Left Ventricle Contraction

Systolic Function and Outflow Tract Obstruction Abnormalities of systolic function also occur in patients with HCM. The hypertrophied left ventricle may cause a powerful but sometimes uncoordinated contraction presumably owing to the abnormal architecture of the myocardium. The increase seen in the LV wall thickness results in decreased wall stress during systole. Therefore, the left ventricle contracts against a decreased afterload so that the left ventricle is described as being hyperdynamic. EF often is increased. 

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. 

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. 

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. 

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

The resistance to flow in the systemic circulation against which the left ventricle must contract (dyne.s.cm 5). 

Ejection fraction (% of blood expelled from the ventricle during contraction), % fractional shortening (contraction of left ventricle), stroke volume Echocardiography Ozkanlar et al. 100 Tsusaki et al. 101 Hanton et al.102 ... 

Pulse The rhythmical expansion and contraction of an artery produced by waves of pressure caused by the ejection of blood from the left ventricle of the heart as it contracts. 

Fig. 12. Left ventricular cavity opacification (a) View/ of the left ventricle (LV) of a patient without contrast agent (b) the same view after a bolus injection of a microbubble contrast agent the LV, endocardial border (LV/ENDO), and papillary muscle (PAP) are now precisely visualized, allowing myocardial (heart muscle) thickening to be evaluated. When watching the heart in motion, normal functioning heart muscle thickens as it contracts abnormal functioning heart muscle moves less and does not thicken. From Ref. [106], with permission.

Q1 Coronary arteries are the first to branch off the aorta. The heart has a large blood flow (200 ml min-1) but also has great metabolic needs and so has a relatively poor oxygen supply, with little in reserve when oxygen demands increase. At each heart beat (systole), the coronary arteries are compressed by cardiac contraction and blood flow diminishes to a low level. This effect is very marked in the left ventricle, and over 80% of coronary flow to the left ventricle occurs in the periods between beats (diastole). When heart rate increases (tachycardia), the duration of diastole decreases much more than the duration of systole, and the period available for perfusion of cardiac muscle diminishes. 

ATP is also the free energy currency for the contraction of muscles (Table 6-1). The ATP-driven contraction of the muscles surrounding the left ventricle of the human heart can increase the blood pressure within it by 20 kPa (0.2 bar or 150 mm Hg). This increases the chemical potential of the water in the blood (i.e., the VWP term), which causes the blood to flow out to the aorta and then to the rest of the circulatory system toward lower hydrostatic pressures. Pressure-driven flow is an efficient way to move fluids for example, it takes only 0.02 kJ of Gibbs free energy to increase the pressure of 10-3 m3 (1 liter) of water by 20 kPa. In particular, in the present case we note that... 

Preload is the load on the heart created by the volume of blood injected into the left ventricle by the left atrium (at the end of ventricular diastole) and that it must eject with each contraction. It... 

Cardiac output is the total volume of blood expelled by the heart in a minute. The average cardiac output is 4 to 8 L/min. The stroke volume is the quantity of blood ejected from the left ventricle during each contraction. The average stroke volume is 70 ml/beat. 

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