query: when are all 4 valves of the heart closed

pos: Cardiac cycle valves, open during ventricular diastole to permit filling. Late in the filling period the atria begin to contract (atrial systole) forcing a final crop of blood into the ventricles under pressure—see cycle diagram. Then, prompted by electrical signals from the sinoatrial node, the ventricles start contracting (ventricular systole), and as back-pressure against them increases the AV valves are forced to close, which stops the blood volumes in the ventricles from flowing in or out; this is known as the "isovolumic contraction" stage. Due to the contractions of the systole, pressures in the ventricles rise quickly, exceeding the pressures in the

neg: Cardiac physiology ventricles, pushing open the tricuspid and mitral valves. As pressure drops within the ventricles, blood flows from the major veins into the relaxed atria and from there into the ventricles. Both chambers are in diastole, the atrioventricular valves are open, and the semilunar valves remain closed. The cardiac cycle is complete. One of the simplest methods of assessing the heart's condition is to listen to it using a stethoscope. In a healthy heart, there are only two audible heart sounds, called S1 and S2. The first heart sound S1, is the sound created by the closing of the atrioventricular valves

neg: Isovolumetric contraction Isovolumetric contraction In cardiac physiology, isovolumetric contraction is an event occurring in early systole during which the ventricles contract with no corresponding volume change (isovolumetrically). This short-lasting portion of the cardiac cycle takes place while all heart valves are closed. In a healthy young adult, blood enters the atria and flows to the ventricles via the opened atrioventricular valves (tricuspid and mitral valves). Atrial contraction rapidly follows, actively pumping about 20% of the returning blood. As diastole ends, the ventricles begin depolarizing and, while ventricular pressure starts to rise owing to contraction, the atrioventricular valves close in order to prevent

neg: Phonocardiogram Phonocardiogram A phonocardiogram (or PCG) is a plot of high-fidelity recording of the sounds and murmurs made by the heart with the help of the machine called the phonocardiograph; thus, phonocardiography is the recording of all the sounds made by the heart during a cardiac cycle. . The sounds result from vibrations created by closure of the heart valves, there are at least two: the first when the atrioventricular valves (tricuspid and mitral) close at the beginning of systole and the second when the aortic valve and pulmonary valve (semilunar valves) close at the end of systole. It allows the

neg: Interference engine Interference engine An interference engine is a type of 4-stroke internal combustion piston engine in which one or more valves in the fully open position extends into any area that the piston may travel into. By contrast, in a non-interference engine the piston does not travel into any area into which the valves open. Interference engines rely on timing gears, chains, or belts to prevent the piston from striking the valves by ensuring that the valves are closed when the piston is near top dead center. Interference engines are prevalent among modern production automobiles and many other 4-stroke engine applications;

neg: Artificial heart valve Artificial heart valve An artificial heart valve is a device implanted in the heart of a patient with valvular heart disease. When one of the four heart valves malfunctions, the medical choice may be to replace the natural valve with an artificial valve. This requires open-heart surgery. Valves are integral to the normal physiological functioning of the human heart. Natural heart valves are evolved to forms that perform the functional requirement of inducing unidirectional blood flow through the valve structure from one chamber of the heart to another. Natural heart valves become dysfunctional for a variety of pathological causes. Some

neg: Valve For some valves, there may be a mechanism to indicate by how much the valve is open, but in many cases other indications of flow rate are used, such as separate flow meters. In plants with remote-controlled process operation, such as oil refineries and petrochemical plants, some 2-way valves can be designated as normally closed (NC) or normally open (NO) during regular operation. Examples of normally-closed valves are "sampling valves", which are only opened while a sample is taken. Other examples of normally-closed valves are emergency shut-down valves, which are kept open when the system is in operation and will

neg: Interference engine damage within the cylinder, possibly affecting the connecting rods. Interference engine An interference engine is a type of 4-stroke internal combustion piston engine in which one or more valves in the fully open position extends into any area that the piston may travel into. By contrast, in a non-interference engine the piston does not travel into any area into which the valves open. Interference engines rely on timing gears, chains, or belts to prevent the piston from striking the valves by ensuring that the valves are closed when the piston is near top dead center. Interference engines are prevalent among

neg: Systole ventricle (lighter blue), connected through the tricuspid valve. The atria are the receiving chambers for the circulation of blood and the ventricles are the discharging chambers. When, in late ventricular diastole, the atrial chambers contract, they send blood down to the larger, lower ventricle chambers. When normal flow is completed, the ventricles are filled and the valves to the atria are closed. The ventricles now perform systole isovolumetrically, which is contraction while all valves are closed—ending the first stage of systole. The second stage proceeds immediately, pumping oxygenated blood from the left ventricle through the aortic valve and aorta to

neg: Heart valve called the "semilunar valves". These two arteries receive blood from the ventricles and their semilunar valves permit blood to be forced into the arteries, and prevent backflow from the arteries into the ventricles. These valves do not have chordae tendineae, and are more similar to the valves in veins than they are to the atrioventricular valves. The closure of the semilunar valves causes the second heart sound. The aortic valve, which has three cusps, lies between the left ventricle and the aorta. During ventricular systole, pressure rises in the left ventricle and when it is greater than the pressure in

neg: Artificial heart valve was later changed to use silicone-coated material. The first implantation of mechanical heart valve to human was performed by Dr. Hufnagel on 11 September 1952, using the valve that he developed. This event accelerated the development of other artificial heart valves. Artificial heart valve An artificial heart valve is a device implanted in the heart of a patient with valvular heart disease. When one of the four heart valves malfunctions, the medical choice may be to replace the natural valve with an artificial valve. This requires open-heart surgery. Valves are integral to the normal physiological functioning of the human heart.

