What are stroke volume and cardiac output

Stroke volume and cardiac output are the core indicators for evaluating the pumping function of the heart. Stroke output refers to the amount of blood ejected from the ventricle in a single heartbeat, ranging from 60-100 milliliters. Cardiac output is the total amount of blood pumped out by the heart per minute, ranging from 4-8 liters per minute. Both are influenced by myocardial contractility, preload, afterload, and heart rate.

1. Stroke output:

Stroke output reflects the pumping efficiency of a single ventricular contraction, with a normal range of 60-100 milliliters. Its value depends on the pre load of ventricular end diastolic volume, post load of arterial blood pressure, and myocardial contractility. Excitement of the sympathetic nervous system during exercise can increase stroke volume, while heart failure patients may experience a decrease in this indicator due to a decrease in myocardial contractility.

2. Cardiac output:

Cardiac output is the total amount of blood pumped out by the heart per minute, calculated as stroke volume multiplied by heart rate. The normal resting state for adult males is about 5-6 liters per minute, while for females it is 10% -20% lower. Long term aerobic exercise can increase cardiac output by more than 30%, while this indicator will sharply decrease during hemorrhagic shock.

3. Influencing factors:

Increased myocardial contractility, such as adrenaline secretion during exercise, can simultaneously increase stroke volume and cardiac output. An increase in preload, such as rapid fluid replacement, mainly increases stroke volume, while an increase in afterload, such as hypertension, inhibits cardiac ejection. A heart rate greater than 160 beats per minute may decrease cardiac output due to insufficient ventricular filling.

4. Clinical significance:

Patients with heart failure often exhibit a decrease in stroke volume accompanied by compensatory increase in heart rate. Monitoring cardiac output is crucial for guiding the treatment of heart failure, and cardiac ultrasound and non-invasive cardiac output testing are commonly used evaluation methods. After cardiac surgery, patients need to maintain a cardiac output greater than 2.5 L/min/m ² to ensure organ perfusion.

5. Regulatory mechanism:

The body maintains stable cardiac output through Frank Starling mechanism preload regulation, autonomic nervous system regulation of sympathetic/parasympathetic, and humoral regulation of catecholamines and angiotensin. The athlete's heart achieves adaptive increase in stroke output through ventricular enlargement and myocardial hypertrophy. Regular aerobic exercise can enhance myocardial contractility and ventricular compliance. It is recommended to engage in 150 minutes of moderate intensity exercise such as brisk walking and swimming per week. Diet should control sodium intake to less than 5g per day, and consume more bananas and dark green vegetables rich in potassium and magnesium. Smoking can damage endothelial function, while quitting alcohol can prevent alcoholic cardiomyopathy. People over 40 years old are recommended to undergo annual electrocardiogram and cardiac ultrasound screening, and hypertensive patients need to regularly monitor blood pressure and ventricular function indicators.