Higher Burst Pressures Research Articles

A new porcine skull base model: Fibrin glue improves strength of cerebrospinal fluid leak repairs

Objectives Fibrin glue is used in addition to grafts and flaps to repair cerebrospinal (CSF) leaks. We designed a porcine model to test the hypothesis that fibrin glue increases biomechanical strength. Study Design A randomized experimental animal study. Methods Ten pigs underwent craniotomy with creation of a fistula through the cribriform plate into the nasal cavity. CSF leaks were endoscopically confirmed and repaired using pericranial grafts. The animals were randomized into a fibrin glue group (n = 5) and a control group (n = 5). Seven days later, endoscopic examination assessed for CSF leaks. The skull bases were harvested and examined for the degree of graft adherence (graded I-V) and subjected to burst pressure testing and histopathological analysis. Results Eight animals survived, four in each group. There were no CSF leaks in the fibrin glue group and one in the control group. The fibrin glue group showed greater graft adherence ( P = 0.029) and higher burst pressures (13.8 ± 5.4 vs 4.6 ± 3.1 psi, P = 0.021). Histopathological analysis revealed no difference in inflammation and bone remodeling. Conclusions The porcine model is a good model for anterior skull base defects. The model confirmed that fibrin glue reduces the rate of CSF leak by improving graft adherence and strength of repair.

Evaluation of Unmeshed and 1:1 Meshed AlloDerm Bolsters for Stapled Rectal Anastomoses in a Porcine Model

The major morbidity of colorectal anastomoses is leaks. The concept of staple-line reinforcement is a growing area of interest. In this study, we evaluated the feasibility and effect of utilizing AlloDerm to bolster end-to-end stapled rectal anastomoses in a porcine model. A total of 30 female 45-kg domestic pigs were studied, and each served as its own control by creating a bolstered and unbolstered anastomosis in each animal. All anastomoses were created with a 29-mm end-to-end stapling device. Bolstered anastomoses were randomized to proximal and distal positions along the rectum, and each rectorectal anastomosis was separated by an average of 10 cm. In 20 pigs, an unmeshed bolster of a 0.5-0.7-mm thickness was used. The remaining 10 pigs had a 1:1 meshed bolster that was 0.34-0.51 mm thick. The animals were survived for 14 days. Barium enemas were then performed and the two anastomotic sites harvested, and each anastomosis underwent burst testing. The internal diameter of each anastomosis was measured and a biochemical analysis was performed for matrix metalloproteinase (MMP), elastin and collagen content. The unmeshed bolstered anastomoses burst fewer times than the unbolstered anastomoses (P=0.004) and had higher burst pressures (P=0.023), though their anastomotic circumferences were smaller (P=0.007). Meshed bolsters offered no strength advantage to anastomoses and were significantly (P=0.009) smaller than unbolstered anastomoses in the same animal. No difference in elastin, collagen, or MMP content was observed between bolstered and unbolstered groups. No animals had clinical or radiographic leaks. The routine use of unmeshed and 1:1 meshed AlloDerm bolsters is safe and does not appear to inhibit healing in elective colorectal surgery on healthy subjects. AlloDerm may have a role as a tissue bolster in select patients who are more prone to develop anastomotic leaks.

Deformation Behaviour of Accumulative Roll Bonded and Friction Stir Welded Aluminium Alloys

Commercial purity aluminium AA1050 and aluminium alloy AA6016 were accumulative roll bonded and subsequently friction stir welded. The microstructure of the conventional and ultrafine-grained materials produced by accumulative roll bonding is strongly affected by friction stir welding. The elongated ultrafine-grained microstructure of roll bonded sheets becomes coarser and equiaxed in the nugget region. Hydraulic bulge tests showed that higher burst pressure can be achieved for samples without friction stir welding than for the ones with friction stir welding. Localised deformation, crack initiation and propagation, as well as the final fracture occurred within the nugget. Friction stir welded AA1050 sheet showed similar achievable burst pressures and von Mises equivalent strains compared to the as-received conventionally grained sheets. On the other hand, significantly higher burst pressures and at the same time higher von Mises equivalent strains were observed for the friction stir welded ultrafine-grained material than for the friction stir welded conventionally grained material.

