Computational prediction of proximal sealing in endovascular abdominal aortic aneurysm repair with unfavorable necks.

BACKGROUND AND OBJECTIVE: Endovascular aortic aneurysm repair (EVAR) has become the standard treatment for abdominal aortic aneurysms in most centers. However, proximal sealing complications leading to endoleaks and migrations sometimes occur, particularly in unfavorable aortic anatomies and are strongly dependent on biomechanical interactions between the aortic wall and the endograft. The objective of the present work is to develop and validate a computational patient-specific model that can accurately predict these complications. METHODS: Based on pre-operative CT-scans, we developed finite element models of the aorta of 10 patients who underwent endovascular aortic aneurysm repair, 7 with standard morphologies and 3 with unfavorable anatomies. We simulated the deployment of stent grafts in each aorta by solving mechanical equilibrium with a virtual shell method. Eventually we compared the actual stent ring positions from post-operative computed-tomography-scans with the predicted simulated positions. RESULTS: A successful deployment simulation could be performed for each patient. Relative radial, transverse and longitudinal deviations were 6.3 ± 4.4%, 2.5 ± 0.9 mm and 1.4 ± 1.1 mm, respectively. CONCLUSIONS: The numerical model predicted accurately stent-graft positions in the aortic neck of 10 patients, even in complex anatomies. This shows the potential of computer simulation to anticipate possible proximal endoleak complications before EVAR interventions.

Predictive Numerical Simulations of Double Branch Stent-Graft Deployment in an Aortic Arch Aneurysm.

Total endovascular repair of the aortic arch represents a promising option for patients ineligible to open surgery. Custom-made design of stent-grafts (SG), such as the Terumo Aortic® RelayBranch device (DB), requires complex preoperative measures. Accurate SG deployment is required to avoid intraoperative or postoperative complications, which is extremely challenging in the aortic arch. In that context, our aim is to develop a computational tool able to predict SG deployment in such highly complex situations. A patient-specific case is performed with complete deployment of the DB and its bridging stents in an aneurysmal aortic arch. Deviations of our simulation predictions from actual stent positions are estimated based on post-operative scan and a sensitivity analysis is performed to assess the effects of material parameters. Results show a very good agreement between simulations and post-operative scan, with especially a torsion effect, which is successfully reproduced by our simulation. Relative diameter, transverse and longitudinal deviations are of 3.2 ± 4.0%, 2.6 ± 2.9 mm and 5.2 ± 3.5 mm respectively. Our numerical simulations show their ability to successfully predict the DB deployment in complex anatomy. The results emphasize the potential of computational simulations to assist practitioners in planning and performing complex and secure interventions.

Model reduction methodology for computational simulations of endovascular repair.

Endovascular aneurysm repair (EVAR) is a current alternative treatment for thoracic and abdominal aortic aneurysms, but is still sometimes compromised by possible complications such as device migration or endoleaks. In order to assist clinicians in preventing these complications, finite element analysis (FEA) is a promising tool. However, the strong material and geometrical nonlinearities added to the complex multiple contacts result in costly finite-element models. To reduce this computational cost, we establish here an alternative and systematic methodology to simplify the computational simulations of stent-grafts (SG) based on FEA. The model reduction methodology relies on equivalent shell models with appropriate geometrical and mechanical parameters. It simplifies significantly the contact interactions but still shows very good agreement with a complete reference finite-element model. Finally, the computational time for EVAR simulations is reduced of a factor 6-10. An application is shown for the deployment of a SG during thoracic endovascular repair, showing that the developed methodology is both effective and accurate to determine the final position of the deployed SG inside the aneurysm.

Editor's Choice - Ex vivo Renal Artery Repair with Kidney Autotransplantation for Renal Artery Branch Aneurysms: Long-term Results of Sixty-seven Procedures.

