Valve Opening Area Research Articles

Einsatz der Dual-source-Computertomographie in der prä- und postoperativen kardiochirurgischen Diagnostik

The aim of this study was to evaluate the clinical potential of dual-source computed tomography (DSCT) in pre- and postsurgical diagnostics in the field of cardiac surgery. A total of 20 patients underwent DSCT of the heart. This CT system with two rotating X-ray tubes (Somatom Definition, Siemens Medical Solutions, Forchheim, Germany) achieves a temporal resolution of 83 ms and a spatial resolution of 0.4 x 0.4 x 0.4 mm. The patient cohort consisted of two subgroups. In a group of ten patients with known coronary artery disease (CAD), scheduled for bypass surgery (i.e., high pretest likelihood for having significant CAD), the results of DSCT coronary angiography (CTA) and invasive quantitative catheter angiography (QCA) were compared to assess the diagnostic accuracy of DSCT in the detection of significant coronary artery stenoses (>50%). In a second group of ten patients with previous aortic valve replacement (homografts), the valve opening area of the transplanted aortic valve graft was measured by DSCT and compared with echocardiography as a standard of reference to exclude postsurgical restenosis of the valve. Of 150 coronary artery segments depicted by CT, 144 (96%) were classified as "assessable." A significant CAD was known in all patients, and altogether 43 significant stenoses were present according to the results of QCA. Blinded to these results, DSCTA reached a sensitivity and specificity of 95% (41/43) and 93% (103/111), yielding a positive and negative predictive value (PPV, NPV) of 79% (31/39) and 98% (103/105), respectively. In patients with aortic valve homografts, all DSCT datasets were considered as being of diagnostic image quality concerning valve depiction. The planimetric evaluation of the CT data as compared to results of echocardiography showed a significant correlation of the results (r=0.64, p=0.0467). A high-grade valve stenosis (opening area <1.0 cm(2)) could be correctly excluded by DSCT in all patients. Dual-source CT shows great diagnostic potential in patients before or after cardiac surgery. DSCT provides a high diagnostic accuracy for detection of coronary artery stenosis before bypass surgery. DSCT also proved to be accurate in the assessment of patients who received aortic valve replacement.

Computational phlebology: the simulation of a vein valve.

We present a three-dimensional computer simulation of the dynamics of a vein valve. In particular, we couple the solid mechanics of the vein wall and valve leaflets with the fluid dynamics of the blood flow in the valve. Our model captures the unidirectional nature of blood flow in vein valves; blood is allowed to flow proximally back to the heart, while retrograde blood flow is prohibited through the occlusion of the vein by the valve cusps. Furthermore, we investigate the dynamics of the valve opening area and the blood flow rate through the valve, gaining new insights into the physics of vein valve operation. It is anticipated that through computer simulations we can help raise our understanding of venous hemodynamics and various forms of venous dysfunction.

Can progression of valvar aortic stenosis be predicted accurately?

Background It was the aim of the present study to elaborate criteria for the assessment of rapid hemodynamic progression of valvar aortic stenosis. These criteria are of special importance when cardiac surgery is indicated for other reasons but the established criteria for aortic valve replacement are not yet fulfilled. Such aspects of therapeutic planing were mostly disregarded in the past so that patients had to undergo cardiac reoperation within a few years. Methods Hemodynamic, echocardiographic, and clinical data of 169 men and 88 women with aortic stenosis, aged 55.2 ± 15.7 years at their first and 63.4 ± 15.6 years at their second cardiac catheterization, were analyzed. Results The progression rate of aortic valve obstruction was found to be dependent on the degree of valvar calcification ([VC] scoring 0 to III) and to be exponentially correlated with the aortic valve opening area (AVA) at initial catheterization. Neither age nor sex of the patient nor etiology of the valvar obstruction significantly influence the progression of aortic stenosis. If AVA decreases below 0.75 cm 2 with a present degree of VC = 0, or AVA of 0.8 with VC of I, AVA of 0.9 with VC of II, or AVA of 1.0 with VC of III, it is probable that aortic stenosis will have to be operated upon in the following years. Conclusions The present data indicate that for clinical purposes and planning of valvar surgery the progression of asymptomatic aortic stenosis can be sufficiently predicted by the present aortic valve opening area and the degree of valvar calcification.

