New Reactive Force Field for Simulations of MoS2 Crystallization.

We present a new reactive force field (ReaxFF) parameter set for simulations of Mo-S structures. We compare our parameterization to the state-of-the-art ones in their performance against density functional theory (DFT) benchmarks and MoS2 crystallization simulations. Our new force field matches DFT data significantly better than any previously published force fields and provides a realistic layered MoS2 structure in crystallization simulations. It significantly improves the state-of-the-art force fields, which tend to crystallize in the experimentally unknown rock-salt MoS structure. Therefore, our new force field is a good candidate for further development and inclusion of other practically relevant elements, such as O, C, N, and H, which can be used to study the formation and tribological or catalytical properties of molybdenum disulfide.

Stochastic thermodynamics of nanoscale friction.

Developing the thermodynamics of nanoscale friction is needed in a wide range of tribological applications, where the key objective is to optimally control the energy dissipation. Here we show that modern stochastic thermodynamics allows us to interpret the measurements obtained by friction force microscopy, which is the standard tool for investigating the frictional properties of materials, in terms of basic thermodynamics concepts such as fluctuating work and entropy. We show that this allows the identification of the heat produced during the friction process as an unambiguous measure of thermodynamic irreversibility. We have applied this procedure to quantify the heat produced during the frictional sliding in a broad velocity range, and we observe velocity-dependent scaling behavior, which is useful for interpreting the experimental outcomes.

Great saphenous vein ablation with steam injection: results of a multicentre study.

OBJECTIVE: To assess the safety and efficiency of steam vein sclerosis (SVS) of the great saphenous vein (GSV) in a multicentre open prospective cohort study. DESIGN: 75 consecutive adult patients with GSV reflux, CEAP C2-C5 and vein diameter 4-13 mm. METHODS: Patients treated using an SVS™ generator delivering homogenous pulses of superheated steam were followed up at 8 days and 1, 3, 6 and 12 months (clinical, duplex ultrasound, quality of life [QoL] with SF12). RESULTS: 88 veins were treated in 75 patients. At 6 months, 72/75 (96%) veins were obliterated (95% CI: 89-99) and Kaplan-Meier analysis found an obliteration rate of 96.1% at 12 months. QoL increased at 6 months for both the physical and mental components (p = 0.049 and p < 0.001 respectively). SVS was well tolerated: no major complications were reported. Adverse events occurred mainly at day 8 and incidents amounted to ecchymosis (n = 60) and pain (n = 7). CONCLUSIONS: SVS achieved an obliteration rate similar to that of other thermal ablation techniques. It was well tolerated with minimal post-operative pain.

Limited hypotensive effect of sildenafil in a high-risk population: a preliminary report.

Erectile dysfunction (ED) is often associated with cardiovascular disease (CVD) and the risk of sildenafil-induced orthostatic hypotension (OH) in subjects with CVD is a matter of concern. We describe our experience in using the tilt test (TT) with continuous plethysmography to evaluate the occurrence of OH in patients with CVD and ED after a test dose of sildenafil. When sildenafil was added on top of their usual pharmacological treatment two patients out of 32 (6.2%) developed asymptomatic OH, with a maximum blood pressure fall of 40/20 mm Hg. The low prevalence and modest clinical relevance of OH in our high-risk population coupled with the known high sensitivity and reproducibility of the TT seem to suggest that sildenafil is haemodynamically safer than is generally believed even when added on top of vasoactive treatment. These findings should be put into perspective against the growing wealth of evidence that PDE5 inhibitors may have therapeutic potential for a number of CV conditions.

Chromosome homogeneity in populations of Triatoma brasiliensis Neiva 1911 (Hemiptera - reduviidae - triatominae).

