Fixation of Bovine Pericardium-Based Tissue Biomaterial with Irreversible Chemistry Improves Biochemical and Biomechanical Properties.

Bioprosthetic heart valves (BHVs), derived from glutaraldehyde crosslinked (GLUT) porcine aortic valve leaflets or bovine pericardium (BP), are used to replace defective heart valves. However, valve failure can occur within 12-15 years due to calcification and/or progressive structural degeneration. We present a novel fabrication method that utilizes carbodiimide, neomycin trisulfate, and pentagalloyl glucose crosslinking chemistry (TRI) to better stabilize the extracellular matrix of BP. We demonstrate that TRI-treated BP is more compliant than GLUT-treated BP. GLUT-treated BP exhibited permanent geometric deformation and complete alteration of apparent mechanical properties when subjected to induced static strain. TRI BP, on the other hand, did not exhibit such permanent geometric deformations or significant alterations of apparent mechanical properties. TRI BP also exhibited better resistance to enzymatic degradation in vitro and calcification in vivo when implanted subcutaneously in juvenile rats for up to 30 days.

In-vivo stretch of term human fetal membranes.

INTRODUCTION: Fetal membranes (FM) usually fail prior to delivery during term labor, but occasionally fail at preterm gestation, precipitating preterm birth. To understand the FM biomechanical properties underlying these events, study of the baseline in-vivo stretch experienced by the FM is required. This study's objective was to utilize high resolution MRI imaging to determine in-vivo FM stretch. METHODS: Eight pregnant women (38.4 ± 0.4wks) underwent abdominal-pelvic MRI prior to (2.88 ± 0.83d) caesarean delivery. Software was utilized to determine the total FM in-vivo surface area (SA) and that of its components: placental disc and reflected FM. At delivery, the SA of the disc and FM in the relaxed state were measured. In-vivo (stretched) to delivered SA ratios were calculated. FM fragments were then biaxially stretched to determine the force required to re-stretch the FM back to in-vivo SA. RESULTS: Total FM SA, in-vivo vs delivered, was 2135.51 ± 108.47 cm(2) vs 842.59 ± 35.86 cm(2); reflected FM was 1778.42 ± 107.39 cm(2) vs 545.41 ± 22.90 cm(2), and disc was 357.10 ± 28.08 cm(2) vs 297.18 ± 22.14 cm(2). The ratio (in-vivo to in-vitro SA) of reflected FM was 3.26 ± 0.11 and disc was 1.22 ± 0.10. Reflected FM re-stretched to in-vivo SA generated a tension of 72.26 N/m, corresponding to approximate pressure of 15.4 mmHg. FM rupture occurred at 295.08 ± 31.73 N/m corresponding to approximate pressure of 34 mmHg. Physiological SA was 70% of that at rupture. DISCUSSION: FM are significantly distended in-vivo. FM collagen fibers were rapidly recruited once loaded and functioned near the failure state during in-vitro testing, suggesting that, in-vivo, minimal additional (beyond physiological) stretch may facilitate rapid, catastrophic failure.

Surgical swab counting: a qualitative analysis from the perspective of the scrub nurse.

The aim of the study was to conduct a qualitative exploration of the sociotechnical processes underlying retained surgical swabs, and to explore the fundamental reasons why the swab count procedure and related protocols fail in practice. Data was collected through a set of 27 semistructured qualitative interviews with scrub nurses from a large, multi-site teaching hospital. Interview transcripts were analysed using established constant comparative methods, moving between inductive and deductive reasoning. Key findings were associated with interprofessional perspectives, team processes and climate and responsibility for the swab count. The analysis of risk factors revealed that perceived social and interprofessional issues played a significant role in the reliability of measures to prevent retained swabs. This work highlights the human, psychological and organisational factors that impact upon the reliability of the process and gives rise to recommendations to address contextual factors and improve perioperative practice and training.

Altered structural and mechanical properties in decellularized rabbit carotid arteries.