OBJECTIVE/BACKGROUND: To evaluate the long-term outcome of renal revascularization by ex vivo renal artery reconstruction and autotransplantation for renal artery branch aneurysms (RABAs). METHODS: Between 1991 and 2015, 67 ex vivo renal artery reconstructions with kidney autotransplantation were performed in 55 adults (mean age 47 years) and 10 children to repair 87 RABAs. The main underlying disease was fibromuscular dysplasia in 34 patients. Other etiologies were systemic congenital disease in eight patients, spontaneous dissecting aneurysms in five, iatrogenic aneurysms in three, atheromatous aneurysms in two and unknown etiology in 13. Median RABA diameter was 20.5 mm. Fifty-three patients (82%) were hypertensive, 60 had normal renal function and no patient was on hemodialysis. Seven patients (11%) were operated on after failure of an endovascular procedure. The mean number of renal artery branches repaired per patient was 3.5 and multiple aneurysms were treated in 14 patients (22%). The hypogastric artery was used in 41 patients, the saphenous vein in 18, the superficial femoral artery in five and a combination of different materials in three. RESULTS: No deaths occurred during the first 30 days. Primary patency at 30 days was 90.8% following to six early thromboses. Three patients (5%) were lost to follow up. No other thrombosis occurred. At 8 years, the primary and primary-assisted patency were 88% and 91%, respectively. Survival was 95% at 9 years. Among the 53 hypertensive patients, two were lost to follow up. At 9 years, 22 (43%) were cured and nine (18%) were improved with a significant reduction of antihypertensive medication (p < .05). The pre-operative modification of the diet in renal disease (MDRD) clearance was 93 ± 29 mL/minute, the immediate post-operative MDRD was 94 ± 33 mL/minute, and at the end of follow up it was 86 ± 26 mL/minute (p > .05). CONCLUSION: Ex vivo renal artery reconstruction for complex RABAs eliminates the risk of rupture, confers a benefit to hypertension, and preserves renal function with a satisfactory long-term patency.

Common hepatic artery as inflow in kidney transplantation.

Kidney transplantation originating from the hepatic artery has not previously been reported. Herein, we report a third kidney transplantation with the common hepatic artery as inflow. A 62-year-old male with chronic renal failure due to polycystic kidney disease was proposed to a third kidney transplantation. CT-scan showed diffuse calcification of the aorto-iliac axis and the splenic artery. The common hepatic artery was the only artery suitable for anastomosis and as such was chosen as the inflow for retransplantation. The operation was performed through a right subcostal laparotomy. A saphenous bypass was interposed between the common hepatic artery and the graft, then the renal vein was anastomosed to the suprarenal inferior vena cava. Duration of warm ischemia was 27 min. Postoperative course was complicated with delayed graft function of 17 days and pulmonary infection. Patient was discharged at day 30. With a follow-up of 40 months, serum creatinine level and eGFR are, respectively, 191 µmol/L and 32 mL/min. Hepato-renal bypass technique can be used in kidney retransplantation when patient anatomy is not compatible with other classical options.

Interpretation of lipoprotein-associated phospholipase A2 levels is influenced by cardiac disease, comorbidities, extension of atherosclerosis and treatments.

PURPOSE: Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an inflammatory biomarker secreted in the atherosclerotic plaque. Blood levels of Lp-PLA2 predict future cardiovascular events in patients with ischemic disease and heart failure. This association seems to be independent of traditional cardiovascular risk factors. The aims of our study were (1) to assess relationships between Lp-PLA2 levels, cardiac disease and treatments; (2) to evaluate the association of Lp-PLA2 level with the severity of angiographic coronary artery disease (CAD) and the extracoronary atherosclerosis. METHODS: Between December 2009 and June 2010, 494 subjects were recruited from a population scheduled for diagnostic coronary angiography. Routine clinical (age, gender, BMI and treatment), cardiac (echocardiography, coronarography, carotid ultrasonography) and biochemical parameters were recorded for all patients. Lp-PLA2 mass concentration was assessed in serum with a Plac®-test turbidimetric immunoassay. Control Lp-PLA2 values were specifically obtained in 61 healthy subjects aged 44.5 ± 17.6 years (range: 25 to 59 years) without known cardiovascular risk factors (diabetes, smoking, hypertension, dyslipidemia) or cardiac treatment. RESULTS: In healthy controls, mean Lp-PLA2 level was 163 ± 43 µg/L (166 ± 45 µg/L in men and 159 ± 39 µg/L in women, non significant difference). In our cohort of 494 patients (69.8% men) aged 64.2 ± 16.7 years, the main etiologies of cardiomyopathies were ischemic (40%), valvular (22%), cardiac failure with left ventricular (LV) dysfunction (14%), infection (5%) and aortic aneurysm (7%). Mean Lp-PLA2 levels were 216 ± 17 µg/L. Lp-PLA2 correlated with age, BMI, current smoking, history of hypertension but not with diabetes and gender. The bivariate analysis showed a significant correlation between Lp-PLA2, and BMI (p=0.001) but no correlation with serum creatinine or NYHA status. A multivariate correlation showed that Lp-PLA2 was associated with total cholesterol, LDL-cholesterol and apoB (r=0.95, p<0.0001) but not with Lp(a). We observed that Lp-PLA2 was significantly associated with treatments such as statins and ACEi/ARA2 but not with ß-blockers, antiaggregant drugs or diuretics. Lp-PLA2 levels were significantly higher in patients with CAD than in patients without CAD (223 ± 54 vs. 208 ± 52 µg/L, respectively; p<0.007). Moreover, Lp-PLA2 levels were significantly higher in patients with the most extensive angiographic CAD [single (n=24)=215.2 ± 52 µg/L; two (n=55)=222 ± 53 µg/L and three vessels (n=140)=251.9 ± 53.7 µg/L, respectively; p<0.0001]. Patients with heart failure, sepsis or aortic aneurysm had increased Lp-PLA2 levels: 256.2 ± 46.8; 226.7 ± 47.3; 218.1 ± 38.9 µg/L, respectively, as compared to controls (p<0.0001). In patients with carotid artery disease, Lp-PLA2 significantly increased with the severity of atherosclerosis. Mean Lp-PLA2 levels were 218.8 ± 51 µg/L in the group without any stenosis (n=108), 224 ± 51 µg/L in the group with mild stenosis (n=101), and 231 ± 46 µg/L in the group with severe stenosis (n=22); p=0.004. CONCLUSION: This study clearly shows that interpretation of Lp-PLA2 levels needs a good assessment of cardiac parameters and treatments, especially statins and ACEi/ARA2. Lp-PLA2 levels are significantly associated with coronary heart disease and with the extension of extra coronary disease after adjustment for age and gender.