Prospective Comparison of Four Laparoscopic Vessel Ligation Devices

The merits of laparoscopic sealing devices have been poorly characterized. The purpose of this study was to compare two bipolar sealing devices [LigaSure V (LS) and Gyrus PK (GP)], an ultrasonic device [Harmonic Scalpel ACE (HS)] and a novel device using nanotechnology [EnSeal PTC (ES)]. The ability of all four 5 mm devices to seal 5 mm bovine arteries was tested under controlled temperature and humidity in accordance with manufacturer specifications. Study endpoints included lateral thermal spread, time to seal, burst pressure, smoke production and subjective (blinded review of video clips) and objective (measured using an aerosol monitor) effect upon visibility. The HS demonstrated the least thermal spread. The LS (10.0 secs) and GP (11.1 secs) had the fastest sealing times (p<0.001 for both) when compared to ES (19.2 sec) and HS (14.3 sec). Mean burst pressure values were: LS 385 mm Hg, GP 290 mm Hg, ES 255 mm Hg and HS 204 mm Hg. The HS had the best subjective visibility score and the lowest objective smoke production (2.88 ppm) compared to the GP (74.1 ppm), ES (21.6 ppm) and LS (12.5 ppm), (p<0.01 for all). The LS has the highest burst pressure and fastest sealing time and was the highest rated overall. The HS produced the lowest thermal spread and smoke but had the lowest mean burst pressure. The GP had the highest smoke production, and variable burst pressures. Despite employing nanotechnology, the ES device was the slowest and had variable burst pressures.

Self-ignition and explosion during discharge of high-pressure hydrogen

The phenomenon of self-ignition and explosion during discharge of high-pressure hydrogen was investigated. To clarify the ignition conditions of high-pressure hydrogen jets, rapid discharge of the high-pressure hydrogen was examined experimentally. A diaphragm was used to allow rapid discharge of the high-pressure hydrogen. The burst pressure was varied from 4 to 30 MPa. The downstream geometry of the diaphragm was a flange and extension pipes, with the pipe length varying from 3 to 300 mm. The diameter of the nozzle was 5 or 10 mm. When short pipes were used, the hydrogen jet did not ignite. However, the hydrogen jet showed an increasing tendency to ignite in the pipe as the length of the pipe became longer. At higher burst pressures, a diffusion jet flame was formed from the pipe. The blast wave from the fireball formed on self-ignition of the hydrogen jet resulted in an extremely rapid pressure rise.

Effect of Bioactive Polypeptides on Leaking Large Bowel Anastomosis and Intestines in the Rat

Anastomotic leakage and postoperative adhesions represent major complications after colorectal surgery. We have previously shown a positive effect on both anastomotic strength and abdominal adhesions by the use of differently charged bioactive polypeptides. The present study aimed to investigate the effect of the same polypeptides on the healing of an insufficient intestinal anastomosis, as well as on accidental intestinal injury, in addition to measuring the preventive effect against the development of abdominal adhesions. An insufficient, and thereby potentially leaking, intestinal anastomosis and punctures of the intestine (“accidental intestinal injury model”) were performed in rats. The treatment groups received intraperitoneal administration of poly-L-lysine and poly-L-glutamate, while controls received sodium chloride. Burst pressure, extent of abdominal adhesions, and postoperative complications were analyzed in both experimental models. A significant decrease of adhesions was seen in all animals treated with polypeptides (p <. 05). Burst pressure was significantly higher (p <. 001) in animals with intestinal perforation as seen on day 1 and then decreasing. A significant decrease in the incidence of peritonitis was also noted early (day 1) in this model (p =. 002). The mortality and complications were high in the intestinal anastomosis model, though not affected by treatment with polypeptides. Intraabdominal adhesions were significantly reduced using polypeptides in this study, with no observed effect on other postsurgical complications. There were signs of less infectious complications in polypeptide treated animals. In animals with accidental intestinal injury, a higher burst pressure was noted in treated animals.

Critical parameter of burst pressure measurement in development of bypass grafts is highly dependent on methodology used