Recently, major achievements in creating decellularized whole tissue scaffolds have drawn considerable attention to decellularization as a promising approach for tissue engineering. Decellularized tissues are expected to have mechanical strength and structure similar to the native tissues from which they are derived. However, numerous studies have shown that mechanical properties change after decellularization. Often, tissue structure is observed by histology and electron microscopy, but the structural alterations that may have occurred are not always evident. Here, a variety of techniques were used to investigate changes in tissue structure and relate them to altered mechanical behavior in decellularized rabbit carotid arteries. Histology and scanning electron microscopy revealed that major extracellular matrix components were preserved and fibers appeared intact, although collagen appeared looser and less crimped after decellularization. Transmission electron microscopy confirmed the presence of proteoglycans (PG), but there was decreased PG density and increased spacing between collagen fibrils. Mechanical testing and opening angle measurements showed that decellularized arteries had significantly increased stiffness, decreased extensibility and decreased residual stress compared with native arteries. Small-angle light scattering revealed that fibers had increased mobility and that structural integrity was compromised in decellularized arteries. Taken together, these studies revealed structural alterations that could be related to changes in mechanical properties. Further studies are warranted to determine the specific effects of different decellularization methods on the structure and performance of decellularized arteries used as vascular grafts.

Measles virus: evidence of an association with Hodgkin's disease.

The quest for an infectious agent that may account for cases of Hodgkin's disease (HD) especially in young adults has proven vain until lately. We have recently reported findings that suggested the presence of measles virus (MV) antigens and MV RNA in the tissues of patients with HD. Support for an association between MV and HD has been provided by recent epidemiological findings relating the occurrence of HD to exposure to measles in pregnancy and the perinatal period. We now present further evidence of this putative association based on immunohistochemical, reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridisation studies (ISH) on HD tissues. Biopsies from 82 (54.3%) of our cohort of 154 patients showed a positive immunostain with at least two of the anti-measles antibodies used. Latent membrane protein-1 immunostaining for Epstein-Barr virus was positive in 46 (31.1%) of the patients examined. Reverse transcriptase-PCR and ISH for measles RNA were positive in seven and 10 of 28 patients, respectively. Preliminary clinicopathological associations between MV and HD are noted in this study, but no causal relationship can be claimed at this stage.

Comparison of 0.2% ropivacaine and 0.25% bupivacaine for axillary brachial plexus blocks in paediatric hand surgery.

BACKGROUND: The purpose of this study was to compare the use of ropivacaine 0.2% with bupivacaine 0.25% for axillary brachial plexus block in children undergoing hand surgery. METHODS: In a double-blind, randomized study, 35 children undergoing hand surgery received axillary brachial plexus blocks with 0.5 ml.kg-1 of either 0.2% ropivacaine or 0.25% bupivacaine. Pain scores were noted at 0, 3, 6, 12 and 24 h after surgery. The time to first dose of codeine phosphate and the total doses of all analgesics given were recorded. RESULTS: There was no significant difference between the two groups in pain scores, the time to first dose of codeine phosphate or in analgesic requirements in the first 24 h. CONCLUSIONS: Ropivacaine 0.2% is as effective as bupivacaine 0.25% for axillary brachial plexus blocks in children undergoing hand surgery.

New candidate virus in association with Hodgkin's disease.

Epidemiologic and molecular investigations of Hodgkin's disease (HD) suggest a strong infectious association. The Epstein-Barr virus (EBV), together with its viral proteins, is expressed in Hodgkin-Reed-Sternberg (HRS) cells in the lymph nodes involved by HD. EBV is more likely to be related to childhood and older adult cases of HD and is much less frequently expressed in young adult HD patients, the group most expected to be associated with an infectious agent. In addition, the "hit and run" theory of EBV infection remains speculative and no other lymphotropic viruses studied to date seem to satisfy the quest for a new candidate virus in young adults with HD. We have recently found preliminary evidence suggesting a possible association between the measles virus (MV) and HD. This evidence is the subject of the present review.

Surface strains in the anterior leaflet of the functioning mitral valve.

