Left ventricle

Valve Problems. The primary solution to valve problems has been implantable replacement valves. The introduction of these devices necessitates open-heart surgery. There are two types of valves available tissue (porcine and bovine) and mechanical. The disadvantage of tissue valves is that these have a limited life of about seven years before they calcify, stiffen, and have to be replaced. The mechanical valves can last a lifetime, but require anticoagulant therapy. In some patients, anticoagulants may not be feasible or may be contraindicated. Of the valves which require replacement, 99% are mitral and aortic valves. The valves on the left side of the heart are under much greater pressure because the left ventricle is pumping blood out to the entire body, instead of only to the lungs. Occasionally, two valves are replaced in the same procedure. 

The heart, a four-chambered muscular pump has as its primary purpose the propelling of blood throughout the cardiovascular system. The left ventricle is the principal pumping chamber and is therefore the largest of the four chambers in terms of muscle mass. The efficiency of the heart as a pump can be assessed by measuring cardiac output, left ventricular pressure, and the amount of work requHed to accomplish any requHed amount of pumping. 

Cardiotonic drugs increase the force of the contraction of the muscle (myocardium) of the heart. This is called a positive inotropic action. When the force of contraction of the myocardium is increased, the amount of blood leaving the left ventricle at the time of each contraction is increased. When the amount of blood leaving the left ventricle is increased, cardiac output (the amount of blood leaving the left ventricle with each contraction) is increased. 

A patient who recently recovered from a minor heart attack is suffering from periods of ectopic ventricular beats, originating from what is believed to be a small area of post-ischaemic fibrosis in the free wall of the left ventricle. 

Excess fluid may be harmful (i.e., shift intraventricular septum into left ventricle, increase right ventricular oxygen demand)... 

Echocardiogram hypocontractile left ventricle, akinesis of anterior apical wall, ejection fraction 20%... 

Left ventricular systolic function is normal. Left ventricular ejection fraction by visual inspection is estimated at 55% to 60%. The left ventricle is grossly normal size. 

Preload The stretched condition of the heart muscle at the end of diastole just before contraction volume in the left ventricle at the end of diastole estimated by the pulmonary artery occlusion pressure (also known as the pulmonary artery wedge pressure or pulmonary capillary wedge pressure). 

The semilunar valves separate the ventricles from their associated arteries. The pulmonary valve is found between the right ventricle and the pulmonary artery and the aortic valve is found between the left ventricle and the aorta. These valves prevent backward flow of blood from the pulmonary artery or the aorta into their preceding ventricles when the ventricles relax. The semilunar valves also have three cusps. There are no valves between the venae cavae or the pulmonary veins and the atria into which they deliver blood. The closure of the valves causes the "lub-dub" associated with the heart beat. Tire first heart sound, or the "lub," occurs when the ventricles contract and the AV valves close. The second heart sound, or the "dub," occurs when the ventricles relax and the semilunar valves close. 

The contractility of the myocardium determines the ejection fraction of the heart, which is the ratio of the volume of blood ejected from the left ventricle per beat (stroke volume) to the volume of blood in the left ventricle at the end of diastole (end-diastolic volume) ... 

Ventricular assist devices are surgically implanted and assist, or in some cases replace, the pumping functions of the right and/or left ventricles. 

A clinically useful indirect estimate of Mvo2 is the double product (DP), which is HR multiplied by systolic blood pressure (SBP) (DP = HR xSBP). The DP does not consider changes in contractility (an independent variable), and because only changes in pressure are considered, volume loading of the left ventricle and increased MVo2 related to ventricular dilation are underestimated. 

Circumflex branch To left ventricle Anterior interventricular (anterior descending) artery... 

Lees Loss Prevention in the Process Industries, 21 862-863 Left atrium, 5 79, 80 Left posterior fascicle, 5 80 Left ventricle, 5 79, 80 Legal actions, patent-related, 75 186 Legal aspects, of standardization,... 

Maseda C, Matsubara K, Shiono H. 1989. Improved gas chromatography with electron-capture detection using a reaction pre-column for the determination of blood cyanide a higher content in the left ventricle of fire victims. J Chromatogr 82 319-327. 

Left Ventricle (LV) A simple inverted U curve is drawn that has its baseline between 0 and 5 mmHg and its peak at 120 mmHg. During diastole, its pressure must be less than that of the CVP to enable forward flow. It only increases above CVP during systole. The curve between points A and B demonstrates why the initial contraction is isovolumic. The LV pressure is greater than CVP so the mitral valve must be closed, but it is less than aortic pressure so the aortic valve must also be closed. The same is true of the curve between points C and D with regards to IVR. 

This trace shows the volume of the left ventricle throughout the cycle. The important point is the atrial kick seen at point a. Loss of this kick in atrial fibrillation and other conditions can adversely affect cardiac function through impaired LV filling. The maximal volume occurs at the end of diastolic filling and is labelled the left ventricular end-diastolic volume (LVEDV). In the same way, the minimum volume is the left ventricular end-systolic volume (LVESV). The difference between these two values must, therefore, be the stroke volume (SV), which is usually 70 ml as demonstrated above. The ejection fraction (EF) is the SV as a percentage of the LVEDV and is around 60% in the diagram above. 

The volume of blood ejected from the left ventricle with every contraction (ml). 

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