Correlation of light microscopic findings with transmission electron microscopy within a vascular occlusion device.

Host response to an implanted biomaterial is a complex process involving microscopic changes in extracellular matrix (ECM) composition. Reliable pathology analysis is imperative for accurate assessment of the tissue response to an implanted device. Plastic histology is commonly used for histology evaluation of medical devices to assess the device-tissue interface; however, this technique is prone to variable staining that can confound histology interpretation. Appropriately, we propose using transmission electron microscopy (TEM) to confirm histologic ECM findings in order to provide sufficient host-response data. Tissue response to an absorbable shape memory polymer intravascular occlusion device with a nitinol wire backbone was evaluated. Representative plastic-embedded, micro-ground sections from 30-day, 60-day, and 90-day timepoints were analyzed. ECM regions were selected, and ultrathin sections were created for TEM evaluation. Histological changes in ECM composition were compared for light microscopy (LM) and TEM findings; specifically, TEM fibrillary patterns for collagen and fibrin were used to confirm LM results. Throughout this study, LM reveals inconsistent staining in plastic-embedded sections. TEM, on the other hand, provides clear insight into the tissue response by morphologically discerning distinct fibrillary patterns within ECM structures; loose to dense collagen surrounds the implant as fibrin degrades, demonstrating progression of postimplant ECM maturation. Moreover, TEM serves as a definitive method for confirming tissue substrate morphology when LM findings prove ambiguous.

Assessment of intravenous pbi-shRNA PDX1 nanoparticle (OFHIRNA-PDX1) in yucatan swine.

PDX1 (pancreatic and duodenal homeobox 1) is overexpressed in pancreatic cancer, and its reduction results in tumor regression. Bi-functional pbi-shRNA PDX1 nanoparticle (OFHIRNA-PDX1) utilizes the endogenous micro-RNA biogenesis pathway to effect cleavage- and non-cleavage-dependent degradation of PDX1 mRNA. We have shown that OFHIRNA-PDX1 reduces pancreatic tumor volume in xenograft models. Thus, we are now exploring biorelevant large animal safety of OFHIRNA-PDX1. Mini pigs were chosen as the biorelevant species based on the similarity of human and pig PDX1 target sequence. In the initial study, animals developed fever, lethargy, hyporexia and cutaneous hyperemia following administration of OFHIRNA-PDX1. Twenty-one days later, the same animals demonstrated less toxicity with a second OFHIRNA-PDX1 infusion in conjunction with a prophylactic regimen involving dexamethasone, diphenhydramine, Indocin and ranitidine. In a new group of animals, PDX1 protein (31 kDa) expression in the pancreas was significantly repressed at 48 and 72 h (85%, P=0.018 and 88%, P=0.013; respectively) following a single infusion of OFHIRNA-PDX1 but recovered to normal state within 7 days. In conclusion, a single intravenous infusion of OFHIRNA-PDX1 in conjunction with premedication in pigs was well tolerated and demonstrated significant PDX1 knockdown.

Bradyarrhythmias and pacemaker therapy in dogs with Chagas disease.

BACKGROUND: Chagas disease (Trypanosomiasis) is a cause of myocarditis in the southern United States causing cardiac conduction abnormalities, arrhythmias, and heart failure. OBJECTIVES: To report clinical findings and outcome in Chagas positive (CP) dogs requiring pacemaker implantation for bradyarrhythmias. ANIMALS: One hundred and forty-four client-owned dogs requiring pacemaker implantation. METHODS: Retrospective case series. Information regarding history, physical exam, laboratory and diagnostic imaging findings, treatment, and survival were obtained from medical records, with additional follow-up information obtained by contacting referring veterinarians and owners. RESULTS: Of the 144 dogs requiring pacemaker implantation from January 2001 to May 2010, 83 (57.6%) had a Chagas titer performed and 9 (10%) were CP. Concurrent ventricular arrhythmias (odds ratio 1.61, P = .005) or atrioventricular (AV) block (odds ratio 4.18, P < .001) increased the likelihood that a Chagas titer was submitted. Median age for CP dogs was 6.2 years (range, 0.3-10); 7 were male. Bradyarrhythmias included high-grade 2nd or 3rd degree AV block (n = 8) and sinus bradycardia with 1st degree AV block (n = 1); 5 had concurrent ventricular arrhythmias. A positive Chagas titer had a negative impact on survival (hazard ratio 4.04; 95% CI 1.36-12.1, P = .012) with a reported median survival time of 365 days (interquartile range, 84-973 days). CONCLUSIONS AND CLINICAL IMPORTANCE: Bradyarrhythmias can result in clinical signs requiring pacemaker implantation in CP dogs, and although the diagnosis negatively impacts survival, pacemaker therapy is a viable treatment option.

