Biomechanical evaluation of fixation properties of fibrin glue for ventral incisional hernia repair.

INTRODUCTION: Use of adhesives for mesh fixation in hernia is increasing. There has been minimal study of mesh incorporation and interface strength with adhesive fixation for ventral hernia repair. The purpose of this study was to evaluate the fixation properties of fibrin glue as it compared to suture fixation of mesh in an onlay position. METHODS: Twenty-four mongrel pigs were divided into three study arms based on time points for biomechanical evaluation: 24 h (n = 8), 7 days (n = 8), and 14 days (n = 8). Initial procedures included placement of two 4 × 6 cm pieces of wide-pore polypropylene mesh in an onlay position. One was fixated with 4 ml of fibrin glue and the other with four interrupted 2-0 polypropylene sutures. The shear strength of fixation was evaluated using a uniaxial testing device along with histological evaluation. Maximum force was normalized by the width of the mesh. RESULTS: Mesh-tissue interface of glued and sutured specimens at 7 and 14 days did not fail in our testing configuration. Only at the 24-h time point the mesh detached from the tissue, and the sutured interface (10.4 N/cm) was significantly stronger than glued interface (4.9 N/cm, p = 0.004). Histopathologic and gross evaluations of the specimens revealed similar histologic features at all time points for both glued and sutured specimens. CONCLUSIONS: With mesh in the onlay position, fixation to the abdominal wall occurs quickly. Though sutures were stronger at 24 h, as early as 1 week, the strength of the fixation exceeded the tissue or the mesh strength in our testing configuration for both glue and suture groups. Fixation strength is independent of technique at the latter time points. There are potential clinical advantages to the exclusive use of fibrin glue for fixation including acute post-operative pain, chronic post-operative pain, and recurrence for ventral incisional hernia repair.

Asymptomatic carriage of toxigenic Clostridium difficile by hospitalized patients.

Asymptomatic carriage of Clostridium difficile is common in hospitals, but the risk for transmission by carriers is unclear. In this point prevalence culture survey of asymptomatic hospitalized patients, 18 of 149 (12%) were carriers of toxigenic C. difficile. By comparison with C. difficile infection (CDI) patients, the prevalence of skin and/or environmental contamination was significantly lower in asymptomatic carriers (3/18, 17% versus 5/6, 83%; P = 0.007), but carriers outnumbered CDI patients in the hospital by a factor of 3 to 1. These data suggest that asymptomatic carriers have the potential to contribute to C. difficile transmission in hospitals.

[Sepsis-like disease in an immunocompromised patient with a travel history to Mallorca]. / Sepsisähnliches Krankheitsbild bei Immunsuppression nach früherem Mallorcaurlaub.

In immunosuppressed patients, a high rate of complications due to opportunistic infection is known. We report the case of a 36 year old patient with ulcerative colitis and a septic complication with ongoing pancytopenia. Due to colonic perforation, colectomy had to be performed. Despite this intervention, the septic constellation persisted. The pancytopenia in peripheral blood counts also persisted with the necessity of repetitive transfusions. A bone marrow biopsy showed an infiltration with Leishmania bodies in macrophages. Tissue culture allowed for typing of the parasites as belonging to the L. donovani/infantum complex, DNA sequencing confirmed infection with L. infantum. This infection must have been contracted during a vacation on Mallorca about 1.5 years earlier. Administration of liposomal amphotericin B cured the patient. Surprisingly, histological examination of the resected colon reveiled the presence of an immunoblastic B-cell lymphoma. In this case, immunosuppression was a prerequisite for the manifestation of leishmaniosis.

Risk factors associated with permanent access-site infections in chronic hemodialysis patients.

OBJECTIVE: To determine the epidemiological risk factors associated with permanent access-site (PAS) infection in a population of chronic hemodialysis patients. DESIGN: Retrospective cohort analysis. SETTING: Hemodialysis unit of a 400-bed Department of Veterans' Affairs hospital. RESULTS: A cohort of 94 males (1,316 patient months) was studied. Fifty-one PAS infections in 31 patients were observed. Six patients had two PAS infections, four patients had three infections, and two patients had four infections. Twenty-nine of the 31 patients with PAS infections were bacteremic at least once. Univariate analysis identified seven factors significantly associated with PAS infection in this population: location of PAS other than forearm, type of vascular access (polytetrafluoroethylene [PTFE] versus endogenous arteriovenous [AV] fistula), limited ambulatory status, residence in a nursing home, bacterial infection at a distant site, number of access-site revisions, and number of hospitalizations. In a logistic regression analysis, only graft type and number of PTFE graft revisions were associated independently with PAS infection. The odds ratio for PAS infection in PTFE grafts compared to endogenous AV fistula was 7.8; the odds ratio for PAS infection with each PTFE graft revision was 1.5. CONCLUSIONS: PAS infections were associated independently with the type of graft and the number of PTFE graft surgical revisions.

