first type 2 shock or the time which the accumulated damage exceeds L, whichever occurs first. The average cost rate is developed and the optimal replacement policy is discussed analytically and computed numerically.

On Non-Homogeneous Markov Reward Model to Availability and Importance Analysis for CNC Machine Tools

This paper exploits the Markov reward method to availability and importance evaluation for CNC machine tools. The presented paper regards CNC machine tools as a multi-state system that state transitions process caused by elements and subsystem’s failures and corresponding maintenance activities during the lifetime. Simultaneously, considering the time-varying characteristics of the failure rates of subsystems, the non-homogeneous Markov reward model is introduced for evaluation of availability and subsystem importance identification for aging multi-state CNC machine tools under minimal repair. Corresponding procedures for the failure rates, state transition matrix, and reward matrix definition are suggested for the availability and importance measures. A numerical example is presented in order to illustrate the approach.

Optimal replacement strategies for warranty products with multiple failure modes after warranty expiry

The optimal replacement problem for a warranty product subject to (M + 1) types of mutually exclusive failure modes, including M repairable failure modes and a catastrophic failure mode, is investigated in this paper. When the product fails with a repairable failure mode, a minimal repair will be conducted to remove the failure. However, if a catastrophic failure mode occurs, the failure product can only be replaced by a new one. Within the warranty period, the seller needs to complete each failure repair within a repair time limit. Once a failure cannot be repaired within the stipulated time, under the rebate warranty, the customer is refunded a proportion of the sale price of the product based on its working time, and the warranty terminates simultaneously; or under the free replacement warranty, the seller is obligated to provide a new product at no charge to the customer. Under both the warranty policies, the repair cost is free of charge to the customer within the warranty time, while the customer is responsible for all the cost for repairs within the post-warranty time. From the customer’s point of view, the expected life cycle cost rate of the product under the rebate and free replacement warranty are respectively derived. The existence and uniqueness of the optimal replacement strategies after warranty expiring are also proved theoretically by minimizing the cost rate. Finally, we give numerical examples to illustrate the two warranty models and show the effectiveness of proposed strategies.

Optimal periodic preventive maintenance policies for systems subject to shocks

External shock process, known as the shot-noise process, will lead to the failure rate increasing of systems operating under random environment. In this paper, assuming that each shock may cause a random increment of the system failure rate, the optimal periodic preventive maintenance (PM) policy for the system is investigated. The system is preventively maintained at periodic time points nT,n=1,2,…,N−1, and is preventively replaced at time point NT. The PM is not perfect, however, it can remove the accumulated failure rate increments caused by external shocks occurred during the last PM interval. When the system fails during the PM intervals, a minimal repair is performed to restore the function of the system. The expression of the average cost rate of the system is derived explicitly. The existence and uniqueness of the optimal bivariate PM policy (N,T) that minimizes the average cost rate are proved theoretically. Numerical examples are presented to illustrate the maintenance model and show the effectiveness of the proposed method.

Tissue engineered axon-based "living scaffolds" promote survival of spinal cord motor neurons following peripheral nerve repair.

Peripheral nerve injury (PNI) impacts millions annually, often leaving debilitated patients with minimal repair options to improve functional recovery. Our group has previously developed tissue engineered nerve grafts (TENGs) featuring long, aligned axonal tracts from dorsal root ganglia (DRG) neurons that are fabricated in custom bioreactors using the process of axon "stretch-growth." We have shown that TENGs effectively serve as "living scaffolds" to promote regeneration across segmental nerve defects by exploiting the newfound mechanism of axon-facilitated axon regeneration, or "AFAR," by simultaneously providing haptic and neurotrophic support. To extend this work, the current study investigated the efficacy of living versus nonliving regenerative scaffolds in preserving host sensory and motor neuronal health following nerve repair. Rats were assigned across five groups: naïve, or repair using autograft, nerve guidance tube (NGT) with collagen, NGT + non-aligned DRG populations in collagen, or TENGs. We found that TENG repairs yielded equivalent regenerative capacity as autograft repairs based on preserved health of host spinal cord motor neurons and acute axonal regeneration, whereas NGT repairs or DRG neurons within an NGT exhibited reduced motor neuron preservation and diminished regenerative capacity. These acute regenerative benefits ultimately resulted in enhanced levels of functional recovery in animals receiving TENGs, at levels matching those attained by autografts. Our findings indicate that TENGs may preserve host spinal cord motor neuron health and regenerative capacity without sacrificing an otherwise uninjured nerve (as in the case of the autograft) and therefore represent a promising alternative strategy for neurosurgical repair following PNI.