On the head-discharge relation of a "duckbill" elastomer check valve

Duckbill-shaped elastomer check valves are often installed on wastewater effluent diffusion systems and stormwater outfalls to prevent baekflow or sea water intrusion. Unlike fixed diameter ports, the jet velocity varies nonlinearly with port discharge flow. A new theory to predict the hydraulic characteristics of a duckbill elastomer check valve (DBV) is presented, and it provides a theoretical basis for the correlation of all DBV hydraulic data. It is shown that a DBV can be considered as a smooth converging nozzle. By modelling the duckbill valve as a two-dimensional rubber membrane, a theory is developed to relate the DBV material properties and flow conditions to the valve deformation. The valve opening area is predicted as a function of the driving pressure head: a linear head-discharge relation is predicted. The predictions are in excellent agreement with ex peri mental data. The derived head-discharge relation can be readily incorporated into a diffuser internal hydraulics code to determine the variation of discharge flow and jet velocity along a multiport diffuser fitted with duckbill check valves.

Optimization of the intake port shape for a five-valve gasoline engine

For the development of a high efficiency gasoline engine, the optimization of the intake port shape for a five-valve engine has been studied. Intake multivalve cylinder heads were manufactured by using a three-dimensional computer-assisted design program, and steady state flow experiments and flow visualization experiments have been performed with these cylinder heads. The five-valve engines, which have larger valve opening areas, have larger intake flowrates and higher tumble ratios than the four-valve engines. The effects of intake port design parameters of a five-valve engine on the intake flowrate and tumble were studied, and the design guidelines for the five-valve engines were established.

A Study on the Design Technique of a 5-valve Combustion Chamber for Subcompact Vehicles

For the purpose of development of high performance gasoline engine, the design technique of the 5-valve(3 intake valves) combustion chamber for a subcompact vehicle has been studied. 3 intake valves cylinder heads were designed by using a 3-dimension CAD program, and steady state flow experiments have been performed with these model. The 5-valve engines, which have larger valve opening areas, have larger intake flow rates and higher flow coefficient than the 4-valve engines. The effects of intake port design parameters of a 5-valve engine on the intake flow rate and bore size were studied, and the design guidelines for the 5-valve engine were established.

Chaotic Oscillation Observed in Low Speed Actuation of Pneumatic Cylinders.

Operating pneumatic cylinders at low velocities, large variation of the friction force acting on the contacting surface between the piston and cylinder wall often causes several characteristic phenomena such as stick-slip motion and random oscillation in the piston velocity. Such phenomena put obstacles to accurate control of the pneumatic cylinders. This paper aims to examine the random oscillation and to account for it in relation to the friction. To begin with, we use an analytical approach with a mathematical model including the effect of the friction in order to investigate the aspects of the velocity responses in the meter-in and meter-out circuit. Then, an experimental study is carried out and shows based on some chaos indices such as Lyapunov exponents that the random oscillation becomes chaotic in the actual situation in certain regions relating to the valve opening area. Moreover, the effect of supply pressure changes and that of load changes are also examined. Finally, from these results we discuss the relation between chaotic behavior and the friction and make it clear that the dynamic behavior is due to the nonlinearity of the friction force.

Early in vivo experience with the hemodynamic plus St. Jude medical heart valves in patients with narrowed aortic annulus

Small aortic orifice primarily resulted in heart prosthesis mismatch in a significant number of patients. The Hemodynamic Plus (HP) series of St. Jude Medical heart valves represents an interesting innovation, allowing a larger valve orifice area with an equivalent tissue annulus diameter. Hemodynamic characteristics of the 21-mm HP St. Jude Medical valve were prospectively compared with those of the standard 21-mm and 23-mm St. Jude Medical valves in three groups of 22 patients. Patients were selected from a database to be rigorously matched for age, sex, body surface area, functional class, underlying lesion, native valve opening area, left ventricular function, and preoperative peak and mean valve gradients. Postoperative evaluation (follow-up ranging from 3 to 24 months; mean, 11.5 months) included clinical examination and echocardiographic studies. There was no operative mortality or significant perioperative complications. Short-term clinical follow-up was marked by a complete absence of valve-related complications. Presently, all but 1 patient in the 21-mm HP group and 2 in the 21-mm standard group are in New York Heart Association functional class I. Doppler echocardiography-derived mean and maximal pressure gradients were significantly lower in the 21-mm HP group (8.1 +/- 1.9 and 16.4 +/- 3.4 mm Hg) than in the 21-mm standard group (13.4 +/- 3.9 and 21.2 +/- 4.3 mm Hg; p = 0.002 and p = 0.0004, respectively), confirming the better hemodynamic performance already described in in vitro studies. Pressure gradients did not differ significantly between the 21-mm HP and the 23-mm standard groups. The 21-mm HP valve demonstrated the highest performance index; 0.66 +/- 0.08, compared with 0.49 +/- 0.09 for the 21-mm standard valve (p < 0.001) and 0.59 +/- 0.07 for the 23-mm standard valve (p < 0.001). In vivo hemodynamic performance of the 21-mm HP valve corresponds closely to that of the 23-mm standard valve and is substantially better than that of the 21-mm standard valve. The 21-mm HP St. Jude Medical valve demonstrates excellent hemodynamic characteristics and can be recommended in normal-sized adult patients with narrow aortic root. This valve will minimize the need for aortic annulus enlargement.

