Large Valve Research Articles

145: Role of radiolabeled leukocyte scintigraphy in management of patients with a suspicion of prosthetic valve endocarditis

In patients with a suspicion of prosthetic valve endocarditis (PVE), detection of perivalvular infection can be difficult based only on echocardiography, but has an important impact in guiding surgical indications. The aim of this retrospective study was to test the interest of leukocyte scintigraphy (LS) for detection of perivalvular infection in patients with suspicion of non-complicated PVE. LS was performed in 42 patients admitted for suspicion of PVE. Results of LS were classified as positive, with either intense or mild accumulation of radiolabeled leukocytes in the cardiac area, or negative. Macroscopical aspects and bacteriology were obtained from patients who underwent cardiac surgery (n=10). Clinical outcome was collected in patients treated medically (n=32). Among patients with an intense signal with LS who underwent surgery (n=6), 5 had an abscess confirmed during intervention, and 1, post-operatively. Patients with an intense accumulation of radiolabeled leukocytes with scintigraphy and treated medically (n=3) had a poor outcome: death (n=1); prosthetic valve dehiscence (n=1); recurrent endocarditis (n=1). Among patients with a mild activity with LS (n=5), one patient developed a large prosthetic valve dehiscence during follow-up. The 4 remaining patients were treated medically and did not present any recurrent endocarditis after a median follow-up of 14 months. No abscess was detected in patients with negative LS who underwent surgery (n=4). Among patients with negative LS treated medically (n=24), none presented recurrent endocarditis after a mean follow-up of 15±16 months. In total, LS helped to identify perivalvular infection or abscesses in 12 out of 42 patients (29%). This retrospective study suggests that LS is useful for identification of perivalvular infection and could help in guiding surgical indications in patients with suspicion of PVE.

160: What are long-term results of percutaneous mitral commissurotomy in patients with few or no symptoms?

Percutaneous mitral commissurotomy (PMC) has enabled patients (pts) to be treated at an earlier stage of their disease than by surgery. However, very long-term results have not been specifically studied in this context. From 1986 to 1995, 237 patients in NYHA class I or II underwent PMC in our department. Mean age was 46±12 years; 74 patients (31%) had atrial fibrillation and 22 (9%) had a history of commissurotomy. Most patients were in NYHA class II (232 pts, 98%). As assessed by echocardiography, mean valve area was 1.1±0.2 cm 2 (≤1.5 cm 2 in all cases); 40 patients (17%) had pliable valves and mild subvalvular disease, 145 (61%) had severe subvalvular disease, and 52 (22%) had calcified valves. PMC used a singleballoon in 5 pts, a double-balloon in 93 and the Inoue balloon in 139. After PMC, valve area increased to 1.9±0.3 cm 2 as assessed by 2D echo. Severe mitral regurgitation (grade ≥3/4) occurred in 4 patients (1.7%). There were no other severe immediate complications. Good immediate results (valve area ≥1.5 cm 2 without mitral regurgitation >2/4) were obtained in 223 patients (94%). The 20-year actuarial rate of survival without surgery or repeat PMC and in NYHA class I or II was 41±4% in the whole population. After good immediate results, the 20-year rate of good functional results was 42±3%. A Cox multivariate model identified 2 predictors of good late functional results after good immediate results: young age (p=0.05) and a large valve area after PMC (p=0.002). In the 142 patients aged ≤50 years, the 20-rate of good functional results was 50±6%.

Assessment of Severe Accident Depressurization Valve Activation Strategy for Chinese Improved 1000 MWe PWR

To prevent HPME and DCH, SADV is proposed to be added to the pressurizer for Chinese improved 1000 MWe PWR NPP with the reference of EPR design. Rapid depressurization capability is assessed using the mechanical analytical code. Three typical severe accident sequences of TMLB’, SBLOCA, and LOFW are selected. It shows that with activation of the SADV the RCS pressure is low enough to prevent HPME and DCH. Natural circulation at upper RPV and hot leg is considered for the rapid depressurization capacity analysis. The result shows that natural circulation phenomenon results in heat transfer from the core to the pipes in RCS which may cause the creep rupture of pipes in RCS and delays the severe accident progression. Different SADV valve areas are investigated to the influence of depressurization of RCS. Analysis shows that the introduction of SADV with right valve area will delay progression of core degradation to RPV failure. Valve area is to be optimized since smaller SADV area will reduce its effect and too large valve area will lead to excessive loss of water inventory in RCS and makes core degradation progression to RPV failure faster without additional core cooling water sources.

