Simulated bioprosthetic heart valve deformation under quasi-static loading

For more than 40 years, the replacement of diseased natural heart valves with prosthetic devices has dramatically extended the quality and length of the lives of millions of patients worldwide. However, bioprosthetic heart valves (BHV) continue to fail due to structural failure resulting from poor tissue durability and faulty design. Clearly, an in-depth understanding of the biomechanical behavior of BHV at both the tissue and functional prosthesis levels is essential to improving BHV design and to reduce rates of failure. In this study, we simulated quasi-static BHV leaflet deformation under 40, 80, and 120 mm Hg quasi-static transvalvular pressures. A Fung-elastic material model was used that incorporated material parameters and axes derived from actual leaflet biaxial tests and measured leaflet collagen fiber structure. Rigorous experimental validation of predicted leaflet strain field was used to validate the model results. An overall maximum discrepancy of 2.36% strain between the finite element (FE) results and experiment measurements was obtained, indicating good agreement between computed and measured major principal strains. Parametric studies utilizing the material parameter set from one leaflet for all three leaflets resulted in substantial variations in leaflet stress and strain distributions. This result suggests that utilization of actual leaflet material properties is essential for accurate BHV FE simulations. The present study also underscores the need for rigorous experimentation and accurate constitutive models in simulating BHV function and design.     

Fine needle aspiration cytology of mucoepidermoid carcinoma. A diagnostic problem

The cytomorphologic findings in fine needle aspirates from 18 cases of histologically confirmed primary mucoepidermoid carcinoma of the salivary gland were reviewed and correlated with the findings on the tissue sections. An accurate diagnosis of these tumors in fine needle aspirates was possible when all three components (i.e., epidermoid cells, intermediate cells and mucus-producing cells) were identified. The pitfalls in the cytologic diagnosis of this tumor are discussed.     

Effect of fiber orientation on the stress distribution within a leaflet of a polymer composite heart valve in the closed position

Polymer trileaflet valves offer natural hemodynamics with the potential for better durability than commercially available tissue valves. Strength and durability of polymer-based valves may be increased through fiber reinforcement. A finite element analysis of the mechanics of a statically loaded polymer trileaflet aortic heart valve has been conducted. A parametric analysis was performed to determine the effects of fiber orientation and volume density in a single and double ply model. A maximum stress value of 1.02MPa was obtained in the non-reinforced model for a transvalvular load (downstream-upstream) of 120mmHg. The maximum stress on the downstream side of the leaflet was approximately twice the maximum stress on the upstream side, and always occurred on the interface with the valve stent. The single ply model reduced the stress on the polymer matrix, with the maximum reduction of at least 64% occurring when the fiber orientation was such that the fibers ran perpendicular to the stent edge. The double ply model further reduced the stress on the polymer matrix, with the maximum reduction of greater than 86% now occurring when the fibers are oriented most perpendicular to one another.     

Biomechanical effect of rapid mucoperiosteal palatal tissue expansion with the use of osmotic expanders

The comparative study was performed to investigate the biomechanical properties (maximum tangential stiffness, maximum tangential modulus and tensile strength) of expanded mucoperiosteal palatal tissue after rapid expansion regimen correlated with histological findings. Rabbit palatal model was used to correlate the non-operated control group, sham-operated control (subperiosteal tissue dissection) groups and 24- and 48-hour tissue expansion groups. There was no observed damage of tissue collagen network in both tissue expansion groups analyzed immediately after expansion, and biomechanical profile was not significantly different from the profile of control groups. However, rapid tissue expansion activates remodeling of mucoperiosteal tissue structure that revealed significant changes in mechanical properties during the 4-week follow-up. The 24-hour expansion induced transient increase of resilience observed 2 weeks after surgery in comparison to the control groups. As a result of maturation of newly created collagen fibers and mucoperiosteum rebuilding, there were no significant differences between any of the analyzed tensile parameters 4 weeks after the 24-hour expansion. Increased and elongated inflammatory response and connective matrix synthesis observed during healing of 48-hour expanded tissue led to a significant decrease of tensile strength value in comparison to the control groups. Even though 4 weeks after surgery, the resilience of 48-hour expanded tissue was similar to the control groups, tissue healing was not completed and limited scar formation might considerably change the final biomechanical tissue profile. These findings provide new information about tensile properties to rapid mucoperiosteal palatal tissue expansion with the use of osmotic expanders for cleft palate repair by tissue augmentation.     