Fluid dynamics of venous valve closure.

In vitro experiment was performed on a stented bovine jugular vein valve (VV, 14 mm I.D. x 2 cm long) and a stentless bovine jugular vein valve conduit (10 mm I.D. x 6 cm long) in a hydraulic flow loop with a downstream oscillatory pressure source to mimic respiratory changes. Simultaneous measurements were made on the valve opening area, conduit and sinus diameter changes using a specially designed laser optic system. Visualization of flow fields both proximal and distal to the venous valve, and the valve opening area were simultaneously recorded by using two video cameras. Laser Doppler anemometer surveys were made at three cross sections: the valve inlet, the valve exist, and 2 cm downstream of the venous valve to quantity flow reflux at valve closure. The experiment confirmed that the VV is a pressure-operated rather than a flow-driven device and that little or no reflux is needed to close the valve completely. The experiment further demonstrated that the VV sinus expands rapidly against back pressure, a critical character to consider in venous prosthesis design.

Use of an intraluminal shunt to repair a coronary bypass graft injury during resternotomy

In recent years, there has been an increase in the number of patients who are subjected to second cardiac procedures for correction of congenital heart defects, valve problems, and repeat coronary artery revascularization. Catastrophic hemorrhage is a rare complication that may occur while the sternum is being reopened. The most frequent causes include tears of the right ventricle and lesions of previous coronary bypass grafts; less common are bleeding from ascending aortic aneurysms or tears in the right atrium. In 1985, a 66-year old patient had undergone an aortic valve replacement with a Capentier-Edwards bioprosthesis (Baxter Healthcare Corp, Edwards Div., Santa Ana, Calif.) and a saphenous vein graft to the circumflex artery with jump anastomoses to an intermediate branch, the first diagonal branch, and the left anterior descending artery. Postoperative recovery was uneventful, and the patient felt well until 1992. At this time, the patient reported having exertional dyspnea and increasing weariness. A cardiologic examination was performed and transthoracic echocardiography demonstrated degeneration of the bioprosthesis, resulting in moderate aortic stenosis (mean systolic gradient 45 mm Hg, peak-to-peak gradient 70 mm Hg, and a valve opening area of 0.8 cm2 ). Left ventricular function was severely depressed with an ejection fraction of 0.26. At coronary angiography, each coronary–saphenous vein anastomosis was patent but some atherosclerotic changes were described in the proximal part of the graft. A median sternotomy was performed with the oscillating saw; during preparation and mobilization of the sternal borders, the aneurysmal proximal part of the saphenous vein bypass graft, which was completely adherent to the sternum, was damaged. Because of the important myocardial area supplied by the graft, it could not have been occluded either with clamps or with Fogarty catheters. Therefore we elected to insert a small intraluminal silicone shunt, which is usually used during carotid endarterectomy to preserve homolateral cerebral perfusion, as a bridge between the proximal and distal vein graft segments and secured it with tourniquets (Fig. 1). With this technical assistance, the bleeding could be easily controlled and no electrocardiographic changes or hemodynamic alterations appeared. Femoral artery cannulation was then performed, the right atrium was dissected, and a single-stage cannula was introduced into the right atrium. Extracorporeal circulation was instituted and conducted at moderate hypothermia. Myocardial protection was performed by retrograde continuous cardioplegia. After the aorta was crossclamped, the bioprosthesis was resected and a mechanical prosthesis was inserted. A short venous graft was interposed to repair the lesion and exclude the aneurysmal segment (Fig. 2). Postoperative recovery was uneventful and no clinical or electrocardiographic signs of perioperative myocardial infarction appeared. The patient was discharged on postoperative day 10. Several factors account for the increased risk of reoperation: age, progressive extent of coronary atherosclerosis, impairment of left ventricular function, additional cardiac procedures, technical difficulties during reentry and caused by intrapericardial adhesions, and prolonged bypass time and more difficult myocardial protection.1Lytle BW Loop FD Coronary reoperations.Surg Clin North Am. 1988; 68: 559-580PubMed Google Scholar Various methods have been proposed in the past for sternal reentry. Femoral artery cannulation can be used when the right ventricle seems to be adherent to the sternum, when there is strong suspicion that the internal mammary artery or a venous bypass graft is crossing the midline, when the chest has been reconstructed by muscle flaps, and when an ascending aortic aneurysm is present.2Mahfood S Higgins TL Loop FD. Management of complications related to coronary artery bypass surgery.in: Complications in cardiothoracic surgery. Mosby, St Louis1991: 265-280Google Scholar, 3Loop FD Catastrophic hemorrhage during sternal reentry.Ann Thorac Surg. 1984; 37: 271-273Abstract Full Text PDF PubMed Scopus (71) Google Scholar When progressive coronary artery disease necessitates a second operation with a new graft to the anterior and posterolateral walls of the left ventricle, thoractomy may allow excellent exposure of the left anterior descending branch and obtuse marginal branches. Proximal anastomoses are then performed to the descending aorta.4Burlingame MW Bonchek LI Vazales BE Left thoracotomy for reoperative coronary bypass.J Thorac Cardiovasc Surg. 1988; 95: 508-511PubMed Google Scholar In the case presented here, the use of an intraluminal shunt allowed us to control the bleeding and maintain a sufficient perfusion to prevent myocardial ischemia; furthermore, it allowed controlled, unhurried institution of cardiopulmonary bypass. This elegant method, preventing bleeding and myocardial ischemia, prompted us to review the literature, and we found only one similar description.5Robison RJ Brown JW Deschner WP King RD Intraluminal shunting of operatively severely injured aortocoronary saphenous vein grafts.Ann Thorac Surg. 1986; 42: 475-476Abstract Full Text PDF PubMed Scopus (3) Google Scholar

