Circular Valve Research Articles

A new self-adjustable glaucoma valve.

Introduction: Glaucoma, the leading cause of irreversible blindness globally, affects more than 70 million people across the world. When initial treatments prove ineffective, especially for cases with high intraocular pressure (IOP), the preferred approach involves employing glaucoma drainage devices (GDDs). Methods: This study introduces a novel self-adjustable glaucoma drainage device (SAGDD) designed to maintain IOP within the desired biological range (10mmHg < IOP <18mmHg) by dynamically modulating its fluidic resistance. Inspired by the starling resistor, we designed a circular valve with a thin, flexible membrane placed over the valve's inlet and outlet. To achieve the ideal design for the SAGDD and optimize its parameters, we utilized fluid-solid interaction (FSI) numerical models and conducted parametric studies, wherein simulations demonstrated the validity of the concept. Subsequently, to confirm and validate the numerical results, we fabricated a SAGDD at a 3:1 scale and subjected it to in vitro testing. Results: Our findings demonstrate that, on a 3:1 scale, a circular SAGDD with a diameter of 8.1mm and a stainless-steel membrane with a thickness of 10µm effectively maintained IOP within the target range when the membrane exposed to external pressures of 7.5 or 10mmHg. Discussion: In summary, our study establishes a strong foundation for further exploration of the potential efficacy of SAGDD as a promising treatment for glaucoma. The cost-effectiveness and simplicity of its design, devoid of costly instrumentation, hold considerable promise in addressing the challenges associated with glaucoma.

Mechanical behaviors of a new elliptical valve stent in bicuspid aortic valve

Background and ObjectiveThe conventional valve stents that are cylindrical in shape will become elliptical when implanted in bicuspid aortic valve, thereby reducing the durability of the artificial valve. In this study, a new design of valve stent is presented where valve stents have elliptical cross-section at the annulus and it is expected to have better expandability and circle shape during the interaction between the stent and bicuspid aortic valve, thereby extending the durability of artificial valve. MethodsFinite element method (FEM) is used to study the mechanical behavior of the novel valve stent in the bicuspid aortic valve. The effects of three matching relationship between the ellipticity of the stents and the ellipticity of the annulus (i.e., the ellipticity of the stent is greater than, equal to and less than the annulus ellipticity, respectively) on the mechanical behavior of stent expansion are studied. In addition, the expansion mechanical behavior of the novel valve stent at different implantation depths is also compared. ResultsResults indicate that novel valve stent implantation with elliptical features is superior to conventional circular valve stent. When the novel valve stent ellipticity is less than the annulus ellipticity, the ellipticity of the novel valve stent after implantation is smaller than that of the conventional circular valve stent. This indicated that the novel valve stent has better expandability and post-expansion shape, making artificial valve to have better durability. The risk of paravalvular leak after implantation is lowest when the novel valve stent ellipticity is less than annulus ellipticity. When the novel valve stent ellipticity coincides with annulus ellipticity, the aortic wall is subjected to greatest stress. With the increase of implantation depth, the stress on the novel valve stent decrease. ConclusionsThis study might provide insights for improving stent design for bicuspid aortic valve.

Research on the influence of check valve on noise performance of variable frequency scroll refrigeration compressor

Check valve is one of the core components of the scroll refrigeration compressor, which can directly affect its efficiency, life, and noise performance. Traditional check valve is the reed valve. This paper deeply studies the dynamic characteristics of reed valve and reveals the main reason of the valve noise under different rotation speeds. The large noise is mainly attributing to the large pressure pulsation as well as fast circulation velocity of fluid and the severe slapping of the reed plate on the valve seat, which is influenced by the high pressure ratio of the working condition and stiffness of the reed valve. In order to reduce the noise of the check valve, the circular valve is designed to replace reed valve in this paper. At each rotation speed, the circular valve shows a continuous exhaust process, which avoids the slapping of the valve plate on the valve seat. More importantly, the exhaust is smooth and the pressure pulsation as well as the flow rate of the fluid is reduced significantly leading to the low aerodynamic noise. Therefore, compared with the reed valve compressor, the sound pressure level of the circular valve compressor at 1800, 4200, and 6600 rpm is decreased by 3.0, 5.2, and 0.3 dB, respectively.