Abstract-The mitral valve (MV) is a complex anatomical structure whose function involves a delicate force balance and synchronized function of each of its components. Elucidation of the role of each component and their interactions is critical to improving our understanding of MV function, and to form the basis for rational surgical repair. In the present study, we present the first known detailed study of the surface strains in the anterior leaflet in the functioning MV. The three-dimensional spatial positions of markers placed in the central region of the MV anterior leaflet in a left ventricle-simulating flow loop over the cardiac cycle were determined. The resulting two-dimensional in-surface strain tensor was computed from the marker positions using a C0 Lagrangian quadratic finite element. Results demonstrated that during valve closure the anterior leaflet experienced large, anisotropic strains with peak stretch rates of 500%-1,000%/s. This rapid stretching was followed by a plateau phase characterized by relatively constant strain state. We hypothesized that the presence of this plateau phase was a result of full straightening of the leaflet collagen fibers upon valve closure. This hypothesis suggests that the MV collagen fibers are designed to allow leaflet coaptation followed by a dramatic increase in stiffness to prevent further leaflet deformation, which would lead to valvular regurgitation. These studies represent a first step in improving our understanding of normal MV function and to help establish the principles for repair and replacement.

Stability of emotions for traumatic memories in acute and chronic PTSD.

While memory for central factual information regarding an emotional event is considered to be relatively accurate, memory for emotions seem to be quite inaccurate (Christianson & Safer, 1995). We extended this line of research to examine memory for the emotional intensity surrounding a traumatic event (e.g., memory for the fear and horror of the event). We conducted a series of two studies. In Study 1, we examined memory for the emotional intensity of the traumatic event in recent sexual or non-sexual assault victims with acute PTSD at 2 and 12 weeks following the assault. In Study 2, we compared memory for emotional intensity in sexual and non-sexual assault victims with either acute or chronic PTSD at initial assessment and 12 weeks later. For both studies, participants were asked to recall general emotional intensity, fear intensity, and dissociative intensity of the traumatic event. Results suggested that memory for the fear of the traumatic event did not fluctuate over time. However, memory for the general emotional and dissociative intensity did fluctuate over time, decreasing for individuals with acute PTSD and increasing for individuals with chronic PTSD.

The biomechanical effects of fatigue on the porcine bioprosthetic heart valve.

Characterization of the mechanisms of degeneration of porcine bioprosthetic heart valves (BHV) during long-term cyclic loading is required for predicting and ultimately preventing their failure. Isolation of purely mechanical effects from host biological ones is a necessary first step in understanding the fatigue process as a whole. Thus, in this review we focus on mechanical factors alone as a means of isolating their role in altering biomechanical properties and ultimately their contribution to the fatigue damage process. Mechanical evaluations included tension controlled biaxial, 3-point flexural, and uniaxial failure tests performed on cuspal tissue following 0, 50, 100, 200, and 300 x 10(6) in vitro accelerated test cycles. Overall, biaxial mechanical results indicate a decreasing radial extensibility that can be explained by stiffening of the effective collagen fiber network as well as a small decrease in the splay of the collagen fibers. Moreover, these results suggest that the loss in flexural rigidity with fatigue that we have previously measured (ASAIO 1999; 45:59-63) may not be because of loss of collagen stiffness alone, but also to fiber debonding and degradation of the amorphous extracellular matrix. We discuss the implications of these results that point toward the development of chemical-treatment methods that seek to maintain the integrity of the amorphous extracellular matrix to ultimately extend BHV long-term durability.

Dynamic in vitro quantification of bioprosthetic heart valve leaflet motion using structured light projection.

