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OP_Valve_Disorders4

OP_Valve_Disorders4 - Mitral valve stenosis results from a...

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Mitral valve stenosis results from a narrowing of the mitral valve orifice when the valve is open. This results in the left atrial (LA) pressure being much greater than left ventricular (LV) pressure during diastolic filling (shaded gray in figure). The high resistance across the stenotic mitral valve causes blood to back up into the left atrium and reduces filling (end-diastolic volume) of the left ventricle despite the elevated LA pressure. The effects of mitral stenosis on ventricular filling can be appreciated better by examining the changes in the LV pressure-volume loop . The reduced ventricular filling (decreased preload ) can result in reduced ventricular stroke volume by the Frank-Starling mechanism . If stroke falls significantly, the reduced cardiac output may result in a reduction in aortic pressure . The increase in LA pressure can result in pulmonary congestion and edema because of increased pulmonary capillary hydrostatic pressure . Mitral valve stenosis is associated with a diastolic murmur because of turbulence that occurs as blood moves across the stenotic valve. Mitral stenosis impairs left ventricular filling so that there is a decrease in end-diastolic volume ( preload ). This leads to a decrease in stroke volume by the Frank-Starling mechanism and a fall in cardiac output and aortic pressure. This reduction in afterload (particularly aortic diastolic pressure) enables the end-systolic volume to decrease slightly, but not enough to overcome the decline in end-diastolic volume. These changes just described do not include cardiac and systemic compensatory mechanisms that attempt to maintain cardiac output and arterial pressure. These compensatory responses include, but are not limited to, systemic vasoconstriction, increased blood volume, and increased heart rate and inotropy. Tricuspid valve stenosis is similar to mitral valve stenosis except that the pressure and volume changes occur on the right side of the heart.
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Aortic valve stenosis is characterized by the left ventricular pressure being much greater than aortic pressure during left ventricular ejection (shaded gray in figure). LV pressure is greatly elevated and the aortic pressure is slightly reduced in this example. The pressure gradient across the stenotic lesion results from both increased resistance (related to narrowing of the valve opening) and turbulence distal to the valve. The magnitude of the pressure changes is determined by the severity of the stenosis and the flow rate across the valve. Severe aortic stenosis results in reduced ventricular stroke volume due to increased afterload , increased end- systolic volume , and a compensatory increase in end-diastolic volume and pressure. These
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