IMPROVEMENT OF DESIGN OF PNEUMATIC HAMMER FOR DRIVING VERTICAL PIPES WITH LARGE DIAMETER INTO SOIL

A brief description of the equipment used for trenchless pipe laying is given. The basic parameters of a pneumatic hammer designed for driving pipes into soil with an open end greater than 426 mm in diameter are substantiated. The description of the device and operating principle of a pneumatic hammer with an air distribution system using an elastic circular valve as the main element is presented. Based on the analysis of many-year operation of equipment for trenchless pipe laying and driving vertical pipes, the frequency and sequence of crack appearance, destruction and failure of the main parts of the pneumatic hammer are determined. New principles of calculation and design of a pneumatic hammer with a large mass of the striking part without loss of work performance are proposed. The solution to the problems associated with fatigue failure of the main parts is a decrease in striking velocity.

원 모양 스핀밸브 박막의 직교 4-단자법으로 측정된 자기저항 특성 연구

단순형 스핀밸브의 Ta/NiFe/Cu/NiFe/Ta 자성박막을 원 모양으로 패턴하여 중심을 직교하는 전류 단자와 전압 단자로 자기저항특성을 조사하였다. 측정 시 인가한 외부자기장 방향을 박막면에서 수평과 수직으로 각각 설정하여 회전각과 방위각에 따라 자화 용이축과 전류 방향이 서로 수직이 되도록 하고 측정한 자기저항곡선으로부터 자기저항비와 외부자기장이 0 Oe 부근에서 자장감응도를 구하였다. 외부자기장 방향을 박막면에서 수평과 수직으로 각각 설정하여 측정한 홀저항의 초기값은 1.29Ω이었다. 수평면상과 수직면상으로 홀저항의 변화에 따라 최대 자기저항비는 회전각과 방위각이-45°에서 각각 -9.65%와 -3.91%를 나타내었다. 회전각 90°에 측정한 자기저항곡선은 외부자기장 ± 2.0Oe 이내 영역에서 선형적 대칭의 모양을 보였다. 최대 자장감응도는 10.0%/Oe이었다. 원 모양으로 미세 패턴한 스핀밸브 자성박막 소자는 높은 감도를 갖는 평면홀센서로 개발할 수 있다는 가능성을 확인하였다.

Improving the performance of heat valve ventilation system: A study on the provided thermal environment

The current study presents and evaluates the performance of two types of supply air terminal devices applied in a heat valve ventilation (HVV) system with regard to the provided thermal environment in a room heated and ventilated by the HVV system. To that end, air temperature and air velocity patterns and local thermal discomfort due to draught were studied both experimentally and numerically. Using numerical simulations, parametric analysis was carried out for investigating the provided indoor thermal environment for a wider range of boundary conditions. The considered parameters included the influence of cold vertical surfaces, supply airflow rate and temperature, and room heating energy demand. The results showed that both of the applied air terminal devices could avoid temperature stratification within the occupied zone. The maximum air temperature difference between 0.1 and 1.8 m above the floor was 2.1 °C when using a circular valve placed in the external wall below the window and 2.6 °C in the case when the air was supplied through three nozzles located in the wall opposite to the window in the upper part of the room. In general, placing the air terminal device below the window provided more uniform air temperature distribution and contributed to the prevention of downdraught caused by a cold window surface. The outcomes of this study are relevant to selecting and designing ventilation and air heating systems for low-energy buildings.

Morphology and molecular phylogeny of Pleurosira nanjiensis sp. nov., a new marine benthic diatom from the Nanji Islands, China

A new marine benthic diatom, Pleurosira nanjiensis sp. nov., is described from the rocky intertidal zone of the Xiaochaiyu Island of the Nanji Islands in China. Its morphology was examined with light and scanning electron microscopy. Molecular phylogeny was reconstructed based on SSU rRNA and rbcL gene sequences. Pleurosira nanjiensis differs from congeners in possession of a combination of morphological features including the domed valve with broadly lanceolate, elliptical or circular valve outline, two elevated marginal ocelli, two (rarely three) rimportulae, and radiate striae.