Quantification of heart valve leaflet deformation during the cardiac cycle is essential in understanding normal and pathological valvular function, as well as in the design of replacement heart valves. Due to the technical complexities involved, little work to date has been performed on dynamic valve leaflet motion. We have developed a novel experimental method utilizing a noncontacting structured laser-light projection technique to investigate dynamic leaflet motion. Using a simulated circulatory loop, a matrix of 150-200 laser light points were projected over the entire leaflet surface. To obtain unobstructed views of the leaflet surface, a stereo system of high-resolution boroscopes was used to track the light points at discrete temporal points during the cardiac cycle. The leaflet surface at each temporal point was reconstructed in three dimensions, and fit using our biquintic hermite finite element approach (Smith et al., Ann. Biomed. Eng. 26:598-611, 2001). To demonstrate our approach, we utilized a bovine pericardial bioprosthetic heart valve, which revealed regions of complex flexural deformation and substantially different shapes during the opening and closing phases. In conclusion, the current method has high spatial and temporal resolution and can reconstruct the entire surface of the cusp simultaneously. Because it is completely noncontacting, this approach is applicable to studies of fatigue and bioreactor technology for tissue engineered heart valves.

Biaxial mechanical properties of the native and glutaraldehyde-treated aortic valve cusp: Part II--A structural constitutive model.

We have formulated the first constitutive model to describe the complete measured planar biaxial stress-strain relationship of the native and glutaraldehyde-treated aortic valve cusp using a structurally guided approach. When applied to native, zero-pressure fixed, and low-pressure fixed cusps, only three parameters were needed to simulate fully the highly anisotropic, and nonlinear in-plane biaxial mechanical behavior. Differences in the behavior of the native and zero- and low-pressure fixed cusps were found to be primarily due to changes in the effective fiber stress-strain behavior. Further, the model was able to account for the effects of small (< 10 deg) misalignments in the cuspal specimens with respect to the biaxial test axes that increased the accuracy of the model material parameters. Although based upon a simplified cuspal structure, the model underscored the role of the angular orientation of the fibers that completely accounted for extreme mechanical anisotropy and pronounced axial coupling. Knowledge of the mechanics of the aortic cusp derived from this model may aid in the understanding of fatigue damage in bioprosthetic heart valves and, potentially, lay the groundwork for the design of tissue-engineered scaffolds for replacement heart valves.

How much work is required to puncture dura with Tuohy needles?

The effects of needle bevel orientation and cerebrospinal fluid (CSF) pressure on dural displacement and force required to penetrate cadaveric dura were studied using 40 samples. A constant hydrostatic pressure was applied to the subdural surface, either high or low, simulating the sitting and lateral positions. A 17-gauge Tuohy needle was advanced through the dura with the bevel oriented parallel or perpendicular to dural fibres. Travel distance and peak force at which dural penetration occurred were measured under both pressure conditions. The work required to produce dural penetration was calculated. Greater force and work were required to penetrate dura in the perpendicular orientation (P < 0.05), regardless of the subdural pressure exerted. Dural displacement was similar under both pressure conditions.

Surface geometric analysis of anatomic structures using biquintic finite element interpolation.

The surface geometry of anatomic structures can have a direct impact upon their mechanical behavior in health and disease. Thus, mechanical analysis requires the accurate quantification of three-dimensional in vivo surface geometry. We present a fully generalized surface fitting method for surface geometric analysis that uses finite element based hermite biquintic polynomial interpolation functions. The method generates a contiguous surface of C2 continuity, allowing computation of the finite strain and curvature tensors over the entire surface with respect to a single in-surface coordinate system. The Sobolev norm, which restricts element length and curvature, was utilized to stabilize the interpolating polynomial at boundaries and in regions of sparse data. A major advantage of the current method is its ability to fully quantify surface deformation from an unstructured grid of data points using a single interpolation scheme. The method was validated by computing both the principal curvature distributions for phantoms of known curvatures and the principal stretch and principal change of curvature distributions for a synthetic spherical patch warping into an ellipsoidal shape. To demonstrate the applicability to biomedical problems, the method was applied to quantify surface curvatures of an abdominal aortic aneurysm and the principal strains and change of curvatures of a deforming bioprosthetic heart valve leaflet. The method proved accurate for the computation of surface curvatures, as well as for strains and curvature change for a surface undergoing large deformations.