Early and late results of ex vivo repair and autotransplantation in solitary kidneys.

INTRODUCTION: Autotransplantation of a solitary kidney provides an excellent opportunity to study the immediate and long-term consequences of intra-operative renal ischaemia. The purpose of this report is to describe a series of nine patients who underwent ex vivo repair and autotransplantation on solitary kidneys. PATIENTS AND METHODS: The series included six females and three males with a mean age of 36 years. Seven of the nine patients were hypertensive (mean number of anti-hypertensive agents: 3). Two patients had chronic renal failure (serum creatinine levels: 192 and 205 µmol l(-1)). All arteries except one with Takayasu disease were affected by dysplastic aneurysm or fibrodysplasia lesion. There was no atherosclerotic lesion. The mean number of renal artery branches repaired was 3.1 per patient. Mean duration of ischaemia was 161 min. RESULTS: Creatinaemia increased in all patients following the procedure. Creatinaemia and clearance returned to preoperative values between the 3rd and 10th postoperative days. One kidney was lost due to renal vein thrombosis. Late findings indicated that renal function was stable and there was no deterioration in the function of the autotransplanted kidneys after a follow-up period of 89 months. Preoperative versus postoperative creatinaemia and clearance levels were respectively 111 vs. 105 µmol l(-1) and 66.9 vs. 62.0 ml min(-1) (ns). During the same time, the mean number of anti-hypertensive agents decreased slightly from 3 to 2.5. CONCLUSION: In this small series of patients who underwent ex vivo repair and autotransplantation on solitary kidneys, intra-operative renal ischaemia had no detrimental effect on renal function.

A standardized aortic aneurysm model for the assessment of endovascular stent-graft technology.

Reliable models of aortic aneurysms are required to test endovascular stent-graft technology prior to human use. We describe the creation of a standardized prosthetic aneurysm in an ovine model to assess endovascular technology. In an adult ovine model under general anesthesia, a polyester sphere measuring 6 cm across was sutured onto the infrarenal aorta following aortotomy. Two weeks later an endovascular stent-graft was deployed in the aorta. Exclusion was confirmed on monthly ultrasound duplex and during angiography at three months and under terminal anesthesia at six months. Autopsy along with histology of the specimen were then performed. A total of 10 sheep underwent aneurysm implantation. Nine received a straight tube endovascular stent-graft (Lombard Medical, Abingdon, Oxon, UK) and seven completed the study. Five prosthetic aneurysms shrank during serial imaging with duplex ultrasound and angiography. However, two remained the same size. One of these had a type I endoleak whereas the other had endotension (type I endoleak confirmed at autopsy). This animal model provides a reliable and reproducible method of creating prosthetic aneurysms for assessing endovascular stent-grafts. It was possible to assess aneurysm exclusion non-invasively using duplex ultrasound. Aneurysms effectively excluded from the circulation shrank whereas those with an endoleak did not.