Impact of Clinically Relevant Elliptical Deformations on the Damage Patterns of Sagging and Stretched Leaflets in a Bioprosthetic Heart Valve.

After implantation of a transcatheter bioprosthetic heart valve its original circular circumference may become distorted, which can lead to changes in leaflet coaptation and leaflets that are stretched or sagging. This may lead to early structural deterioration of the valve as seen in some explanted transcatheter heart valves. Our in vitro study evaluates the effect of leaflet deformations seen in elliptical configurations on the damage patterns of the leaflets, with circular valve deformation as the control. Bovine pericardial tissue heart valves were subjected to accelerated wear testing under both circular (N = 2) and elliptical (N = 4) configurations. The elliptical configurations were created by placing the valve inside custom-made elliptical holders, which caused the leaflets to sag or stretch. The hydrodynamic performance of the valves was monitored and high resolution images were acquired to evaluate leaflet damage patterns over time. In the elliptically deformed valves, sagging leaflets experienced more damage from wear compared to stretched leaflets; the undistorted leaflets of the circular valves experienced the least leaflet damage. Free-edge thinning and tearing were the primary modes of damage in the sagging leaflets. Belly region thinning was seen in the undistorted and stretched leaflets. Leaflet and fabric tears at the commissures were seen in all valve configurations. Free-edge tearing and commissure tears were the leading cause of valve hydrodynamic incompetence. Our study shows that mechanical wear affects heart valve pericardial leaflets differently based on whether they are undistorted, stretched, or sagging in a valve configuration. Sagging leaflets are more likely to be subjected to free-edge tear than stretched or undistorted leaflets. Reducing leaflet stress at the free edge of non-circular valve configurations should be an important factor to consider in the design and/or deployment of transcatheter bioprosthetic heart valves to improve their long-term performance.

Proposal and Preliminary Feasibility Study of a Novel Toroidal Magnetorheological Piston

A new magnetorheological piston head design inspired by toroidal electromagnets was proposed in previous work as an alternative to conventional annular dampers. A prototype with a circular valve array integrated inside the piston head was built and tested to measure its passive performance. The mechanical, electromagnetic, and hydraulic models used in the new design were explained, and the relevant parameters of the actuator were analyzed to construct a mathematical model to estimate its performance. These works showed the feasibility of the concept and its potential as an alternative to current damper technology, but lacked a baseline for comparison. This paper reviews and widens this groundwork. It adds a magnetic finite element method study to address the previously found leakage, and a new set of experiments, including a force controller, to compare its performance against a conventional annular piston head. The new findings show how the current force limitations can be overcome by striking a balance between the coil space and the size of electromagnet cores to achieve the performance of current dampers. They also highlight its potential in force control applications to provide a wider range of customization options, such as number and size of holes, electromagnets, and coils, and a better use of the active area of the gap.

Visual Grasp Affordance Localization in Point Clouds Using Curved Contact Patches

Detecting affordances on objects is one of the main open problems in robotic manipulation. This paper presents a new method to represent and localize grasp affordances as bounded curved contact patches (paraboloids) of the size of the robotic hand. In particular, given a three-dimensional (3D) point cloud from a range sensor, a set of potential grasps is localized on a detected object by a fast contact patch fitting and validation process. For the object detection, three standard methods from the literature are used and compared. The potential grasps on the object are then refined to a single affordance using their shape (size and curvature) and pose (reachability and minimum torque effort) properties, with respect to the robot and the manipulation task. We apply the proposed method to a circular valve turning task, verifying the ability to accurately and rapidly localize grasp affordances, under significant uncertainty in the environment. We experimentally validate the method with the humanoid robot COMAN on 10 circular control valves fixed on a wall, from five different viewpoints and robot poses for each valve. We compare the reliability of the introduced local grasp affordances method to the baseline that relies only on object detection, illustrating the superiority of ours for the valve turning task.

Total ellipse of the heart valve: the impact of eccentric stent distortion on the regional dynamic deformation of pericardial tissue leaflets of a transcatheter aortic valve replacement.

