Cardiac preload and afterload
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The preload and anterior load of the heart are a point of knowledge that is very easy to confuse. Preload refers to the end of diastole. Factors such as daily diet and psychological state may lead to the preload and anterior load of the heart. Therefore, in order to avoid such problems, we need to develop good eating habits in our daily lives and do not overwork. Today I will introduce to you the relevant knowledge about cardiac preload and afterload. (1) Valvular disease, such as mitral valve, tricuspid valve, and aortic valve insufficiency. Valvular insufficiency leads to blood reflux, increased ventricular end-diastolic blood volume, and increased volume load. Mitral valve and tricuspid valve stenosis reduces the amount of blood entering the ventricle, which can reduce the volume load. (2) Internal-external shunt diseases , such as atrial septal defect, ventricular septal defect, and patent ductus arteriosus. When we see these three types, we will inevitably think of the left-to-right shunt type of congenital heart disease. For the first two types of congenital heart disease, with age, systemic circulation pressure increases, pulmonary resistance and right heart pressure decrease, and horizontal shunt from left to right in the cardiac cavity increases. The shunt causes overload of the right atrium and right ventricle, resulting in right atrium and right ventricle enlargement. If the ductus arteriosus is not closed, the aortic pressure is higher than the pulmonary artery pressure, and blood is shunted from the aorta to the pulmonary artery regardless of systole or diastole. In all three cases, the pulmonary circulation volume increases and the systemic circulation volume decreases. The increased blood flow returning to the left atrium and left ventricle increases the load on the left atrium and left ventricle, that is, the volume load borne by the ventricle increases at the end of diastole. (3) Systemic changes in blood volume, such as the infusion of large amounts of fluid in a short period of time, hyperthyroidism, chronic anemia, etc., can increase the volume load. Sweating, diarrhea, blood loss, etc. lead to a decrease in effective circulating blood volume, which can reduce the preload. Afterload refers to the resistance or load encountered after myocardial contraction, also known as pressure load. An increase in afterload means that the resistance that the heart has to overcome when it contracts increases. Left ventricular afterload is common in hypertension and aortic outflow obstruction (aortic stenosis, aortic coarctation). At this time, the resistance to heart ejection is large and the heart afterload increases. Right ventricular afterload is common in pulmonary hypertension, pulmonary artery stenosis, pulmonary obstructive disease and pulmonary embolism. At this time, pulmonary artery pressure is high, right heart ejection resistance increases, and cardiac afterload increases. Relatively speaking, the increase in cardiac afterload is easier to understand and remember, so you can write down the increase in cardiac afterload and use the elimination method to solve the questions. To sum up, excessive ventricular preload is seen in mitral regurgitation, tricuspid regurgitation, aortic regurgitation; atrial septal defect, ventricular septal defect, patent ductus arteriosus; large amount of fluid infusion in a short period of time, hyperthyroidism, and chronic anemia. Excessive ventricular afterload is seen in hypertension, aortic stenosis, aortic coarctation; pulmonary hypertension, pulmonary artery stenosis, pulmonary obstructive disease and pulmonary embolism. |
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