Water relations and growth of tomato fruit pericarp tissue

The water relations of young tomato fruit pericarp tissue were examined and related to tissue expansion. The relationship between bulk turgor pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing fruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol. The bulk turgor of this tissue was low (about 0.2 MPa), even in fruit from plants that were otherwise fully turgid, whether measured psychrometrically or by length change in osmotic solutions. The rate of tissue growth at maximum turgor was less than that at moderate turgor unless calcium was added to the incubation medium. However, added calcium also decreased the rate of growth at lower turgor pressures. Yield turgor was < 0.1 MPa, but it was increased by the addition of calcium ions. Electrolyte leakage from tissue was greatest at maximum turgor pressure but was decreased by the addition of calcium ions or osmoticum. Tissue growth was unaffected by a range of plant growth regulators (IAA, abscisic acid, benzyladenine and GA₃) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed. Thus, fruit tissue may be able to maintain optimal expansion rates only at moderate turgor and low calcium concentration.     

Liquid-based vs. conventional smears in fine needle aspiration of bone and soft tissue tumors

OBJECTIVE: To compare the accuracy of fine needle aspiration cytology of bone and soft tissue tumors utilizing ThinPrep (TP) (Cytyc Corporation, Boxborough, Massachusetts, U.S.A.) vs. conventional smears (CS). STUDY DESIGN: Fine needle aspiration cytology from bone and soft tissue tumors was processed and assessed for cellularity, nuclear and cytoplasmic preservation, cellular architecture and stromal background with both the TP liquid-based smear technique and conventional methods. RESULTS: An accurate diagnosis was made in 13% of TP cases as compared to 64% in CS cases. CONCLUSION: CS of fine needle aspiration sample is far superior to TP in diagnosing tumors of bone and soft tissues. Preservation of cytoplasmic features and cellular architecture was superior in conventionally prepared smears.     

Fine Needle Aspiration Cytodiagnosis of A Carcinoid Tumour of the Male Breast

The diagnosis of a primary carcinoid tumour of the breast in a 38-year-old male was initially made from a fine needle aspiration sample. The cytodiagnosis was supported by the histochemical demonstration of Grimelius-positive granules in tumour cells which were also found in tissue removed in a subsequent biopsy. An immunocytochemical study using markers for neuron-specific enolase and chromagranin in the aspirated sample and tissue was found to be negative. A total mastectomy with axillary node dissection was performed which showed no residual or metastatic tumour. No primary tumour was found elsewhere.     

Histologic analysis and comparison of techniques in fine needle aspiration-induced alterations in thyroid

OBJECTIVE: To assess histologic alterations following fine needle aspiration (FNA) of the thyroid and differentiate these from ominous lesions, such as papillary carcinoma thyroid, as well as assess and compare the degree of tissue trauma from the techniques: needle only vs. needle with syringe, size of needle and number of aspirations. STUDY DESIGN: Thyroidectomy specimens of 100 cases with prior FNA biopsy were selected. The changes called "worrisome histologic alteration following fine needle aspiration of the thyroid" (WHAFFT) were studied. Number of FNAs, needle size and technique were tabulated for 73 of 100 cases. RESULTS: Worrisome changes were confined to areas near the needle tract and hence could be differentiated from ominous lesions. Control cases did not show WHAFFT lesions. Non-aspiration FNA cytology (FNAC) technique results in fewer, less frequent WHAFFT changes. The increasing number of FNAs leads to statistically significant increase in infarction, necrosis and vascular changes. A gradation in the WHAFFT changes, directly proportional to the increasing diameter of the needle, was observed. CONCLUSION: The pathologist should be aware of WHAFFT to avoid misinterpretation. The technique of non-aspiration FNAC is significantly less traumatic. An increase in FNAs or size of needle results in more severe WHAFFT changes.     

