Cardiac cycle left ventricle

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 telemetry reading shows a bimdle branch block (BBB) that occnrs when the right or left ventricle depolarizes late in the cardiac cycle. BBB commonly occms in clients diagnosed with coronary artery disease. Nitroglycerin (NTG) dilates coronary arteries to allow increased blood flow to the myocardinm therefore, the nurse would anticipate the HCP prescribing this medication. 

Hypertension is usually a temporary adjustment to emotional stress or trauma, but after sustained hypertension, the condition perpetuates itself, becoming essential hypertension. The left ventricle of the heart, challenged by the need to pump blood against pressure higher than normal, develops a thickened muscular wall, called cardiac hypertrophy. The extra muscular mass requires additional oxygen, and any decrease in coronary blood flow has more serious consequences in hypertensive patients than in normal individuals. Myocardial infarction (muscle cells die due to lack of oxygen) is therefore more of a threat in hypertensive patients than in normals. Even with the implantation of a replacement heart, the underlying causes of the heart failure have not been eliminated, and the cycle is likely to repeat. 

FIGURE 10.5 (a) The chambers and valves of the heart. LV, left ventricle RV, right ventricle LA, left atrium RA, right atrium M, mitral valve A, aortic valve T, tricuspid valve P, pulmonary valve, (b) The left ventricular cardiac cycle in the P-V plane. See text. 

From the perspective of engineering mechanics, the ventricles are three-dimensional thick-walled pressure vessels with substantial variations in wall thickness and principal curvatures both regionally and temporally through the cardiac cycle. The ventricular walls in the normal heart are thickest at the equator and base of the left ventricle and thinnest at the left ventricular apex and right ventricular free wall. There are also variations in the principal dimensions of the left ventricle with species, age, phase of the cardiac cycle, and disease (Table 54.3). But, in general, the ratio of wall thickness to radius is too high to be treated accurately by all but the most sophisticated thick-waU shell theories [1]. 

There is continuous pressure in arteries to propel blood through them. The level of blood pressure fluctuates during each cardiac cycle. Pressure is highest during systole (contraction) when blood is ejected from the left ventricle into the aorta this pressure is labeled SBP. Pressure is lowest during diastole (relaxation) and labeled... 

The adult human left ventricle (LV) weighs about 250 g and has about 10 myocytes (typical dimension 10 X 25 X 100 pm) and about an equal number of (much smaller) fibroblasts. It beats about 4x 10 beats/year amounting to 3 x 10 cycles in a lifetime. From an engineering/thermodynamic perspective, a useful way of characterizing global LV pump function is in terms of the external work performed. The external work performed per cardiac cycle... 

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