First principles surface thermodynamics of industrial supported catalysts in working conditions.

Ever stronger environmental concerns prompt the research in the area of heterogeneous catalysis to play an ever more crucial role to produce ever cleaner fuel from the refining of petroleum effluents. The catalytic active phase is often used in a dispersed state over a porous oxide material. This paper is a review of recent progress brought by periodic density functional theory (DFT) calculations in the area of two relevant industrial supported catalysts. We focus on two important supports used in the refining industry: anatase-TiO(2) and γ-alumina. According to the various reaction conditions, the presence of H(2)O, H(2) and H(2)S may change the surface states of the support. In particular, it is crucial to know and control the hydroxylation state depending on temperature and partial pressure of reactants (H(2)O, H(2), H(2)S). The support effects on the catalytic active phases are presented for MoS(2) particles, used in hydrodesulfurization catalysis, and for Pd particles, used in hydrogenation catalysis. It is shown how the wetting property and equilibrium morphology of the active phase depend on the support. A discussion on the impact for catalytic activities is provided.

Nonlinear analysis of arterial oscillated flow in experimental stenosis and microsurgical anastomosis.

BACKGROUND: Thrombotic vascular occlusion is one of the main complications that can occur during microsurgical anastomosis and is frequent when the blood becomes turbulent. The aim of this ex vivo study was to test the use of nonlinear mathematical tools to detect turbulence flow upstream and downstream of an arterial stenosis and of a microsurgical anastomosis technique in arteries with diameters in the range of microsurgical practice. MATERIALS AND METHODS: Rat carotid arteries (0.8 to 1.2 mm diameter) were transferred to a flow chamber and perfused with Krebs solution. An oscillated vascular flow was initiated with a peristaltic pump and a transit time flowmeter was used to measure flow with two probes. An arterial stenosis was created by a ligature and progressively increased ranging from 0 to 95%. For each flow signal three nonlinear analytical procedures were applied: time-delayed procedures, correlation dimension, and computing of the largest Lyapunov exponent. RESULTS: Our results indicated that the level of turbulence flow is correlated with the area reduction stenosis. In the range of 60-95% area reduction stenosis, we noted an experimental increase of turbulence flow. We also founded that a classical end-to-end anastomosis technique induced an increase of the turbulence flow in comparison with a control artery. CONCLUSIONS: Thus nonlinear analysis can be useful in characterizing the complexity of an oscillated flow in small arteries submitted to stenosis or microsurgical anastomosis and may have clinical uses in detecting high level turbulent flow after microsurgery.

[VCS microclip anastomosis on blood vessels of less than 2 millimeters in diameter. Preliminary experimental study in the rat]. / Anastomoses par microagrafes VCS sur des vaisseaux de diamètre inferieur à 2 millimètres. Etude expérimentale préliminaire chez le rat.

The aim of this work was to study the possibilities and limits of the vascular microanastomoses with VCS microclips. VCS Microclips are a new mechanical anastomotic device, allowing a single operator to perform anastomoses without microsutures. The two arcuate limbs of the titanium microclips do not penetrate the vascular intima. The microclip anastomosis technique is based on symmetric eversion of the vessel walls, facilitated by everting forceps. We studied the medium and small Autosuture VCS microclips on different vessels ranging from 0.3 to 2 millimeters in diameter: aorta, carotid artery, femoral artery and femoral vein. Thirty nine end-to-end or end-to-side anastomoses were performed on Wistar rats. These anastomoses were performed by a single operator without the use of sutures. Patency was studied by the "empty and refill" test immediately and at two months. Histologic analysis of the anastomosis was performed at two months (hematein-eosin and orcein stains on longitudinal sections). Four out of thirty nine anastomoses were occluded during the 15 minutes following clamp release. Failure was always due to a technical error and occurred during the first trials. The thirty five other anastomoses were patent immediately and at two months post-operatively, except for the by-pass which was not viable. These anastomoses were still patent 30 minutes post-operatively. Light microscopy analysis confirmed that the microclip extremities did not penetrate the lumen, although the internal media was usually very thin at the level of the microclip jaws, especially for the smallest vessels. For vessels larger than 1 mm in diameter, the microclip extremities were usually outside the internal elastic lamina. No anastomotic aneurysm was found. Vascular healing was comparable with microsutures at 2 months. Microvascular anastomoses performed with microclips have numerous advantages, compared to usual microsutures: they are two to three times quicker, they can be performed step by step without turning the clamp and they can be performed with the right or left hand. There is theoretically no thrombogenic risk. The drawbacks are the need for complementary training and the cost of microclips which is five to six times that of sutures. End-to-side anastomoses of small vessels are more difficult than end-to-end anastomoses. The recipient vessels must be larger than 1.5 mm in diameter, otherwise the anastomosis may become stenosed. Microclips are especially useful to save time, i.e. for multiple anastomoses and for anastomoses of vessels larger than 1 millimeter in diameter. Some modifications of the material could allow vascular or hollow organ anastomoses with endoscopic assistance.

