Small Valve Research Articles

A New Elastic Non Contacting Sealing Concept for Valves

The hydraulic binary counter concept was proposed as a means to realize compact and lightweight digital hydraulic cylinder drives for exoskeleton actuation. This counter principle is based on hydraulically actuated switching valves which have a hysteretic response with respect to the pilot pressure. Manufacturing tolerances of the tiny components caused unexpected high leakage which, in turn, led to a malfunction of the system.
 In this paper a new sealing concept, is introduced to solve this problem. It is based on a non-contact seal (sealing gap), which exploits a self-regulating, elasto-hydrodynamic effect to reduce a rather large initial gap h0 – to allow a rough tolerance – into a very small sealing gap h(x) to avoid dry friction of valve spool movement on the one hand but have very small leakage on the other hand.
 As sealing, an annular flexible ring made, e.g. of PTFE, is used which combines sufficient flexibility to allow this self adapting mechanism to a sufficient extent and to stay the high pressure loads.
 For the mathematical analysis of the concept, an approximate elasto-hydrodynamic analytical model is used. It sets the gap pressure, obtained from the Reynold’s equation for the sealing gap, the elastic restoring forces of the sealing ring, and the imparting pressure in equilibrium.
 The sealing concept is then simulated with a numerical model built with the finite element code ABAQUS, this results are compared with the one of the analytical model.
 It solves the Reynolds equation by a user defined subroutine. The simulation results indicate that this sealing principle delivers way better results than standard gap seals despite its rough manufacturing tolerances with one order of magnitude higher tolerance ranges. The application of this concept is not limited to small valves as needed for exoskeleton hydraulics but can be transferred to conventional type of hydraulics as well.

Are small-sized mechanical valves adequate for patients with small aortic roots?

Concerns have been raised over patient outcomes following implantation of small aortic valves (size: 19 and 17 mm). However, in patients with a smaller body surface area, these valves may be adequate. The aim of th study was to assess the hemodynamic and functional performance of these valves and their impact on clinical outcomes in patients with a small aortic root. This was a prospective observational study that included all consecutive patients undergoing aortic valve replacement (AVR) with a small-sized aortic valve over a 3-year period. Patients were followed up at 1 week, 6 weeks, and 1 year. Functional and clinical evaluation along with echocardiography was carried out for hemodynamic assessment. In-hospital mortality and hemodynamic outcomes at 1-year follow-up were recorded. Isolated AVR with a size 17 mm valve was carried out in 15 (25%) and with a 19 mm valve in 45 (75%) patients. The mean annular size was 19.12 ± 2.03 mm. The mean indexed effective orifice area was 1.08 ± 0.16 cm2/m2. Satisfactory decrease in peak and mean trans-prosthetic gradient were evident (peak gradient preoperatively was 92.15 ± 26.2 mmHg, and 25.68 ± 12.28 mmHg at 1 year, mean gradient was 55.31 ± 17.41 mmHg preoperatively and 13.71 ± 7.39 mmHg at 1 year). The functional status of patients also showed significant improvement post AVR. Left ventricular ejection fraction pre-operatively was 59.67% ± 10.38% and 59.57% ± 7.98% at 1-week, 59.15% ± 8.17% at 6 weeks, and 59.59% ± 7.48% at 1 year. When confronted with a small aortic root, AVR with a small-sized prosthesis provides a satisfactory hemodynamic and functional outcome. In patients with small body surface area, implantation of a small-sized valve is a viable option.

Cymbella biseriata sp. nov.—a unique living species of Cymbella Agardh (Bacillariophyceae) with biseriate striae

Alpine ponds are known biodiversity hot-spots and refugia for many rare and endangered species. They are also considered to be vulnerable habitats in terms of acidification, eutrophication, modification and climatic changes. Recently, a detailed study of diatoms in these habitats in North Macedonia has been started to evaluate their status and threats. During these studies, specimens of a species of Cymbella that lacked apical pore fields and had a small valve size were recorded. Scanning electron microscope observations revealed biseriate striae composed of small, slit-like to tilde-like areolae, a character so far not observed in any living representatives of the genus Cymbella. Herein, these specimens are assigned to the new species Cymbella biseriata sp. nov. based on detailed observations with light and scanning electron microscope. Comparison with similar taxa from the C. helvetica species complex and fossil species with biseriate striae is provided.