Transcatheter aortic valve replacements (TAVRs) are a percutaneous alternative to surgical aortic valve replacements and are used to treat patients with aortic valve stenosis. This minimally invasive procedure relies on expansion of the TAVR stent to radially displace calcified aortic valve leaflets against the aortic root wall. However, these calcium deposits can impede the expansion of the device causing distortion of the valve stent and pericardial tissue leaflets. The objective of this study was to elucidate the impact of eccentric TAVR stent distortion on the dynamic deformation of the tissue leaflets of the prosthesis in vitro. Dual-camera stereophotogrammetry was used to measure the regional variation in strain in a leaflet of a TAVR deployed in nominal circular and eccentric (eccentricity index = 28%) orifices, representative of deployed TAVRs in vivo. It was observed that (i) eccentric stent distortion caused incorrect coaptation of the leaflets at peak diastole resulting in a 'peel-back' leaflet geometry that was not present in the circular valve and (ii) adverse bending of the leaflet, arising in the eccentric valve at peak diastole, caused significantly higher commissure strains compared with the circular valve in both normotensive and hypertensive pressure conditions (normotension: eccentric = 13.76 ± 2.04% versus circular = 11.77 ± 1.61%, p = 0.0014, hypertension: eccentric = 15.07 ± 1.13% versus circular = 13.56 ± 0.87%, p = 0.0042). This study reveals that eccentric distortion of a TAVR stent can have a considerable impact on dynamic leaflet deformation, inducing deleterious bending of the leaflet and increasing commissures strains, which might expedite leaflet structural failure compared to leaflets in a circular deployed valve.

Simple and cost-effective fabrication of microvalve arrays in PDMS using laser cut molds with application to C. elegans manipulation in microfluidics

We present a new fabrication protocol for fabricating pneumatically controlled microvalve arrays (consisting of 100 s of microvalves) in PDMS substrates. The protocol utilizes rapid and cost-effective fabrication of molds using laser cutting of adhesive vinyl tapes and replica molding of PDMS. Hence the protocol is fast, simple and avoids cleanroom use. The results show that effective doormat-style microvalves can be easily fabricated in arrays by manipulating the stiffness of the actuating membrane through varying the valve-chamber area/shape. Three frequently used valve-chamber shapes (circle, square and capsule) were tested and all showed advantages in different situations. Circular valve chambers were best for small valves, square valves were best for medium-sized valves, and the capsule valves were best for larger valves. An application of this protocol has been demonstrated in the fabrication of a microfluidic 32-well plate for high-throughput manipulation of C. elegans for biomedical research.

Hemodynamic Impact of Transcatheter Aortic Valve Deployment Configuration.

Transcatheter aortic valve (TAV) replacement holds promise for a large number of patients who otherwise have limited or no treatment options. However, it also poses various challenges, due to its unique disease treatment mechanism. Successful TAV deployment and function are heavily reliant on the tissue-stent interaction [1,2]. For patients with aortic stenosis, heavy calcium deposition on the valve leaflets and the aortic root can also cause distortion of TAV geometries, resulting in a valve of an elliptical shape [3–5] instead of a nominal circular shape. In a recent study by Schultz et al. [5], the geometry and apposition of the TAV after implantation in 30 patients with aortic stenosis were evaluated using multislice computed tomography. The results indicated that none of the TAV frames reached exactly nominal designed dimensions. The difference between the orthogonal smallest and largest diameters of TAV cross section at the ventricular end was 4.4 mm, which was clearly an asymmetric elliptical shape [5]. In this study, we sought to develop computational models of valve hemodynamics under clinically relevant deployment scenarios.The geometry of a “generic” TAV has been described in detail [6]. It is a thin pericardial bioprosthetic valve with similar design features to TAVs used commercially. This model has been extended previously to the development of elliptical valves, with eccentricities of 0.3, 0.5, and 0.68 and alignment of either the major or minor axis of the ellipse to a native commissure [7]. In the current study, the open configuration for each of these elliptical models was obtained using abaqus finite element simulation (Fig. 1(a)). The leaflets were attached to a circular mounting ring (Fig. 1(b)) and then sealed in a 38-mm tube (Fig. 1(c)) in preparation for import into computational fluid dynamics (CFD) software using Hypermesh (Altair Engineering, Troy, MI).The CFD software star-CCM+ was used, with a polyhedral mesh and boundary conditions of 30 liters per minute (LPM) mass flow at the inlet and 100 mmHg pressure at the outlet. A Newtonian fluid was used, with a viscosity of 0.0035 Pa-s and a density of 1056 kg/m3. Turbulence was modeled by specifying intensity and length scale for the k-ε model.The sealed geometry was also used to fabricate physical models through additive manufacturing, which were then used for experimental validation using steady forward flow at 30 LPM. A centerline probe was advanced upstream, measuring pressure at 1-mm spacing.For the baseline circular valve, a peak transvalvular pressure of 10.92 mmHg was simulated (Fig. 2), which correlated to an effective orifice area (EOA) of 2.93 cm2. In a long-axis view, the peak centerline velocity was 2.16 m/s and the peak turbulent kinetic energy (TKE) was 0.30 J/kg. We observed that EOA dropped for more elliptical conditions, particularly when the minor axis of the ellipse was aligned with the TAV commissures. The changes in flow were also observed as higher transvalvular pressure, higher peak velocity, and higher TKE as compared with the baseline circular condition.Experimental pressure versus axial position curves can be used to validate steady-flow models. Best turbulence modeling was obtained for 10% turbulent intensity and a length scale of 4.6 mm. TAV ellipticity tended to cause increased EOA with higher peak velocity. These models may be used in the future to investigate more complicated clinical scenarios.The authors gratefully acknowledge the funding provided by the NSF, NIH, and Edwards Lifesciences, Inc.