[Arterial phenomenon of autonomization of vascularized island flaps reviewed by expansion of the vascular pedicle. An experimental study in the rat]. / Les phénomènes artériels de l'autonomisation des lambeaux cutanés en îlot vasculaire revus par l'expansion d'un pédicule vasculaire. Une étude expérimentale chez le rat.

This experimental study performed in rats examined the possible vascular extensions of a periprosthetic membrane neoflap with an axial vascular pedicle towards an adjacent cutaneous angiotome. 22 Wistar rats were operated. After tattooing the superficial iliac circumflex angiotome, the adjacent epigastric pedicle was expanded. After expansion and a two-month rest period, clinical and microangiographic studies were performed. In 50% of cases, the iliac island skin flap raised on the periprosthetic membrane created by the epigastric pedicle was considered to be viable. The microangiographic results were identical. The pathophysiological mechanism is analysed in the light of the literature.

[Experimental study of the reliability of end to end arterial microanastomosis]. / Etude expérimentale de la fiabilité des micro-anastomoses artérielles intériorisées.

Since 1978 (Lauritzen), several experimental and clinical procedures of end-in-end vascular microanastomosis have been described, including that proposed by Wang (1986) in which the tubulisation is accompanied by a counter-incision of the recipient vessel. Our experimental study was designed to assess the reliability of this procedure, to quantify it in relation to the diameter of the artery and direction of flow and to verify the existence of absence of any particular intraluminal histological phenomena. 42 Wistar rats were operated under general anaesthesia. 42 microanastomoses were performed: 15 carotid and 15 femoral in the direction of arterial blood flow, and 15 carotid anastomoses in the opposite direction to flow. The 15 carotid anastomoses performed in the direction of flow were all patent at each of the postoperative examinations (D0, D + 15, D + 90). Patency decreased in the anastomoses performed in the opposite direction to blood flow (10 out of 15 carotid anastomoses were patent) and as a function of the arterial diamenter (5 out of 12 femoral anastomoses were patent). Horizontal and transverse histological sections performed on the 15th and 90th days demonstrated continuity of the intimal endothelial lining and thickening of the adventitia of the two internalised and recipient walls in every case. In practice, although this experimental study demonstrates the clinical reliability of this internalised microanastomosis procedure in rat carotid arteries, the other results and the anatomo-clinical discrepancy do not justify its clinical use in all circumstances, particularly in the opposite direction to blood flow and in arteries with a diameter less than or equal to 1 mm.

[Periprosthetic membrane island flap with axial pedicle. Experimental study on the effect of time and expanded volume]. / Néo-lambeau de membrane péri-prothétique à pédicule axial. Etude expérimentale de l'influence du temps et du volume expansé.

This experimental study, conducted in the rat, assessed the influence the volume of expansion and time after expansion on the vascularised area of a periprosthetic membrane axial pedicle (epigastric) expanded island flap. 15 Wistar rats were operated on and divided into 3 series according to the expanded volume (20 cc, 40 cc) and the time (1, 2 months). The membrane vascularisation derived from the pedicle was study by microradiography based on geometric parameters. At equal times, the volume essentially increased the length of the pedicle and had little effect on the vascularised area. For equal expanded volumes, increasing latency time increased the length and especially the width of opacification derived from the pedicle. The periprosthetic membrane axial pedicle island flap is an experimental entity whose vascularised area, obtained after a certain amount of expansion, is influenced more by time than by the volume of expansion.

[Experimental concept of periprosthetic membrane neo-flap with axial vascular pedicle]. / Concept expérimental de néo-lambeau de membrane péri-prothétique à pédicule vasculaire axial.

This study was designed to demonstrate that progressive inflation of an expansion prosthesis placed under the epigastric pedicle of the rat induced the formation of vascular connections between this vessel and the periprosthetic membrane. 17 Wistar rats were operated under general anaesthesia. The 7 cc prosthesis was implanted into the inguinal fold and the valve was placed in a dorsal position via limited incisions. 11 rats were studied, divided into 3 series: 3 control rats (non-inflated prosthesis), a series in which the prosthesis was inflated up to 20 cc (at a rate of 5 cc per week) and a series in which the fate of the capsular flap isolated as a vascular island flap in a prefabricated silicone block was studied. The assessment was threefold: clinical, microradiographic after injection of lipiodol into the epigastric artery and histological. The clinical and microradiographic studies demonstrated the reality of the blood supply of part of the periprosthetic membrane and its connections with the epigastric axial pedicle. This membrane surface, constituting a real biological flap prefabricated by expansion, corresponds to the peripedicular zone (2 x 1 cm). The viability of the island flaps was confirmed after 8, 14 and 21 days. Histological studies confirmed the hypervascularisation and richness of the collagen fibres as a result of expansion.