Validation of the orifice formula for estimating effective heart valve opening area

Interest in the Gorlin formula for estimating heart valve effective orifice area (EOA) has recently been rekindled and the formula itself has been challenged. In this validation study, explanted native heart valves, unimplanted mechanical prostheses, unimplanted bioprostheses and explanted bioprostheses have been tested in vitro in a pulsatile flow simulator. Pressures have been measured 30 mm upstream and 100 mm downstream from the plane of the valve sewing ring (to give pressure drop, pd in kPa). Flow (Q in 1 min-1) has been measured directly by electromagnetic flowmeter and orifice areas have either been taken from manufacturer supplied data (mechanical valves) or have been digitised from video images at maximum orifice (biological valves). The formula EOA = Q/(6.96 x pd 1/2) - 0.7 fitted the data with good correlation, r = 0.96 (n = 179). The orifice assumption on which this formula is based (cf. Gorlin formula) is confirmed though it is recommended that the formula should be modified to account for (i) the pressure recovery phenomenon and (ii) the fact that forward flow through a valve only occurs over a portion of the cycle in pulsatile flow. Heart rates used in the study ranged from 40 to 140 min-1, stroke volumes ranged from 20 to 114.3 ml, cardiac outputs from 2.0 to 8.0 1 min-1 and peripheral resistance from 0.1 to 1.6 kPa 1-1 min (1 - 12 mmHg l-1 min). Application of the formula was independent of the flow conditions.

Prediction of stenotic valve orifice area: an in vitro study on a bioprosthesis.

The Gorlin equation for the hemodynamic assessment of valve area is commonly used in cardiac catheterization laboratories. A study was performed to test the prediction capabilities of the Gorlin formula, as well as those of the Aaslid and Gabbay formulas for the effective orifice area of a porcine valve of varying degrees of stenosis. Pressure gradient, flow, and valve opening area measurements were performed on Carpentier-Edwards porcine valve prostheses (made stenotic by suturing at the commissures) mounted in the aortic position of an in vitro pulse duplicator. With the known valve orifice area, a discharge coefficient was computed for each of the three orifice area formulas. After some theoretical considerations, it was proposed that the discharge coefficient would be a function of the flow rate through the valve. The discharge coefficient was observed to increase with increasing systolic flow rate. An empirical relationship of the discharge coefficient as a linear function of the systolic flow rate was determined through a regression analysis, with a different relationship for each orifice area formula. Using this relationship in the orifice area formulas improved the accuracy of the prediction of the effective orifice area with all three formulas performing equally well.

