Cardiac Output | Heart Rate| Affecting Factors | Physiology

                 Cardiac Output |Affecting Factors | Physiology 

Do you know how much blood leaves and returns to your heart in one minute? And how many times your heart beats in a minute?

Keywords: Stroke volume |end diastolic volume| end-systolic volume |cardiac index| after load| pre load| ejection fraction.

Definition

Cardiac output is the amount of blood pumped out by each ventricle in one minute. The range of cardiac output is 5- 6 liters, and the average is 5.5 liters.

Table of contents:

Sr.no.	Contents
1.	Definition
2.	Factors affecting it Heart rate Stroke volume
3.	Cardiac index
4.	Ejection fraction
5.	End systolic volume
6.	End diastolic volume
7.	Afterload
8.	Preload

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Factors affecting Cardiac output

It depends on two factors :

1. Heart rate, and

2. Stroke volume.

Cardiac output = heart rate X stroke volume

Heart rate is the number of heartbeats in one minute. The heart rate range is 70-80 bpm, and the average is 72 bpm.

The amount of blood pumped out by each ventricle in one beat is stroke volume. The normal range is 70-80 ml, and the average is 70 ml.

We know that blood volume is 5 liter, so whole blood circulates in the systemic and pulmonary circulation in one minute.

The cardiac index is the cardiac output per meter square of the body surface. In other words, cardiac output divided by body surface in square meters is the cardiac index. It is 3.2 liter /minute /meter square of the body surface.

Cardiac output depends on Heart rate and Stroke volume, and factors affecting these factors will also affect cardiac output.

Heart rate

Heart rate depends on

1. Sympathetic nerve stimulation increases the heart rate. The neurotransmitters are epinephrine and norepinephrine.

2. The parasympathetic nerve decreases the heart rate. The neurotransmitter is acetylcholine.

3. Hormones:

T3-T4 stimulates the myocardium's nucleus. This increases the number of epinephrine and norepinephrine receptors in the myocardium, which in turn increases the neurotransmitter's effects and the heart rate.

4. Body temperature –The body temperature affects the heart rate.

5. Baroreceptor stimulation decreases the heart rate by complex mechanisms through the parasympathetic and sympathetic nerve supply and

Vasomotor center (VMC)in the medulla.

6. Higher centers also increase and decrease the heart rate. Exercise, Excitement, fear,  and anger will increase or reduce the heart rate.

Stroke volume depends on the following:

1. Preload- End diastolic volume,

2. Contractility of heart, and

3. After load.

The end-diastolic volume(EDV) is the blood volume in the ventricles at the end of ventricular diastole. It is 120 ml.

The end-systolic volume (ESV) is the blood volume in the ventricles at the end of ventricular systole. It is 50 ml.

Stroke volume (SV) is blood volume pumped out by each ventricle in one beat. The normal range is 70-80 ml, and the average is 70 ml. It is EDV-ESV.

Ejection fraction is the percentage of EDV that ejected EDV's average value is 65%. ± 6%.

Preload causes stretching of myocardial muscles. The more significant the stretching, the greater the force of contraction, leading to more cardiac output.

EDV is responsible for the stretching of the myocardial muscles. EDV depends on venous return. More venous returns more EDV.

The venous return depends on the 

1. Muscle pump,

2. Respiratory pump,

3. Venomotor pump, and 

4. Ventricular diastolic suction.

In tachycardia -when the heart rate is fast diastolic phase becomes short. Therefore ventricular filling is reduced, and so is the EDV.

In pericardial effusion, the ventricular filling is reduced.

Myocardial contractility is an essential factor in deciding cardiac output. It depends on the sympathetic nerve supply. Epinephrine and norepinephrine stimulate protein kinase, which activates the transfer of Ca++ ions to the sarcoplasmic reticulum, and myocardial contractility increases.

Hormones T3-T4, Glucagon, epinephrine, norepinephrine, etc., increase myocardial contractility.

Drugs like xanthine, caffeine, digitalis, Dopamine, etc., increase myocardial contractility.

Afterload means resistance offered to the ventricular output. When the afterload increases, the stroke volume decreases. Afterload increases the work of the heart. It is raised in hypertension, coarctation of the aorta, infarction, and arteriolar constriction.

Changes in CO are associated with almost all cardiac diseases -hypertension, cardiomyopathy, heart failure, and other diseases-infection, sepsis, dehydration, etc.

Heart showing ECG

The amount of blood the cardiac output provides to various body parts for adequate tissue perfusion. Therefore, it is essential for heart efficiency to fulfill adequate tissue perfusion failure; CO fails to support the increased oxygen demand of the tissues. If not treated, the CO may reduce to such a level that it cannot maintain even simple activities.

Summary:

Knowledge of Cardiac Output is vital in diagnosing diseases and appropriate management.

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Hashtag:  Normal heart rate# Heart failure #Stroke volume# end diastolic volume # end-systolic volume #cardiac index # after load # pre load # ejection fraction

Internal Link: https:// blog.totalphysiology.com/2021/09/heart rate.html

https:// blog.totalphysiology.com/2021/09/BP regulation .html

https:// blog.totalphysiology.com/2022/11/ isometric-isotonic-contraction.html

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https://www.webmd.com>heart>h

 heart rate

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