K-130 Cyclotron vacuum system

The vacuum system for K-130 cyclotron has been operational since 1977. It consists of two sub-systems, main vacuum system and beam line vacuum system. The main vacuum system is designed to achieve and maintain vacuum of about 1 × 10−6 mbar inside the 23 m3 volume of acceleration chamber comprising the Resonator tank and the Dee tank. The beam line vacuum system is required for transporting the extracted beam with minimum loss. These vacuum systems consist of diffusion pumps backed by mechanical pumps like roots and rotary pumps. The large vacuum pumps and valves of the cyclotron vacuum system were operational for more than twenty five years. In recent times, problems of frequent failures and maintenance were occurring due to aging and lack of appropriate spares. Hence, modernisation of the vacuum systems was taken up in order to ensure a stable high voltage for radio frequency system and the extraction system. This is required for efficient acceleration and transportation of high intensity ion beam. The vacuum systems have been upgraded by replacing several pumps, valves, gauges and freon units. The relay based control system for main vacuum system has also been replaced by PLC based state of the art control system. The upgraded control system enables inclusion of additional operational logics and safety interlocks into the system. The paper presents the details of the vacuum system and describes the modifications carried out for improving the performance and reliability of the vacuum system.

Application of Non-Circular Planetary Gear Mechanism in the Gear Pump

Gear pump is the most commonly used hydraulic component in hydraulic drive system.Volumetric efficiency of the traditional gear pump is low, big flow ripple causes large pressure fluctuations, makes pipes and valves vibration, noisy. The imbalance pressure on gear pump’s gears, shafts and bearings and the large radial load limits its pressure increased. Planetary gear transmission compared with ordinary gear transmission, it has many unique advantages. So the writer on the basis of the combination of proposed non-circular planetary gear pumps and gear pump works discussed the structure and working principle of the pump. The non-circular planetary gear pump with many advantages such as big flow, uniform flow, low noise and so on. It can be widely used in various hydraulic transmission systems.

Potentiodynamic polarization study on electropolished nitinol vascular implants

The electrochemical properties of electropolished Nitinol vascular implants manufactured in a serial-production manner starting with laser cutting of tubing and ending with electropolishing and final inspection were analyzed and evaluated over a time period of 1 year. Potentiodynamic polarization tests in phosphate-buffered saline were conducted on over 1250 Nitinol implants covering the entire serial production range at ADMEDES Schuessler GmbH - from tiny stents for neurovascular applications up to large heart valve frames. Breakdown potentials were evaluated and correlated to product group, properties of the semifinished material and raw material supplier. Results of this study give clear indications for the interrelation between material quality and the event of electrochemical breakdown in a potentiodynamic polarization test.

Encyonopsis neerlandica, a new freshwater diatom species (Bacillariophyta) from moorland pools in The Netherlands

A new cymbelloid diatom species, Encyonopsis neerlandica sp. nov., is described from several moorland pools from The Netherlands. The new species belongs to the complex of species around E. microcephala. Based on light and detailed scanning electron microscopy, the morphology of Encyonopsis neerlandica is discussed and compared to similar species from this complex. Encyonopsis neerlandica is characterized by its rather large valve dimensions, the narrowly to clearly lanceolate valve outline with convex to weakly convex margins and rostrate to subcapitate apices. The distal raphe fissures are ventrally deflected. There is a clear difference between the rounded areolae near the valve margin and the transapically elongated areolae near the axial area.Notes on the ecology of the species are included.