A new small marine Diploneis species (Diploneidaceae, Bacillariophyta) from Guangdong Province, China

A Diploneis species new to science is described here, collected from an intertidal sandy beach in Guangdong Province, China. The species has morphological features such as small elongated-elliptical valves, a linear longitudinal canal open outside by one row of C-shaped areolae throughout the whole length, a straight and simple raphe, alveoli occluded externally by a vola and internally by a thin hymen, perforations arranged in a hexagonal array that occupy approximately one-fourth to one-sixth of the valve width, and the other part of the alveolate striae covered by a broadly semilune hyaline area at the middle of the valve. Differences with other similar taxa of this genus are discussed.

Impact of high-pressure balloon aortic valvuloplasty on the hydrodynamic result after a transcatheter valve-in-valve procedure.

The aim of this study was to investigate the degree of functional improvement of a transcatheter heart valve (THV) for valve-in-valve after bioprosthetic valve fracture (BVF) of three small surgical aortic valve bioprostheses (SAVBP) using high-pressure balloon aortic valvuloplasty (HP-BAV) under standardized ex-vivo-conditions. A THV 26 mm (Evolut R) and SAVBP 21 mm (Perimount Magna Ease, Trifecta, and Epic supra [n = 4] were used. Mean pressure gradient (MPG), effective orifice area (EOA), geometric orifice area (GOA), minimal internal diameter (MID), and pinwheeling index (PWI) were analyzed before and after HP-BAV of the SAVBP using a noncompliant balloon. Fracturing of the SAVBP was done before implantation of the THV and the balloon pressures at the point of fracture were recorded. The Magna Ease and Epic fractured at balloon pressures of 18 and 8 atm, respectively. The Trifecta did not fracture up to a balloon pressure of 30 atm but was dilated. HP-BAV led to increased THV expansion as evident by straightened coaptation lines of the Evolut R 26 mm with reduced PWI, increased MID, and increased GOA in all 21 mm SAVBP. Evolut R showed significantly lower MPG and higher EOA as ViV in all prostheses after HP-BAV (p < 0.001). MPG and EOA of Evolut R differed regarding the SAVBP. Evolut R presented the lowest MPG and highest EOA in Magna Ease and the highest MPG and lowest EOA in Epic supra. The degree of function improvement of the same THV as ViV after HP-BAV depends on the surgical valve model. Functional improvement can also be achieved without valve fracture.

Functional performance of 8 small surgical aortic valve bioprostheses: an in vitro study.

Selection of a surgical aortic valve (SAV) bioprosthesis model for the treatment of aortic valve disease remains controversial. The aim of this study was to characterize the functional performance of 8 SAV models in a standardized in vitro setting. The hydrodynamic performance of 8 SAVs with labelled size 21 mm (Avalus™, Hancock® II, Mosaic® Ultra™, Perimount®, Perimount® Magna Ease, Epic™ Supra, Trifecta™ GT; Freestyle®), was investigated in a pulse duplicator. Transvalvular pressure gradients and effective orifice area (EOA) were recorded. The geometrical orifice area and physical dimensions of the valves were determined, and new functional dimensions were introduced. Mean pressure gradient (MPG) and EOA differed significantly between the analysed SAVs. The Epic presented with the lowest EOA and highest MPG, while the Trifecta showed the highest EOA and the lowest MPG. We introduce a useful way to determine the minimal internal diameter and a new measure termed 'relative orifice area' to characterize a valve's performance. SAVs showed significant differences in their hydrodynamic performance despite the same label size. This finding was related to the construction of the valves. We introduce a new measure that characterizes the functional performance of a valve model and size for the treatment of an aortic annulus of a specific size. Our data emphasize that SAV selection should carefully be done using an individual patient approach and that future research is necessary to improve the current generation of SAVs.

Gut anatomy and ultrastructural features of the paunch epithelium in the Neotropical termite Serritermes serrifer (Blattaria, Isoptera, Serritermitidae)

Termite gut comprises a long tube divided into several compartments. The well-developed hindgut includes five distinct portions, in which microbial communities are harbored, being responsible for different physiological and digestive processes. An enlarged compartment of the hindgut, the paunch, comprises a sac–like structure whose morphological features differ among termite taxa. The Neotropical termite Serritermes serrifer is the unique inquiline lower termite, and its cryptic habit results in sampling difficulties. Thus, studies regarding this termite species are rare. Here we provide a morphological approach of the gut regions in pseudergates and soldiers of S. serrifer, highlighting the ultrastructure features of the paunch, especially what concerns its function and association with microbial communities. The general morphology of the gut resembles those reported for other “lower termites”, and comprises a short foregut with a small stomodeal valve, a midgut devoid of mixed segment, and a long–compartmentalized hindgut. Eight Malpighian tubules are attached at the mesenteric–proctodeal transition, some of them extending towards the rectum. The ultrastructure of the paunch epithelium reinforces an involvement in content uptake, especially due to the extensive apical invaginations associated with mitochondria. Bacteria are attached to the paunch cuticle by an electron–dense material or are freely distributed in the lumen. The paunch of S. serrifer shares morphological similarities to that of Rhinotermitidae, but cup–like depressions, a likely synapomorphy for the Reticulitermes + Coptotermes + Heterotermes group, were absent. It suggests that bacterial attachment in S. serrifer paunch, as well as the uptake of compounds and microbial metabolites, occur along the epithelium rather than in specific sites, reinforcing the close relationship with basal rhinotermitids, in which such structures are also absent. Moreover, such characters also resemble those reported for Termitidae species.

