Lexicographically Maximum Flows under an Arc Interdiction

Network interdiction problem arises when an unwanted agent attacks the network system to deteriorate its transshipment efficiency. Literature is flourished with models and solution approaches for the problem. This paper considers a single commodity lexicographic maximum flow problem on a directed network with capacitated vertices to study two network flow problems under an arc interdiction. In the first, the objective is to find an arc on input network to be destroyed so that the residual lexicographically maximum flow is lexicographically minimum. The second problem aims to find a flow pattern resulting lexicographically maximum flow on the input network so that the total residual flow, if an arc is destroyed, is maximum. The paper proposes strongly polynomial time solution procedures for these problems.

EPICARDIAL CLIP CLOSURE OF THE LEFT ATRIAL APPENDAGE: REPLY

Epicardial surgical clip is showed to be a safe and effective tool in order to achieve a complete left atrial appendage (LAA) exclusion thus reducing the risk of stroke in patients with atrial fibrillation. Historically, other methods as surgical ligation, internal oversewing or external stapling showed to be largely uneffective with an incidence of LAA residual flow ranging from 25% to 35% thus, increasing per se 5- to 10-fold the risk of stroke. Epicardial LAA exclusion by means of external clip could be potentially released under transesophageal echocardiographic guidance thus increasing the procedural success rate of complete closure with no residual stump left.

A new three-dimensional residual flow theory and its application to Brewer–Dobson circulation in the middle and upper stratosphere

This study formulates three-dimensional (3-D) residual flow, treating both stationary and transient waves. The zonal and meridional momentum equations contain four terms: the geostrophic wind tendency, Coriolis force for the residual horizontal flow, product of the geostrophic wind and potential vorticity other than the constant planetary vorticity, and friction. The thermodynamic equation contains three terms: the potential temperature tendency, advection of the basic potential temperature by the residual vertical flow, and diabatic heating. The zonal mean of the 3-D residual flow equals the time mean of the residual flow of the transformed Eulerian mean equations. The new residual flow is the sum of that derived by Plumb for transient waves and the quadratic terms of the time-mean fields, which correspond approximately to the Stokes correction due to stationary waves. The 3-D residual flow and momentum equations are symmetric in the zonal and meridional directions, in contrast with those formulated by Kinoshita et al., which treat the time-mean zonal-mean zonal wind as the basic wind. The newly derived formulae are applied to the climatology of the 3-D structure of the deep branch of the Brewer–Dobson circulation. In the Northern Hemisphere in December–January–February, the residual flows are directed inward toward the polar vortex strongly over East Siberia, where the downward flow is maximized, and weakly over the Atlantic; meanwhile, they are directed outward from the vortex over North America and Europe. A longitudinal dependence of the poleward flow is also observed in the Southern Hemisphere in June–July–August.

Radiographic Characteristics of Mild Ischemic Stroke Patients With Visible Intracranial Occlusion: The INTERRSeCT Study

Background and Purpose: Early neurological deterioration occurs in one-third of mild strokes primarily due to the presence of a relevant intracranial occlusion. We studied vascular occlusive patterns, thrombus characteristics, and recanalization rates in these patients. Methods: Among patients enrolled in INTERRSeCT (Identifying New Approaches to Optimize Thrombus Characterization for Predicting Early Recanalization and Reperfusion With IV Alteplase and Other Treatments Using Serial CT Angiography), a multicenter prospective study of acute ischemic strokes with a visible intracranial occlusion, we compared characteristics of mild (National Institutes of Health Stroke Scale score, ≤5) to moderate/severe strokes. Results: Among 575 patients, 12.9% had a National Institutes of Health Stroke Scale score ≤5 (median age, 70.5 [63–79]; 58% male; median National Institutes of Health Stroke Scale score, 4 [2–4]). Demographics and vascular risk factors were similar between the two groups. As compared with those with a National Institutes of Health Stroke Scale score >5, mild patients had longer symptom onset to assessment times (onset to computed tomography [240 versus 167 minutes] and computed tomography angiography [246 versus 172 minutes]), more distal occlusions (M3, anterior cerebral artery and posterior cerebral artery; 22% versus 6%), higher clot burden score (median, 9 [6–9] versus 6 [4–9]), similar favorable thrombus permeability (residual flow grades I–II, 21% versus 19%), higher collateral flow (9.1 versus 7.6), and lower intravenous alteplase treatment rates (55% versus 85%). Mild patients were more likely to recanalize (revised arterial occlusion scale score 2b/3, 45%; 49% with alteplase) compared with moderate/severe strokes (26%; 29% with alteplase). In an adjusted model for sex, alteplase, residual flow, and time between the two vessel imagings, intravenous alteplase use (odds ratio, 3.80 [95% CI, 1.11–13.00]) and residual flow grade (odds ratio, 8.70 [95% CI, 1.26–60.13]) were associated with successful recanalization among mild patients. Conclusions: Mild strokes with visible intracranial occlusions have different vascular occlusive patterns but similar thrombus permeability compared with moderate/severe strokes. Higher thrombus permeability and alteplase use were associated with successful recanalization, although the majority do not recanalize. Randomized controlled trials are needed to assess the efficacy of new thrombolytics and endovascular therapy in this population.