neg: Valve replacement valves have similar overall outcomes with respect to stroke and survival. Valve replacement Valve replacement surgery is the replacement of one or more of the heart valves with either an artificial heart valve or a bioprosthesis (homograft from human tissue or xenograft e.g. from pig). It is an alternative to valve repair. There are four procedures Current aortic valve replacement approaches include closed heart surgery, Very invasive cardiac surgery (VICS) and Very invasive, Scapulae-based aortic valve replacement. Catheter replacement of the aortic valve (called trans-aortic valve replacement or implementation [TAVR or TAVI]) is a minimally invasive option for those suffering

neg: Heart murmur Heart murmur Heart murmurs are heart sounds produced when blood flows across one of the heart valves that are loud enough to be heard with a stethoscope. There are two types of murmurs. A functional murmur or "physiologic murmur" is a heart murmur that is primarily due to physiologic conditions outside the heart. Other types of murmurs are due to structural defects in the heart itself. Functional murmurs are benign (an "innocent murmur"). Murmurs may also be the result of various problems, such as narrowing or leaking of valves, or the presence of abnormal passages through which blood flows in

neg: Pericardial heart valves ml per second. The opening of the cusps of both types of pericardial valves is synchronous and regular, without three-dimensional flexure and the low-profile pericardial valve shows an even larger opening when compared with the standard pericardial valve. There are no crevices or dead spaces behind the open cusps of the pericardial valves. The difference between the porcine and the pericardial valves is flagrant in all respects. (Fig ) Many authors had studied, in-vitro, the hydrodynamic performance of the pericardial valve and found that it possesses better functional characteristics than the porcine valves and similar to those of the best

neg: Heart valve the valve: Heart valve A heart valve normally allows blood to flow in only one direction through the heart. The four valves are commonly represented in a mammalian heart that determines the pathway of blood flow through the heart. A heart valve opens or closes incumbent on differential blood pressure on each side. The four main valves in the heart are: The mitral valve and the aortic valve are in the left heart; the tricuspid valve and the pulmonary valve are in the right heart. There are also the coronary sinus and the inferior vena cava valves. The heart valves

neg: Heart valve Heart valve A heart valve normally allows blood to flow in only one direction through the heart. The four valves are commonly represented in a mammalian heart that determines the pathway of blood flow through the heart. A heart valve opens or closes incumbent on differential blood pressure on each side. The four main valves in the heart are: The mitral valve and the aortic valve are in the left heart; the tricuspid valve and the pulmonary valve are in the right heart. There are also the coronary sinus and the inferior vena cava valves. The heart valves and the

neg: Tap (valve) applications for coarse control of the release of fuel gases (such as natural gas, coal gas, and syngas). Like all ball valves its handle will parallel the gas line when open and be perpendicular when closed, making for easy visual identification of its status. Water and gas taps have adjustable flow: gate valves are more progressive; ball valves more coarse, typically used in on-off applications. Turning a valve knob or lever adjusts flow by varying the aperture of the control device in the valve assembly. The result when opened in any degree is a choked flow. Its rate is independent

neg: Heart walls of the heart to valves by cartilaginous connections called chordae tendinae. These muscles prevent the valves from falling too far back when they close. During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight. As the heart chambers contract, so do the papillary muscles. This creates tension on the chordae tendineae, helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria. Two additional semilunar valves sit at the exit of each of the ventricles. The

neg: Pericardial heart valves 1971 Ionescu in Leeds, England, creates the first bovine pericardial heart valve and begins its implantation in humans. 1980 Since the early 1980s several modified pericardial valves have been built. Three of them with improved characteristics are being successfully used, as shown in this article. It becomes obvious from this description that the two important creative stages in tissue heart valves (from 1964 to 1971) took place in a short space of seven years and that since 1971 when the concept of 'man-made pericardial valves' was created, no other significant invention has occurred in this field except the use of

neg: Victor Skumin on cardiopulmonary bypass. With a valve replacement surgery, there are some risks. Skumin researched a neuropsychological and psychopathologic changes following open heart surgery, nonpsychotic mental disorders in patients with valvular heart disease before and after surgery, associated with mechanical artificial heart valve (MHV) implant. An artificial heart valve is a device implanted in the heart of a patient with valvular heart disease, congenital heart defect, etc. When one or two of the four heart valves malfunctions, the medical choice may be to replace the natural valve with an artificial valve. There are three major types of mechanical valves with many

neg: Kingston valve also incorporate Kingston valves. Uses include the fire extinguishing system and the system to flood the artillery magazine. On vintage submarines, Kingston valves are fitted at the bottom of certain ballast tanks, such as safety, negative, and bow buoyancy tanks. The submarine's ballast tank valves are used to admit water when the submarine dives. The valves allow water to enter the ballast tanks, while the enclosed air escapes through the open main vents at the top of the ballast tanks. During peacetime the Kingston valves are closed when the submarine is on the surface, the valves and vents being opened

neg: Isovolumetric contraction maintain the correct unidirectional flow of blood through the heart and circulatory system. The word contains the prefix iso-, derived from the Ancient Greek ἴσος (ísos), meaning equal. Therefore, an isovolumetric contraction is one in which the volume of fluid remains constant. Isovolumetric contraction In cardiac physiology, isovolumetric contraction is an event occurring in early systole during which the ventricles contract with no corresponding volume change (isovolumetrically). This short-lasting portion of the cardiac cycle takes place while all heart valves are closed. In a healthy young adult, blood enters the atria and flows to the ventricles via the opened atrioventricular

neg: Artificial heart valve thinners which must be tested and monitored constantly or it may be the constant ticking noise of the valve, which can be heard sometimes several feet away from the patient forever 24-7. There are three main types of artificial heart valves: the "mechanical,"the "biological," and the "tissue engineered" valves. Mechanical heart valves (MHV) are prosthetics designed to replicate the function of the natural valves of the human heart. The human heart contains four valves: tricuspid valve, pulmonic valve, mitral valve and aortic valve. Their main purpose is to maintain unimpeded forward flow through the heart and from the heart into

neg: Valvular heart disease Don't smoke . 2. Avoid excessive alcohol consumption. 3. Antibiotics drugs . 4. Antithrombotic medication such as Aspirin. 5. Anticoagulant such as warfarin. 6. Balloon dilatation . 7. Water pills medication. And in some cases surgery may be necessary... Valvular heart disease Valvular heart disease is any disease process involving one or more of the four valves of the heart (the aortic and bicuspid valves on the left side of heart and the pulmonary and tricuspid valves on the right side of heart. These conditions occur largely as a consequence of aging, but may also be the result of congenital

neg: Valvular heart disease Valvular heart disease Valvular heart disease is any disease process involving one or more of the four valves of the heart (the aortic and bicuspid valves on the left side of heart and the pulmonary and tricuspid valves on the right side of heart. These conditions occur largely as a consequence of aging, but may also be the result of congenital (inborn) abnormalities or specific disease or physiologic processes including rheumatic heart disease and pregnancy. Anatomically, the valves are part of the dense connective tissue of the heart known as the cardiac skeleton and are responsible for the regulation of

neg: Valvetrain coil springs, appropriately named valve springs, to keep them closed when not actuated by the camshaft. They are attached to the valve stem ends, seating within spring retainers. Other mechanisms can be used in place of valve springs to keep the valves closed: Formula 1 engines employ pneumatic valve springs in which pneumatic pressure closes the valves, while motorcycle manufacturer Ducati uses desmodromic valve drive which mechanically close the valves. Depending on the design used, the valves are actuated directly by a rocker arm, finger, or bucket tappet. Overhead camshaft engines use fingers or bucket tappets, upon which the cam

neg: Valve or 1 directions respectively. Operating positions for 2-port valves can be either shut (closed) so that no flow at all goes through, fully open for maximum flow, or sometimes partially open to any degree in between. Many valves are not designed to precisely control intermediate degree of flow; such valves are considered to be either open or shut. Some valves are specially designed to regulate varying amounts of flow. Such valves have been called by various names such as "regulating", "throttling", "metering", or "needle valves". For example, needle valves have elongated conically-tapered discs and matching seats for fine flow control.