Triatoma brasiliensis is the most important vector of Chagas disease in the semiarid zone of the Northeast of Brazil. Several authors have reported the occurrence of four chromatic patterns with morphological, ecological, and genetic differences. In order to determine the existence of cytogenetic differentiation between these chromatic forms, we analyzed their karyotypes and the chromosome behavior during the male meiotic process. Triatoma brasiliensis shows distinct and specific chromosome characteristics, which differ from those observed in all other triatomine species. However, no cytogenetic differences were observed between the four chromatic forms of T. brasiliensis. The lack of chromosome differentiation among them could indicate that the populations of this species are in a process of differentiation that does not involve their chromosomal organization.

Management of symptomatic and asymptomatic popliteal venous aneurysms: a retrospective analysis of 25 patients and review of the literature.

OBJECTIVE: Popliteal venous aneurysms (PVAs) are an uncommon but potentially life-threatening disease because they can be a source for pulmonary emboli (PE). With the widespread use of venous duplex scanning, PVAs are increasingly found in patients with deep or superficial vein insufficiency, and questions have arisen as to the management of these aneurysms. The purpose of this study was to review our experience in the management of PVAs diagnosed in patients with PE and in patients with chronic venous diseases. METHODS: Twenty-five patients with PVAs were treated in two centers between 1985 and 1999. There were 20 women and five men, with an average age ranging from 33 to 79 years (mean age, 59 years). Twenty-four percent (6/25) presented with PE, and 76% (19/25) of PVAs were discovered during investigation for chronic venous disease (varicosities, n = 13; post-thrombotic symptoms, n = 6). The diagnosis of PVA was achieved in all cases with venous duplex scanning and phlebography. Aneurysms were located in the proximal popliteal vein (n = 17) and at the saphenopopliteal junction (n = 8). Seventy-two percent (18/25) of PVAs were saccular, and 40% (10/25) had an intraluminal thrombus. Two patients with PE underwent cardiac arrest, with one requiring a pulmonary embolectomy. The Fisher exact test showed a statistically significant correlation between PE and the presence of thrombus (50% vs 7% without thrombus, P =.02). Aneurysms were treated with tangential aneurysmectomy and lateral venorrhaphy (n = 19), resection with end-to-end anastomosis (n = 2), resection with interposition of the greater saphenous vein (n = 2) or the superficial femoral vein (n = 1), and resection with vein transposition (n = 1). Two patients who experienced a PE had an inferior vena cava filter placement before surgical repair of the PVA. RESULTS: Mean follow-up was 63 months (range, 11-168 months). No operative deaths occurred, and no patient had evidence of a recurrent PE. Postoperative minor complications (20%) included transient common peroneal nerve palsy (n = 2), postoperative hematoma (n = 2), and wound infection (n = 1). Postoperative thrombosis of the surgical repair occurred in three patients, and patency was restored with anticoagulation therapy. CONCLUSION: Despite its rarity, PVAs should be ruled out with venous duplex scanning in patients with PE and in patients presenting with chronic venous diseases. Because of the unpredictable risk of thromboembolic complications, surgical treatment that is accompanied by a low morbidity rate is indicated in all PVAs. Tangential aneurysmectomy with lateral venorrhaphy is the procedure of choice.

Evolution of ocular clinical and electrophysiological findings in pediatric Bardet-Biedl syndrome.

Bardet-Biedl syndrome (BBS) is a hereditary autosomal-recessive disorder, characterized by mental retardation, obesity, pigmentary retinopathy, polydactyly and, only in males, hypogenitalism. Even though genetic studies have revealed five different forms of BBS correlated to distinct loci on different chromosomes, a diagnosis of BBS is still primarily based on clinical data. The present study discusses the evolution of clinical ophthalmological and electrophysiological characteristics of BBS patients in developmental age. The main results obtained on a sample of 13 pediatric patients are the following: * progressive loss of visual acuity arised early in the first decade of life * ophthalmoscopic signs of pigmentary retinopathy were present only in 46% of the children studied * striking anomalies in the electroretinogram were also detected in the cases without pigmentary retinopathy * the electroretinographic results, when detectable, suggested a greater involvement of the photopic system as against the scotopic system.