Molecules mediating cell-ECM and cell-cell communication in human heart valves

The specific phenotype of different tissues depends on the interactions of cells with neighboring cells and the surrounding extracellular matrix, which is mediated by cell adhesion receptors including integrins, immunoglobulin family members, syndecans, and selectins. The aim of this study was to investigate the adhesion profile of native human valve interstitial cells (ICs) in situ and in vitro by analyzing these adhesion receptors. Flow cytometry and immunocytochemistry was used to quantify the expression of the specific receptors on ICs cultured from all human cardiac valves, and immunohistochemistry were used to profile their distribution pattern in valve tissue sections. The valve leaflets and cultured ICs from all valves expressed alpha1, alpha2, alpha3, alpha4, and alpha5 integrins to varying degrees and percentages with very little expression of alpha6 and alphaV. Valve leaflet ICs from all valves, expressed predominantly beta1 integrin but no beta3 or beta4 integrin. Syndecan-1 and Syndecan-4 were not detected. Intercellular adhesion molecule-1 was weakly detected, whereas vascular adhesion molecule-1 was barely detectable and E-selectin was not detected. This study has delineated the identity of some of the integrins synthesized and expressed by human valve ICs and the specificity of adhesion molecules with which the valve ICs interact with the extracellular matrix and mediate intercellular interactions. This pattern of expression of cell surface adhesion molecules may be considered as a basis for a fingerprint on which to base future cell alternatives and would provide useful information for valve tissue engineering.     

Ontogeny in terminal buds of Abies nordmanniana (Pinaceae) characterized by ubiquitin

Meristematic activity in the bud meristem of Abies nordmanniana was visualized by ubiquitin immunohistochemical localization from before bud break and throughout shoot expansion. Ubiquitin was detected in meristematic cells either in the cytosol or nucleus, or both, depending on tissue type and developmental stage. During winter dormancy, ubiquitin was only observed in the protodermal/hypodermal layers, but at bud break in mid May, the signal expanded to the entire shoot tip. At the end of May, a clear zonation in ubiquitin localization appeared that lasted about one month. Throughout this period, ubiquitin was barely detectable in a central group of cells that might indicate an organizing center with stem cells. At the end of June, coinciding with the transition from scale leaf to needle primordia production, ubiquitin again was more prevalent in the peripheral cell layers. During shoot expansion, a strong ubiquitin signal developed in the axil of all needles. Most of these signals later disappeared, except for those few axils where buds actually developed. A strong ubiquitin signal was also observed in cells lining the young resin ducts. Our data showed that ubiquitin may be used as a marker for metabolic activity associated with seasonal development in the apical meristem.     

SECONDARY GROWTH IN NEEDLE LEAVES OF PINUS LONGAEVA (BRISTLECONE PINE) AND OTHER CONIFERS: QUANTITATIVE DATA

Needle leaves of Pinus longaeva can be accurately dated and remain alive on branches for 30 or more yrs, making this species ideal to study secondary growth in leaves. Field observations and regression analysis of needle age versus mean needle length both indicate primary (elongation) growth of needles is completed in the first year. Statistical analysis of cell counts for one- to 33-yr-old needles indicate production along the entire length of needles of 1.0-1.7 cell layers per year of secondary phloem, but no secondary xylem. Microscopic measurements and cell counts reveal that with advancing needle age phloem increases radially and transfusion tissue buckles, but the number of endodermal cells and xylem width do not change. Living phloem remains constant in amount (ca. 9 layers) with advancing needle age, indicating yearly replacement of old by new phloem. For comparison to P. longaeva, needle leaves were also studied for ten other conifer taxa with maximum needle longevities ranging from 3 to 19 yrs. In needles of each taxon no secondary xylem is produced, but secondary phloem production occurs throughout the post-elongation lifespan of the needles regardless of maximum needle longevity.     

Are heart valves from donors over 65 years of age morphologically suitable for transplantation?

Since there is no upper age limit for general organ donation, unlike heart valve donation, and since a quarter of all organ donors are 65 years and older, we examined whether the heart valves from these donors are suitable as allografts. In the period 1999–2004 the aortic valve and pulmonary valve of 100 organ donors above 65 years of age were examined to establish whether they would have been suitable as valve grafts. To compare the valve grafts above and below the age limit of 65 years, we used data on the aortic and pulmonary valves of 380 organ donors below the age limit in the same time period. Examination of the 200 heart valves showed that – just like valves from donors below the age limit – 100 of them would have met the medical quality standards for transplantation, which discriminate among optimal, suitable and unsuitable tissue morphology. The morphological suitability of the aortic valves decreases rapidly during the 4th decade of life and near to the age limit only 6% of them are accepted as grafts. The rate of potentially acceptable aortic valve grafts from organ donors aged over 65 years of 15% is also small. By contrast, the pulmonary valves are not affected by age-related tissue changes that might reduce their transplantability. The predominant majority (85%) of potential pulmonary valve grafts from organ donors over 65 years of age fulfilled the acceptance criteria, half of them (48%) even showing good tissue quality. In light of these results the age limit was raised to 70 years in 2005.     