Manganese superoxide dismutase dimorphism relationship with severity and prognosis in cardiogenic shock due to dilated cardiomyopathy.

The aim was to determine (a) Ala-16Val-SOD2 dimorphisms; (b) allelic frequency and phenotype of a common Pro-Leu polymorphism in GPx1, in a cohort of patients with a cardiogenic shock (CS) due to dilated cardiomyopathy without acute coronary syndrome. Consecutive patients with de novo CS that worsened a dilated (DCM) or ischemic (ICM) cardiomyopathy. Congenital heart disease, pacemaker and other shock aetiologies were excluded. To determine oxidative stress (OS), this study evaluated lipid peroxidation, protein oxidation and erythrocyte GPx, SOD and catalase activities. Ala16Val-SOD2 (dbSNP: rs4880) and Pro198Leu-GPx1 (dbSNP: rs1050450) polymorphisms were studied by allelic discrimination using fluorogenic probes and the 5'nuclease (TaqMan) assay. Twenty-four patients (with ICM (n = 8) or DCM (n = 16), age = 57.5 ± 10.7 years, LVEF = 25.3 ± 8.5%, NT-proBNP levels = 8540 ± 1703 ng/L) were included during a 15 month follow-up. OS parameters were significantly higher in patients than in controls. Distribution of MnSOD genotypes was 47% Val/Val-variant, 29.5% Ala/Val and 23.5% Ala/Ala-variants. Severity of CS was more important in patients with Val/Val-variant and can be put in parallel with NT-proBNP levels (Val/Val-variant: 11 310 ± 3875 ng/L vs Ala/Ala-variant: 6486 ± 1375 ng/L and Ala/Val-variant: 6004 ± 2228 ng/L; p < 0.05) and hemodynamic support duration (144.6 vs Ala/Val-variant: 108.8 h and Ala/Ala-variant: 52.5 h; p < 0.05) with a positive correlation (Spearman rho = 0.72, p < 0.05). Moreover, Val/Val-variant significantly influenced the mortality (Spearman rho = 0.67, p < 0.05), but not the morbidity (p = 0.3). Distribution of GPx genotypes was 64% Pro/Pro, 18% Pro/Leu and 18% Leu/Leu. GPx-variants influenced neither GPx activities nor cardiac events. In conclusion, CS was associated with markers of increased OS. GPx polymorphism did not influence the GPx activity. Only the Val-encoding MnSOD allele was significantly correlated with the severity and prognosis of CS.

B-type natriuretic peptide, a marker of asymptomatic left ventricular dysfunction in type 2 diabetic patients.

AIM: To evaluate BNP in assessing LV functions in asymptomatic type 2 diabetic patients. METHODS: BNP was measured in 91 consecutive patients with type 2 diabetes mellitus. According to Doppler echocardiography, patients were first separated into three categories: normal LV function, or isolated diastolic or systolic LV dysfunction. As some patients with diastolic dysfunction were treated for hypertension, the population was divided into four groups: groups 1, 2 and 3 all had no antihypertensive treatment, and had normal LV function, and isolated diastolic and systolic LV dysfunction, respectively; and group 4 were being treated with antihypertensive drugs and had diastolic LV dysfunction. RESULTS: In group 1, BNP levels (13+/-2 ng/L) were lower than in group 2 (87+/-20 ng/L, P<0.0001) or group 3 (213+/-32 ng/L, P<0.0001), but were similar to those of group 4 (32+/-6 ng/L, P=0.14). ROC analysis revealed a rule-out value of 23 ng/L for group 1 versus group 2, and of 239 ng/L for group 2 versus group 3. In groups 1, 2 and 3 taken together, BNP levels were correlated with urinary albumin excretion rate (r=0.80, P<0.0001) and pulse pressure (r=0.65, P<0.0001). In group 4, patients receiving ACE inhibitors had lower BNP levels than those receiving ss-blockers. CONCLUSION: BNP can be used to pre-screen asymptomatic type 2 diabetic patients with LV dysfunction, and may reveal vascular remodelling in type 2 diabetes mellitus.

Effect of cerivastatin on peripheral capillary permeability to albumin and peripheral nerve function in diabetic rats.