neg: Heart sounds the ventricles against closed semilunar valves, sends blood rushing back toward the atria, and the parachute-like valves catch the rush of blood in their leaflets causing the valve to snap shut. The S1 sound results from reverberation within the blood associated with the sudden block of flow reversal by the valves. The delay of T1 even more than normally causes the split S1 which is heard in a right bundle branch blockage. The second heart sound, or S, forms the "dub" of "lub-dub" and is composed of components A (aortic valve closure) and P (pulmonary valve closure). Normally A precedes

neg: Medical imaging etc. Tomography is the imaging by sections or sectioning. The main such methods in medical imaging are: When ultrasound is used to image the heart it is referred to as an echocardiogram. Echocardiography allows detailed structures of the heart, including chamber size, heart function, the valves of the heart, as well as the pericardium (the sac around the heart) to be seen. Echocardiography uses 2D, 3D, and Doppler imaging to create pictures of the heart and visualize the blood flowing through each of the four heart valves. Echocardiography is widely used in an array of patients ranging from those experiencing

neg: Artificial heart valve that the biological markers are removed, eliminating a response from the host's immune system. The leaflets are flexible and durable and do not require the patient to take blood thinners for the rest of their life. The most used heart valves in the US, Britain and EU are those utilizing tissue leaflets. Mechanical valves are more commonly used in Asia and Latin America. The following companies manufacture tissue heart valves: Edwards Lifesciences, Medtronic, St. Jude Medical, Sorin, Medtronic ATS Medical, 3F Therapeutics, CryoLife, and LifeNet Health. Recently, researchers have begun working to grow heart valves in vitro. Autologous cells are

neg: Fabry disease heart rhythms such as complete heart block, but also abnormally rapid heart rhythms such as ventricular tachycardia. These abnormal heart rhythms can cause blackouts, palpitations, or even sudden cardiac death. Sphingolipids can also build up within the heart valves, thickening the valves and affecting the way they open and close. If severe, this can cause the valves to leak (regurgitation) or to restrict the forward flow of blood (stenosis). The aortic and mitral valves are more commonly affected than the valves on the right side of the heart. Angiokeratomas (tiny, painless papules that can appear on any region of the

neg: Pericardial heart valves to another. All 4 valves were manufactured for clinical use and all were 25mm in diameter. The valves were photographed under identical conditions in the mitral side of a 'pulse duplicator' and the flow rates, at peak of diastole were: for each frame, from left to right: 0, 100, 200, 300, and 400 ml/s. Regarding infective endocarditis, embolic complications and bleeding due to anticoagulant treatment, there is only scant data in the publications analysed for this article. It is presumed, and not without good reason, that the main emphasis was placed by the authors on structural valve deterioration (SVD). It

neg: Marian Ionescu the high pressure environment of the left heart.These valves became incompetent after various durations post implantation – from 3 to 12 years. However, two important facts were established by the use of such valves. The haemodynamic performance in both mitral and aortic positions was superior to all known artificial heart valves and that the risk of thrombosis and embolisation was minimal when compared with mechanical valves. Freehand insertion of stentless fascia lata aortic valves was also used in a small number of cases with similar results. In his continuous search for the 'Holy Grail', Ionescu experimented with valves made from

neg: Aortic valve replacement for a relatively long time before symptoms develop. Surgery is indicated for symptoms such as shortness of breath, and in cases where the heart has begun to enlarge (dilate) from pumping the increased volume of blood that leaks back through the valve. There are two basic types of artificial heart valve: mechanical valves and tissue valves. Tissue heart valves are usually made from animal tissue, either animal heart valve tissue or animal pericardial tissue. The tissue is treated to prevent rejection and calcification. There are alternatives to animal tissue valves. In some cases a homograft – a human aortic valve

neg: Pericardial heart valves endocarditis and he advocates the use of such valves in similar situations because the pericardial valves are considered to be more resistant to infection than other devices. (D): This group considers that in its hands the pericardial valves were more prone to infection than the porcine valves, and also when compared to the results with pericardial valves published by other surgeons. In conclusion, it is obvious that the risk of infective endocarditis in pericardial valves is not dissimilar from that encountered in porcine valves at least up to ten years after valve insertion. It can also be considered that the

neg: Cardiac physiology in blood pressure tracings. The semilunar valves close to prevent backflow into the heart. Since the atrioventricular valves remain closed at this point, there is no change in the volume of blood in the ventricle, so the early phase of ventricular diastole is called the isovolumic ventricular relaxation phase, also called isovolumetric ventricular relaxation phase. In the second phase of ventricular diastole, called late ventricular diastole, as the ventricular muscle relaxes, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria. When this occurs, blood flows from the atria into the

neg: Primary tumors of the heart heart valves. The vast majority of these are papillary fibroelastomas. Primary tumors of the valves of the heart are more likely to occur in males. While most primary tumors of the valves of the heart are not malignant, they are more likely to have symptoms related to the valve, including neurologic symptoms and (in a few cases) sudden cardiac death. The vast majority of the tumors of the heart have a benign course and are not directly fatal. However, even the benign tumors of the heart can be lethal due to either direct extension into the electrical conduction system of

neg: Artificial heart valve they have a greater effective opening area (2.4–3.2 square cm c.f. 1.5–2.1 for the single-leaflet valves). Also, they are the least thrombogenic of the artificial valves. Mechanical heart valves are today very reliable and allow the patient to live a normal life. Most mechanical valves last for at least 20 to 30 years. Mechanical heart valves have been traditionally considered to be more durable in comparison to their bioprosthetic counterparts. The struts and occluders are made out of either pyrolytic carbon or titanium coated with pyrolytic carbon, and the sewing ring cuff is Teflon (PTFE), polyester or dacron. The major

