Hyperbolic contraction measuring systems for extensional flow

In this paper an experimental method for extensional measurements on medium viscosity fluids in contraction flow is evaluated through numerical simulations and experimental measurements. This measuring technique measures the pressure drop over a hyperbolic contraction, caused by fluid extension and fluid shear, where the extensional component is assumed to dominate. The present evaluative work advances our previous studies on this experimental method by introducing several contraction ratios and addressing different constitutive models of varying shear and extensional response. The constitutive models included are those of the constant viscosity Oldroyd-B and FENE-CR models, and the shear-thinning LPTT model. Examining the results, the impact of shear and first normal stress difference on the measured pressure drop are studied through numerical pressure drop predictions. In addition, stream function patterns are investigated to detect vortex development and influence of contraction ratio. The numerical predictions are further related to experimental measurements for the flow through a 15:1 contraction ratio with three different test fluids. The measured pressure drops are observed to exhibit the same trends as predicted in the numerical simulations, offering close correlation and tight predictive windows for experimental data capture. This result has demonstrated that the hyperbolic contraction flow is well able to detect such elastic fluid properties and that this is matched by numerical predictions in evaluation of their flow response. The hyperbolical contraction flow technique is commended for its distinct benefits: it is straightforward and simple to perform, the Hencky strain can be set by changing contraction ratio, non-homogeneous fluids can be tested, and one can directly determine the degree of elastic fluid behaviour. Based on matching of viscometric extensional viscosity response for FENE-CR and LPTT models, a decline is predicted in pressure drop for the shear-thinning LPTT model. This would indicate a modest impact of shear in the flow since such a pressure drop decline is relatively small. It is particularly noteworthy that the increase in pressure drop gathered from the experimental measurements is relatively high despite the low Deborah number range explored

Obliteration of the fistulous tract with BioGlue® adversely affects the outcome of transanal advancement flap repair

Background: Transanal advancement flap repair (TAFR) is useful in the treatment of high transsphincteric fistulas. Initially, promising results were reported. More recent studies have indicated that TAFR fails in one out of three patients. In almost all of our patients with a failure, we have observed healing of the flap except at the site of the original internal opening. A possible explanation for this remarkable finding might be persistent inflammation in the fistulous tract, finding a way out through the original internal opening. The question is whether obliteration of the fistulous tract by local installation at a surgical adhesive, can prevent persistent inflammation to break through the original opening. The aim of this pilot study was to investigate whether concomitant instillation of BioGlue could improve the healing rate following TAFR for high transsphincteric fistulas. Methods: Between March 2006 and April 2006 a consecutive series of eight patients (four men, four women; median age 46 years) with a high transsphincteric fistula underwent TAFR after instillation of BioGlue in the fistulous tract. All patients were seen in the outpatient department for postoperative evaluation. Results: Fistula healing was observed in only one patient (12.5%). All other patients experienced one or more of the following complications: prolonged severe pain (n=5), discharge of great amounts of purulent liquid from the external opening (n=3) and abscess formation (n=2), necessitating incision and drainage. Because of this unexpected outcome we decided to terminate the study prematurely. Conclusions: Our findings indicate that obliteration of the fistulous tract with BioGlue adversely affects the outcome of TAFR for high transsphincteric fistulas