Chiari’s Network: An Unusual but not Uncommon Finding

A 23-year-old male patient with the diagnosis of rheumatic heart disease with severe mitral stenosis and mitral regurgitation was scheduled to undergo mitral valve replacement. After induction of anaesthesia, transoesophageal echocardiography (TEE) confirmed mitral valve disease. In addition, echocardiography revealed thin, filamentous, and freely mobile structure showing whiplike motion in the right atrium (Figs 1 and 2). The diagnosis of Chiari’s network was made based on the fine fibres originating near the inferior vena cava (Eustachian valve). The Chiari’s network was first described in 1897 in an autopsy series by Dr Chiari.1 This is a reticulated web-like network of fibres originating from the eustachian and thebesian valves at the orifice of the inferior vena cava and the coronary sinus and show attachments to different parts of the right atrium. The network results from incomplete reabsorption of the right valve of the sinus venosus during embryonic development1 and is present in approximately 2% of the population.2 According to definition1 Chiari’s network is considered, if coarse or fine fibres originating from a eustachian or thebesian valve at the orifice of the inferior vena cava or the coronary sinus are seen and they demonstrate attachments to the upper wall of the right atrium or the interatrial septum. Chiari’s network should be carefully differentiated from a large eustachian valve by looking for attachments to other parts of the right atrium as seen in the present patient (Fig. 2). Chiari’s network is often considered clinically insignificant. However, association has been made with the persistence of patent foramen ovale,2 formation of atrial septal aneurysm,2 thromboembolic events,2 intra-atrial thrombus,3 catheter entrapment,4 infective endocarditis5,6 and atrial tachyarrhythmias.7 It also poses diagnostic difficulties during echocardiography where it could be confused with right atrial thrombi, tumours, right heart vegetation’s, flail tricuspid leaflet, or a ruptured chordae tendineae. Chiari’s network can also cause difficult cannulation of the coronary sinus for retrograde coronary perfusion.8 Because of its proximity to atrial structures, TEE provides a high resolution imaging technique for atrial pathology. In summary, echocardiographic features of a rare case of Chiari’s network are presented.

Analysis of the hydrodynamic torque effects on large size butterfly valves and comparing results with AWWA C504 standard recommendations

Butterfly valves are widely used in various industries such as water distribution, sewage, oil and gas plants. The hydrodynamic torque applied on the butterfly valve disk is one of the most important factors which should be considered in their design and application. Although several methods have been used to calculate the total torque on these valves, most of them are based on hydrostatic analysis and ignore the hydrodynamic effect which has a major role to determine the torque of the large-size valves. For finding the dynamic-valvetorque, some empirical formulas and methods have been proposed; for example in AWWA C504 standard, a relationship for calculating the dynamic torque has been given and its variation versus disk angle has been stated. However, the use of these empirical relationships is restricted due to the conditions defined in the standards. In this paper, the dynamic-valve-torque has been calculated for a large butterfly valve under different conditions and also at the different opening angles of the valve disk. For this purpose a computational fluid dynamics (CFD) method has been used. The results have been compared with those given in the AWWA C504 standard recommendations. Moreover, the effects of the disk shape and its deformation, surface roughness, upstream/downstream pressure variation and disk-offset value have been studied.

Valvular heart disease in a patient taking 3,4‐methylenedioxymethamphetamine (MDMA, ‘Ecstasy’)