Complaint review procedures of state licensing boards.

In the highly litigious society in which we practice, situations all too frequently arise in which a dentist and a patient disagree. The disagreement may be as minor as a misunderstanding regarding fees charged for services rendered, or as substantial as that resulting from an injury secondary to dental treatment. Regardless of the exact nature of the incident, it nonetheless may result in the filing of a complaint by the aggrieved patient with the state board of dentistry against the treating clinician. This article explains the process leading to the resolution of a complaint.

Ceftazidime-resistant Klebsiella pneumoniae isolates recovered at the Cleveland Department of Veterans Affairs Medical Center.

The rate of ceftazidime resistance among Klebsiella pneumoniae isolates recovered from patients at the Cleveland Department of Veterans Affairs Medical Center increased from 6% in the first quarter of 1993 to 28% in the first quarter of 1994. The outbreak was hospitalwide, with the highest rates of resistance occurring on wards where ceftazidime was administered most frequently. Although many plasmid patterns were observed in the clinical isolates, molecular epidemiological analysis with use of pulsed field gel electrophoresis revealed substantial similarities between the strains; this finding suggested that most of the strains-if not all of them-were derived from the original clone. The addition of piperacillin/tazobactam to the hospital formulary and educational efforts focused on minimizing the administration of ceftazidime were associated with a marked decrease in the drug's use and a concomitant decrease in the percentage of ceftazidime-resistant isolates. We have not yet observed a significant rise in the rate of resistance to piperacillin/tazobactam among clinical isolates of K. pneumoniae.

A fluid dynamics study of the Trac catheter.

A fluid mechanics study of the Trac catheter was done using a 10 x scaled model. Wall pressure distributions and particle and dye flow visualization studies show that a primary vortex develops due to the spinning tip, and a secondary flow recirculates material along the chamber wall to the base of the chamber and back to the tip. Strong, nearly instantaneous mixing occurs throughout the vortex for speeds above 50,000 rpm scaled for the full-scale catheter. Close-contact pressure studies also show that wall pressures of the order of 0.4 MPa may be obtained for a full-scale catheter.

An estimated shape function for drift in a platelet-transport model.

Prior work has shown that concentration profiles of platelets in flowing whole blood and of platelet-sized beads in flowing blood suspensions can include near-wall excesses. A model to describe this phenomenon was built about a single-component convective diffusion equation. To incorporate redistribution to preferred sites by shear flows of red cell suspensions, the model used a drift shape function (in addition to the commonly used augmented diffusion coefficient). This paper reports experiments that provide an average concentration profile from which the shape function for that model is calculated; the experiments and shape function are for the particular conditions of 40% hematocrit, platelet-sized latex beads (2.5 microns diameter), tube ID of 217 microns, and a wall shear rate of 555 s-1. Less precise estimates of the shape function obtained from data of previous studies indicate that the shape function is similar for the hematocrit of 15%.

Transient lateral transport of platelet-sized particles in flowing blood suspensions.

Concentration profiles of 2.5 microns latex beads were measured to demonstrate lateral transport of platelet-sized objects in flows of blood suspensions; the flows had equivalent Poiseuille wall shear rates (WSRs) from 250 to 1220 s-1. Each experimental trial began with a steady flow of suspension without beads in a thin-walled capillary tube (219 microns ID; 10.2 microns SD). The tube entrance was then switched to a reservoir containing suspension of equal hematocrit, but with beads, for a short interval of flow at the same WSR. This process established a paraboloidal tongue of labeled suspension with a transient concentration gradient at its surface. The tube and contents were rapidly frozen to fix the suspended particles in flow-determined locations. Segments of frozen tube were collected at distances from the entrance corresponding to 13%, 39%, and 65% of the axial extent of the ideal paraboloidal tongue. Concentration profiles were estimated from distances measured on fluorescence microscope images of cross-cut tube segments. Experiments used tubes either 40 or 50 cm long, suspension hematocrits of 0, 15, or 40%, and bead concentrations in the range of 1.5-2.2 x 10(5)/mm3. Profiles for 0% hematocrit suspension, a dilute, single-component suspension, had features expected in normal diffusive mixing in a flow. Distinctly different profiles and more lateral transport occurred when the suspensions contained red cells; then, all profiles for 13% extent had regions of excess bead concentration near the wall. Suspension flows with 40% hematocrit exhibited the largest amount of lateral transport. A case is made that, to a first approximation, the rate of lateral transport grew linearly with WSR; however, statistical analysis showed that for 40% hematocrit, less lateral transport occurred when the WSR was 250 s-1 or 1220 s-1 than 560 s-1, thus indicating that the rate behavior is more complex.

