Heavy traffic analysis of open processing networks with complete resource pooling: asymptotic optimality of discrete review policies

We consider a class of open stochastic processing networks, with feedback routing and overlapping server capabilities, in heavy traffic. The networks we consider satisfy the so-called complete resource pooling condition and therefore have one-dimensional approximating Brownian control problems. We propose a simple discrete review policy for controlling such networks. Assuming 2+\epsilon moments on the interarrival times and processing times, we provide a conceptually simple proof of asymptotic optimality of the proposed policy.Comment: Published at http://dx.doi.org/10.1214/105051604000000495 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

The role of corifollitropin alfa in controlled ovarian stimulation for IVF in combination with GnRH antagonist

Corifollitropin alfa is a synthetic recombinant follicle-stimulating hormone (rFSH) molecule containing a hybrid beta subunit, which provides a plasma half-life of ∼65 hours while maintaining its pharmocodynamic activity. A single injection of corifollitropin alfa can replace daily FSH injections for the first week of ovarian stimulation for in vitro fertilization. Stimulation can be continued with daily FSH injections if the need arises. To date, more than 2500 anticipated normoresponder women have participated in clinical trials with corifollitropin alfa. It is noteworthy that one-third of women did not require additional gonadotropin injections and reached human chorionic gonadotropin criterion on day 8. The optimal corifollitropin dose has been calculated to be 100 μg for women with a body weight ≤60 kg and 150 μg for women with a body weight >60 kg, respectively. Combination of corifollitropin with daily gonadotropin-releasing hormone antagonist injections starting on stimulation day 5 seems to yield similar or significantly higher numbers of oocytes and good quality embryos, as well as similar ongoing pregnancy rates compared with women stimulated with daily rFSH injections. Stimulation characteristics, embryology, and clinical outcomes seem consistent with repeated corifollitropin-stimulated assisted reproductive technologies cycles. Multiple pregnancy or ovarian hyperstimulation syndrome rates with corifollitropin were not increased over daily FSH regimen. The corifollitropin alfa molecule does not seem to be immunogenic and does not induce neutralizing antibody formation. Drug hypersensitivity and injection-site reactions are not increased. Incidence and nature of adverse events and serious adverse events are similar to daily FSH injections. Current trials do not provide information regarding use of corifollitropin alfa in anticipated hyper- and poor responders to gonadotropin stimulation. Although corifollitropin alfa is unlikely to be teratogenic, at the moment data on congenital malformations is missing

A new definition of recurrent implantation failure on the basis of anticipated blastocyst aneuploidy rates across female age.

Objective: To present a definition of recurrent implantation failure that accounts for the effects of female age and anticipated blastocyst euploidy rates on cumulative implantation rates. Design: Mathematical modeling. Setting: Not applicable. Patient(s): Not applicable. Intervention(s): Mathematical modeling of cumulative implantation probability on the basis of published blastocyst euploidy rates across categories of female age. Main Outcome Measure(s): The number of blastocysts required to achieve 95% cumulative implantation probability under the assumption of the absence of any other factor affecting implantation. Result(s): When the euploidy status of the transferred embryo is unknown (i.e., not subjected to preimplantation genetic testing for aneuploidies), our simulation shows that no age category reaches 95% cumulative probability of implantation of at least one embryo until after transfer of seven blastocysts. The number of blastocysts required to reach the same threshold is higher for older patients. For example, women older than 38 years require transfer of more than 10 untested blastocysts for the upper range of predictive probability to meet the threshold of 95%. On the other hand, if the implantation rate for a euploid blastocyst is assumed to be 55%, then 4 blastocysts are enough to reach a cumulative probability rate greater than 95%, regardless of age. Conclusion(s): The term "recurrent implantation failure"should be a functional term guiding further management. We suggest that recurrent implantation failure should not be called until implantation failure becomes reasonably likely to be caused by factors other than embryo aneuploidy, the leading cause of implantation failure. We propose a new definition that factors in anticipated blastocyst euploidy rates across categories of female age, euploid blastocyst implantation rate, and a specified threshold of cumulative probability of implantation