OBJECTIVE: To examine the effect of cerivastatin on capillary permeability to albumin and peripheral nerve function in diabetic rats. ANIMALS: Diabetes was induced in male Wistar rats by i.p. injection of streptozotocin (STZ) at the age of 5 days. Forty diabetic rats were randomized in two groups: one treated by cerivastatin (diabetic treated group, DT) and the other untreated (diabetic untreated group, DU). The data were compared to a group of normal rats. MEASUREMENTS: The peripheral capillary filtration of albumin (CFA) was studied on a limb by a non-invasive isotopic method, and nerve electrophysiological measurements were performed. Rats were followed-up until 6 months. In group DU albumin retention (AR) increased by 3 months and lymphatic uptake of interstitial albumin was impaired at 6 months. None of these disorders was observed in group DT. Motor and sensory nerve conduction velocities (MNCV and SNCV) were significantly slower at 6 months in group DU but not in group DT as compared to control rats. The duration of the sensory nerve action potential (SNAP) was significantly longer in group DU than in control rats at 6 months whereas it did not differ in group DT and in control animals. CONCLUSIONS: This study shows that cerivastatin may prevent the peripheral increase in CFA and lymphatic dysfunction induced by diabetes. These beneficial effects on microcirculation may be involved in the prevention of nerve function deterioration. The underlying mechanisms are likely to be independent of a lipid-lowering effect, but their clarification needs further investigations.

[Carotid endarterectomy: current indications]. / Chirurgie carotide conventionnelle: mise au point des indications.

Indications for carotid endarterectomy have been clarified after the publication of European and North American randomised controlled trials between 1990 and 2004. Recent analysis of pooled data concerning symptomatic carotid stenosis has enhanced the initial results. Surgery in complement to best medical treatment is indicated for stenosis equal or superior to 70% (American calculation of degree of stenosis), especially if the patient is a man, older then 75 years, during the first 2 weeks after the initial neurological event. Benefit of surgery for stenosis between 50 and 69% appears only after 2 years. Surgery is also beneficial for asymptomatic severe stenosis but the precise threshold of carotid stenosis remains unclear. The benefit is lower for women and would be greater in case of stenosis more than 70%, and for patients less than 75 years.

Endovascular repair of abdominal aortic aneurysms in patients with severe angulation of the proximal neck using a flexible stent-graft: European Multicenter Experience.

AIM: The aim of this paper was to report the results of a multicenter study on endovascular repair of abdominal aortic aneurysms (AAA) in patients with important angulation of proximal neck using a flexible stent-graft (Aorfix). METHODS: Endovascular repair of AAA using a flexible stent-graft was performed at 16 centers in 29 patients with angulation of proximal neck greater than 45 degrees. Twenty-three patients (79%) had angulation greater than 60 degrees and were therefore contraindicated for repair with other contemporary devices. RESULTS: Technical success was achieved in all but one case (96%). There was one postoperative death due to multiorgan failure following revision of groin wound for hemorrhage. No patients were converted to open repair. One patient had persisting proximal endoleak despite placement of proximal extension. One patient in whom wireform fractures had been detected died from ruptured aneurysm at nearly 4 year follow-up. CONCLUSION: Endovascular repair using a flexible stent-graft is feasible in patients with highly angulated necks. This stent-graft allows the possibility of a to offer repair for patients un-suitable for the currently available commercial grafts. Mid-term results are acceptable and need to be confirmed by longer follow-up and larger series.

Endovascular treatment of anastomotic false aneurysms of the abdominal aorta.

Conventional surgical treatment of anastomotic false abdominal aortic aneurysms (AFAA) is technically difficult. Morbidity-mortality rates are higher than those for surgery of infrarenal abdominal aortic aneurysm (AAA). Endovascular management without laparotomy or aortic clamping represents an attractive alternative. The purpose of this study was to determine the immediate and middle-term outcome of endovascular management of AFAA. Between 1998 and 2001, 10 patients were treated for AFAA by placement of an endograft. The initial procedure was aortobifemoral bypass for occlusive artery disease in eight cases and resection and grafting for AAA in two cases. Mean age was 70 years. Seven patients were classified ASA 3 or 4. Three patients presented cardiac insufficiency with left ventricular ejection fraction <40%. Eight patients were treated using an aortounilateral iliac artery endograft in association with crossover femorofemoral bypass (3 AneuRx, 2 Endologix, 1 Talent, 1 Zenith, 1 surgeon-made stent). Two patients were treated with an aortoaortic endograft (1 Talent, 1 surgeon-made stent). In two patients extraperitoneal exposure of the common iliac artery was required for introduction of the stent in one case and for surgical closure of the iliac artery in the other case. A total of nine patients underwent another surgical procedure in association with stenting. Four endografts were custom-made. Endograft deployment was successful in all cases. No patient died during the postoperative period. Postoperative computed tomography (CT) scan confirmed exclusion of the aneurysmal sac in all cases. The mean duration of hospitalization was 13 days (range, 5-28 days). During follow-up (mean duration, 17.7 months; range, 5-42 months), one patient died from heart-related causes. No direct or indirect endoleak was detected by CT scan follow-up and a significant reduction in AFAA diameter was noted in the eight patients with follow-up periods lasting 6 months or more. One patient developed occlusion of an aortounilateral iliac artery endograft and was treated by axillobifemoral bypass. In one patient stenosis of the distal end of an aortounilateral iliac endograft was discovered by duplex scan and successfully treated by dilatation. Endovascular treatment of AFAA is technically feasible but requires more complex procedures involving associated surgical procedures and use of custom-made endografts. The morbidity-mortality rate in this small series of high-risk patients was low. Immediate and middleterm exclusion of AFAA was good.

