Chronic systemic hypertension results in increased afterload (“pressure load”) o

Question

Chronic systemic hypertension results in increased afterload (“pressure load”) on the left ventricle of the heart, affecting the pressure-volume relationship of the left ventricle. What effect does this have on the normal electrical and/or pressure events of the cardiac cycle? In your answer, you should include terms and processes such as right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary circulation, left atrium, bicuspid valve, left ventricle, aortic valve, systemic circulation, systole, diastole, ventricular systole/diastole, atrial systole/diastole, passive ventricular filling, “atrial kick,” isovolumic ventricular contraction, ventricular ejection, isovolumic relaxation, stroke volume, preload, afterload, pressure-volume loop, and physiologic vs. pathogenic cardiac hypertrophy.

Explanation / Answer

Afterload is the pressure against which the left ventricle has to pump blood to the systemic circulation. The afterload increases in case of increased vascular resistance and peripheral resistance. This afterload causes the left ventricle to exert more work to pump blood into systemic circulation. This causes the muscles of the left ventricle to become thick. This condition is called as left ventricular hypertrophy. Left ventricular hypertrophy is the compansatory mechanism for the increased afterload and tension in the wall of left ventricle. Thickness and hypertrophy causes distribution of tension in the hypwrtrophied wall. Afterload can also be increased by aortic valve stenosis and ventricular dilatation. This causes increase in end systolic volume and decrease in stroke volume. According to the Frank starling pressure volume curve, as the pressure increases the volume is decreased. Preload is the end diastolic volume at the beginning of the systolic contraction. It is the pressure exerted by the blood on the left ventricular wall at the end of diastole. This left ventricular hypertrophy is physiological. When it occurs in some diseases like aortic stenosis due to infection then this is pathological left ventricular hypertrophy.

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