Altın ve Gümüş Madenciliğinde Siyanür Kaynaklı Kimyasal Kazalarda Acil Durum Yönetimi Örneği

Sürdürülebilir kalkınmanın temel hedeflerinden biri ham madde olarak kullanılan doğal kaynakların en az tahribatla kullanılması ve tahribatın onarılmasıdır. Yüksek ekonomik katkılı ve istihdam sağlayan bir sektör olan değerli metallerin kazanımı çevreyle doğrudan ilişkili bir alandır. Bu da doğada bazen istenmeyen kalıcı tahribatlara neden olmaktadır. Sağlıklı toplum sağlıklı bir çevreyle mümkün olacağından, çevre tahribatının azaltılması ve istenmeyen çevre kazaları karşısında hazırlıklı olunması elzemdir. Altın ve gümüş madenciliğinde günümüzde en ekonomik yöntem olarak kullanılan siyanürleme tekniğinin çevreye etkileri devam eden bir tartışma konusudur. Bununla ilgili abartılı veya tehlikeyi küçümseyici değerlendirmeler yapılmaktadır. Bu çalışmada altın-gümüş elde edilmesinde kullanılan ve atık barajlarında depolanan siyanürlü atıkların, Afet ve Acil Durum Yönetimi Başkanlığı’na (AFAD) bağlı Kimyasal Biyolojik Radyolojik Nükleer Tehditler (KBRN) birimi mevzuatına göre tehlike boyutu ve alınabilecek önlemler değerlendirilmektedir. Risk azaltma, hazırlık, müdahale ve iyileştirme uygulamalarından oluşan KBRN tehlikeleriyle mücadele adımlarının, siyanürlü baraj atıklarının çevreye dağılma tehlikesi karşısında nasıl uygulanması gerektiği tartışılmaktadır. 2011 yılında Kütahya sınırlarında bulunan gümüş işletmesinde atık barajının iç duvarlarının çökmesi sonucu siyanürlü atıkların etrafa dağılması tehlikesine karşı alınan tedbirler yaşanmış bir örnek olarak değerlendirilmektedir. Kriz masasının kurulması, tahliye planları, baraj duvarlarını güçlendirme faaliyetleri alınan tedbirlerden bazıları olup, çevre ve canlı sağlığına siyanürün etkileri ile öneriler verilmektedir. KBRN tehlike grubunda yer alan siyanürlü atıklara karşı öncelikle işletmenin sorumluluğundaki tedbirlerin alınması, çevre sakinleri ile iletişim halinde olunması, etkilenebilecek canlıların tespit edilmesi ve muhtemel senaryoların tahmin edilerek, gerekli hazırlıkların yapılmasına gerek duyulduğu varılan sonuçlardandır.