neg: Heart sounds heart sound, or S, forms the "lub" of "lub-dub" and is composed of components M (mitral valve closure) and T (tricuspid valve closure). Normally M precedes T slightly. It is caused by the closure of the atrioventricular valves, i.e. tricuspid and mitral (bicuspid), at the beginning of ventricular contraction, or systole. When the ventricles begin to contract, so do the papillary muscles in each ventricle. The papillary muscles are attached to the cusps or leaflets of the tricuspid and mitral valves via chordae tendineae (heart strings). When the papillary muscles contract, the chordae tendineae become tense and thereby prevent the

neg: Brachiopod sockets; their valves are held together only by muscles. (R. C. Moore, 1952) All brachiopods have adductor muscles that are set on the inside of the pedicle valve and which close the valves by pulling on the part of the brachial valve ahead of the hinge. These muscles have both "quick" fibers that close the valves in emergencies and "catch" fibers that are slower but can keep the valves closed for long periods. Articulate brachiopods open the valves by means of abductor muscles, also known as diductors, which lie further to the rear and pull on the part of the

neg: Artificial heart valve last indefinitely (the equivalent of over 50,000 years in an accelerated valve wear tester). However, current mechanical heart valves all require lifelong treatment with anticoagulants (blood thinners), e.g. warfarin, which requires monthly blood tests to monitor. This process of thinning the blood is called anticoagulation. Tissue heart valves, in contrast, do not require the use of anticoagulant drugs due to the improved blood flow dynamics resulting in less red cell damage and hence less clot formation. Their main weakness however, is their limited lifespan. Traditional tissue valves, made of pig heart valves, will last on average 15 years before they

neg: Artificial heart valve the major blood vessels connected to the heart, the pulmonary artery and the aorta. As a result of a number of disease processes, both acquired and congenital, any one of the four heart valves may malfunction and result in either stenosis (impeded forward flow) and/or backward flow (regurgitation). Either process burdens the heart and may lead to serious problems including heart failure. A mechanical heart valve is intended to replace a diseased heart valve with its prosthetic equivalent. There are two basic types of valves that can be used for valve replacement, mechanical and tissue valves. Modern mechanical valves can

neg: Tap (valve) is preferred. Gate valves use a metal disc the same diameter as the pipe which is screwed into place perpendicularly to the flow, cutting it off. There is no resistance to flow when the tap is fully open, but this type of tap rarely gives a perfect seal when closed. In the UK this type of tap normally has a wheel-shaped handle rather than a crutch or capstan handle. Cone valves or ball valves are another alternative. These are commonly found as the service shut-off valves in more-expensive water systems and usually found in gas taps (and, incidentally, the cask

neg: Pericardial heart valves touching of the valve's cusps, and a 'freeze-watch' indicator as a safe—guard against exposing the valves during transportation or storage at temperatures below 4 degrees Celsius. The geometry of the valve was slightly modified due to changes in the shape of the stent and by removing the outside plegets around the posts. This gave a more streamlined shape of the whole structure. These modifications had been progressively introduced and all of them were incorporated in the 'Ionescu - Shiley Low Profile Pericardial Xenograft' valve, which became available in 1983. Approximately 200,000 pericardial valves manufactured by Shiley Laboratories were distributed around

neg: Pericardial heart valves when the tissue was attached on the outside of the stent. The in-vitro testing of this modified pericardial valve showed almost identical hydrodynamic results when compared with the existing pericardial valve. Accelerated life-testing showed that failure of this new valve occurred some 3 to 4 times later than that of existing valves. When valve failure occurred, it was not due to abrasion but through progressive fraying of the pericardium. Encouraged by these results, Shiley decided to start manufacturing this modified, improved valve called the 'Ionescu-Shiley Pericardial Optimograft'. At about that time, grave problems were encountered by Shiley with the increasing

neg: Aortic valve diseases and require aortic valve replacement. The valve can become either leaky (regurgitant or insufficient) or stuck partially shut (stenotic). Aortic valve replacement traditionally required open heart surgery. A new alternative is transcatheter aortic valve replacement (TAVR), which delivers a mechanical valve to the site of the diseased valve through a catheter. There are two basic types of artificial heart valve, mechanical valves and tissue valves. Tissue heart valves are usually made from animal tissues, either animal heart valve tissue or animal pericardial tissue. The tissue is pretreated by removing antigens to prevent rejection and to prevent calcification. There are

neg: Valve process, including water and sewage processing, mining, power generation, processing of oil, gas and petroleum, food manufacturing, chemical and plastic manufacturing and many other fields. People in developed nations use valves in their daily lives, including plumbing valves, such as taps for tap water, gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, and poppet valves in car engines. In nature there are valves, for example one-way valves in veins controlling the blood circulation, and heart valves controlling the flow of blood in the chambers of the heart and

neg: Check valve simple, or inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal. An important concept in check valves is the cracking pressure which is the minimum differential upstream pressure between inlet and outlet at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure. Heart valves are essentially inlet and outlet check valves for the heart ventricles,

neg: Diastole and pulmonary valves open—and now blood is ejected from the heart. Ejection causes pressure within the ventricles to fall, and, simultaneously, the atria begin to refill (atrial diastole). Finally, pressures within the ventricles fall below the back pressures in the trunks of the aorta and the pulmonary arteries, and the aortic and pulmonary valves close. The ventricles start to relax, the mitral and tricuspid valves begin to open, and the cycle begins again. In summary, when the ventricles are in systole and contracting, the atria are relaxed and collecting blood as 'return' flows. When, in late diastole, the ventricles become

neg: Ostium primum atrial septal defect be closed surgically. The long term prognosis is excellent. Shunt reversal is a contraindication for surgery. Ostium primum atrial septal defect The ostium primum atrial septal defect (also known as an endocardial cushion defect) is a defect in the atrial septum at the level of the tricuspid and mitral valves. This is sometimes known as an endocardial cushion defect because it often involves the endocardial cushion, which is the portion of the heart where the atrial septum meets the ventricular septum and the mitral valve meets the tricuspid valve. Endocardial cushion defects are associated with abnormalities of the atrioventricular valves

neg: Edwards Lifesciences an independent, publicly held corporation and began trading on the New York Stock Exchange under the symbol “EW.” Today, Edwards continues as a leader in the field of tissue replacement heart valves and repair products and advanced hemodynamic monitoring, which have helped treat and manage more than 2 million patients worldwide. Each year, more than 300,000 valve replacements are performed worldwide through open-heart surgery, utilizing either bioprosthetic tissue valves or mechanical valves. Edwards products include tissue replacement heart valves, sold under such brand names as Carpentier-Edwards PERIMOUNT and Carpentier-Edwards PERIMOUNT MAGNA, and also valve repair products that are used by