Clinical application of digital indocyanine green angiography in choroidal neurofibromatosis.

Indocyanine green angiography (ICGA) was used to investigate 2 cases of type 1 systemic neurofibromatosis that had appeared at birth with café-au-lait skin spots, gradually developing into multiple cutaneous neurofibromas. Patients underwent periodical visual acuity examinations, the fundus was checked and fluorescein angiography (FA) was done; all findings appeared extremely stable. In 1995 these 2 patients underwent ICGA to check for pathological choroidal involvement. In both cases the initial examination stages showed multiple extensive areas of hypofluorescence, their morphology and extension coinciding with the retinal pigment epithelium (RPE) lesions shown by FA and by ophthalmoscopic examination. In later stages the hypofluorescent areas became smaller, generally shrinking to small isolated dots in the middle of the original areas. These initially hypofluorescent areas appeared to be due to slow focal choroidal filling caused by deep alterations to the walls of the choroidal arterioles induced by the disease. Chronic hypoperfusion of the choriocapillaris results in impairment of the overlying RPE, causing it to atrophy. The late hypofluorescent areas could be either persistent nonperfused lobules of choriocapillaris or neurofibromatose choroidal nodules. ICGA examination showed that the FA lesions described in the literature as choroidal nodules are in fact alterations to the RPE secondary to areas of hypoperfusion in the choriocapillaris.

Albumin-impregnated prosthetic graft for infrarenal aortic replacement: effects on the incidence and volume of perioperative blood transfusion.

We retrospectively reviewed 290 cases in which an albumin-impregnated polyester prosthetic graft was used for surgical management of aortic bifurcation disease between November 1987 and December 1990. The purpose of this review was to determine the incidence and volume of blood transfusion and to evaluate the rate of patency and the incidence of infection achieved using this type of prosthesis. The indication for surgery was abdominal aortic aneurysm (AAA) in 218 cases (190 elective procedures and 28 emergency procedures) and occlusive disease of the aortic bifurcation (ODAB) in 72 cases. Mean follow-up was 25.5 +/- 13.4 months (range: 1 and 50 months). The incidence of blood transfusion for elective AAA and ODAB surgery was 30.2% and 32.3% intraoperatively, 21.3% and 12.9% postoperatively, and 40.4% and 42.6% overall. The mean number of red cell packs transfused for elective AAA and ODAB surgery was respectively 1 and 0.8 intraoperatively, 0.4 and 0.6 postoperatively, and 1.4 and 1 overall. No immediate or late graft infection prosthesis was observed in any patient in this series. Primary and secondary patency was 95.5% and 97.5% at 6 months with no graft thrombosis during further follow-up. The fact that use of an impregnated graft in management of aortic bifurcation disease was accompanied by a high incidence and volume of blood transfusion suggests that these grafts do not reduce perioperative blood loss. Use of an impregnated prosthesis had no effect on the rate of patency and the incidence infection.

The impact of knee joint flexion on infrainguinal vascular grafts: an angiographic study.

OBJECTIVES: To characterise the morphologic behaviour of infrainguinal vascular grafts during flexion of the knee. DESIGN: A prospective angiographic study. MATERIALS AND METHODS: In 64 infrainguinal bypass grafts, intravenous digital subtraction angiography was performed within the first postoperative week. Frontal and lateral projection angiograms with the knee joint extended and with a 80-90 degrees flexion were taken. The distal anastomosis of the bypass was performed below-knee in 49 cases (18 in situ veins, 8 reversed veins with an anatomic course, 2 reversed veins with an extra-anatomic course, 4 composite grafts, 15 synthetic grafts with an anatomic course (14 polytetrafluoroethylene (ePTFE), 1 polyurethane), and two synthetic grafts with an extra-anatomic course. Fifteen ePTFE prostheses were implanted in the above-knee position. RESULTS: Out of 64 cases a total of 16 grafts showed stenotic kinking during flexion: two of the 18 in situ vein grafts, four of the 12 reversed vein grafts implanted with an anatomic course, one of the two reversed vein grafts implanted in an extra-anatomic site, eight of the 15 synthetic grafts crossing the knee, 0 of the two extra-anatomic ePTFE grafts, and one of the 15 cases of above-knee femoropopliteal ePTFE grafts. CONCLUSIONS: Stenotic kinking due to knee flexion can affect all kinds of bypass grafts including vein grafts placed anatomically and above-knee prostheses.

