What Is Cardiac Output?

Cardiac output (CO) is the amount of blood pumped by the left or right ventricle per minute. The product of heart rate and stroke volume. If the heart rate is calculated at 75 beats per minute, the cardiac output is 5-6L in men and slightly lower in women. Cardiac output varies with the body's metabolism and activity. Cardiac output increases during muscle movements, emotional agitation, and pregnancy.

Basic Information

Chinese name

Cardiac output

Foreign name

cardiac output

Stroke volume

About 70 ml (60 to 80 ml) at rest

Function

Evaluate the efficiency of the circulatory system

Commonly known

Output per distraction

Related

Metabolic rate of whole body tissue cells

Factors affecting cardiac output

Cardiac output is equal to the product of stroke volume and heart rate. Therefore, all factors that affect stroke volume and heart rate can affect cardiac output.

Stroke volume

(1) The preload is within a certain range, and the end-diastolic filling volume is large, the myocardial fibers are stretched, and the stroke volume is increased. We call the end-diastolic blood volume or pressure, that is, the load existing before ventricular contraction, called the preload. When the preload increases, the myocardial contractility increases, and the stroke volume or stroke volume increases.

(2) Myocardial contractility Myocardial contractility is an intrinsic characteristic and is an intrinsic factor that determines the level of myocardial cell function. Myocardial contractility is directly proportional to cardiac stroke volume or stroke work. As myocardial contractility increases, stroke volume and stroke work increase.

(3) Post-load The load or resistance encountered after myocardial contraction is called post-load. During ventricular ejection, the resistance of the aortic pressure must be overcome in order for the ventricular blood to open the semilunar valve and enter the aorta. Therefore, the aortic blood pressure plays a role of afterload, and the afterload of ventricular muscle depends on the level of arterial blood pressure and arterial blood pressure The changes will affect the contraction process of the myocardium, which in turn affects the stroke volume.

Heart rate

Heart rate changes within a certain range can affect stroke volume or cardiac output. Increased heart rate can increase cardiac output, but there are limits. Because the heart rate is too fast (such as more than 180 beats per minute), the diastole is significantly shortened, and the ventricular filling volume is insufficient. Although the number of beats per minute increases, the cardiac output decreases due to the significant decrease in the stroke volume. The heart rate is too slow (less than 40 beats per minute), and the cardiac output is also reduced, because the diastolic period is too long, and the filling volume of the ventricle is close to the limit. Increasing the filling time cannot increase the filling volume and stroke volume accordingly.

Clinical significance of cardiac output

The heart continuously ejects blood to supply the body's metabolic needs. Cardiac output is an indicator of the strength and normality of cardiac ejection function, and it is also a very important issue in clinical and experimental research. The normal value of cardiac output is 3.5 to 5.5 L / min. Cardiac index refers to the cardiac output per unit surface area, and the normal value is 2.5 to 3.5 L / (min · m ² ). Cardiac index is an index of pumping function of the heart after the cardiac output is normalized by the unit body surface area, which has good comparability. In patients with low cardiac output and heart failure, both of them are reduced. In patients with severe heart failure, the cardiac output is significantly reduced even in bed rest. Most patients have a cardiac output of <3.5L / min and a cardiac index of <2. 2L / (min · m ² ). A small number of patients with high-volume heart failure, although the heart index can be greater than normal, but due to high tissue metabolic rate, blood flow and other reasons, still can not meet the metabolic needs.