Microfluidic valves made from polymerized polyethylene glycol diacrylate

Pneumatically actuated, non-elastomeric membrane valves fabricated from polymerized polyethylene glycol diacrylate (poly-PEGDA) have been characterized for temporal response, valve closure, and long-term durability. A ∼100ms valve opening time and a ∼20ms closure time offer valve operation as fast as 8Hz with potential for further improvement. Comparison of circular and rectangular valve geometries indicates that the surface area for membrane interaction in the valve region is important for valve performance. After initial fabrication, the fluid pressure required to open a closed circular valve is ∼50kPa higher than the control pressure holding the valve closed. However, after ∼1000 actuations to reconfigure polymer chains and increase elasticity in the membrane, the fluid pressure required to open a valve becomes the same as the control pressure holding the valve closed. After these initial conditioning actuations, poly-PEGDA valves show considerable robustness with no change in effective operation after 115,000 actuations. Such valves constructed from non-adsorptive poly-PEGDA could also find use as pumps, for application in small volume assays interfaced with biosensors or impedance detection, for example.

Sizing the annulus for transcatheter aortic valve implantation: more than a simple measure?

Accurate preoperative assessment of the aortic annulus dimension is crucial for the success of transcatheter aortic valve implantation (TAVI). All the available imaging modalities, however, have some weak points, and the ‘gold standard’ to be used is still under debate. In this context, the recent work by Dr Blanke and coworkers is a commendable attempt to develop a standardized, easy to reproduce method for the identification and measurement of the aortic annulus [1, 2]. A very interesting finding of this study is the close correlation found between the preoperative cross-sectional area (CSA) of the virtual ring passing through the nadir of the three aortic cusps and the postoperative CSA. This observation would suggest that preoperative determination of the CSA could help in predicting the final form and size of the aortic annulus in most TAVI patients [1]. However, the behaviour of the aortic root and aortic annulus is not always predictable based on the preoperative exams [3]. This is partly due to intrinsic anatomic properties of the aortic root—the ‘virtual ring’ is largely inhomogeneous, coursing through the muscular septum, the membranous septum and the mitro-aortic curtain. Moreover, leaflet and annular calcifications are often asymmetrical, adding further complexity to any attempt to predict the final shape of the prosthetic valve, the displacement of the native calcified leaflets and the sealing of the annulus around the prosthesis. A very good exemplification of this problem is given by the bicuspid aortic valve, which is usually ovoidal and heavily calcified, and may fail to adapt to the circular transcatheter valve [4]. For this reason, we have developed a simple method to analyse the reaction of the aortic root to the balloon inflation, and to obtain a dynamic measure of the CSA. In the uncertain cases (‘borderline’ annulus, important discrepancy between TEE and CT measurements, massive and/or eccentric calcifications), we proceed to a ‘calibrated’ balloon valvuloplasty. A conventional valvuloplasty balloon (Cristal Balloon, Balt, Montmorency, France) is inflated with a diluted contrast agent through a threeway stopcock. When the waist generated on the balloon profile by the aortic annulus is stretched, the stopcock is closed and an aortography is performed to exclude the presence of aortic regurgitation. The amount of contrast agent used to inflate the balloon is carefully recorded, and the balloon is deflated and withdrawn. On the bench, the balloon is inflated again to the same volume, and is then sized with a sizing plate (Amplatzer sizing plate, AGA Medical