Differential expression of sialyl and non-sialyl-CD15 antigens on Hodgkin-Reed-Sternberg cells: significance in Hodgkin's disease.

CD15 expression has been used for years to confirm the diagnosis of Hodgkin's disease (HD). Little is, however, known on the relevance of the CD15 antigen to the pathobiology of the disease and there is conflicting evidence as to the prognostic value of its expression. To investigate the significance of the differential expression of CD15 in Hodgkin's disease, a retrospective study of 102 patients with "classical" Hodgkin's disease was performed. Immunohistochemical studies were carried out using antibodies against two types of CD15: non-sialylated CD15 (LeuM1 and 80H5) and sialylated CD15 (FH6 and CSLEX1). Cases that were negative for non-sialylated CD15 or positive for the sialylated variant were stained again following neuraminidase pretreatment. The cohort included 27 patients in whom sequential biopsies were available. Both CD15 expression in its non-sialylated form and absence of sialyl-CD15 expression correlate with a favorable outcome. Subsequent biopsies show a preferential expression of sialyl-CD15, notably in bone marrow metastases. Our findings suggest that, in the progression of HD towards a widely disseminated disease, the LewisX moiety of the CD15 antigen on the tumor cells acquires a sialyl-group. This change may confer on the tumor cells the capacity to metastasize.

Hodgkin's lymphoma in the Bedouin of southern Israel: epidemiological and clinical features.

BACKGROUND: A previous study on Hodgkin's lymphoma in southern Israel found that Bedouin patients had an increased rate of Epstein-Barr virus expression in their tumor cells. OBJECTIVES: To determine the influence of the patients' communities on the pattern of disease in HL. METHODS: We compared the clinical features, demographic data, stage at diagnosis, treatment modality and outcome, as well as laboratory findings, in four community-based subgroups. These groups comprised kibbutz residents (n = 11), Bedouin (n = 19), new immigrants from the former USSR (n = 22), and town-dwellers (n = 82). RESULTS: The Bedouin patients differed significantly from the new immigrants and town-dwellers, particularly regarding the rate of EBV sequences in the tumor tissues, and a poorer response to treatment. The kibbutz patients did not differ significantly from the other populations regarding most of the parameters studied, but showed an intermediate expression of EBV antigens compared to Bedouin patients and the rest of the cohort. CONCLUSIONS: This study indicates that HL may behave differently in different population groups in a given geographic area. Notably, the Bedouin patients showed markedly different clinical and biological patterns of this malignancy.

Mechanical evaluation and design of a multilayered collagenous repair biomaterial.

One method of fabricating implantable biomaterials is to utilize biologically derived, chemically modified tissues to form constructs that are both biocompatible and remodelable. Rigorous mechanical characterization is a necessary component in material evaluation to ensure that the constructs will withstand in vivo loading. In this study we performed an in-depth biaxial mechanical and quantitative structural analysis of GraftPatch (GP), a biomaterial constructed by assembling chemically treated layers of porcine small intestinal submucosa (SIS). The mechanical behavior of GP was compared to both native SIS and to glutaraldehyde-treated bovine pericardium (GLBP) as a reference biomaterial. Under biaxial loading, GP was found to be stiffer than native SIS and mechanically anisotropic, with the preferred fiber direction demonstrating greater stiffness. Quantitative structural analysis using small-angle light scattering indicated a uniform fiber structure similar to GLBP and SIS. To enable test-protocol-independent quantitative comparisons, the biaxial mechanical data were fit to an orthotropic constitutive model, which indicated a similar degree of mechanical anisotropy between the three groups. We also demonstrate how the constitutive model can be used to design layered biocomposite materials that can undergo large deformations.

Bilateral recurrent laryngeal nerve neuropraxia following laryngeal mask insertion: a rare cause of serious upper airway morbidity.

We report the case of a 4-year-old boy who developed bilateral recurrent laryngeal nerve neuropraxia following a routine anaesthetic with a laryngeal mask airway. The possible mechanisms of injury and the ways that this rare but critical complication might be avoided are discussed.