Psammothidium elnatanianum sp. nov. (Achnanthidiaceae, Bacillariophyta) a new diatom species found in Holocene sediments (Meghalayan Age) of the Xingu River, Eastern Amazon

ABSTRACT An unknown species of Psammothidium (Achnanthidiaceae) was found in core sediment (~4000 cal yr BP) collected from Xingu ria, located in eastern Amazon Basin (Brazilian Amazon). The detailed morphology of the new species was examined and described using light (LM) and scanning electron (SEM) microscopy. The new species described here is mainly characterized by small valve dimensions, an irregular and expanded central area in rapheless valve (RLV) clearly visible in LM. Under SEM observations, the new species show slightly radiate striae with rectangular to rounded areolae present both on the surface and the valve mantle. Morphology and ecology of the new species is compared to those already described for the genus. Moreover, information about core chronology and the co-occurrence of other diatom species in the sample are also provided.

Balloon- vs Self-Expanding Valve Systems for Failed Small Surgical Aortic Valve Bioprostheses

BackgroundData comparing valve systems in the valve-in-valve transcatheter aortic valve replacement (ViV-TAVR) field have been obtained from retrospective studies. ObjectivesThe purpose of this study was to compare the hemodynamic results between the balloon-expandable valve (BEV) SAPIEN (3/ULTRA, Edwards Lifesciences) and self-expanding valve (SEV) Evolut (R/PRO/PRO+, Medtronic) in ViV-TAVR. MethodsPatients with a failed small (≤23 mm) surgical valve were randomized to receive a BEV or an SEV. The primary endpoint was valve hemodynamics (maximal/mean residual gradients, severe prosthesis patient mismatch [PPM], or moderate-severe aortic regurgitation) at 30 days as evaluated by Doppler echocardiography. ResultsA total of 102 patients were randomized, and of these, 98 patients finally underwent a ViV-TAVR procedure (BEV: n = 46, SEV: n = 52). The procedure was successful in all cases, with no differences in clinical outcomes at 30 days between groups (no death or stroke events). Patients in the SEV group exhibited lower mean and maximal transvalvular gradient values (15 ± 8 mm Hg vs 23 ± 8 mm Hg; P ˂ 0.001; 28 ± 16 mm Hg vs 40 ± 13 mm Hg, P ˂ 0.001), and a tendency toward a lower rate of severe PPM (44% vs 64%; P = 0.07). There were no cases of moderate-severe aortic regurgitation. In total, 55 consecutive patients (SEV: n = 27; BEV: n = 28) underwent invasive valve hemodynamic evaluation during the procedure, with no differences in mean and peak transvalvular gradients between both groups (P = 0.41 and P = 0.70, respectively). ConclusionsIn patients with small failed aortic bioprostheses, ViV-TAVR with an SEV was associated with improved valve hemodynamics as evaluated by echocardiography. There were no differences between groups in intraprocedural invasive valve hemodynamics and 30-day clinical outcomes (Comparison of the Balloon-Expandable Edwards Valve and Self-Expandable CoreValve Evolut R or Evolut PRO System for the Treatment of Small, Severely Dysfunctional Surgical Aortic Bioprostheses. The 'LYTEN' Trial; NCT03520101)

Averaged Transaortic Mean Gradient during Atrial Fibrillation Does Not Accurately Reflect Aortic Stenosis Severity

The diagnosis of severe aortic stenosis (AS) is challenging when a small aortic valve area (AVA) is associated with low gradients not consistent with severe AS. Low-gradient AS (LGAS) is present in a significant proportion of patients with AS and is commonly due to low forward flow states. Atrial fibrillation (AF) is associated with lower forward flow compared with sinus rhythm (SR)1 and may result in underestimation of AS severity by the flow-dependent mean gradient (MG).2-4 We aimed to compare forward flow parameters and transaortic valve MG in the same patient(s) during AF versus SR.