A Simplified Concept for a Bileaflet Atrioventricular Valve that Maintains Annular-Papillary Muscle Continuity

We have developed a simplified concept for a bileaflet atrioventricular prosthesis that can be constructed from a simple sheet of glutaraldehyde preserved pericardium. The valve has no rigid ring or stent and no cloth sewing ring. Insertion of the valve reestablishes normal continuity between the annulus and the papillary muscles. We have replaced the mitral valve in nine dogs using this prosthesis. All valves have been competent with excellent valve opening areas as confirmed by echo-Doppler assessment. Studies up to 4 1/2 months have confirmed excellent hemodynamics and there has been no evidence of early tissue failure. Possible advantages of this simple valve design are improved hemodynamics, ease of construction and insertion, and low cost.

Effect of systolic flow rate on the prediction of effective prosthetic valve orifice area

The Gorlin equation for the hemodynamic assessment of valve area is commonly used in cardiac catheterization laboratories. A study was performed to test the prediction capabilities of the Gorlin formula as well as the Aaslid and Gabbay formula for the effective orifice area of prosthetic heart valves. Pressure gradient, flow, and valve opening area measurements were performed on four 27 mm valve prostheses (two mechanical bileaflet designs, St. Jude and Edwards-Duromedics, an Edwards pericardial tissue valve, and a trileaflet polyurethane valve) each mounted in the aortic position of an in vitro pulse duplicator. With the known valve orifice area, a different discharge coefficient was computed for each of the four valves and three orifice area formulas. After some theoretical considerations, it was proposed that the discharge coefficient would be a function of the flow rate through the valve. All discharge coefficients were observed to increase with increasing systolic flow rate. An empirical relationship of discharge coefficient as a linear function of systolic flow rate was determined through a regression analysis, with a different relationship for each valve and each orifice area formula. Using this relationship in the orifice area formulas improved the accuracy of the prediction of the effective orifice area with all three formulas performing equally well.

On the fluid dynamics of the aortic valve

An aortic-valve model is developed, having a quadratic cross-section, two rigid cusps and two wedge-shaped aortic sinuses. The flow through this valve is assumed to be one-dimensional, just as the flow behind the cusps should be one-dimensional. The resulting model equations are two nonlinear ordinary differential equations of second order for the valve opening area as a function of time in two different ranges.This model allows the size of the aortic sinus to be varied; it also permits a computation of the pressure at both sides of the cusps (unlike previous models of this kind, which consider the flow behind the cusps as stagnant). The computed valve motion due to this pressure difference is in good agreement with experimental results, although no vortex with circular streamlines is postulated in the aortic sinuses. Obviously such vortices trapped in the sinuses are not important for the valve closure, which is controlled solely by the flow deceleration.

Echocardiographic aortic to mitral valve opening area ratio for determining the presence and severity of mitral regurgitation

A simple and accurate noninvasive method to quantify the degree of mitral regurgitation (MR) is lacking. Therefore, the ratio of the aortic (AVO) to mitral valve opening area (MVO) from 2-dimensionally guided M-mode echocardiographic tracings was examined as an estimate for the presence and severity of MR. Seventy-two patients who had undergone catheterization were studied: 49 with idiopathic dilated cardiomyopathy, 7 with coronary artery disease and 16 with organic MR. Twenty-eight patients had no MR (group I), 23 had mild/moderate MR (group II) and 21 had severe MR (group III). The AVO MVO ratio was 0.86 ± 0.2 in group I, 0.53 ± 0.1 in group II and 0.31 ± 0.1 in group III (p < 0.001). An AVO MVO ratio of 0.65 or less predicted MR with a sensitivity of 98% and a specificity of 86%. Furthermore, a strong relation was found between the ratio and the angiographic severity of MR. Thus, the AVO MVO ratio is a simple echocardiographic parameter for detecting the presence and severity of MR.

Pulsatile flow past aortic valve bioprostheses in a model human aorta

Pulsatile flow development past tissue valve prostheses in a model human aorta has been studied using qualitative flow visualization and quantitative laser-Doppler techniques. Experiments were conducted both in steady and physiological pulsatile flow situations and the measurements included the pressure drop across the valve, the instantaneous flow rate as well as the velocity profiles and turbulent stresses downstream to the valves. Our study shows that the velocity profiles with pericardial valves are closer to those measured past natural aortic valves. The porcine valves with a smaller valve opening area produce a narrower and stronger jet downstream from the valve with relatively larger turbulent axial stresses in the boundary of the jet. Our study suggests that the pericardial valves with turbulent stresses comparable to those of caged ball and tilting disc valves are preferable from a hemodynamic point of view.