Anatomic and biomechanical properties of human lumbar dura mater.

Determinants of dural defects subsequent to deliberate or accidental dural puncture include the equipment, techniques, and the inherent anatomic and biomechanical properties of dura mater. These properties were studied in specimens of human and canine lumbar dura mater in an attempt to delineate the structure of the tissue and to characterize its behavior in biomechanical terms. Human dura had a longitudinal orientation on gross appearance, and was confirmed microscopically to be composed of longitudinal lamella of collagen and elastin fibers. Longitudinal tensile strength and stiffness were greater than transverse tensile strength and stiffness, which is consistent with the dura's apparent anatomic structure and functional requirements. Additional biomechanical testing of the dura demonstrated the property of relaxation which is a characteristic of a viscoelastic material. Significant differences were observed between human and canine dural properties, suggesting limited value of this animal model. Integration of these observed anatomic and biomechanical properties of the lumbar dura provides a greater understanding of dural puncture and may explain previous and often confusing clinical and experimental findings.

Model of platelet transport in flowing blood with drift and diffusion terms.

A drift term is added to the convective diffusion equation for platelet transport so that situations with near-wall excesses of platelets can be described. The mathematical relationship between the drift and the fully developed, steady-state platelet concentration profile is shown and a functional form of the drift that leads to concentration profiles similar to experimentally determined profiles is provided. The transport equation is numerically integrated to determine concentration profiles in the developing region of a tube flow. With the approximate drift function and typical values of augmented diffusion constant, the calculated concentration profiles have near-wall excesses that mimic experimental results, thus implying the extended equation is a valid description of rheological events. Stochastic differential equations that are equivalent to the convective diffusion transport equation are shown, and simulations with them are used to illustrate the impact of the drift term on platelet concentration profiles during deposition in a tube flow.

Expression of MHC class I and II molecules by cadaver retinal pigment epithelium cells: optimization of post-mortem HLA typing.

The objective of this study was to investigate the expression of MHC antigens by retinal pigment epithelium cells (RPE) after stimulation with interferon-gamma (IFN-gamma) and to improve the currently practised technique of cadaver HLA typing. A concentration of 100 U/ml IFN-gamma induced expression of class I molecules up to greater than 90% 3 days after stimulation, whereas 50 U/ml were required for the expression of HLA-DR to greater than 90%. A concentration of 750 U/ml induced 35-45% expression of HLA-DP and less than 25% HLA-DQ after 3 days. Cells were serologically typed using the standard lymphocytotoxicity assay 3 days after stimulation with 250 U/ml IFN-gamma. Typing of class I specificities was complemented by one-dimensional isoelectric focusing (1D-IEF). We observed high concordance between the results of the RPE typing and the lymphocytotoxicity test on the same donors. Our results show complete typing of class I and II antigens post-mortem, which, in particular, enables graft matching and improvement of graft survival in recipients of organs removed many hours after death such as the cornea.

Near wall concentration profiles of 1.0 and 2.5 microns beads during flow of blood suspensions.

A freeze-capture method was used to determine the concentration profiles of latex beads in the flow of blood suspensions at a wall shear rate of 400 s-1 in hollow fibers of 200 microns i.d. Bead diameters of 1.0 and 2.5 microns and suspension hematocrits from 15 to 80% were used. All profiles exhibited an excess of beads in the 20 microns closest to the wall and a uniform central concentration. Near-wall excesses greater than 2.5 times the central concentration occurred with suspensions having 2.5 microns beads when the hematocrit was 15-40%. Although large near-wall excesses sometimes occurred for the small beads and higher hematocrits, the usual event was a small near-wall excess. A Mann-Whitney-Wilcoxan test showed that the group of data for 2.5 microns beads in suspensions with hematocrits ranging from 15 to 40% was significantly different from all other data (p less than 0.0002). As the 2.5 microns beads approximate the average platelet, these data suggest that blood flows with physiologic hematocrits are associated with larger near-wall excesses of platelets than blood flows with elevated hematocrits.

The dynamics of platelet thrombus formation rate, thrombus retention time, and rate of embolization on a control and heparin bonded polyurethane angio-catheter.