3, 4-methylenedioxymethamphetamine, (MDMA, ‘Ecstasy’), an amphetamine-derived drug, is a psychoactive stimulant used as a recreational drug. In vitro experiments have suggested that ecstasy can lead to fenfluramine-like proliferation of cardiac valves through activation of 5-hydroxytryptamine 2B (5-HT2B) receptors and can induce mitogenic responses in human valvular interstitial cells [1]. We report the first observation of valvular heart disease (VHD) with pathological confirmation after long term use of ecstasy. A 33-year-old male patient was admitted for shortness of breath and chest pain. The only risk factor reported was active smoking. He reported long lasting exposure to ecstasy (several pills week−1 since the age of 17 years). At examination a systolic and diastolic mitral murmur was diagnosed. Mean blood pressure was 106/70 mmHg. ECG showed sinus rhythm (91 beats min−1) with a right bundle branch block. Echocardiography revealed a slight left ventricular dilation (endiastolic diameter of 55 mm) with an ejection fraction of 55% and typical features of mitral valve disease. There was a left atrial enlargement (area of 42 cm2) thick mitral valve with decreased opening of the mitral valve leaflets. Mean pressure gradient across the mitral valve was of 14.7 mmHg with mitral valve areas of 1.56 cm2. These moderate to severe mitral stenosis features were associated with severe mitral regurgitation (regurgitant orifice area = 0.49 cm2) with a central blood jet. Other valves and heart chambers were normal. This patient had pulmonary hypertension (40 mm Hg) without right heart failure. Coronary angiogram showed normal coronary arteries with a decreased cardiac index and post capillary pulmonary hypertension. Surgery was decided. Macroscopic analysis made the surgeon hypothesize about a possible cardiac tumour. Mitral valve leaflets and the chordae tendinae were markedly thickened and fibrous. The chordae tendinae were retracted (Figure 1). After resection, the surgeon decided to perform mitral valve replacement with a mechanical Saint Jude prosthesis despite severe damage of the mitral annulus. At histology, the endocardium on both sides was fibrous up to 2 mm thick. It was stratified with layers of collagen bundles and spindle cells. Density of spindle cells was heterogeneous, but more frequently low. In this abundant extracellular matrix, rare foci contained abundant elastic fibres. No inflammation or myxoid matrix accumulations were observed, ruling out rheumatic and Barlow diseases (Figure 1B, C). Common disease (Osler endocarditis, carcinoid syndrome, rheumatic fever, autoimmune disease …) or intake of other drugs (ergot derivatives, appetite-suppressant drugs including benfluorex) known to affect cardiac valves were not found. One month later, the patient came back with chest pain, fatigue and loss of weight. Trans-thoracic echocardiography showed a para-prosthetic leak with prosthesis dehiscence. The patient underwent re-operation with fixation of his prosthesis. At follow-up there were no complications. Figure 1 Anatomical and histological findings. (A) a short leaflet mitral valve (left) and a large leaflet mitral valve with a part of the left ventricle which was also removed (right). (B) Gross pathology of the mitral valve: on this section the valve is markedly ... This is the first case of VHD with pathological confirmation related to long term exposure to ecstasy. Except for an in vitro study [1], few data are available [1]. Among 29 subjects using ecstasy, eight had abnormal mitral valve echocardiography vs. 0 in controls [2]. The fact that the lesions in our patient were very similar to those described with appetite-suppressant drugs [3] and the ability of ecstasy to activate 5-HT2B receptors, like fenfluramine [1, 4], suggests its role in the pathophysiology of this VHD. VHD is unusual in young subjects. The present work allows the addition of ecstasy to the list of substances able to induce VHD [5]. The data also underline the important (and probably underestimated) harm associated with the now large use of ecstasy in young subjects. Information must be given about this risk.