neg: Butterfly valve has a reduced pressure rating. For example, a lug-style butterfly valve mounted between two flanges has a pressure rating. The same valve mounted with one flange, in dead end service, has a rating. Lugged valves are extremely resistant to chemicals and solvents and can handle temperatures up to 200 °C, which makes it a versatile solution. Rotary valves constitute a derivation of the general butterfly valves and are used mainly in powder processing industries. Instead of being flat, the butterfly is equipped with pockets. When closed, it acts exactly like a butterfly valve and is tight. But when it is

neg: Hypoplastic left heart syndrome 18 (Edwards syndrome), partial trisomy 9, Turner's syndrome (XO), Jacobsen syndrome (11q deletion syndrome), Holt-Oram syndrome, and Smith-Lemli-Opitz syndrome. Presence of a cystic hygroma increases the risk of HLHS in a fetus. In typical anatomy, the left side of the heart receives oxygen-rich blood from the lungs and pumps it to the rest of the body. In people with HLHS, the aorta and left ventricle are underdeveloped (beginning "in utero"), and the aortic and mitral valves are either too small to allow sufficient blood flow or are atretic (closed) altogether. As blood returns from the lungs to the left atrium,

neg: Heart valve chambers are lined with endocardium. Heart valves separate the atria from the ventricles, or the ventricles from a blood vessel. Heart valves are situated around the fibrous rings of the cardiac skeleton. The valves incorporate leaflets or cusps, which are pushed open to allow blood flow and which then close together to seal and prevent backflow. The mitral valve has two cusps, whereas the others have three. There are nodules at the tips of the cusps that make the seal tighter. The pulmonary valve has left, right, and anterior cusps. The aortic valve has left, right, and posterior cusps. The

neg: Pericardial heart valves once again, the advantage of the versatility of the 'man-made concept' of the pericardial valve. The haemodynamic characteristics of these 3 types of valve are similar to the excellent results found with the original Ionescu-Shiley valve as described by Tandon's group. The minor differences in gradients and in calculated surface area do not show a significant difference at clinical level. The adjacent image portrays the opening characteristics of 4 pericardial valves - Hancock (no longer available), Mitroflow, Edwards and Shiley. The cusps of these valves open synchronously up to a very large surface area only minimally different from one valve

neg: Valve replacement Valve replacement Valve replacement surgery is the replacement of one or more of the heart valves with either an artificial heart valve or a bioprosthesis (homograft from human tissue or xenograft e.g. from pig). It is an alternative to valve repair. There are four procedures Current aortic valve replacement approaches include closed heart surgery, Very invasive cardiac surgery (VICS) and Very invasive, Scapulae-based aortic valve replacement. Catheter replacement of the aortic valve (called trans-aortic valve replacement or implementation [TAVR or TAVI]) is a minimally invasive option for those suffering from aortic valve stenosis. TAVR is commonly performed by guiding a

neg: Transplantable organs and tissues a gene that works by attaching to RNA. Pander, when active, causes the beta cells to be blocked at S phase, which induces apoptosis. This loss of beta cell mass eventually leads to a loss of most of the transplanted beta cells. "Biological valves" are valves of animals, like pigs, which undergo several chemical procedures in order to make them suitable for implantation in the human heart. The porcine (or pig) heart is most similar to the human heart, and therefore represents the best anatomical fit for replacement. Implantation of a porcine valve is a type of Xenotransplantation, or Xenograft,

neg: Periostin in these different mechanisms. Periostin is transiently upregulated during cell fate changes, whether they are related to alterations in physiology or to pathological changes. It influences extracellular matrix restructuring, tissue remodeling, and the epithelial-mesenchymal transition, all of which can be related to tissue healing, development, and disease. Thus, it functions as a mediator, balancing appropriate and inappropriate responses to tissue damage. Periostin plays a critical role in the development of cardiac valves and in degenerative valvular heart disease. While periostin usually is localized to the subendothelial layer in healthy heart valves, its levels are highly increased in infiltrated inflammatory cells

neg: Pericardial heart valves Pericardial heart valves The pericardial heart valve was invented by Marian Ionescu, a British surgeon working at the General Infirmary in Leeds, England. He created this artificial bioprosthetic heart valve as a three-cusp structure made of chemically treated bovine pericardium attached to a Dacron cloth-covered titanium frame. The experimental and in vitro testing of this novel device took place in 1970, and in March 1971, Ionescu began, for the first time, the implantation of the pericardial valve in all three cardiac positions in humans.Between 1971 and 1976 the valves had been made in Ionescu's own hospital laboratory. Throughout these five

neg: Crocodilia has a four-chambered heart and two ventricles, an unusual trait among extant reptiles, and both a left and right aorta which are connected by a hole called the Foramen of Panizza. Like birds and mammals, crocodilians have heart valves that direct blood flow in a single direction through the heart chambers. They also have unique cog-teeth-like valves that, when interlocked, direct blood to the left aorta and away from the lungs, and then back around the body. This system may allow the animals to remain submerged for a longer period, but this explanation has been questioned. Other possible reasons for

neg: Turner syndrome one study were bicuspid aortic valves or coarctation of the aorta (usually preductal), alone or in combination. Other congenital cardiovascular malformations, such as partial anomalous venous drainage and aortic valve stenosis or aortic regurgitation, are also more common in Turner syndrome than in the general population. Hypoplastic left heart syndrome represents the most severe reduction in left-sided structures. Up to 15% of adults with Turner syndrome have bicuspid aortic valves, meaning only two, instead of three, parts to the valves in the main blood vessel leading from the heart are present. Since bicuspid valves are capable of regulating blood flow

neg: Artificial heart valve patients older than age 55. Mechanical heart valves can also cause mechanical hemolytic anemia with hemolysis of the red blood cells as they pass through the valve. "Biological valves" are valves of animals, like pigs, which undergo several chemical procedures in order to make them suitable for implantation in the human heart. The porcine (or pig) heart is most similar to the human heart, and therefore represents the best anatomical fit for replacement. Implantation of a porcine valve is a type of xenotransplantation, also known as a xenograft, which means a transplant from one species (in this case a pig)