A Diffusion Model of Dynamic Participant Inflow Management

This paper studies a diffusion control problem motivated by challenges faced by public health agencies who run clinics to serve the public. A key challenge for these agencies is to motivate individuals to participate in the services provided. They must manage the flow of (voluntary) participants so that the clinic capacity is highly utilized, but not overwhelmed. The organization can deploy costly promotion activities to increase the inflow of participants. Ideally, the system manager would like to have enough participants waiting in a queue to serve as many individuals as possible and efficiently use clinic capacity. However, if too many participants sign up, resulting in a long wait, participants may become irritated and hesitate to participate again in the future. We develop a diffusion model of managing participant inflow mechanisms. Each mechanism corresponds to choosing a particular drift rate parameter for the diffusion model. The system manager seeks to balance three different costs optimally: i) a linear holding cost that captures the congestion concerns; ii) an idleness penalty corresponding to wasted clinic capacity and negative impact on public health, and iii) costs of promotion activities. We show that a nested-threshold policy for deployment of participant inflow mechanisms is optimal under the long-run average cost criterion. In this policy, the system manager progressively deploys mechanisms in increasing order of cost, as the number of participants in the queue decreases. We derive explicit formulas for the queue length thresholds that trigger each promotion activity, providing the system manager with guidance on when to use each mechanism

A Dynamic Model for Managing Volunteer Engagement

Non-profit organizations that provide food, shelter, and other services to people in need, rely on volunteers to deliver their services. Unlike paid labor, non-profit organizations have less control over unpaid volunteers' schedules, efforts, and reliability. However, these organizations can invest in volunteer engagement activities to ensure a steady and adequate supply of volunteer labor. We study a key operational question of how a non-profit organization can manage its volunteer workforce capacity to ensure consistent provision of services. In particular, we formulate a multiclass queueing network model to characterize the optimal engagement activities for the non-profit organization to minimize the costs of enhancing volunteer engagement, while maximizing productive work done by volunteers. Because this problem appears intractable, we formulate an approximating Brownian control problem in the heavy traffic limit and study the dynamic control of that system. Our solution is a nested threshold policy with explicit congestion thresholds that indicate when the non-profit should optimally pursue various types of volunteer engagement activities. A numerical example calibrated using data from a large food bank shows that our dynamic policy for deploying engagement activities can significantly reduce the food bank's total annual cost of its volunteer operations while still maintaining almost the same level of social impact. This improvement in performance does not require any additional resources - it only requires that the food bank strategically deploy its engagement activities based on the number of volunteers signed up to work volunteer shifts

Systematic review of native and graft-related aortic infection outcome managed with orthotopic xenopericardial grafts

International audienceObjective: Limited data are available on the use of xenopericardium in the treatment of native and graft-related aortic infections. The aim of this review was to assess outcomes of neoaortic reconstruction using xenopericardium in this challenging group of patients.Methods: Studies involving xenopericardial graft reconstruction to treat native and aortic graft infections were systematically searched and reviewed (Embase, Medline, and Cochrane databases) for the period of January 2007 to December 2017.Results: A total of 4 studies describing 71 patients treated for aortic graft (n = 54) and native aortic (n = 17) infections were included; 25 patients (35%) were operated on in an acute setting. The technical success rate was 100%. The mean 30-day mortality was 25% (range, 7.7%-31%). Only one death (1.4%) was linked to the operator-made pericardial tube graft (acute postoperative bleeding from proximal anastomosis). Septic multiorgan failure was the most common cause of perioperative death (72% [13/18]). Among the 53 patients who survived, only 3 presented with recurrent infection (5.7%), so 70.4% of patients were alive after intervention without evidence of infection (50/71). During follow-up, 2 false aneurysms (3.7% [2/53]), 1 early rupture (1.4% [1/71]), and 2 cases (3.7% [2/53]) of late rupture were reported. Other causes of late deaths unrelated to the aortic xenopericardial repair were not reported in the different series. The early reintervention rate was 1.4% (1/71), treated by open repair for rupture. The late reintervention rate was 7.5% (4/53) with thoracic endovascular aortic repair in three patients (one false aneurysm and two ruptures) and open repair in one patient (one false aneurysm). There were no cases of early or late graft thrombosis. One-year mortality rate was 38% but only 4.2% were related to the aortic repair using orthotopic xenopericardium (one early and two late ruptures).Conclusions: These data confirm the high morbidity of native and graft-related aortic infections and provide insight into the results of orthotopic xenografts as a treatment alternative. Larger series and longer follow-up will be required to compare the role of operator-made pericardial tube graft with other treatment options in infected fields

Double homemade fenestrated stent graft for total endovascular aortic arch repair.

International audienceThe aim of this retrospective analysis was to evaluate the outcomes of physician-modified double fenestrated stent grafts for total endovascular aortic arch repair: one proximal large fenestration for the brachiocephalic trunk and the left common carotid artery and one distal fenestration for the left subclavian artery (LSA)