The unexpected diversity in Amphora sensu lato (Bacillariophyta) at Sozopol Bay, the western Black Sea

During a survey of benthic diatoms from the Bulgarian Black Sea coast near the historic town of Sozopol, we found a high diversity of Amphora sensu lato taxa at a single site and on a single type of artificial substratum. A total of 40 taxa from the current genera Amphora, Halamphora, Seminavis and Tetramphora were recognized during light microscopy (LM) and scanning electron microscopy (SEM) observations. We were able to identify with a high degree of certainty only 6 taxa based on the literature, whereas for 19 taxa (or almost 50% of all taxa) we could not find even sufficiently similar species, and they remained unidentified to species level. Many of the species had small valve dimensions. The paper presents all taxa with short morphometric data and microphotographs under LM and SEM, where possible. All taxa are discussed and compared with similar known taxa. The illustrative materials in earlier works from the Black Sea and species descriptions, where such were available, were also consulted. Diversity of Amphora sensu lato in the Black Sea coastal waters seems to be underestimated, whereas some of the past records are uncertain. A discussion on the current state of knowledge of Amphora sensu lato species from the Black Sea is given.

Impact of Small Valve Size on 1-Year Outcomes After Transcatheter Aortic Valve Implantation in Women (from the WIN-TAVI Registry)

Although most patients with small aortic annulus are women, there is paucity of data on the prognostic impact of small aortic prosthesis in women who underwent transcatheter aortic valve implantation (TAVI). Therefore, we aimed to evaluate the impact of small valve size on 1-year clinical outcomes after TAVI in women. The Women's INternational Transcatheter Aortic Valve Implantation is an all-women registry evaluating patients with severe aortic stenosis who underwent TAVI. Based on the size of the aortic bioprosthesis implanted, women were stratified into small (≤23 mm) and nonsmall (>23 mm) valve. The primary efficacy endpoint was the Valve Academic Research Consortium-2 composite of all-cause death, stroke, myocardial infarction, hospitalization for valve-related symptoms or heart failure or valve-related dysfunction at 1-year follow-up. Of 934 women who underwent TAVI, 388 (41.5%) received a small valve. Women with a small valve size had a lower body mass index, lower surgical risk scores, were less likely to suffer from atrial fibrillation, less often required postdilation and had a lower rate of residual aortic regurgitation grade ≥2. The occurrence of the Valve Academic Research Consortium-2 efficacy endpoint was similar between women treated with small and nonsmall valve (16.0% vs 16.3%, p=0.881; adjusted hazard ratio 1.34, 95% confidence interval 0.90 to 2.00). Likewise, there were no significant differences in the occurrence of other secondary endpoints after multivariable adjustment. In conclusion, women with severe aortic stenosis who underwent TAVI with the implantation of a small valve bioprosthesis had similar 1-year outcomes as those receiving a nonsmall bioprosthesis.

Micro Flow Control Valve with Stable Condition Using Particle-Excitation

This paper proposes a drive principle that aims to improve the control characteristics of a particle-excitation flow control valve capable of continuous air flow control. Aiming at application to a small servo valve, the authors have developed a particle-excitation flow control valve that controls flow rate by separating particles, which act as a valve element, from an orifice that is opened by the oscillation of a piezoelectric element. This paper proposes a method of more finely adjusting the motion of the particles. This method makes it possible to adjust to what degree each orifice opens, thereby refining the control of the flow rate and improving the responsiveness of the valve. Here, the authors produce a prototype, evaluate its characteristics, and confirm its effectiveness.

Technical modification and safe explantation of the Melody valve in the mitral position in small children.

Technical modification and safe explantation of the Melody valve in the mitral position in small children.

Staged left ventricular recruitment facilitated by Sano conduit upsizing

Staged left ventricular recruitment facilitated by Sano conduit upsizing

Oscillatory valve effect on temperature synchronization in microchannel cooling systems