Biosilica structures obtained from Nitzschia, Ditylum, Skeletonema, and Coscinodiscus diatom by a filtration-aided acid cleaning method

A filtration-aided acid cleaning method was used to collect biosilica structures from a diatom culture medium, natural seawater, or water bloom. Cell extraction, acid cleaning, and acid removal were all performed on a polytetrafluoroethylene (PTFE) filter cloth, significantly improving the treatment capacity and efficiency of the traditional acid wash method. Five typical diatoms were cultivated in the laboratory for acid cleaning. Different growth speeds were introduced, and different process parameters for acid cleaning were utilized. After the acid cleaning, biosilica structures were collected from the frustules of diatoms using different methods. Girdle bands and valves of Coscinodiscus sp. were separated by floating of the valves. Central spines of Ditylum brightwellii and valves of Skeletonema costatum were separately collected by settling or filtration. Rod-like frustules, such as those of Bacillaris paradoxa, are not suitable for large quantities of acid wash. The silica structures were observed and tested using an AFM-calibrated glass needle to determine their elasticity. Elasticity tests showed that ringent girdle bands are more flexible than complete ones (Coscinodiscus sp.) and that both long-chain clusters of Nitzschia palea and central spines of D. brightwellii have certain elasticities. The required pressure for deforming or breaking the biosilica structures of diatoms was also determined.     

Fine needle aspiration cytology of focal liver lesions. Results obtained with examination of both cytologic and histologic preparations

The results of 197 consecutive fine needle aspirations (FNA) of focal liver lesions performed on 176 patients were reviewed, and the 176 single most diagnostic aspirates were analyzed in detail. The majority of specimens were obtained using a 20-gauge or 22-gauge needle with ultrasound guidance. An attempt was made to obtain both a cytologic and a tissue specimen from each aspirate. The overall accuracy of the procedure was 85%; the accuracies of the tissue and cytologic specimens were 67% and 73%, respectively. The combined procedure detected 81% of the documented malignant tumors; the tissue specimen detected 62%. Eleven tumors were identified only in the tissue specimen and 23 were identified only in the cytologic specimen. There were no false-positive diagnoses. Six of nine hepatocellular carcinomas were detected. These results show that FNA cytology is a safe, accurate, relatively noninvasive technique whose diagnostic yield may be improved by examination of both a histologic tissue and a cytologic preparation.     

Regional structure–function relationships in mouse aortic valve tissue

Site-specific biomechanical properties of the aortic valve play an important role in native valve function, and alterations in these properties may reflect mechanisms of degeneration and disease. Small animals such as targeted mutagenesis mice provide a powerful approach to model human valve disease pathogenesis; however, physical mechanical testing in small animals is limited by valve tissue size. Aortic valves are comprised of highly organized extracellular matrix compartmentalized in cusp and annulus regions, which have different functions. The objective of this study was to measure regional mechanical properties of mouse aortic valve tissue using a modified micropipette aspiration technique. Aortic valves were isolated from juvenile, adult and aged adult C57BL/6 wild type mice. Tissue tensile stiffness was determined for annulus and cusp regions using a half-space punch model. Stiffness for the annulus region was significantly higher compared to the cusp region at all stages. Further, aged adult valve tissue had decreased stiffness in both the cusp and annulus. Quantitative histochemical analysis revealed a collagen-rich annulus and a proteoglycan-rich cusp at all stages. In aged adult valves, there was proteoglycan infiltration of the annulus hinge, consistent with the observed mechanical differences over time. These findings indicate that valve tissue biomechanical properties vary in wild type mice in a region-specific and age-related manner. The micropipette aspiration technique provides a promising approach for studies of valve structure and function in small animal models, such as transgenic mouse models of valve disease.     

Changes of monoterpene concentrations in needles of pollution-injured Picea abies exhibiting montane yellowing

Terpenes were analyzed in needles of pollution injured Picea abies (L.) Karst. of the Southern Black Forest (SW Germany) showing symptoms of montane yellowing. Compared to a set of healthy trees, a set of injured trees showed increased terpene hydrocarbon concentrations relative to needle fresh weight. This difference was even more pronounced when the terpene concentrations of green, healthy and yellowing, injured needles from the same internode of individual injured trees were compared. Increased terpene concentrations were observed in the basal parts of injured needles, while their distal parts exhibited a loss of terpenes. In addition, an alteration in the pattern of terpene occurrence was observable. Most striking was the changed ratio of α-pinene to β -pinene. with marked increase of the latter, in injured needles. As indicated by ultratrace analysis of isolated mesophyll. vascular tissue and resin ducts of the needles, mono- and sesquiterpenes were found exclusively in resin ducts. The other tissues were virtually free of terpenes. Isolated resin from a single resin duct contained all terpenes (monoterpene hydrocarbons, alcohols and ketones, and sesquiterpene hydrocarbons) that are typical for the needle. An individual response to air pollution of each separate short resin duct in the needle may be deduced.     

