Cardiac output: is the total blood flow through the tissues depending on the peripheral circulation

2021-05-27 09:05 AM

The total blood flow of the peripheral circulation is venous circulation, and the heart works automatically to pump blood back into the general circulation of the body.

Cardiac output: is the volume of blood pumped by the heart into the aorta per minute, which is also the volume of blood circulating in the general circulation of the body. Cardiac output is one of the important factors of circulation because it measures the total blood supply to all tissues in the body.

Venous circulation is the volume of peripheral blood that is returned to the heart through the atria per minute. Venous circulation and cardiac output must be in balance except for a few beats when blood is temporarily inflowed and out of the heart and lungs.

Venous circulation is the sum of all blood flows from body tissues through the peripheral circulatory system.

Therefore, changes in cardiac output also lead to changes in the peripheral circulation.

The law of peripheral circulation changes, in most tissues, the increase in blood circulation mainly depends on the percentage of metabolism of each tissue. For example, peripheral circulation increases as tissue O2 requirements increase, with different physical conditions. Note that for each given intensity of physical activity, CO2 consumption and cardiac output increase proportionally.

In summary, cardiac output is determined by the sum of the factors that regulate peripheral circulation. The total blood flow of the peripheral circulation is venous circulation, and the heart works automatically to pump blood back into the general circulation of the body.

Figure. Cardiac output equals venous circulation and total peripheral blood volume through tissues and organs.

Figure. Physical activity increases cardiac output (red line) and oxygen demand (blue line).

Cardiac output is inversely proportional to peripheral resistance when arterial blood pressure is constant

An important factor influencing cardiac output control: the change in cardiac output is inversely proportional to peripheral resistance when blood pressure is constant. Note that when peripheral resistance is normal (at 100%) cardiac output also remains the same, when the heart is working better, the ejection volume is more than normal and vice versa.

Figure. Chronic effect of peripheral resistance on cardiac output, showing a reciprocal relationship between total peripheral resistance and cardiac output. AV, atrioventricular.

As peripheral resistance increases, cardiac output decreases and vice versa. This phenomenon can be explained through Ohm's law.

Cardiac output = (arterial blood pressure)/(total peripheral resistance)

Therefore, every time the peripheral circulatory resistance changes with other functional factors constant, the cardiac output changes inversely proportionally.

The heart can become factors that inhibit cardiac output

 The amount of blood that can be pumped by the heart, expressed through a volume, is called the physiological cardiac output curve.

The figure shows cardiac output per minute at different levels of right atrial pressure. It is also a form of cardiac function curve. Note that a cardiac output that can reach 13 L/min is 2.5 times the physiological cardiac output of 5 L/min, which is still considered normal. That means a healthy person whose heart is functioning at a level unaffected by the stimulus can pump 2.5 times as much blood into the general circulation as normal before the heart becomes a sex factor. cardiac output limit.

The figure also shows cardiac output curves when the heart is operating non-physiologically.

Figure. The cardiac output curve is normal, and as it increases, the ejection efficiency of the heart decreases.

Factors affecting the effective functioning of the heart

Two factors make the heart pump blood better (1) nerve stimulation (2) dilation of the heart muscle conduction.

Nerve stimulation increases heart rate

Sympathetic stimulation and parasympathetic inhibition are two factors that increase the efficiency of heart activity (1) increase heart rate, in young people the normal heart rate is 72 beats/min, which can increase to 180-200 beats/minute. min (2) increases myocardial contractility (may be 2 times the normal force of contraction). The combination of two factors, a maximal nerve stimulation causes cardiac output to peak at 2 times normal At the highest cardiac output curve with 25 l/min.

Cardiac dilation increases blood pumping efficiency

Cardiac dilation over a long period of time can increase cardiac efficiency, but do not overwork it as it can affect heart function because dilation causes the myocardium to increase in volume and force, like exercise. Strength training helps to relax muscles. For example, with a marathoner, the heart can be 50-70% larger than normal. This factor can increase peak cardiac output by 60-100% and thus can help the heart to eject more blood than normal.

When nerve stimulation is combined with myocardial hypertrophy, in athletes, the heart can pump a blood volume of 30 to 40 L/min, 2.5 times that of a normal person. Increased cardiac output is also one of the important factors affecting the playing time of athletes.

Factors that decrease cardiac performance

Any factor that reduces the total blood volume of the heart causes a decrease in cardiac performance. Inside:

Increased arterial pressure causes the heart to need a greater force to eject blood, as in malignant hypertension.

Inhibitory and excitatory nervous system.

Pathological factors that cause abnormal heart rhythms.

Heart attack.

Heart valve disease.

Congenital heart disease.

Myocarditis.

Ischemic heart disease.