Penetration of Dissected Membrane for False Lumen Embolization in a Case of Chronic Aortic Dissection

Background: Patent false lumens carry a high risk of aortic events including rupture. False lumen embolization is a useful method to promote thrombosis of false lumen. In the case presented here, direct penetration of the dissected membrane was employed to obtain access to the false lumen, enabling embolization. Case report: The case was a 64-year-old female who developed a Stanford type A acute aortic dissection. Replacement of ascending aorta and aortic arch with frozen elephant trunk technique was performed. After the operation, there was a residual flow through the false lumen in the descending thoracic and abdominal aorta. Twenty months later, the patient complained of sudden back pain, and a CT scan demonstrated another new dissection at the distal edge of the open stent. Additionally, the false lumen that had remained since the onset of the type A aortic dissection enlarged during the observation period. An endovascular procedure was planned to exclude the false lumen. Despite closing all communicating channels between true and false lumen using a vascular plug, coils, and stent grafts, the false lumen continued to expand due to the residual flow at the visceral segment. The origin responsible for the flow was not identified. To perform an embolization of the false lumen, access into the false lumen was obtained by penetration of the dissected flap using a trans-septal needle. Following the successful penetration of the flap, embolization of the false lumen was performed using coils and glue. After the embolization, an angiogram of the false lumen confirmed the significant reduction of leakage into the true lumen. The size of the aorta and false lumen decreased after the embolization. Conclusion: Direct penetration of the dissected membrane of the aorta was a safe and useful measure for regaining access to the false lumen and for the following endovascular intervention.

Left ventricular four-dimensional blood flow energetics and vorticity in chronic myocardial infarction patients with/without left ventricular thrombus

Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): The British Heart Foundation [FS/10/62/28409] and Dutch ZonMw [104003001]. Background Left ventricular thrombus (LVT) formation is a frequent and serious complication of myocardial infarction (MI). How global LV flow characteristics are related to this phenomenon is yet uncertain. In this study, we investigated LV flow differences using 4D flow cardiovascular magnetic resonance (CMR) between chronic MI patients with LVT [MI-LVT(+)] and without LVT [MI-LVT(-)], and healthy controls. Methods In this prospective cohort study, the 4D flow CMR data were acquired in 19 chronic MI patients (MI-LVT(+), n= 9 and MI-LVT(-), n= 10) and 9 age-matched controls. All included subjects were in sinus rhythm. The following LV flow parameters were obtained: LV flow components (direct, retained, delayed, residual), mean and peak KE values (indexed to instantaneous LV volume), mean and peak vorticity values, and diastolic vortex ring properties (position, orientation, shape). Results The MI patients demonstrated a significantly larger amount of delayed and residual flow, and a smaller amount of direct flow compared to controls (p = 0.02, p = 0.03, and p < 0.001, respectively). The MI-LVT(+) patients demonstrated numerically increased residual flow and reduced retained and direct flow in comparison to MI-LVT(-) patients. Systolic mean and peak LV blood flow KE values were significantly lower in MI patients compared to controls (p = 0.04, p = 0.03, respectively). Overall, the mean and peak LV vorticity values were significantly lower in MI patients compared to controls. The mean vorticity at the basal level was significantly higher in MI-LVT(+) than in MI-LVT(-) patients (p < 0.01). The vortex ring core during E-wave in MI-LVT(-) group was located closer to the mitral annulus and in a less tilted orientation to the LV compared to MI-LVT(+) group (p = 0.05, p < 0.01, respectively). Conclusion Chronic MI patients with LVT express a different distribution of LV flow components, irregular vorticity vector fields, and altered diastolic vortex ring geometric properties as assessed by 4D flow CMR. Larger prospective studies are warranted to further evaluate these initial observations.

Congenital renal arteriovenous malformation: a rare cause of visible haematuria

We report a case of renal arteriovenous malformation (AVM) and describe its angioarchitecture and endovascular management. A 28-year-old male patient presented with visible painless haematuria. CT of the abdomen showed a right renal AVM. Digital subtraction angiography of the right renal vessels showed an AVM of middle and lower pole segmental arteries with communication to a large saccular aneurysm, which was arising from the right main renal vein. Complete occlusion of the AVM was done by using glue (a mixture of n-butyl-cyanoacrylate and lipiodol), resulting in nonvisualisation of the aneurysm on angiography. His vital signs were stable during the procedure. Follow-up CT after 12 months showed no residual flow in the aneurysm, normal upper pole renal parenchyma and nonvisualisation of AVM. Early diagnosis of this clinical entity is of paramount importance for proper management as it can cause massive blood loss and rapid clinical deterioration.