Mortality and morbidity following endovascular repair of abdominal aortic aneurysms: analysis of two single centre experiences.

OBJECTIVE: to show how differences in anatomical and physiological risk factors can affect the outcome of endovascular repair of AAA by describing the experience of two centres with different selection policies. METHODS: one hundred and thirty-five patients (group I) were treated at Queen's Medical Centre (Nottingham, U.K.) using 101 in-house made and 34 manufactured stent-grafts. Median diameter, length and angulation of the proximal aneurysm neck were 26 mm, 27 mm, 40 degrees, respectively. Seventy-six patients had ischaemic heart disease, 47 had left ventricular failure, median forced expiratory volume in one second (FEV1) was 83%, median creatinine was 100 micromol/l and median age was 72 years. Fifty patients (group II) were treated at Timone Hospital (Marseilles, France) using seven in-house made and 43 manufactured stent-grafts. Median diameter, length and angulation of the proximal aneurysm neck were 25 mm, 34 mm, 33 degrees, respectively. Thirteen patients had ischaemic heart disease, two had left ventricular failure, median forced expiratory volume in one second was 101%, median creatinine was 108 micromol/l and mean age was 72 years. RESULTS: anatomical characteristics of the proximal neck were significantly worse in group I (p=0.02 for the three variables). Cardiac comorbidities were more frequent and mean FEV1 was lower in group I (p<0.0001 and p=0.001, respectively. Median aneurysm diameter was significantly greater in group I (65 mm) than in group II (53 mm) (p<0.001). Postoperative mortality was 9% and 0% in groups I and II respectively (p=0.03). The incidence of technical complications (groin wound complications and side branches endoleaks being excluded) was 20% and 0% in groups I and II, respectively (p=0.0006). CONCLUSION: postoperative mortality and technical complication rates were significantly greater in group I than in group II, readily explained by poorer general condition and worse anatomical characteristics of the proximal neck in group I.

Pathophysiology of proximal perigraft endoleak following endovascular repair of abdominal aortic aneurysms: a study using a flow model.

OBJECTIVE: to design a flow model to determine whether and why increased proximal neck angulation correlates with increased risk of proximal perigraft endoleak (PPE) flow. METHODS: a tapered stent-graft (Gianturco stent + Dacron) was deployed with proximal and distal necks made of silicone. The amount of PPE was measured over 30-s periods while the angulation of the proximal neck was increased. RESULTS: PPE flow increased significantly for angulations > or =30 degrees. The graft was lifted off the neck wall and gaps between the stent-graft and the neck created. CONCLUSION: greater neck angulation increased PPE flow. The stent-graft was lifted off the neck and subsequent gaps created. This model could be used to compare available stent-grafts and to test new designs that would improve the seal in angulated necks.

Construction of meaning in the authentic science writing of deaf students.

This study examines how students construct meaning through writing during authentic science activities. To determine how well students understood science concepts, we analyzed 228 writing samples from deaf students in grades 6 through 11 as well as the explanatory and reflective comments of their teachers. The analyses indicate that certain process writing strategies were differentially useful in helping deaf students to construct meaning and in allowing teachers to evaluate the constructed meaning. Three instructional conditions and two teacher variables were found to play roles in determining the accuracy and adequacy of the writing: (1) the writing prompts the teachers used, (2) the focus for the writing, (3) follow-up to the initial writing activity, (4) the teacher's content knowledge, and (5) the teacher's ability to interpret student writing. The authors recommend future applications of writing-to-learn strategies and suggest directions for further research and changes in teacher education.