An improved method for electron microscopic study (SEM and TEM) of vessel prosthesis anastomoses in microsurgery.

In order to study the replacement of vessels by biological vascular prostheses in microsurgery, an improved method for scanning electron microscopy preparation which is rapid and minimizes artifacts was developed. To limit endothelial surface injury, the vessel and prosthesis unity is, at first, prefixed by injection into one end of a 2.5% isotonic solution of glutaraldehyde. After fixation by osmium tetroxide, the samples are dehydrated by a graded series of acetone solutions and critical point dried. They are then trimmed around each suture line to pieces of 1 cm including 1/3 vessel and 2/3 prosthesis for further orientation and sectioned longitudinally, with a new razor blade, for microvascular anastomoses observations. The same chemical treatment applied to samples for transmission electron microscopy studies permitted verification of the good preservation of the cellular structures.

[EEG effects of sodium nitroprusside and hemodynamic references]. / Effets EER du nitroprussiate de sodium et references hemodynamiques

A study was performed on baboons (Papio papio) of various hemodynamic and EEG effects of sodium nitroprussiate (SNP), substance with powerful vasodilator action. Three different procedures of drug injection were used: (1) in isolation, either in doses close to those used in clinical practice or in high doses; (2) after neuroleptanalgesia (NLA); (3) after causing vasospasm. With isolated SNP, effects on blood pressure were unstable; in certain cases hypotension could be maintained only with toxic doses. Hypotension was facilitated when NLA had been previously induced. At low doses the cerebral blood flow (CBF) was practically unmodified, whereas at toxic doses it first increased then decreased. In animals under NLA, the CBF drop was only moderate, suggesting persistence of adequate spasm, CBF was significantly improved through SNP. The EEG did not undergo sizeable change at low SNP doses given in isolation; toxic doses always induced alterations with peculiar morphology, but developing only tardily after SNP perfusion was begun. This lag may indicate that hypotensive and toxic SNP effects are dissociated. These alterations suggest that screening of the EEG is necessary during prolonged administration of SNP, e.g., in surgical procedures. Combining NLA and SNP (at low doses) causes EEG deceleration, but no great alteration of the rhythms, as observed during other types of controlled experimental hypotension. Hence, cerebral circulation may be relatively well protected during SNP hypotension.

[Experimental study of the cerebrovascular effects of sodium nitroprusside in the baboon Papio papio. Its action on the experimental vasospasm]. / Etude expérimentale des effets cérébro-vasculaires du nitroprussiate de soude chez le babouin Papio papio. Son action sur le vasospasme expérimental

Sodium nitroprusside (SNP) has been suggested as hypotensive agent in the surgery of cerebral aneurysms. As a preliminary step to neurosurgery, a study of its cerebro-vascular and EEG action had been carried out in 42 papio-papio baboons. On the unanaesthetized analgesic-free animal, doses below 20 mumg/kg/min. induce only a moderate decrease of mean arterial blood pressure (MABP), a slight rise of intracranial pressure (ICP) and a neat fall of cerebro-vascular resistance (CVR) without EEG modifications. Doses above 50 mumg/kg/min. induce a neat fall of MABP with a rise of cerebral blood flow (CBF), of ICP and signs of poisoning with metabolic acidosis and prolonged EEG disturbances. Beyond 90 mumg/kg/min. irreversible hypotension occured accompanied by metabolic acidosis and progressive abolition of cerebral electrogenesis. The hypotensive action of SNP is potentiated by neuroleptanalgesic drugs (phenoperidine and dehydrobenzoperidol). Using this combination marked hypotension was achieved with non toxic doses of SNP (6 to 10 mumg/kg/min.). During those hypotensions cerebral auto-regulation was maintained up to a MABP of 50 mmHg. Deeper brief hypotensions up to a MABP of 25 to 45 mmHg induce a 23% fall of CBF (p less than 0, 05) but without major EEG alterations. During experimental arterial spasms induced by injection of blood in the cisterna magna or serotonin infusion, SNP has a vasodilating action. It induces a significant rise of CBF (p less than 0, 01) for doses between 8 and 19 mumg/kg/min.