The Healing Response of LAMax LAACTM Left Atrial Appendage Occluder in a Canine Model: The Potential Influence of the Implantation Technique on the Healing Response

Background: Device-associated thrombus are potential causes for thromboembolic events post left atrial appendage closure (LAAC), and correlated with the complete endothelialization of the device surface. Our aim was to evaluate the endothelialization of LAMax LAACTM occluder surface and analyze the potential influence of the implantation technique on the healing response.Methods: A total of 29 healthy dogs (28.0±3.7 kg) were implanted with the devices successfully after ensuring COVER signs was met (Concavity of the disc, Oversizing by 20-50%, Verifying position, Ensuring stability, Residual flow <5 mm by transesophageal echocardiographic (TEE) examination), and sacrificed at <24 hours, 1-, 2-, 3-, and 6-months. Gross examinations were conducted to evaluate healing response.Results: The mean diameters of LAA orifice measured by angiography and TEE were 19.0±2.9 mm and 16.1±2.0 mm (P<0.05), respectively. TEE found that the discs in 18 dogs (62.1%) were completely pulled into the LAA with concavity and in 11 dogs incompletely pulled into the LAA with suboptimally concavity, while 5 of them had residual flow. Gross examinations showed that the complete endothelialization on the device surface with concaved disc was found at 1-month after LAAC. Microscopic examinations confirmed complete healing on the device with optimal closure effect. Conclusions: The good healing response and the optimal closure effect were observed using the LAMax device in a canine model by following the COVER implantation technique.

A novel multi-parameter approach to assess the effects of river restoration measures on the sediment matrix

&lt;p&gt;Clogging of riverbeds, also referred to colmation, has been frequently reported in residual flow river reaches. In such river reaches, colmation occurs mostly due to regulated (minimum) flow conditions without significant flood events that drive morphodynamics. Consequently, incoming fine sediments continuously deposit, infiltrate, and accumulate in the gravel matrix of the riverbed. The negative effect of such clogged layers on river ecology is well-known, especially with respect to the hyporheic interstitial leading to reduced porosity and hydraulic conductivity. These limitations results in a reduced supply of dissolved oxygen for aquatic species living in the hyporheic interstitial. However, no standardized quantitative measuring technique exists to determine the vertical location and the degree of colmation. Most available measuring methods involve a variety of mapping methods or single-parameter approaches. While mapping methods enable only qualitative assessments, single-parameter approaches are insufficient to describe the complexity of colmation.&lt;/p&gt;&lt;p&gt;The objective of this study is to test a novel multi-parameter approach in a residual flow river reach to assess the effect of river restoration measures on colmation. The multi-parameter approach includes four key parameters to describe colmation: i) the grain size distribution of the riverbed using freeze core sampling and sieving, ii) the hydraulic conductivity using a newly developed double packer system, iii) the porosity identified with a photogrammetric approach, and iv) the interstitial dissolved oxygen content (DOC) using optodes. This novel approach enables a quantitative description of colmation and an identification of clogged layers in stratified riverbeds as the hydraulic conductivity and the DOC are measured in vertical profiles. The entire measuring concept is applied before and after the implementation of river restoration measures to detect the intervention&amp;#8217;s effects on colmation.&lt;/p&gt;&lt;p&gt;The first analyses of the measurement show clearly the effects of dredging with an artificial alteration of the riverbed on the sediment matrix. The vertical profiles of hydraulic conductivity and dissolved oxygen show typically high values in the permeable upper sediment layer and significant reductions in deeper sediment layers. The thickness range of the permeable upper layer is between 5 and 15&amp;#160;cm before the intervention and increased up to 30 and 50&amp;#160;cm after the interventions. The analyses of a coarsened grain size distribution and porosity support the observation of this declogging effect, although a direct correlation is challenging because both parameters are not detected in the form of vertical profiles, but rather as a bulk information for every measurement point.&lt;/p&gt;&lt;p&gt;These very first results provide the conclusion that the measured vertical profiles of hydraulic conductivity and DOC are promising data to assess the location and degree of colmation and their modification as a result of river restoration action. Yet, grain size and porosity analyses provide only little evidence because those represent bulk information only. In summary, the multi-parameter approach represents an innovative and quantitative approach to objectively assess the degree and vertical location of clogged layers in gravel riverbed, which is a major advantage over existing methods for assessing colmation.&lt;/p&gt;