How is the one-way flow in the heart realized? ② The arterial pressure is relatively high. How does the heart pump blood into arteries? ③ How does low-pressure venous blood return to the heart?
Taking the left ventricle as an example, this paper explains the process of ventricular ejection and filling in order to understand the mechanism of heart pumping blood.
The contraction and relaxation of the ventricular wall is the fundamental reason for the indoor pressure change, which leads to the pressure gradient between atrium and ventricle and between ventricle and aorta. Pressure gradient is the main driving force to promote blood flow between corresponding chambers, and one-way blood flow is realized with the cooperation of valve activity. It should also be noted that the valve plays an important role in the change of indoor pressure. Without the cooperation of valves, the indoor pressure in isovolumic contraction and isovolumic relaxation can not be greatly increased or decreased.
Cardiac pump function evaluation
Whether the function of heart pump is normal or abnormal, whether it is enhanced or weakened, is a common problem in medical practice and experimental research. Therefore, it is very important in theory and practice to use what methods and indicators to measure and evaluate cardiac function.
(A) the output of the heart
The main function of the heart in the circulatory system is to pump blood to meet the needs of body metabolism. It goes without saying that the cardiac output is the basic index to measure the cardiac function.
1. The cardiac output per minute and the blood volume discharged from the ventricle on one side of the stroke output are called stroke output, which is referred to as stroke output for short. The amount of blood injected per minute, called output per minute, or cardiac output for short, is equal to the product of heart rate and stroke output. The output of the left and right ventricles is basically equal.
Cardiac output is adapted to the metabolic level of the body, and the metabolic level may be different due to gender, age and other physiological conditions. For example, in a healthy adult male, the heart rotates 75 times per minute on average, the stroke volume is about 70 ml (60-80 ml), and the cardiac output is 5 liters/minute (4.5-6.0 liters/minute). The cardiac output of women is about 10% lower than that of men of the same weight, and the cardiac output in youth is higher than that in old age. The cardiac output can be as high as 25 ~ 35l/min during strenuous exercise, and can be reduced to 2.5L/min under anesthesia.
2. Cardiac index Cardiac output is calculated in units of individuals. The total metabolism of short people and tall people is not equal, so it is not comprehensive to compare the heart function between different individuals with the absolute value of output as an index. Group survey data show that the resting cardiac output time of human body, like basal metabolic rate, is not directly proportional to body weight, but directly proportional to body surface area. The cardiac output calculated by unit body surface area (m2) is called cardiac index; An adult of medium build has a body surface area of about 1.6 ~ 1.7m2 and a cardiac output of about 5 ~ 6L/min at rest and on an empty stomach, so the cardiac index is about 3.0 ~ 3.5L/min·m2. Resting heart index, also known as resting heart index, is a commonly used evaluation index when analyzing and comparing the cardiac function of different individuals.
The heart index changes with different body weight. When the age is about 10 years old, the resting heart index is the largest, which can reach more than 4L/min·m2, and then gradually decreases with age. By the age of 80, the resting heart index is close to 2L/ min m2. During muscle exercise, the cardiac index increases in direct proportion with the increase of exercise intensity. During pregnancy, when you are emotional and eating, your heart index increases.