Integrated microscopy techniques for comprehensive pathology evaluation of an implantable left atrial pressure sensor.

The safety and efficacy of an implantable left atrial pressure (LAP) monitoring system is being evaluated in a clinical trial setting. Because the number of available specimens from the clinical trial for histopathology analysis is limited, it is beneficial to maximize the usage of each available specimen by relying on integrated microscopy techniques. The aim of this study is to demonstrate how a comprehensive pathology analysis of a single specimen may be reliably achieved using integrated microscopy techniques. Integrated microscopy techniques consisting of high-resolution gross digital photography followed by micro-computed tomography (micro-CT) scanning, low-vacuum scanning electron microscopy (LVSEM), and microground histology with special stains were applied to the same specimen. Integrated microscopy techniques were applied to eight human specimens. Micro-CT evaluation was beneficial for pinpointing the location and position of the device within the tissue, and for identifying any areas of interest or structural flaws that required additional examination. Usage of LVSEM was reliable in analyzing surface topography and cell type without destroying the integrity of the specimen. Following LVSEM, the specimen remained suitable for embedding in plastic and sectioning for light microscopy, using the positional data gathered from the micro-CT to intersect areas of interest in the slide. Finally, hematoxylin and eosin (H&E) and methylene blue staining was deployed on the slides with high-resolution results. The integration of multiple techniques on a single specimen maximized the usage of the limited number of available specimens from the clinical trial setting. Additionally, this integrated microscopic evaluation approach was found to have the added benefit of providing greater assurance of the derived conclusions because it was possible to cross-validate the results from multiple tests on the same specimen.

Pathologic evaluation of canine renal biopsies: methods for identifying features that differentiate immune-mediated glomerulonephritides from other categories of glomerular diseases.

BACKGROUND: Human renal biopsies are routinely evaluated with light microscopy (LM) using a panel of histologic stains, transmission electron microscopy (TEM), and immunofluorescence (IF) microscopy to obtain a diagnosis. In contrast, the pathologic evaluation of glomerular disease in veterinary medicine has relied mostly on LM and was of limited utility. To address this problem, recently established veterinary renal diagnostic centers have adopted methods used in human nephropathology for evaluation of renal biopsies. Three broad categories of disease, which have the greatest implications for clinical management of proteinuric dogs, have been established and include amyloidosis, immune complex-mediated glomerulonephritis (ICGN), and non-ICGN. OBJECTIVE: To demonstrate histopathologic, ultrastructural, and IF findings in renal biopsy specimens that experienced veterinary nephropathologists utilize to make accurate and clinically useful diagnoses in dogs with proteinuric glomerular disease and to provide guidelines for the proper evaluation of renal biopsies. METHODS: Renal biopsy specimens were routinely examined by LM, IF, and TEM. Samples were reviewed by members of the World Small Animal Veterinary Association Renal Standardization Study Group to identify lesions that were diagnostic for, or suggestive of, the presence of immune complexes (IC) or amyloidosis in all modalities. Ten guidelines for renal biopsy evaluation were formulated. RESULTS: Each method of investigation contributed important findings that were integrated to make an accurate final morphological diagnosis. The guidelines were validated by an independent group of veterinary pathologists. CONCLUSIONS AND CLINICAL IMPORTANCE: Routine evaluation of renal biopsies with LM, TEM, and IF is feasible and necessary for making accurate, morphologic diagnoses that can be used to guide clinical management of dogs with glomerular disease.

Prevalence of immune-complex glomerulonephritides in dogs biopsied for suspected glomerular disease: 501 cases (2007-2012).