neg: Pericardial heart valves is regretable that pericardial valves, which are known to carry a very low risk of embolisation, were not used more often in the mitral position where the need and benefit would have been greater. However, in general, the second generation pericardial valves represent a progress in the armoury of devices for the treatment of heart valve disease. If the process of valve calcification could be controlled, these pericarial valves would become the panacea for patients in need of heart valve replacement. In general, it is known that success depends on knowing how long it will take to succeed. For the

neg: Atrioventricular canal within the first six months of life for a child. Half of the children who are untreated with this condition die during their first year due to heart failure or pneumonia. Atrioventricular canal defect is a combination of abnormalities of the heart and is present at birth. There is a problem when there are holes present in the walls that separate chambers (septa), as well as when valves are incorrectly constructed. There are other names for these heart abnormalities such as endocardial cushion defects or atrioventricular septal defect In a normal healthy heart there are four chambers. This consists of

neg: Pericardial heart valves great haemodynamic difference between the pericardial and porcine valves, Ionescu recorded in a 'pulse duplicator' the opening characteristics of two porcine valves (Hancock Modified Orifice and the recently modified Edwards valve) and two pericardial valves ( the Standard and the Low-Profile Shiley valves). All four valves were manufactured for clinical use and all had an implantation diameter of 25mm. The valves were tested under identical conditions in the mitral compartment of the pulse duplicator and photographs were taken at the peak of diastole. The flow rates were for each frame, from left to right: 0, 100, 200, 300 and 400

neg: Heart murmur quality (high pitched - hence the name) and is associated with aortic valve regurgitation (or mitral regurgitation before rupture of chordae). It is a diastolic murmur which can be heard over the mid-precordium. Heart murmur Heart murmurs are heart sounds produced when blood flows across one of the heart valves that are loud enough to be heard with a stethoscope. There are two types of murmurs. A functional murmur or "physiologic murmur" is a heart murmur that is primarily due to physiologic conditions outside the heart. Other types of murmurs are due to structural defects in the heart itself. Functional

neg: Pump engineering systems. In a valveless pumping system, no valves (or physical occlusions) are present to regulate the flow direction. The fluid pumping efficiency of a valveless system, however, is not necessarily lower than that having valves. In fact, many fluid-dynamical systems in nature and engineering more or less rely upon valveless pumping to transport the working fluids therein. For instance, blood circulation in the cardiovascular system is maintained to some extent even when the heart’s valves fail. Meanwhile, the embryonic vertebrate heart begins pumping blood long before the development of discernible chambers and valves. In microfluidics, valveless impedance pumps have

neg: Bash valve it approaches top dead centre, forcing the valve open. Bash valves are usually held closed by the pressure of fluid in the reservoir behind them. There may be a light spring to assist closing when the reservoir is empty. For this reason they are used as inlet valves, not exhaust. An exhaust bash valve would have the cylinder pressure and the piston actuation both acting to open it, with nothing to close it. Bash valves are not widely used in steam engines, although they are known. Most examples were applied to some form of uniflow steam engine; unlike the more

neg: Autogas and carburettor. Check valves are fitted in the filler and on the fill input to the fuel tank to prevent fuel flowing back the wrong way. Service valves are fitted to the outlet from the tank to the service line. These have a tap to turn the fuel on and off. The tap is usually only closed when the tank is being worked on. In some countries, an electrical shut-off valve is built into the service valve. Where multiple tanks are fitted, a combination of check valves and a hydrostatic relief valve are usually installed to prevent fuel from flowing

neg: Heart sounds patient's condition. Heart sounds Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart. In healthy adults, there are two normal heart sounds, often described as a "lub" and a "dub" (or "dup"), that occur in sequence with each heartbeat. These are the first heart sound (S) and second heart sound

neg: Heart sounds Heart sounds Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart. In healthy adults, there are two normal heart sounds, often described as a "lub" and a "dub" (or "dup"), that occur in sequence with each heartbeat. These are the first heart sound (S) and second heart sound (S), produced

neg: Primary tumors of the heart nodal region. About 20 percent of primary tumors of the heart are malignant in nature. Malignant tumors of the heart include rhabdomyosarcomas, angiosarcomas, myxosarcomas, fibrosarcomas, leiomyosarcomas, reticulum cell sarcomas, desmoplastic small round cell tumor, and liposarcomas. The cardiac sarcomas may occur at any age, but are more commonly seen in individuals in their 20s to 40s. They occur equally in males and females. A subset of the primary tumors of the heart are tumors that are found on the valves of the heart. Tumors that affect the valves of the heart are found in an equal distribution among the four

neg: Artificial heart valve seeded on a scaffold, typically made from a biodegradable polymer such as PGA or PLA. The scaffolding acts as an artificial extra-cellular matrix, guiding tissue growth into the correct 3D structure of the heart valve. Mechanical stimuli must be simulated in the culture in order to condition the tissue for physiological stress in vivo. These heart valves have not yet reached clinical trials. The functioning of natural heart valves is characterized by many advantages: Mechanical or biological (bioprostheses or "tissue valves"), the replaceable models of implantable heart valve prostheses are made by two or three mechanical components. The gear attachment

neg: Decellularization of porcine heart valve the valve is decreased. Decellularized porcine valves are calcified to a lesser degree and may have increased mechanical strength due to decreased aggregation of IgG immunoglobins in response to alpha-Gal, which is significantly increased in conventional glutaraldehyde treated biological valves. Decellularized porcine valves have growth and remodeling potential as well. Decellularization of porcine heart valve Decellularization of porcine heart valves is the removal of cells along with antigenic cellular elements by either physical or chemical decellularization of the tissue. This decellularized valve tissue provides a scaffold with the remaining extracellular matrix (ECM) that can then be used for tissue engineering

neg: Fourth heart sound sound. The normal heart sounds, S and S, are produced during the closing of the atrioventricular valves and semilunar valves, respectively. The closing of these valves produces a brief period of turbulent flow, which produces sound. The S sound occurs, by definition, immediately before S, while the atria of the heart are vigorously contracting. It is manifest as a vibration of 20 to 30 Hz within the ventricle. While the mechanism is not absolutely certain, it is generally accepted that S is caused by stiffening of the walls of the ventricles (usually the left), which produces abnormally turbulent flow as

neg: Papillary muscle Papillary muscle The papillary muscles are muscles located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves (also known as the mitral and tricuspid valves) via the chordae tendineae and contract to prevent inversion or prolapse of these valves on systole (or ventricular contraction). The papillary muscles constitute about 10% of the total heart mass. There are five total papillary muscles in the heart; three in the right ventricle and two in the left. The anterior, posterior, and septal papillary muscles of the right ventricle each attach via chordae tendineae to the tricuspid valve.