Prestress as an optimal biomechanical parameter for needle penetration

Drug delivery requires precise intradermal and subcutaneous injections of formulations to clinically relevant penetration depths. However, penetration depth is confounded by skin deflection, which occurs prior to and during penetration as the skin surface deforms axially with the needle, and which varies profoundly due to differing intrinsic mechanical (e.g. viscoelastic) tissue properties, disease state, aging, and ethnicity. Herein, an ex vivo model was utilized to study factors that affect skin deflection and the efficacy of injection, including prestress applied at the tissue surface, needle gauge, velocity, and actuation depth. The application of prestress minimized skin deflection during needle penetration and allowed for needle actuation to the targeted penetration depths with minimum variability. The force required to achieve target penetration depths was found to increase with prestress and decrease with needle gauge. Our findings emphasize the need for prestress applied to the skin surface to minimize variation in skin properties and administer formulations for intradermal and subcutaneous treatments with maximum precision.     

Turbulence downstream of subcoronary stentless and stented aortic valves

Regions of turbulence downstream of bioprosthetic heart valves may cause damage to blood components, vessel wall as well as to aortic valve leaflets. Stentless aortic heart valves are known to posses several hemodynamic benefits such as larger effective orifice areas, lower aortic transvalvular pressure difference and faster left ventricular mass regression compared with their stented counterpart. Whether this is reflected by diminished turbulence formation, remains to be shown. We implanted either stented pericardial valve prostheses (Mitroflow), stentless valve prostheses (Solo or Toronto SPV) in pigs or they preserved their native valves. Following surgery, blood velocity was measured in the cross sectional area downstream of the valves using 10MHz ultrasonic probes connected to a dedicated pulsed Doppler equipment. As a measure of turbulence, Reynolds normal stress (RNS) was calculated at two different blood pressures (baseline and 50% increase). We found no difference in maximum RNS measurements between any of the investigated valve groups. The native valve had significantly lower mean RNS values than the Mitroflow (p=0.004), Toronto SPV (p=0.008) and Solo valve (p=0.02). There were no statistically significant differences between the artificial valve groups (p=0.3). The mean RNS was significantly larger when increasing blood pressure (p=0.0006). We, thus, found no advantages for the stentless aortic valves compared with stented prosthesis in terms of lower maximum or mean RNS values. Native valves have a significantly lower mean RNS value than all investigated bioprostheses.     

Evidence for a second valve system in lymphatics: endothelial microvalves.

The mechanism for interstitial fluid uptake into the lymphatics remains speculative and unresolved. A system of intralymphatic valves exists that prevents reflow along the length of the lymphatic channels. However, these valves are not sufficient to provide unidirectional flow at the level of the initial lymphatics. We investigate here the hypothesis that initial lymphatics have a second, separate valve system that permits fluid to enter from the interstitium into the initial lymph channels but prevents escape back out into the tissue. The transport of fluorescent microspheres (0.31 microm) across endothelium of initial lymphatics in rat cremaster muscle was investigated with micropipette manipulation techniques. The results indicate that microspheres can readily pass from the interstitium across the endothelium into the lumen of the initial lymphatics. Once inside the lymphatic lumen, the microspheres cannot be forced out of the lumen even after elevation of the lymphatic pressure by outflow obstruction. Reaspiration of the microspheres inside the lymphatic lumen with a micropipette is blocked by the lymphatic endothelium. This blockade exists whether the aspiration is carried out at the microsphere entry site or anywhere along the initial lymphatics. Nevertheless, puncture of the initial lymphatic endothelium with the micropipette leads to rapid aspiration of intralymphatic microspheres. Investigation of lymphatic endothelial sections fixed during lymph pumping shows open interendothelial junctions not found in resting initial lymphatics. These results suggest that initial lymphatics have a (primary) valve system at the level of the endothelium. In conjunction with the classical (secondary) intralymphatic valves, the primary valves provide the mechanism that facilitates the unidirectional flow during periodic compression and expansion of initial lymphatics.