Because of the low patency rate of currently available vascular bypass grafts, researchers are working towards the development of alternative bypass grafts, ranging from synthetic prostheses to wholly biologic living grafts. The philosophy of measurement required by regulatory agencies such as the United States Food and Drug Administration (FDA) as well as to gain the Conformité Européene (CE) mark is to test above and beyond the limits that would be expected physiologically. The critical parameter of burst pressure is needed for Conformité Européene (CE) mark or United States Food and Drug Administration (FDA) approval before clinical trials can proceed. An accurate measurement of burst pressure in potential porous vascular bypass grafts is, therefore, of utmost importance to ensure adequate strength on implantation in animals and subsequent clinical use. A wide range of methods to measure burst pressure have been used. We tested the burst pressure of a new polyurethane-based nanocomposite vascular prosthesis by using different methods to assess whether the method used affected the results. Water was infused at flow rates of 0.2, 50, and 100 mL/min through a syringe pump into latex sleeve-lined porous prostheses manufactured from a poly(carbonate-urea)urethane nanocomposite incorporating silsesquioxane. At the lowest infusion rate, the inflation was done with and without a nonporous inner lining sleeve. A pressure transducer was used to record the peak pressure achieved. Using a nonporous sleeve resulted in a higher burst pressure (428 mm Hg vs 341 mm Hg) at a flow rate of 0.2 mL/min. A lower infusion rate (0.2 mL/min) produced a lower burst pressure than 50 mL/min (428 mm Hg vs 451 mm Hg). No significant difference was found in burst pressure using infusion rates of 50 mL/min and 100 mL/min. The use of a nonporous sleeve removes the potential weakness presented by the pores themselves. A continuous high infusion rate consistently overestimates burst pressure. These methods may not reflect the physiologic state. Care needs to be taken in interpretation of methodology for burst pressure measurement, and the rate of infusion should be stated in any description of the method. The poor patency of small-caliber vascular bypass prostheses has stimulated a large body of research into alternative graft materials. This includes synthetic and, more recently, tissue-engineered hybrid products. Acceptance for international standards requires demonstration of a rigorous mechanical testing regimen, including graft strength, which has on the whole involved burst strength measurement. However, the methods used to measure burst strength have varied with respect to apparatus used and rate of graft inflation. We show that these variables lead to markedly different results. In particular, fast infusion rates may overestimate the actual burst pressure, leading to a false sense of security.

The Use of Staple-Line Reinforcement During Laparoscopic Gastric Bypass

Divided linear staple-lines are a mainstay of gastrointestinal surgery, and in particular, bariatric surgery. Staple-line failure, although uncommon, can result in significant morbidity and even mortality. Staple-line buttressing has been developed to improve staple-line strength, decrease bleeding and minimize the risk of leak. Many different products are currently available. However, most have not been proven in clinical trials. Bovine pericardial strips (BPS) are a buttressing material that fits onto the stapler device and gets "stapled" onto the tissue when the device is fired. The strips add thickness and potentially strength to the staple-line. Animal research has shown that staple-lines incorporated with BPS had higher burst pressures than those without. Human experience has suggested that BPS decreased the risk of acute staple-line failures in laparoscopic Roux-en-Y gastric bypass surgery. This report reviews the clinical and research experience with this product.

Burst-Induced Stresses in Cemented Wellbores

Summary This paper presents the results of a finite element study of the resistance to burst pressure. Results from the 2D model quantify the effects of various mechanical properties of cement on a cemented wellbore. Comparison of the predicted stresses with experimental results demonstrated that ductile cement is far less likely to crack radially from high internal burst pressures than a brittle cement. It is demonstrated that the in-situ formation stresses acting on the cemented wellbore greatly affect the burst resistance of the cemented wellbore. The industry acknowledges that there is an increase in the burst resistance of cemented pipe vs. uncemented pipe; but the effects of cement and formation mechanical properties, and in-situ stresses are not well understood. This paper presents the results of a finite element study of the resistance of casing to internal burst pressure under a variety of conditions. This will provide for better design understanding of the stress conditions developed in casing under burst loading. 2D stress-distribution model results are presented in graphical and tabular format for a variety of geometrical and mechanical material properties of formations, cement slurries, and casing combinations. A better understanding of the true stress profile in cemented pipe allows for less expensive decisions concerning casing design parameters and safety-factor criteria. Applications using the burst resistance of the cemented pipe as a system as opposed to using the burst resistance of free pipe can include deeper drilling with thinnerwalled pipe, smaller rigs, and better casing integrity decisions for refracturing candidates.

A pressure transducer with a single-sided multilevel structure by maskless etching technology

A novel single-sided multilevel beam-diaphragm-mass structure has been designed and fabricated for high sensitivity silicon pressure transducers by using a novel anisotropic etching technology. The structure consists of three thin beams on a deep-etched thin diaphragm and two masses. Each mass consists of a mesa for stress concentration and a small island (post) on the mesa for overrange protection. As all the structures are on the back side of the wafer, the front side remains flat. The piezoresistors are diffused resistors on the front side in the locations with beams on the back. The multilevel structure features (1) flat front side facilitating metal interconnection; (2) small islands for overrange protection so that the electrostatic force caused by electrostatic bonding between the masses and the glass substrate is minimal; and (3) high burst pressure of the diaphragm. A prototype pressure transducer of 400 Pa operation range and 0.6% nonlinearity has been tested.