neg: Heart valve from prolapsing into the atria when they close. The subvalvular apparatus has no effect on the opening and closure of the valves, however, which is caused entirely by the pressure gradient across the valve. The peculiar insertion of chords on the leaflet free margin, however, provides systolic stress sharing between chords according to their different thickness. The closure of the AV valves is heard as lub, the first heart sound (S1). The closure of the SL valves is heard as dub, the second heart sound (S2). The mitral valve is also called the bicuspid valve because it contains two leaflets

neg: Pericardial heart valves The durability of the pericardial valve, like that of all other artificial heart valves, depends on multiple factors, one of the most important being the environment in which the artificial valves function. Primary or intrinsic tissue failure occurred with pericardial valves and it has been reported in several publications. Unfortunately, many reports do not contain some of the essential data and details necessary for building a clear image of this crucial aspect of valve performance. Table III tabulates some of the available data on primary tissue failure. TABLE III. Primary tissue failure Remarks for primary tissue failure (A): The ages

neg: Collet package. Some of them are made with rubber, and use vacuum for picking. Most internal combustion engines use a split collet to hold both the inlet and exhaust valves under constant valve spring pressure which returns the valves to their closed position when the camshaft lobes are not in contact with the top of the valves. The two collet halves have an internal raised rib which locate into a circular groove near the top of each valve stem, the outer side of the collet halves are a taper fit into the spring retainer (also known as a collar), this taper

neg: Heart to form a primitive heart tube known as the tubular heart. Between the third and fourth week, the heart tube lengthens, and begins to fold to form an S-shape within the pericardium. This places the chambers and major vessels into the correct alignment for the developed heart. Further development will include the septa and valves formation and remodelling of the heart chambers. By the end of the fifth week the septa are complete and the heart valves are completed by the ninth week. Before the fifth week, there is an opening in the fetal heart known as the foramen ovale.

neg: Heart valve bicuspid and the tricuspid valves, develop on either side of the atrioventricular canals. The upward extension of the bases of the ventricles causes the canal to become invaginated into the ventricle cavities. The invaginated margins form the rudiments of the lateral cusps of the AV valves. The middle and septal cusps develop from the downward extension of the septum intermedium. The semilunar valves (the pulmonary and aortic valves) are formed from four thickenings at the cardiac end of the truncus arteriosus. These thickenings are called endocardial cushions. The truncus arteriosus is originally a single outflow tract from the embryonic heart

neg: Heart from the ventricles, and the fibrous rings which serve as bases for the four heart valves. The cardiac skeleton also provides an important boundary in the heart's electrical conduction system since collagen cannot conduct electricity. The interatrial septum separates the atria and the interventricular septum separates the ventricles. The interventricular septum is much thicker than the interatrial septum, since the ventricles need to generate greater pressure when they contract. The heart has four valves, which separate its chambers. One valve lies between each atrium and ventricle, and one valve rests at the exit of each ventricle. The valves between the

neg: Varicose veins Varicose veins Varicose veins are veins that have become enlarged and twisted. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have pairs of leaflet valves to prevent blood from flowing backwards (retrograde flow or venous reflux). Leg muscles pump the veins to return blood to the heart, against the effect of gravity. When veins become varicose, the leaflets of the valves no longer meet properly, and the valves do not work. This allows blood to flow backwards and the veins to enlarge even more. Varicose veins are most common in the

neg: Christmas tree (oil well) opened or closed when the well is flowing (except in an emergency) to prevent erosion of the valve sealing surfaces. The lower master valve will normally be manually operated, while the upper master valve is often hydraulically actuated, allowing it to be used as a means of remotely shutting in the well in the event of emergency. An actuated wing valve is normally used to shut in the well when flowing, thus preserving the master valves for positive shut off for maintenance purposes. Hydraulic operated wing valves are usually built to be fail safe closed, meaning they require active hydraulic

neg: Cadillac V8 engine a significant improvement in the company's CAFE numbers, so Cadillac and Eaton Corporation devised a cylinder deactivation system called Modulated Displacement that would shut off two or four cylinders in low-load conditions such as highway cruising, then reactivate them when more power was needed. When deactivated, solenoids mounted to those cylinders' rocker-arm studs would disengage the fulcrums, allowing the rockers to "float" and leave the valves closed despite the continued action of the pushrods. These engines are easily identified by their rocker covers, which each have elevated sections over 2 cylinders with electrical connectors on top. With the valves closed

neg: Pulmonary atresia Pulmonary atresia Pulmonary atresia is a congenital malformation of the pulmonary valve in which the valve orifice fails to develop. The valve is completely closed thereby obstructing the outflow of blood from the heart to the lungs. The pulmonary valve is located on the right side of the heart between the right ventricle and pulmonary artery. In a normal functioning heart, the opening to the pulmonary valve has three flaps that open and close In congenital heart defects such as pulmonary atresia, structural abnormalities can include the valves of the heart, and the walls and arteries/veins near the heart muscle.

neg: Heart valve dysplasia older dogs. Valve leakage leads to heart enlargement, arrhythmias, and congestive heart failure. Heart valve dysplasia can be tolerated for years or progress to heart failure in the first year of life. Diagnosis is with an echocardiogram. The prognosis is poor with significant heart enlargement. Heart valve dysplasia Heart valve dysplasia is a congenital heart defect which affects the aortic, pulmonary, mitral, and tricuspid heart valves. Dysplasia of the mitral and tricuspid valves can cause leakage of blood or stenosis. Dysplasia of the mitral and tricuspid valves - also known as the atrioventricular (AV) valves - can appear as thickened,

neg: Valvular heart disease in some cases the aortic and mitral valves are both involved (25%). Involvement of other heart valves without damage to the mitral are exceedingly rare. While developed countries once had a significant burden of rheumatic fever and rheumatic heart disease, medical advances and improved social conditions have dramatically reduced their incidence. Many developing countries, as well as indigenous populations within developed countries, still carry a significant burden of rheumatic fever and rheumatic heart disease and there has been a resurgence in efforts to eradicate the diseases in these populations. The evaluation of individuals with valvular heart disease who are or

neg: Artificial heart valve 1979 and while they take care of some of the issues that were seen in the other models, bileaflets are vulnerable to backflow and so they cannot be considered as ideal. Bileaflet valves do, however, provide much more natural blood flow than caged-ball or tilting-disc implants. One of the main advantages of these valves is that they are well tolerated by the body. Only a small amount of blood thinner is needed to be taken by the patient each day in order to prevent clotting of the blood when flowing through the valve. These "bileaflet" valves have the advantage that