Reply to the Editor

We thank Dr Bozok and colleagues for their useful comments and suggestions to reduce paravalvular leak after transapical aortic valve implantation. In our study based on data from the Italian Registry of Trans-Apical Aortic Valve Implantation,1D’Onofrio A. Rubino P. Fusari M. Salvador L. Musumeci F. Rinaldi M. et al.Clinical and hemodynamic outcomes of “all-comers” undergoing transapical aortic valve implantation: results from the Italian Registry of Trans-Apical Aortic Valve Implantation (I-TA).J Thorac Cardiovasc Surg. 2011; 142: 768-775Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar the incidence of paravalvular leak (trivial and mild) was 38%, and this is consistent with the incidence reported by other series.2Unbehaun A. Pasic M. Dreysse S. Drews T. Kukucka M. Mladenow A. et al.Transapical aortic valve implantation: incidence and predictors of paravalvular leakage and transvalvular regurgitation in a series of 358 patients.J Am Coll Cardiol. 2012; 59: 211-221Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar Reducing the incidence of paravalvular leak is of outmost importance to improve patient outcomes. In fact, it has been demonstrated that the presence of paravalvular aortic regurgitation after transcatheter aortic valve implantation is associated with an increased rate of late mortality and that the effect of aortic regurgitation on mortality is proportional to the severity of the regurgitation. Furthermore, even mild aortic regurgitation is associated with an increased rate of late deaths.3Kodali S.K. Williams M.R. Smith C.R. Svensson L.G. Webb J.G. Makkar R.R. et al.Two-year outcomes after transcatheter or surgical aortic-valve replacement.N Engl J Med. 2012; 366: 1686-1695Crossref PubMed Scopus (1896) Google Scholar Overexpansion of the Sapien valve after deployment might be useful, but it is controversial and should be performed carefully. Many complications can occur after this procedure, including not only coronary ostia occlusion, but also rupture of the aortic annulus and injury to the prosthetic valve leaflets. Furthermore, in our experience, overexpansion of the Sapien valve after deployment is often associated with a small (or none) reduction of the degree of paravalvular regurgitation. We agree with Dr Bozok that asymmetry of the calcium distribution over the leaflets and annulus is a major determinant of paravalvular regurgitation; however, other important causes should be also carefully considered such as correct sizing and correct positioning. Correct sizing needs an experienced multidisciplinary and multimodal (2-dimensional and 3-dimensional transthoracic and transesophageal echocardiography, multidetector computerized tomography scan) evaluation of the annulus dimensions and shape (the annulus is often oval and not circular) and a semiquantitative evaluation of the amount of calcium on the annulus and the leaflets. In fact, for the intermediate annulus diameters, the choice of a larger or a smaller valve depends on the amount of calcium. A larger valve in an extremely calcified annulus can cause rupture of the aortoventricular junction with consequent massive hemorrhage. However, a small valve in a poorly calcified annulus can lead to paravalvular regurgitation or, more dramatically, device embolization. Correct positioning requires experience and a strong synergic cooperation among all the components of the transcatheter aortic valve implantation team. The definition of valve malpositioning includes not only a valve positioned too high or too low, but also a problem of alignment between the valve and longitudinal axis of the aortic annulus. An asymmetric “diagonal” landing of the prosthesis on the annulus might lead to paravalvular regurgitation and to an abnormal stress on the leaflets with a greater potential risk of early structural dysfunction. In conclusion, we believe that even if valve overexpansion might be carefully considered to reduce paravalvular leak, the transcatheter aortic valve implantation results can be increased mainly by improving patient selection, annulus sizing, valve positioning, and cooperation among members, as well as the experience of the transcatheter aortic valve implantation team. Can the success of transcatheter aortic valve implantation be increased?The Journal of Thoracic and Cardiovascular SurgeryVol. 144Issue 2PreviewWe congratulate the authors on their study.1 After application of a size 26 Sapien valve to one third of the patients, the postoperative effective orifice area was noted to be 1.67 cm2 and the geometric size was 2.5 cm2 in the size 21 Sapien valve. This suggests that the balloon should be inflated more. Instead of “hinge-to-hinge” or “virtual ring” calculations, we suggest that an experienced cardiac surgeon can decide which leaflet should be dilated to what degree, while inflating the valve using computed tomography or echocardiography, because the Sapien valve is located at the leaflet and not at the annulus. Full-Text PDF

Comparison of Need for Operative Therapy in Patients With Mitral Valve Prolapse Involving Both Leaflets Versus Posterior Leaflet Only

Mitral valve prolapse may involve 1 leaflet or 2 leaflets, yet management guidelines do not differentiate posterior leaflet (PML) from bileaflet (BML) prolapse. We hypothesized that patients with BML have a prolonged natural history with more severe atrial and ventricular enlargement but less severe mitral regurgitation (MR) compared to patients with PML. Patients with mitral valve prolapse undergoing mitral repair were identified and preoperative characteristics were recorded. Patients with predominant PML prolapse (n = 304) versus BML prolapse (n = 131) were identified based on preoperative echocardiographic and intraoperative findings. Timing of operation was based on standard guidelines. Despite being equally symptomatic, patients with BML differed significantly from those with PML in being younger (54 vs 60 years, p <0.0001), more likely to be women (51% vs 24%, p <0.0001), and having a larger valve (37 vs 32 mm, p <0.0001). Despite similar cardiac function and dimensions, patients with BML had less severe MR (24% vs 13% with <4+ MR, p = 0.01) and less severe pulmonary hypertension (14% vs 31%, p <0.0001) at time of operation. In conclusion, patients with BML often meet indications for mitral valve repair with similar cardiac enlargement but less MR than patients with PML prolapse. Patients with BML prolapse may benefit from timing mitral repair based more on symptomatic 3+ MR or cardiac enlargement and less on presence of severe MR.