BACKGROUND: Glomerulonephropathies are common causes of kidney disease in dogs. OBJECTIVE: To determine the prevalence of immune-complex glomerulonephritis (ICGN) in North American dogs biopsied for suspected glomerular disease. ANIMALS: Renal biopsies (n = 733) submitted to the Texas Veterinary Renal Pathology Service between January 1, 2007 and December 31, 2012 were reviewed. Dogs were included if the biopsy was performed for suspected glomerular disease. METHODS: Specimens were evaluated by light microscopy (LM), immunofluorescence (IF), and transmission electron microscopy (TEM). Findings were retrospectively evaluated to categorize the diagnosis for each case. For the diagnosis of ICGN, TEM findings were considered conclusive when LM and IF were equivocal. RESULTS: Of the 501 dogs included in the study, 241 (48.1%) had ICGN; 103 (20.6%) had primary glomerulosclerosis; 76 (15.2%) had amyloidosis; 45 (9.0%) had nonimmune complex (IC) glomerulopathy; 24 (4.8%) had non-IC nephropathy; and, 12 (2.4%) had primary tubulointerstitial disease. Many (66/241; 27.4%) ICGN cases required TEM for definitive diagnosis, including 14 cases (5.8%) that were not suspected on LM. Of cases not diagnosed as ICGN, a substantial proportion (60/260; 23.1%) required TEM to rule out immune complex deposits, including 14 of 189 cases (7.4%) presumptively diagnosed as ICGN on LM. CONCLUSIONS AND CLINICAL IMPORTANCE: Approximately half of all dogs biopsied for suspected glomerular disease had conditions other than ICGN. Renal biopsy is needed to accurately categorize the underlying disease and direct appropriate treatment. Additionally, TEM and IF evaluations by experienced nephropathologists are necessary to obtain an accurate diagnosis in many cases.

Characterization of the genetic basis for autosomal recessive hereditary nephropathy in the English Springer Spaniel.

BACKGROUND: Autosomal recessive hereditary nephropathy (ARHN) was diagnosed in 2 English Springer Spaniels (ESS), a breed not previously reported to be affected by hereditary nephropathy (HN). OBJECTIVE: To identify and characterize the genetic cause of ARHN in ESS. ANIMALS: Sixty-three ESS (2 with ARHN, 2 obligate carriers, and 59 others), 2 mixed-breed dogs with X-linked HN, and 2 English Cocker Spaniels (ECS) with ARHN were included. METHODS: ARHN was diagnosed based on transmission electron microscopy and immunostaining of kidney. DNA from affected dogs was screened for the mutation known to cause ARHN in ECS. Quantities of COL4A3, COL4A4, and COL4A5 mRNA transcripts in renal cortex were determined using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for ARHN-affected dogs and 7 other dogs. The coding regions of COL4A3 and COL4A4 were sequenced for the 2 ARHN-affected ESS and an unaffected dog. Exon 30 of COL4A4 was sequenced for all 63 ESS. RESULTS: qRT-PCR indicated a significant reduction in transcript levels of both COL4A3 and COL4A4 mRNA in the kidney of ARHN-affected ESS. Sequencing identified a single nucleotide substitution in COL4A4 at base 2806 resulting in a premature stop codon. Thirteen of 25 related dogs were identified as carriers. CONCLUSIONS AND CLINICAL IMPORTANCE: A mutation highly likely to cause ARHN in ESS has been identified.

Multilayer vascular grafts based on collagen-mimetic proteins.

A major roadblock in the development of an off-the-shelf, small-caliber vascular graft is achieving rapid endothelialization of the conduit while minimizing the risk of thrombosis, intimal hyperplasia, and mechanical failure. To address this need, a collagen-mimetic protein derived from group A Streptococcus, Scl2.28 (Scl2), was conjugated into a poly(ethylene glycol) (PEG) hydrogel to generate bioactive hydrogels that bind to endothelial cells (ECs) and resist platelet adhesion. The PEG-Scl2 hydrogel was then reinforced with an electrospun polyurethane mesh to achieve suitable biomechanical properties. In the current study, initial evaluation of this multilayer design as a potential off-the-shelf graft was conducted. First, electrospinning parameters were varied to achieve composite burst pressure, compliance, and suture retention strength that matched reported values of saphenous vein autografts. Composite stability following drying, sterilization, and physiological conditioning under pulsatile flow was then demonstrated. Scl2 bioactivity was also maintained after drying and sterilization as indicated by EC adhesion and spreading. Evaluation of platelet adhesion, aggregation, and activation indicated that PEG-Scl2 hydrogels had minimal platelet interactions and thus appear to provide a thromboresistant blood contacting layer. Finally, evaluation of EC migration speed demonstrated that PEG-Scl2 hydrogels promoted higher migration speeds than PEG-collagen analogs and that migration speed was readily tuned by altering protein concentration. Collectively, these results indicate that this multilayer design warrants further investigation and may have the potential to improve on current synthetic options.

Swine as models in biomedical research and toxicology testing.