[Recurrent varicose veins in the groin after surgery]. / Les récidives au pli de l'aine après chirurgie des varices.

Recurrence of varicose veins following surgery of the long saphenous system are common. It is important to differentiate several causes. These, in fact, dictate the therapeutic decision. Physiopathologically, there are different types of recurrences: persistent reflux from the femoral veins into the superficial varicose network due to: an incomplete long sapheno-femoral high ligation (crossectomy), a neoangiogenesis at the level of the previous sapheno-femoral junction. separate termination of an incompetent long saphenous vein (LSV) into the common femoral vein or the superficial femoral vein (antero lateral or postero medial tributaries of LSV); persistent reflux from perineal and (or) paricto-abdominal veins into the varicose network of the thigh. Dynamic popliteal phlebography was, until the advent of echo-doppler, the author's method of choice for investigation as it was easier to interpret than varicography. At the present time it is only requested on the rare occasions where doubt persists even after echo-doppler. Additionally, with this investigation, the reflux (major or minor) can be analysed at its point of origin and a map of the underlying varicose network can be drawn. Therapeutically, we make the following suggestions: in the presence of a site of major reflux (incomplete crossectomy, high flow neoangiogenesis, separate termination of the saphenous tributaries), a further operation would be justified. The removal of the site of reflux can be associated with the placing of a PTFE patch on the common femoral vein. in the presence of a site of minor reflux, sclerotherapy or, preferably, echosclerotherapy would appear to be the treatment of choice. Elimination of the site (s) of reflux must be associated with suppression of the underlying varicose network by sclerotherapy or phlebectomy.

[Deep venous insufficiency and recurrent varicose veins after surgery of superficial venous insufficiency]. / Insuffisance veineuse profonde et récidive variqueuse après chirurgie de l'insuffisance veineuse superficielle.

Combination of deep and superficial venous insufficiency is far from exceptional and often causes severe chronic venous insufficiency (CVI). Does this association increase the risk of recurrent varicose veins after surgery of superficial insufficiency? After brief clinical and instrumental considerations in this situation, four series on this topic are analysed. Those published by Almgren, Guarnera, Darke and our personal series in which valve repair in the deep system was the inclusion criteria. Among the sixty seven patients included (80 lower limbs), fifty had previous surgery for varicose veins before valvuloplasty. Recurrence rate has been evaluated in both saphenous territories: great saphenous vein: 51% and short saphenous vein: 38.5%. It appears difficult to determine whether varicose vein recurrence is related to technical error at the initial operative procedure or due to the Primary Deep Vein Incompetence (PDVI). Nevertheless recurrence of varicose vein would appear to be frequent in the four series analysed. Many questions remain unanswered in this situation.

[Forensic medical implications in surgery of chronic venous insufficiency of the legs]. / Implications médico-légales dans la chirurgie de l'insuffisance veineuse chronique des membres inférieurs.

Current literature and personal experience with these complications are discussed. Complications with medicolegal implications have been analyzed in three studies, in France by J. Natali and A. Rispoli (Marseille, 1994) and in Great Britain by W.G. Tennant and C.V. Ruckley. The incidences reported are certainly underestimated as only those complications leading to an official expert opinion were counted. We also report our personal experience with medicolegal implications after 15,340 limb operations performed from 1968 to 1994. The conclusions provide an overall view of how to reduce the number of complications and provide adequate therapeutic management.

Albumin-impregnated polyester vascular prosthesis for abdominal aortic surgery: an improvement?