Italia, Milan, Italy). This simple manoeuvre allows us to accurately measure the aortic annulus, to estimate the risk of postoperative paraprosthetic leakage and to check the relationships between the dislocated aortic valve leaflets and the coronary arteries ostia. In our experience, this procedure has led to a change in the size of the percutaneous prosthesis in three patients, and to the conversion to transapical approach in two patients needing a 29 mm prosthesis. In conclusion, we believe that the CT protocol described by Blanke could greatly enhance our ability to evaluate the anatomy of the aortic root preoperatively. In doubtful cases, however, calibrated balloon valvuloplasty could add fundamental dynamic information, allowing us to ‘feel’ the aortic annulus while measuring it [3].

Fabrication of a normally-closed microvalve utilizing lithographically defined silicone micro O-rings

The focus of this work is on the development of a simple and variable process chain for the integration of flexible silicone material into silicon-based microfluidic devices. A normally-closed microvalve is chosen as a demonstrator device, as it combines features that are not easily obtained from silicon devices alone, especially, a high leak tightness of up to 1 bar pressure difference in the closed state and a high forward flow of several mL in the open state. For this purpose, a photopatternable silicone is used as a deformable circular valve lip between a piezoelectrically actuated membrane and a valve seat, similar to a micro O-ring with a width of 50 µm. The microvalve is piezo actuated by monolayer piezo actuators with a peak-to-peak driving voltage of = 200 V. The micro O-ring is pre-deformed by 2.8 µm during the valve fabrication process to yield the normally-closed behavior. A dry film resist lamination technology is developed for this critical process step to mate the two silicon wafers with the actuation membrane, the valve seat and the silicone O-ring in between at a well-defined distance. The dry film resist is used in a multifunctional way, not only to pre-deform the valve lip, but also to define the geometry of the valve chamber and to ensure a leak-tight connection of both wafers. Altogether, a peak value for the on- to off-ratio of the normally-closed microvalve higher than 30 000 is measured. This opens a wide range of potential applications, e.g. in micro-dosing, drug delivery, μ-TAS and microfluidics for biological or chemical applications in general.

Application of Magnetic Fluid Membrane for Flow Control

To study the application of a magnetic e uid membrane for e ow rate control, an experimental investigation was conducted to obtain the basic characteristics and to verify the feasibility of practical use. The working principle of a magnetically controlled magnetic e uid membrane is based on the magnetic attraction body force exerted on the magnetic e uid, which is sustained in the cross-sectional area of a pipe. In the experiments, rupture pressure was obtained at various conditions for an oil ‐magnetic e uid interface. Also, from the results obtained for the e ow rate ontrol characteristics, it was found that the magnetically controlled membrane has a function similar to that of an ordinary buttere y valve, and it was shown that the membrane would be feasible for controlling lower e ow rates at lower driving pressure gradients. Nomenclature D = circular valve diameter of buttere y valve, m D0 = pipe diameter of buttere y valve, m d = pipe diameter of test section, m H = magnetic e eld intensity, A/m H = magnetic e eld vector Hr = intensity of magnetic e eld in r direction, A/m Hz = intensity of magnetic e eld in z direction, A/m .Hz/max = maximum of Hz, A/m I = applied dc current, A l = pipe length, m le = effective length, m lm = length covered by magnetic e uid, m M = magnetization, Wb/m 2 M = magnetization vector, Wb/m 2 Ploss = pressure loss, Pa ¢s Pr = rupture pressure, Pa ¢s Re = Reynolds number r, µ, z = cyclindrical coordinates (see Fig. 6)