The dynamics of platelet deposition and embolization from control and heparin bonded polyurethane catheters (CPC and HBPC) was evaluated with In-111 labeled autologous platelets (IN-PLT) and a computerized gamma camera (CGC). Ten non-heparinized dogs (18-25 kg) were catheterized in both femoral arteries with 10 cm of CPC and HBPC (5 Fr., Cordis) 24 hr after injection of 300-420 microCi of In-PLT, and imaged for 3 hr with the computerized gamma camera. The regional platelet deposition curves (RPDC) indicated multiple peaks and valleys; the curves were analyzed for early rate of thrombus formation (upswing), thrombus retention time (full width at half maxima of the RPDC-peak), and rate of embolization (downswing) on both catheters. The four parameters (mean +/- SD) of thrombosis on catheters and integral of the radioactivity time curve for the 3 hr duration of imaging were calculated from normalized counts/sec. The rate of thrombus formation and rate of embolization are higher for the control than HBPC, suggesting that heparin-bonding decreases the early rate of thrombosis and embolization. The thrombus adhesivity and retention time appear shorter for the control catheter, indicating that the control thrombogenic catheter forms multiple thrombi and emboli than HBPC. The integral appears larger for the control catheter than HBPC. In vivo (dynamic) studies, in vitro studies, and critical analyses of the radioactivity time curve were essential for complete evaluation of thrombogenicity of catheters and other cardiovascular prostheses.

Concentration profiles of platelet-sized latex beads for conditions relevant to hollow-fiber hemodialyzers.

A freeze-capture method was used to obtain the concentration profiles of platelet-sized latex beads (2.5 microns diameter) in saline-based red cell suspensions flowing through tubes with inner diameters of 135 and 200 microns. Without red cells the concentration profile exhibited a slight deficit near the wall. For hematocrits from 15 through 52%, the concentration profile exhibited a near-wall excess of beads, from two to eight times the central concentration. Near-wall excesses were small or nonexistent in the first half centimeter of the tube. For hematocrits of 15 and 30%, the profile and near-wall excess were equal at stations 2 cm or more from the entrance. These results suggest that there is a flow-driven mechanism that moves platelet-sized beads toward, but not to, the wall.

Concentration profiles of 1 and 2.5 microns beads during blood flow. Hematocrit effects.

Freeze-capture techniques were used to obtain concentration profiles of 1.0 and 2.5 microns latex beads in suspension flows with hematocrits from 15 to 60%. Profiles with near-wall concentrations more than twice the central concentration occurred for 2.5 microns beads in this range of hematocrits, but the near-wall excess appeared wider and shorter in 60% suspensions. For suspensions with 1.0 microns beads, the nature of the profile was dependent upon hematocrit. In all cases, at least a small near-wall excess was observed. For hematocrits of 40 and 60%, profiles for 1.0 microns beads were sometimes similar to those for 2.5 microns beads. For the 60% hematocrit and small beads, however, the excess was less than twice the central concentration in two of five trials. These findings are discussed in the context of previous experiments.

A freeze-capture method for the study of platelet-sized particle distributions.

A rapid freezing method was developed to study the distributions of fluorescent platelet-sized particles in flows of blood suspensions through thin-walled capillary tubes. Segments of frozen tubes were mounted in a refrigerated microtome on the stage of an epifluorescence microscope. Sections of tube were cut away, images of newly exposed cross-sections were recorded on video tape, and distances of the particles from the wall were measured from recorded images. The distance data were used to construct histograms that were proportional to the local concentration. Results indicated that this method is suitable for the study of the distribution of platelet-sized particles over a wide range of hematocrit, that the basic profile is reproducible to within 15%, and that the non-uniform profile is not a result of events at the tube entrance.

Conditions for the occurrence of large near-wall excesses of small particles during blood flow.

Prior work showed that the near-wall concentration of platelet-sized latex beads (2.38 microns diam) in flowing blood suspensions can be greater than three times the concentration in the central region of the flow. Similar methods were used to explore the dependence of the near-wall excess (NWE) of beads on the channel height and suspension composition. The bead diameter, suspending fluid viscosity, and red blood cell deformability were varied; the hematocrit was fixed at 15%. Results showed that NWEs greater than or equal to three times the central concentration were associated with shear stress, rather than with strain rate, required red cell deformability, and occurred with bead diameters of 2.2 microns or larger. The amplitude of NWEs observed in the 30- and 50-microns channels changed sharply from small to large as the wall shear rate (WSR) was increased, while those observed in 100-microns channels exhibited a more gradual dependence on WSR.