• Flow maldistribution with oscillation can result in large temperature differences. • Periodic opening and closing of expansion valve can mitigate flow maldistribution. • Only some combinations of valve opening amplitude and frequency can balance flow. • Large amplitude periodic valve opening can balance flow over wider frequency range. • Very small valve opening amplitudes do not synchronize flow for any frequency. Microchannel evaporator cooling systems are widely studied for their ability to remove high heat fluxes. However, flow instabilities during microchannel boiling, like pressure drop oscillation and flow maldistribution, can cause an uneven temperature variation and deteriorate the cooling performance. This study analyzes the effect of using an oscillatory valve opening on the flow distribution and channel temperatures across a two-channel evaporator. Experiments and prediction models indicate that a specific range of valve oscillation amplitude and frequency may cause synchronization resulting in balancing the flow distribution and temperature across the channels, even when they are thermally isolated from each other. Analysis of system performance at different conditions indicates that larger oscillation amplitudes in the valve opening may allow a wider frequency range for temperature synchronization. For a fixed valve opening amplitude, using either significantly small or large frequencies may not be helpful. Moreover, for small amplitudes in valve opening, synchronization may never occur for any frequency. These observations lead us to believe that deliberate oscillations in the valve opening can serve as an active control strategy to mitigate flow maldistribution in parallel channels, suppress temperature oscillation, and improve the overall cooling performance.

A new small-celled diatom from Brazil - Luticola minutissima sp. nov., with comparison to the type of the Antarctic L. neglecta Zidarova, Levkov & Van de Vijv

The samples for this study were collected from terrestrial mosses and lichens growing on palm tree trunks and concrete walls in the city of Rio de Janeiro, south-eastern Brazil. During the investigation on diatom diversity, a new species from the genus Luticola was found. The new species occurred individually at all sampling sites. The aim of this paper is to provide a morphological and ecological description of Luticola minutissima sp. nov. from an aerophytic environment. The species is characterized by a small valve size (5.2–16.8 μm length and 3.7–4.4 wide) and abruptly hooked proximal raphe endings (ca. 90-degree angle). Additionally for comparison, type material of the most similar species, Luticola neglecta Zidarova, Levkov & Van de Vijver, was studied and new information for the ultrastructure of the latter species is provided as well.

Navicula blazencicae (Bacillariophyta) — синоним N. trivialis

Navicula blazencicae was described from Lake Prespa (North Macedonia) in 2007 and to date is known from the type locality only. We have observed the taxon in two samples from the Krasnodar Territory. The morphology of Russian specimens is described on the base of light and scanning electron microscopy investigations. In addition, a population of Navicula trivialis of a good size range from the same region was studied for comparison. Samples of N. blazencicae observed in this study morphologically are very close to samples of N. trivialis with small valves at the ends of size reduction. Our data demonstrate that both names are conspecific.

Low-Gradient Aortic Stenosis; the Diagnostic Dilemma.

ABSTRACTLow-gradient (LG) aortic valve stenosis (AS) constitutes a significant subset among patients with severe aortic stenosis. This entity represents one of the most challenging heart conditions when it comes to diagnosis and management, mainly because of the discrepancy between the small aortic valve area (≤1.0 cm2) that is considered a severe AS, and low mean transvalvular pressure gradient (<40 mmHg), which is one of the criteria for nonsevere AS. LG AS is divided according to transvalvular aortic flow rate into normal-flow LG AS and low-flow LG (LFLG) AS; the latter category can be divided further according to left ventricular ejection fraction (LVEF) into classical LFLG AS if LVEF is depressed or paradoxical LFLG AS if LVEF is preserved. The primary diagnostic challenge in patients with LG AS is to confirm that AS is truly severe and not pseudosevere, which is assessed mainly by either dobutamine stress echocardiography or multidetector computed tomography. The management of symptomatic true severe LG AS is mainly by aortic valve replacement (AVR), whether surgical or transcatheter approach. Patients with LG severe AS have a generally worse prognosis and higher mortality compared with patients with high-gradient severe AS. Despite the survival benefit of AVR in patients with true severe LG AS, these patients have higher surgical risk post-AVR compared with high-gradient AS patients. Early recognition and correct diagnosis of a patient with LG AS is crucial to improve their mortality and morbidity.

Validation of suitable reference genes for quantitative expression analysis by qPCR in bovine terminal ileum and ileocecal valve.

The use of reference genes is commonly accepted as the most reliable approach to normalize qRT-PCR and to reduce possible errors in the quantification of gene expression. The aim of this study was to identify a set of reference genes suitable for gene expression analysis in the distal portion of small intestine and ileocecal valve in cattle. These sites of intestine are of interest in veterinary science as they are the main sites of inflammation caused by Mycobacterium avium subsp. paratuberculosis, agent of paratuberculosis. We employed ten PCR assays for commonly used reference genes belonging to various functional classes and then determined their expression stability. The most stable genes were RPL13A and HMBS, followed by TFRC and B-ACT. NormFinder analysis provided similar results with B-ACT as the best reference gene, followed by RLP13A and TFRC. This validated gene panel may be useful for studies on paratuberculosis aiming to identify genes differentially expressed by qRT-PCR.