A study of the human aortic valve orifice by transesophageal echocardiography

The transverse short-axis plane of the aortic valve was imaged by transesophageal echocardiography at a relatively high frame rate in 25 anesthetized patients undergoing heart surgery. The effective, time-averaged aortic valve area (a-AVA) was compared with areas obtained with triangular and circular valve orifice models (t-AVA and c-AVA, respectively). The aortic valve orifice was circular during 33.6% ± 17.5% of systole. The relations between the triangular or circular aortic valve areas and a-AVA were as follows: t-AVA = 1.04 × a-AVA − 0.14 ( r = 0.90; standard error of the estimate = 0.24 cm 2) and c-AVA = 1.37 × a-AVA + 0.00 ( r = 0.90; SEE = 0.30 cm 2). Bias analysis showed no significant difference between a-AVA and t-AVA (bias = −0.04 ± 0.23 cm 2; difference not significant) but a significant overestimation of the average valve area by c-AVA (bias = +0.88 ± 0.30 cm 2; p < 0.001). Thus the aortic valve orifice was not circular for the entire duration of systole and valve area calculations based on a triangular model approximated a-AVA more closely than did those based on a circular model. These findings suggest that, for echocardiographic measurements that incorporate the aortic valve orifice area (e.g., stroke volume determinations), the use of a triangular valve area model, rather than a circular model, may produce more accurate results in anesthetized patients with heart disease.

Aortic valve morphology influences regurgitant volume in aortic regurgitation: in vivo evaluation

According to the Gorlin hydraulic orifice equation, aortic regurgitation volume can be determined by the regurgitant orifice cross sectional area, diastolic filling period, mean pressure gradient between the aorta and left ventricle, and a constant relating the coefficients of contraction (Cc) and velocity (Cv). This study was performed to determine whether variation in aortic valve morphology affects regurgitant flow volume, Cc and Cv. Four aortic valve templates, modelled after circular, rheumatic, degenerative, and bicuspid lesions, were constructed with equal orifice cross sectional areas in two sizes, 0.2 and 0.7 cm2. These valves were studied in vitro in a flow model of aortic regurgitation, wherein aortic pressure was regulated by varying the height of a column of fluid. Flow, pressure, and velocity were measured, and the coefficient Cc and Cv were calculated from standard equations. Regurgitant volume was assessed at diastolic filling periods of 0.5 and 1.0 s and averaged 15% greater for bicuspid and degenerative as compared to circular or rheumatic valve shapes (p = 0.0001). This difference was accentuated at the shorter diastolic filling time and higher pressure gradient, such that bicuspid lesions allowed 29% more regurgitant flow across the 0.2 cm2 orifice at fluid height of 120 cm over 0.5 s. This difference in regurgitant volume between valve shapes was due to an increased Cc for the bicuspid and degenerative valve shapes, suggesting that they are more efficient orifices than rheumatic or circular valve shapes. Aortic valve morphology influences regurgitant volume in aortic regurgitation. Specifically, degenerative and bicuspid orifice shapes have a higher contraction coefficient and allow more regurgitant flow than rheumatic or circular orifices at a given driving pressure and diastolic filling time.

Reentrant cannulation of the small intestine in sheep: cannula and surgical method.

The function, design and production of a reentrant cannula for the small intestine of sheep and the corresponding surgical procedure are described. The cannula is molded in one piece from polyvinylchloride plastisol. It consists of a curved intestinal tube joined to a stem with an external elliptical ring on the distal end and a perforated flange that encircles the stem above the intestinal tube. A circular perspex valve with two curved channels was made to fit into the interior of the cannula, making it capable of either a "maintenance" or a "collection" function. The cannula was inserted into the proximal duodenum and(or) terminal ileum of sheep via a 5-cm incision on the antimesenteric side of the intestine. The intestine was attached to the cannula by a Dacron straight arterial graft. This reentrant cannulation method does not require an intestinal transection and a mesenteric incision under the transection. Therefore, little damage was done to the blood and nervous system.