Determination of Optimal Warranty Period with Preventive Maintenance Actions for Items from Heterogeneous Populations

In this study, we develop an optimal maintenance policy with replacement service and minimal repair service for items from heterogeneous populations and determine the optimal warranty length and repair time threshold. We consider the information-based repair-replacement policy model and develop the formula to evaluate the expected cost rate during the product life cycle. A general formulation is derived for the expected cost rate under a warranty policy for items of heterogeneous populations. When a replacement service and minimal repair service are provided for a failed item, then an item from a weak population has the property of an item from a weak population after service. Similarly, an item from a strong population has the property of an item from a strong population after service. We define the optimal maintenance strategies to minimize the expected cost rate with failure time and repair time for items with heterogeneous reliability characteristics. The effects of parameters of the intensity function for the failure times on the optimal length of the warranty period are studied numerically. Assuming that the product deteriorates, we illustrate the proposed approach using numerical applications and observe the impacts of relevant parameters on the optimal length of the warranty period.

Minimally Invasive Aortic Arch Repair: Technical Considerations and Mid-Term Outcomes.

Reports of minimal invasive aortic arch surgery are scarce. We reviewed our experience with minimal access aortic arch surgery performed through an upper mini-sternotomy, with emphasis on details of operative technique and early and mid-term outcomes. The medical records of 123 adult patients (mean age 66 ± 12 years), who underwent primary elective minimal access aortic arch surgery in two aortic referral centers, were reviewed. The most common indication was degenerative aortic arch aneurysm in 92 (75%) patients. Standard operative and organ protection techniques used in all patients were upper mini-sternotomy, uninterrupted antegrade cerebral perfusion, and moderate systemic hypothermia (27.4 ± 1°C). Sixty-eight (55%) patients received partial aortic arch replacement; the remaining 55 (45%) patients received total arch replacement, further extended with either a frozen elephant trunk in 43 (35%) patients or a conventional elephant trunk procedure in nine (7%) patients. No conversion to full sternotomy was required. New permanent renal failure occurred in one (0.8%) patient, stroke in two (1.6%), and spinal cord injury in four (3.3%) patients. Early mortality was observed in four (3.3%) patients. At five years, survival was 80 ± 6% and freedom from reoperation was 96 ± 3%. Minimal invasive aortic arch repair through an upper mini-sternotomy can be safely performed, with early and mid-term outcomes well comparable to series performed through a standard median sternotomy.

Age-replacement policies under age-dependent replacement costs

We consider a stochastically deteriorating system with self-announcing failures that require immediate reactive replacement. For such a system, we consider an age-replacement policy (without minimal repair) under which the system is replaced at failure (reactive replacement) or at a prescribed replacement time (preventive replacement), whichever occurs first. Motivated by factors such as decreasing salvage value or increasing costs associated with obtaining spare parts, we assume that replacement costs are non-decreasing in system age. We formulate a long-run expected cost-rate minimization model with instantaneous replacements that captures this dependency, and provide conditions under which there exists a unique optimal solution. We provide analytical and numerical results that compare the cost-rate minimizing optimal replacement policy, and its performance, to those for the case in which replacement costs are assumed to be constant. Finally, we also consider non-instantaneous replacements, and compare cost-rate minimizing and availability maximizing policies.

Maintenance policies with minimal repair and replacement on failures: analysis and comparison

The main objective of a maintenance policy consists of conducting maintenance actions at lower costs. This paper proposes an approach for comparing numerically three maintenance strategies, involving minimal repairs at failure, replacement with complete renewal only at the first failure, and replacement with complete renewal at each failure. These strategies are integrated into a modified block replacement policy that includes corrective and preventive maintenances. The approach proceeds by presenting the mathematical models at the component level and at the system level. As the renewal function for generalised Weibull distributions is impossible to obtain, a novel asymptotic algorithm is introduced for estimating the replacements number. However, a multi-component industrial example is proposed for selecting the strategy that minimises the maintenance costs. A sensitivity analysis is performed for comparing an opportunistic maintenance policy with the proposed replacement policy to check if substantial cost reduction still possible. The experiment results show clearly that the third strategy is the most efficient and reduces maintenance costs to a very low level. Finally, we think that the developed study provides a flexible and less costly solution to deal with maintenance decision-making for systems that do not have modern technological equipment to collect data from system breakdowns.

Potential sealing and repair of human FM defects after trauma with peptide amphiphiles and Cx43 antisense.