neg: Heart blood into the ventricles and priming the pump. Next, the ventricles start to contract. As the pressure rises within the cavities of the ventricles, the mitral and tricuspid valves are forced shut. As the pressure within the ventricles rises further, exceeding the pressure with the aorta and pulmonary arteries, the aortic and pulmonary valves open. Blood is ejected from the heart, causing the pressure within the ventricles to fall. Simultaneously, the atria refill as blood flows into the right atrium through the superior and inferior vena cavae, and into the left atrium through the pulmonary veins. Finally, when the pressure

neg: Gas cabinet and purge up processes can also be performed without any interruption of connected cylinders. The port and valve specifications for gas cabinets and distribution systems are an important part of the selection process. Gas cabinets may be distinguished by the types of valves used to control flow. Manual valves. Valves are manually adjusted or deployed via a control knob, lever, or other manual device. Solenoid valves. Valves are opened and closed via a solenoid magnet deployed by an electrical signal. Air pilot valves. Valves are deployed via a pneumatic signal. Ports are openings in the manifold or distribution system where

neg: Mitral valve replacement biological or mechanical valve. The left artium is then closed, and the patient weaned from cardiopulmonary bypass. After surgery patients are typically taken to an intensive care unit (ICU). There are two primary types of artificial mitral valves: mechanical valves and bioprosthetic tissue (biological) valves. The mechanical valves are made from metal and pyrolytic carbon, and can last a lifetime. Patients with mechanical valves must take blood-thinning medications to prevent clotting. Bioprosthetic valves are made from animal tissues. Use of these biological valves allows patients to avoid blood thinners. However, the bioprosthetic valves may only last 10 to 15 years.

neg: Aortic valve replacement aortic valve replacement have been developed. The American Heart Association and American College of Cardiology Guidelines for the Management of Patients with Valvular Heart Disease are a widely accepted source of information for cardiologists and surgeons. Patients with severe aortic stenosis, where the aortic valve is narrowed and blood flow from the heart is obstructed, are candidates for surgery when they develop symptoms or when the heart function is impacted. Certain asymptomatic patients may also be candidates for surgery, especially if exercise stress testing is positive. Patients with leaky aortic valves (aortic insufficiency) often tolerate even severe degrees of insufficiency

neg: Diving regulator closed by the valve spring and gas flow stops. When the diver exhales, one-way valves (made from a flexible air-tight material) flex outwards under the pressure of the exhalation, letting gas escape from the chamber. They close, making a seal, when the exhalation stops and the pressure inside the chamber reduces to ambient pressure. The vast majority of demand valves are open circuit, which means that the exhaled gas is discharged into the surrounding environment and lost. Reclaim valves can be fitted to helmets to allow the used gas to be returned to the surface for reuse after removing the

neg: Hypoplastic right heart syndrome Expression of these genes expression is regulated by various processes, including transcription and growth factors, as well as proteins like fibrillin, Wnt, BMP2, BMP 4, BMP5, BMP7, which aid in different heart development features like the valves and septum, and other substances, such as retinoid and folic acid.[5] Crucial steps in heart formation are development of the ventricles and atrium formation, as well as septation and valve formation. Any disturbances of such processes may lead to various congenital heart diseases and defects that could be initiated by various genetic, epigenetic or environmental factors. The most common heart malformations from genetic

neg: Yamaha Genesis engine limited by the size of the largest valves: in a 3-valver, the exhaust valve is larger, and in a 4-valver, the inlet valves are larger. The significance of the five-valve engine compared to other multivalve configurations engines is that (like a 3-valver) there were more intake valves than exhaust ones; yet all valves were small and of very similar sizes and weights. There are diminishing returns: the benefits of increasing numbers of valves actually decrease after five-valves-per-cylinder. Downdraft carburettors were adopted for improved gas flow, but, for motorcycles, a disadvantage was that the intake airbox was above the engine, taking

neg: Heart valve dysplasia Heart valve dysplasia Heart valve dysplasia is a congenital heart defect which affects the aortic, pulmonary, mitral, and tricuspid heart valves. Dysplasia of the mitral and tricuspid valves can cause leakage of blood or stenosis. Dysplasia of the mitral and tricuspid valves - also known as the atrioventricular (AV) valves - can appear as thickened, shortened, or notched valves. The chordae tendinae can be fused or thickened. The papillary muscles can be enlarged or atrophied. The cause is unknown, but genetics play a large role. Dogs and cats with tricuspid valve dysplasia often also have an open foramen ovale, an

neg: Syncope (medicine) Causes range from non-serious to potentially fatal. There are three broad categories of causes: heart or blood vessel related, reflex also known as neurally mediated, and orthostatic hypotension. Issues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common. Heart related causes may include an abnormal heart rhythm, problems with the heart valves or heart muscle and blockages of blood vessels from a pulmonary embolism or aortic dissection among others. Neurally mediated syncope occurs when blood vessels expand and heart rate decreases inappropriately. This may occur

neg: Infective endocarditis organism (such as "Staphylococcus aureus") can cause infective endocarditis by infecting even a normal heart valve. Intravenous drug users tend to get their right-sided heart valves infected because the veins that are injected drain into the right side of the heart. In rheumatic heart disease, infection occurs on the aortic and the mitral valves on the left side of the heart. Other factors that increase the risk of developing infective endocarditis are low levels of white blood cells, immunodeficiency or immunosuppression, malignancy, diabetes mellitus, and alcohol abuse. In the past, 1 in 8 cases of infective endocarditis were because of

neg: Downhole safety valve Downhole safety valve A downhole safety valve refers to a component on an oil and gas well, which acts as a failsafe to prevent the uncontrolled release of reservoir fluids in the event of a worst-case-scenario surface disaster. It is almost always installed as a vital component on the completion. These valves are commonly uni-directional flapper valves which open downwards such that the flow of wellbore fluids tries to push it shut, while pressure from the surface pushes it open. This means that when closed, it will isolate the reservoir fluids from the surface. Most downhole safety valves are controlled

neg: Pneumatic non-return valve have a longer service life when compared to pneumatic bladder systems. Pneumatic non-return valve Pneumatic non-return valves are used where a normal non-return valve would be ineffective. This is for example where there is a risk of flood water entering a site but an equal risk of pollution or a chemical spills leaving a site and polluting the environment. Pneumatic non-return valves are installed below ground and can be used to pneumatically lock the non-return valve closed thus containing a site in the event of a spill. It is common practice to lock sites using pneumatic non-return valves during the