Wear Life Prediction for a Large Diameter Spool Valve

Life prediction for a component can’t instead of its life tests, even so it has a very important guiding significance for the optimization design and material selection of the component, and it can decrease great loss caused by design mistakes, also possibly avoid detours, especially on initial development stage. It also is an important stage of the lifecycle design of a component. According to a certain working condition, this paper predicts the wear life of a large diameter hydraulic directional spool valve with 2-position 4-way for the hydraulic system of a high speed winch, combined with the surface micro-topography of the valve body and spool, and influence factors to the fit clearance changing caused by wear, such as shaping form errors, lateral force, matching materials, hydraulic medium and so on. The result shows that the wear life of the large diameter spool valve is more than 10 million times. The prediction provides a theoretical basis for the independent development of this valve, and has a certain reference for the design of this kind of components.

Editorial Comment: Re: The worldwide experience with the 29-mm Edwards SAPIEN XTTM transcatheter heart valve in patients with a large aortic annulus

This series chronicles the results of 120 patients receiving the 29-mm Edwards SAPIEN XT™ bioprosthesis over a 15-month period in 20 centres [1]. It is instructive from a number of different standpoints. First, it is apparent from this experience that there are a significant number of patients with aortic annuli between 24 and 27 mm who were previously not able to be treated because of the unavailability of a larger-sized valve. It is also noteworthy that in the whole Prevail TA experience approximately one-third of the patients received the 29-mm valve indicative of the clinical need for the larger sized valve [2]. Second, there is a notably high procedural success rate (95.8%) with remarkably few complications. In point of fact, the 30-day survival of 95.8% and 1-year survival of 79.8% are among the better results reported with transcatheter aortic valve replacement (TAVR). It is, of course, unlikely that these improved results are due to the valve itself, but is in all likelihood multifactorial and encouraging nonetheless. Possible reasons for better results include the fact that the patients are somewhat better-risk patients (Society of Thoracic Surgeons predicted risk of mortality score of 6.8 versus 11.2% in the Partner trial), the implanting centres had gained significant previous experience with the TA approach and perhaps improved 1-year survival due to less paravalvular leak. This is indicative that both procedural and intermediate term results continue to improve with TAVR. Third, and perhaps most important, there is a remarkably low rate of paravalvular leak. Specifically, there were only two patients (2.2%) who had a moderate paravalvular leak and 12.8% with mild aortic regurgitation. This contrasts with a 12.2% incidence of moderate or severe paravalvular leak in the Partner cohort A series in which only 23 or 26 mm valves were available [3]. As annular sizing becomes more sophisticated with the realization that echocardiographic assessment frequently undersizes the aortic annulus and that calculation of true aortic annular size by computed tomography scan leads to greater use of larger diameter valves, it could be anticipated that a significant number of patients currently receiving 26-mm valves may in fact be better treated with 29-mm valves and perhaps have less paravalvular leak and thus improved longterm survival. Fourth, a slight note of caution is warranted, to indicate that there may be a higher permanent pacemaker implantation rate with the 29-mm valve. The pacemaker implantation rate of 12.5% in this series is higher compared with an average 5% pacemaker implantation rate with the 23- and 26-mm Edwards SAPIEN valves. Although this series is small and no conclusions can be definitively drawn, it is possible that the larger valves cause more compression of the membranous septum and therefore a higher permanent pacemaker rate. A larger experience is necessary to determine whether this observation is true. Fifth, despite the use of the larger valves, it is noteworthy that there were minimal procedural complications including no annular disruptions and a stroke rate of 1.7%. This stroke rate is among the lowest reported with TAVR.