We examined whether peptide amphiphiles functionalised with adhesive, migratory or regenerative sequences could be combined with amniotic fluid (AF) to form plugs that repair fetal membrane (FM) defects after trauma and co-culture with connexin 43 (Cx43) antisense. We assessed interactions between peptide amphiphiles and AF and examined the plugs in FM defects after trauma and co-culture with the Cx43antisense. Confocal microscopy confirmed directed self-assembly of peptide amphiphiles with AF to form a plug within minutes, with good mechanical properties. SEM of the plug revealed a multi-layered, nanofibrous network that sealed the FM defect after trauma. Co-culture of the FM defect with Cx43 antisense and plug increased collagen levels but reduced GAG. Culture of the FM defect with peptide amphiphiles incorporating regenerative sequences for 5 days, increased F-actin and nuclear cell contraction, migration and polarization of collagen fibers across the FM defect when compared to control specimens with minimal repair. Whilst the nanoarchitecture revealed promising conditions to seal iatrogenic FM defects, the peptide amphiphiles need to be designed to maximize repair mechanisms and promote structural compliance with high mechanical tolerance that maintains tissue remodeling with Cx43 antisense for future treatment.

Optimal preventive 'maintenance-first or -last' policies with generalized imperfect maintenance models

<p style='text-indent:20px;'>This paper presents modified preventive maintenance policies for an operating system that works at random processing times and is imperfectly maintained. The system may suffer from one of the two types of failures based on a time-dependent imperfect maintenance mechanism: type-Ⅰ (minor) failure, which can be rectified by minimal repair, and type-Ⅱ (catastrophic) failure, which can be removed by corrective maintenance. When the system needs to be maintained, two policies "preventive maintenance-first (PMF) and preventive maintenance-last (PML)" may be applied. In each maintenance interval, before any type-Ⅱ failure occurs, the system is maintained at a planned time <inline-formula><tex-math id="M1">\begin{document}$ T $\end{document}</tex-math></inline-formula> or at the completion of a working time, whichever occurs first and last, which are called PMF and PML, respectively. After any maintenance activity, the system improves but its failure characteristic is also altered. At the <inline-formula><tex-math id="M2">\begin{document}$ N $\end{document}</tex-math></inline-formula>-th maintenance, the system is replaced rather than maintained. For each policy, the optimal preventive maintenance schedule (<inline-formula><tex-math id="M3">\begin{document}$ T $\end{document}</tex-math></inline-formula>, <inline-formula><tex-math id="M4">\begin{document}$ N $\end{document}</tex-math></inline-formula>)<inline-formula><tex-math id="M5">\begin{document}$ ^{*} $\end{document}</tex-math></inline-formula> that minimizes the mean cost rate function is derived analytically and determined numerically in terms of its existence and uniqueness. The proposed models provide a general framework for analyzing the maintenance policies in reliability theory.

Optimal design of facility allocation and maintenance strategy for a cellular network

A cellular network is widely used for transmitting text (i.e., alphanumeric) messages between subscribers from different geographical locations. The geographic area of a cellular network is divided into a large number of cells, which are served by at least one facilities from base stations among predetermined positions. Both reliability and cost of a cellular network depend on the number, location and failure rate of facilities in the base stations. Thus, the joint optimization of facility allocation and maintenance strategy in a cellular network is relevant and significant for guiding optimal decisions on cellular network planning. This paper models a cellular network with repairable facilities characterized by a two-parameter Weibull distribution.The objective is to jointly optimize the facility allocation among predetermined positions and the facilities maintenance strategy in order to minimize the expected life cycle cost of the cellular network. An optimization algorithm for the proposed model is given based on heuristic algorithm and simulation. A case study is presented to illustrate the application of the proposed model, and sensitivity analysis shows the relationship between the optimal preventive replacement interval and the ratio of the preventive replacement cost to the minimal repair cost.