Swine are considered to be one of the major animal species used in translational research, surgical models, and procedural training and are increasingly being used as an alternative to the dog or monkey as the choice of nonrodent species in preclinical toxicologic testing of pharmaceuticals. There are unique advantages to the use of swine in this setting given that they share with humans similar anatomic and physiologic characteristics involving the cardiovascular, urinary, integumentary, and digestive systems. However, the investigator needs to be familiar with important anatomic, histopathologic, and clinicopathologic features of the laboratory pig and minipig in order to put background lesions or xenobiotically induced toxicologic changes in their proper perspective and also needs to consider specific anatomic differences when using the pig as a surgical model. Ethical considerations, as well as the existence of significant amounts of background data, from a regulatory perspective, provide further support for the use of this species in experimental or pharmaceutical research studies. It is likely that pigs and minipigs will become an increasingly important animal model for research and pharmaceutical development applications.

Platelet inhibition reduces cyclic flow variations and neointimal proliferation in normal and hypercholesterolemic-atherosclerotic canine coronary arteries.

BACKGROUND: Platelet-derived growth factors help stimulate the neointimal proliferation of restenosis after coronary interventions. Reducing platelet accumulation at treated sites may attenuate restenosis. We tested this hypothesis by inducing repetitive platelet aggregation at coronary angioplasty sites in dogs and measuring subsequent neointima formation. METHODS AND RESULTS: Cholesterol-sensitive dogs (n=74) received either 4% cholesterol-enriched diets for >8 months (n=29), creating visible atheromas, or normal canine diets (n=45). A coronary balloon angioplasty cyclic flow variation (CFV) model was used. One group of control dogs (group 1, n=8) had angioplasty with no arterial constriction applied and no drug treatment. Three other groups had arterial constrictors applied to provoke CFVs: group 2 (n=28) received no drug therapy, group 3 (n=18) received oral aspirin alone, and group 4 (n=20) received 3 oral antiplatelet agents: ridogrel, ketanserin, and clopidogrel (R+K+C) to simultaneously inhibit the thromboxane A(2), serotonin, and ADP pathways of platelet aggregation, respectively. Bleeding times were moderately prolonged in the aspirin-treated group (124+/-9 seconds after 3 weeks versus 76+/-6 seconds at baseline, P<0.01) and greatly prolonged on R+K+C (>600 versus 104+/-5 seconds, P<0.001). The frequency and severity of CFVs were inversely related to the degree of platelet inhibition and prolongation of bleeding times, as was sudden death due to acute thrombotic coronary occlusion. Quantitative histology at 8 weeks revealed increased intima-to-media ratio with CFVs: 0.89+/-0.14 in the untreated group 2 versus 0.11+/-0.04 in the control group (P<0.001). Intima-to-media ratio was significantly reduced with antiplatelet treatment (0.27+/-0.05 with aspirin treatment and 0.20+/-0.05 with R+K+C treatment, respectively, P<0.001). Cholesterol feeding did not appear to influence results. CONCLUSIONS: Repetitive platelet accumulation at coronary angioplasty sites caused enhanced neointimal proliferation by 8 weeks. Oral inhibitors of platelet aggregation attenuated platelet function, prolonged bleeding times, reduced or prevented cyclic flows and abrupt thrombotic occlusions, and thereby inhibited neointimal proliferation. Platelet inhibition should continue to receive attention in efforts to reduce restenosis after coronary interventions.

Calcitonin gene-related peptide is not essential for the development of pressure overload-induced hypertrophy in vivo.

The regulatory neuropeptide calcitonin-gene related peptide (CGRP) has been shown to evoke a hypertrophic response in isolated cardiomyocytes in vitro, an effect which was attributed to PKC activation. Activation of PKC has previously been implicated in the development of cardiac hypertrophy. We therefore investigated the role of CGRP in pressure overload-induced hypertrophy in vivo, which has not previously been reported. Constriction of the ascending aorta of rats resulted in an increase in the heart weight to body weight ratio, increased myocyte diameter, re-expression of the fetal genes ANF, MHCbeta and skeletal alpha-actin, and decreased expression of the adult genes GLUT4 and SERCA2a. Treatment of neonatal rat pups (1-2 days old) with capsaicin (50 mg/kg), resulted in the permanent de-afferentation of small-diameter unmyelinated CGRP-containing sensory C-fibres. Such treatment caused a 68% decrease in the CGRP-like immunoreactivity of hearts isolated from 10 week old rats (p < 0.001). Contrary to expectations, aortic constriction of capsaicin treated rats had no effect on the development of hypertrophy at the trophic, morphometric or gene expression levels. The results suggest that the development of pressure overload-induced hypertrophy in vivo does not require the regulatory neuropeptide CGRP.