Understanding the Atrioventricular Dissociation

A 56-year old male patient was addressed to our intensive cardiac care unit with a diagnosis of “complete atrioventricular (AV) block”, 4 days following surgical treatment of symptomatic obstructive hypertrophic cardiomyopathy including large septal resection and mitral valve replacement. We noted no relevant medical history. On physical examination, at admission, the patient presented normal hemodynamic, regular heart rate about 60 bpm, no signs of right heart failure. An abnormal transient jugular vein pulse was noted. The EKG on admission is presented in Fig. 1. Do you agree with the diagnosis of complete AV block? Diagnosisof considered “complex”EKG features appears tobe reserved for cardiologists or even to electrophysiologists, although good sense and simple logical approach allowmaking the diagnosis yourself in a number of cases. Let‘s go for a typical case of a suspected AV conduction disorder following cardiac surgery. First, let’s review some elementary considerations on the cardiac conduction physiology. Sinoatrial node is a part of a specialized type of myocardial network which has the particularity of being also pacemaker myocyte cells. This specialized network is represented by sinoatrial node, AV node, His and bundle branch as well as distal Purkinje fibers. Unlike the rest of themyocytes, these pacemaker cells may initiate action potential through spontaneous diastolic depolarization. Because of a higher depolarization slope, the impulse initiated from sinoatrial node depresses the activity of subsidiary pacemaker sites, and also automatically generates electrical pulses that spread as waves of electrical excitation over the atria and then to ventricles via AV node. Interruption of the conduction at any level enables subsidiary pacemakers to emerge usually at a slower rate (the lower andmore distal is the block, the slower is the rate). On the opposite, enhanced automaticity in any part of this specialized myocardial network may overdrive normal sinus node activity, particularly when the latest is slower.

Reducing the idle speed of an SI CNG engine fueled by HCNG with high hydrogen ratio

This paper presents an experimental study aimed at idle characteristics of a CNG engine fueled by HCNG with 55% hydrogen blend. The idle speed was reduced from original 800 r/min to 750 r/min and 700 r/min, and the characteristics of combustion & emissions at reduced idle speed were investigated. It is found that, for the HCNG engine, only reducing idle speed cannot reduce fuel consumption at conditions of fixed λ. In order to reduce fuel consumption and keep the COV at rather low levels, the excess air ratio must be increased properly while reducing the engine idle speed. Due to the large valve overlap (30°) of this inlet inject HCNG engine, CH4 emissions are mainly caused by scavenging, which account for the vast majority of THC emissions. The emissions of CO, THC and NOx are reduced with the decrease of ignition advance angle at a fixed λ.

The Implications of CT Sizing on Valve Selection and Paravalvular Regurgitation in Transcatheter Aortic Valve Replacement

Background: Computed tomography (CT) provides three dimensional measurement of the aortic annulus which can be used for valve sizing in transcatheter aortic valve replacement (TAVR). Methods: 120 patients underwent CT prior to TAVR with a balloon expandable aortic valve. Valve sizing was by TEE annular diameter and clinical features. A theoretical CT based valve size was retrospectively determined by ensuring the nominal external valve area is greater than the CT annular area. The impact of CT sizing on valve selection and grade of paravalvular regurgitation by transthoracic echocardiography was assessed. Results: The mean aortic annular measurements were: TEE annular diameter 22.4 ± 1.8 mm, CT annular area 4.5 ± 0.9 cm2 and mean CT annular diameter 23.4 ± 2.3 mm. Using traditional TEE sizing the THV was undersized (external area of a fully expanded valve < CT annular area) in 33.3% (40/120). By using CT sizing criteria there was a trend towards using larger valves (Table 1). Eighty-five percent (34/40) of patients where CT suggested using a larger valve had mild or moderate paravalvular regurgitation (Table 1).Table 1The Effect of Using CT Sizing GuidelinesaExternal area of a fully expanded valve>CT annular area. on Valve Selection Compared to TEE.Change in Valve sizeN (%)Paravalvular Regurgitation GradeNone/trivial N (%)MildModerateSevereDownsize by 113 (10.8)10 (76.9)2 (15.4)0 (0)0No change67 (55.8)37 (55.2)26 (38.8)3 (4.5)0Upsize by 140 (33.3)6 (15.0)24 (60.0)10 (25.0)0Total12053 (44.2%)52 (43.3)13 (10.8)0a External area of a fully expanded valve > CT annular area. Open table in a new tab Conclusions: CT based sizing may reduce the risk of significant paravalvular regurgitation post TAVR.