AIM: To compare the peroperative blood loss and the postoperative systemic inflammatory reaction in patients receiving either a Vasculour II Albumin pre-impregnated prosthesis (VA group, n = 32) or a preclotted Vasculour II prosthesis (V group, n = 33) for elective surgery of the abdominal aorta. SETTING: University Hospital. DESIGN: Prospective, randomised study. METHODS: Peroperative blood loss was measured over two different periods: Phase I from the beginning of the operation to the completion of the proximal anastomosis, when blood loss cannot be related to the model of prosthesis implanted and phase II after the completion of the proximal anastomosis to the end of the operation. Postoperative blood loss was evaluated by the determination of the retroperitoneal drainage volume over a period of 2 days immediately following the operation. The presence of periprosthetic fluid was measured with echography at days 4, 9, 30 and 60. The postoperative systemic inflammatory reaction was evaluated by measuring the sedimentation rate and the C reactive protein levels daily from day 1 to day 9, and at days 14, 21, 28, 45, and 60, and by measuring the body temperature daily from day 1 to day 9. RESULTS: No significant differences of peroperative blood loss were observed. The same proportion of patients (35%) in both groups received homologous transfusion. The mean number of units of homologous blood transfused per patient was respectively 0.77 and 0.91 for the VA and the V group. The retroperitoneal drainage volume and the percentage of patients with periprosthetic fluid did not differ significantly. No significant differences in systemic postoperative inflammatory reaction were observed. CONCLUSION: There were no benefits in using albumin-impregnated prosthesis as opposed to preclotted prosthesis in terms of peroperative and postoperative blood loss, or by looking at the incidence of homologous blood transfusion. However, the glutaraldehyde cross-linked albumin did not induce any systemic inflammatory reaction.

Albumin as a sealant for a polyester vascular prosthesis: its impact on the healing sequence in humans.

OBJECTIVE: Although the healing characteristics of albumin impregnated vascular prostheses have been extensively studied in animal models, they have never been studied in humans. We therefore examined the healing sequence and the albumin degradation rate of this type of prosthesis harvested from humans. We also addressed the possible relationship between the implantation of cross-linked albumin and a specific inflammatory reaction. METHODS: Thirty albumin-impregnated polyester vascular prostheses were collected in our institution from January 1991 to February 1993. The mean duration of implantation of the prostheses was 8.4+/-9.7 (SD) months (range: 1 hour to 26 months). Twenty two prostheses were patent at the time of explantation and 4 had been thrombosed for less than 24 hours. In 18 cases, the prostheses were surgically removed because of a complication or a reoperation, and during an autopsy in 12 cases. Each harvested specimen was submitted to histological and immunohistochemical studies in order to demonstrate the presence of human albumin sealant, and to determine the inflammatory cell constituents. RESULTS: The albumin-impregnated prostheses were poorly infiltrated by healing tissues after 2 years of implantation. An external capsule was constantly observed after 2 months of implantation with a nonspecific chronic inflammatory reaction localized between the capsule and the polyester yarns. We observed large amounts of albumin sealant after 2 months, a gradual degradation with time, and traces after 2 years of implantation in humans. The luminal surface of the explant was mainly covered with organized fibrin. No histological signs of a specific inflammatory reaction were observed. CONCLUSIONS: The healing of the albumin impregnated prosthesis was poor and the degradation rate of the albumin sealant was significantly delayed, when compared to animal models. This difference in degradation rate could be related to interspecies differences of phagocytic cells enzymatic machinery. Finally, implantation of glutaraldehyde cross-linked albumin in humans is safe, since we observed an aspecific chronic foreign body inflammatory reaction.

Chromosome numbers in the Triatominae (Hemiptera-Reduviidae): a review.

The chromosome numbers of 46 out of the 122 currently recognized species of Triatominae (Hemiptera, Reduviidae) are summarized. We present the number of autosomes, the sex mechanism and the first reference for each karyotype.