Development of atherosclerotic plaque with endothelial disruption in Watanabe heritable hyperlipidemic rabbit aortas.

To better understand the morphogenesis of atherosclerotic plaque, we evaluated temporal distribution of leukocytes, macrophages, foam cells, vascular smooth muscle cells, and subendothelial lipid in Watanabe heritable hyperlipedimic (WHHL) rabbit aortas. Aortas of WHHL (n=20) and New Zealand White (NZW, controls; n=8) rabbits were perfusion fixed at 1, 3, 6, and 12 months of age. At initial gross evaluation of lipid distribution, we identified aortic areas at high risk for lesion development. In WHHL rabbits, the lipid-positive portion of high-risk areas increased from 3% at 1 month to 50% at 12 months; during the same period, adherent cell count increased from <1 leukocyte and monocyte/mm(2) to 25 leukocytes, 44 monocytes, and 10 foam cells/mm(2). Controls showed no increase over time in lipid-positive areas or cellular adherence to the endothelium. One-month-old WHHL rabbit aortas had scattered lipid-positive cells in the intima (primarily branch points). Immunostaining of these areas did not show rabbit macrophages (RAM antibody) but were actin positive. Occasionally, platelets and monocytes adhered to the endothelial surface. By age 3 months, well-defined fatty streaks/atherosclerotic plaques had RAM-positive cells within foam cell core, along core margins, and in focal clusters in the fibrous cap and subendothelium. By age 12 months, isolated RAM-positive cells were on the endothelial surface, and surface morphology showed endothelial cell disruption foci containing clusters of macrophages and foam cells. Our results indicate that lipid accumulation (extra- and intracellular) is important in the early development of atherosclerotic lesions; a corresponding, slower accumulation of adherent cells on the lesion surface promotes lipid conversion from fatty streak to plaque.

Morphological changes in atrial appendages removed during the maze procedure: a comparison with autopsy controls.

Atrial fibrillation (AF) is commonly encountered in clinical practice and typically it is treated with pharmacological agents. Some patients whose arrhythmias are resistant to pharmacological therapy undergo the maze procedure, which is a surgical treatment. The atrial appendages are removed as part of the surgical procedure. These appendages often demonstrate mycocyte hypertrophy, vacuolar degeneration and other changes that may be seen in cardiomyopathies. We examined 19 of these appendages and compared them with 17 autopsy controls, 12 of whom had documented coronary atherosclerotic disease and 5 of whom did not. We semiquantitatively measured the amount of vacuolar degeneration, interstitial fibrosis, myocyte hypertrophy and intramyocardial adipose tissue. Univariate and multivariate analysis was performed and revealed that vacuolar degeneration were significantly more common in appendages of patients with arrhythmias than the autopsy controls (P<.0004). The other three histological features studied were not significantly different in the three groups. Ultrastructural studies on atrial tissue excised during the maze procedure, retrieved from the paraffin blocks, revealed degenerative changes similar to cardiomyopathic myocardial tissue. Vacuolar degeneration is commonly seen in atrial appendages removed in patients with chronic AF. Myocyte hypertrophy is a nonspecific finding and may occur in patients with arrhthymias and coronary artery disease.

Inhibition of coronary thrombosis and local inflammation by a noncarbohydrate selectin inhibitor.

We tested the hypothesis that selectin inhibition with blocking antibodies or a small-molecular-weight inhibitor of L-, P-, and E-selectin, methoxybenzoylpropionic acid (MBPA), prevents thrombus formation in a canine coronary Folts' model. Cyclic flow variations (CFVs) were induced by crush injury and constriction of the left anterior descending coronary artery in dogs. Systemic infusion of antibodies to P- and L-selectin abolished CFVs, respectively, in 50% and 17% of treated dogs [P = not significant (NS)]. The combination of P- and L-selectin antibodies suppressed CFVs in 60% of treated dogs (P = NS). In contrast, systemic selectin blockade by intravenous infusion or local adventitial application of MBPA markedly reduced CFVs and, in addition, reduced myocardial myeloperoxidase (MPO) activity. We conclude that inhibition of L-, P-, and E-selectin binding by a small-molecular-weight, noncarbohydrate compound markedly reduces arterial thrombosis, whereas systemic administration of antibodies to L- and P-selectin fail to reproduce this antithrombotic effect. These results underscore the role of selectins in the pathogenesis of arterial thrombosis under high shear stress and suggest that inhibition of P- and L- selectin may not suffice to prevent thrombus formation in this model. The role of E-selectin in thrombus formation in this model awaits further testing.