Actinocyclus nipponicus sp. nov. and A. bradburyii sp. nov. (Bacillariophyta) from Miocene lacustrine sediments of the proto-Japan Sea

Hayashi T., Saito-Kato M. and Tanimura Y. 2012. Actinocyclus nipponicus sp. nov. and A. bradburyii sp. nov. (Bacillariophyta) from Miocene lacustrine sediments of the proto-Japan Sea. Phycologia 51: 98–112. DOI: 10.2216/11-17.1Fossil nonmarine Actinocyclus species, A. nipponicus sp. nov. and A. bradburyii sp. nov., are described from Miocene lake sediments in the Yamato Bank, the central part of the Japan Sea. Actinocyclus nipponicus is characterized by an inflated valve composed of a nearly flat valve face and an inclined mantle, a bullulate valve wall, fascicles sectioned by combinations of independent areola rows and hyaline stripes, loculate areolae with external cribra, rimoportulae at ends of hyaline stripes in the mantle, a single pseudonodulus at the valve face/mantle junction and well-developed spines. On the other hand, A. bradburyii is characterized by a noninflated valve composed of a nearly flat valve face and a very gently inclined mantle, a bullulate valve wall, loculate areolae with external cribra, fascicles sectioned by combinations of independent areola rows and hyaline stripes, rimoportulae at ends of hyaline stripes in the mantle, a single pseudonodulus within the valve face and misshapen cribra behind the pseudonodulus. In A. nipponicus, fascicles are composed of parallel areola rows in large valves, but are composed of radial areola rows in small valves. Additionally, in both A. nipponicus and A. bradburyii, changes in the number of rimoportulae (fascicles) occur as a function of valve size. Actinocyclus nipponicus and A. bradburyii are the most similar to A. trapeziformis and A. cupreus, respectively.

Design and operation of the wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source

The wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source (SNS) is optimized to provide a high neutron flux at the sample position with a large solid angle of detector coverage. The instrument incorporates modern neutron instrumentation, such as an elliptically focused neutron guide, high speed magnetic bearing choppers, and a massive array of (3)He linear position sensitive detectors. Novel features of the spectrometer include the use of a large gate valve between the sample and detector vacuum chambers and the placement of the detectors within the vacuum, both of which provide a window-free final flight path to minimize background scattering while allowing rapid changing of the sample and sample environment equipment. ARCS views the SNS decoupled ambient temperature water moderator, using neutrons with incident energy typically in the range from 15 to 1500 meV. This range, coupled with the large detector coverage, allows a wide variety of studies of excitations in condensed matter, such as lattice dynamics and magnetism, in both powder and single-crystal samples. Comparisons of early results to both analytical and Monte Carlo simulation of the instrument performance demonstrate that the instrument is operating as expected and its neutronic performance is understood. ARCS is currently in the SNS user program and continues to improve its scientific productivity by incorporating new instrumentation to increase the range of science covered and improve its effectiveness in data collection.

The Integral Test Facility Karlstein

The Integral Test Facility Karlstein (INKA) test facility was designed and erected to test the performance of the passive safety systems of KERENA, the new AREVA Boiling Water Reactor design. The experimental program included single component/system tests of the Emergency Condenser, the Containment Cooling Condenser and the Passive Core Flooding System. Integral system tests, including also the Passive Pressure Pulse Transmitter, will be performed to simulate transients and Loss of Coolant Accident scenarios at the test facility. The INKA test facility represents the KERENA Containment with a volume scaling of 1 : 24. Component heights and levels are in full scale. The reactor pressure vessel is simulated by the accumulator vessel of the large valve test facility of Karlstein—a vessel with a design pressure of 11 MPa and a storage capacity of 125 m3. The vessel is fed by a benson boiler with a maximum power supply of 22 MW. The INKA multi compartment pressure suppression Containment meets the requirements of modern and existing BWR designs. As a result of the large power supply at the facility, INKA is capable of simulating various accident scenarios, including a full train of passive systems, starting with the initiating event—for example pipe rupture.