Cardiac-specific overexpression of tumor necrosis factor-alpha causes oxidative stress and contractile dysfunction in mouse diaphragm.

BACKGROUND: We have developed a transgenic mouse with cardiac-restricted overexpression of tumor necrosis factor-alpha (TNF-alpha). These mice develop a heart failure phenotype characterized by left ventricular dysfunction and remodeling, pulmonary edema, and elevated levels of TNF-alpha in the peripheral circulation from cardiac spillover. Given that TNF-alpha causes atrophy and loss of function in respiratory muscle, we asked whether transgenic mice developed diaphragm dysfunction and whether contractile losses were caused by oxidative stress or tissue remodeling. METHODS AND RESULTS: muscles excised from transgenic mice and littermate controls were studied in vitro with direct electrical stimulation. Cytosolic oxidant levels were measured with 2', 7'-dichlorofluorescin diacetate; emissions of the oxidized product were detected by fluorescence microscopy. Force generation by the diaphragm of transgenic animals was 47% less than control (13.2+/-0. 8 [+/-SEM] versus 25.1+/-0.6 N/cm(2); P:<0.001); this weakness was associated with greater intracellular oxidant levels (P:<0.025) and was partially reversed by 30-minute incubation with the antioxidant N:-acetylcysteine 10 mmol/L (P:<0.01). Exogenous TNF-alpha 500 micromol/L increased oxidant production in diaphragm of wild-type mice and caused weakness that was inhibited by N:-acetylcysteine, suggesting that changes observed in the diaphragm of transgenic animals were mediated by TNF-alpha. There were no differences in body or diaphragm weights between transgenic and control animals, nor was there evidence of muscle injury or apoptosis. CONCLUSIONS: Elevated circulating levels of TNF-alpha provoke contractile dysfunction in the diaphragm through an endocrine mechanism thought to be mediated by oxidative stress.

A bovine model for detecting high intensity transient signals originating from mechanical heart valves.

In patients with mechanical heart valves (MHVs), transcranial Doppler methods commonly detect high intensity transient signals (HITS) representing microemboli. These microemboli, which are presumably gaseous, may cause stroke and cognitive deterioration. A bovine model was therefore developed for studying the relationship between mitral MHV induced HITS and potential etiogenic factors. We placed an 18 mm, 4 MHz Doppler probe in the brachiocephalic artery to detect MHV induced microbubbles at baseline (rest) and under 9 other conditions. To elucidate the gas composition (CO2 or N2) of the microbubbles, we administered 1%, 3%, and 5% CO2, and 100% O2. To determine effect of the heart rate, we paced the heart at 120, 160, and 180 bpm. To alter the myocardial contractility, we gave dobutamine and esmolol. Two independent, blinded observers counted the HITS from recorded doppler spectra. HITS were defined by an initial unidirectional spectral deviation, a signal power of >8 dB relative to the background power, and lack of a cyclic appearance. The electrocardiogram, aortic and LV pressures, and LV dP/dt were obtained telemetrically. The calves were studied 4 to 6, 8 to 10, and 12 to 14 weeks postoperatively, after which the animals were sacrificed at an approximate 4 month study duration, and a postmortem evaluation of the heart and the main viscera was performed. In all, 27 HITS recordings were made in 10 calves. Myocardial contractility was the only factor to significantly affect HITS frequency; the heart rate and blood gas concentrations had minimal effect on HITS frequency. Our bovine model will be useful for assessing valve designs, as well as the mechanism of HITS, the composition of the microemboli, and their possible pathophysiologic effects on the kidneys and brain.

Surface texturing and coating of biomaterial implants: effects on tissue integration and fibrosis.

To determine whether texturing and coating have additive effects in promoting tissue integration and inhibiting fibrosis, we evaluated smooth silicone rubber (SSR), textured silicone rubber (TSR), porous silicone rubber (PSR), expanded polytetrafluoroethylene (ePTFE), and porous polyurethane (PPU) subcutaneous implants in eight minipigs. Some of the implants were coated with type IV collagen (Col) and/or fibronectin (Fn). At 6 months, we removed the implants and examined them microscopically. Texturing was more important than Col and Fn in reducing fibrosis and inflammation. The PSR yielded the best response, including reduced fibrosis and inflammation, satisfactory adherence, and no dystrophic mineralization.