Question

In a normal adult human, the average cardiac output (stroke volume) is:
(a) 47 ml
(b) 70 ml
(c) 5 litre
(d) 3.3 litre

Answer 1

Hint: Stroke volume is a term in cardiovascular physiology and is volume of blood pumped from the left ventricle per beat. Since stroke volume decreases in certain conditions and disease symptoms, determination of stroke volume gives an idea of the cardiac function.

Complete step by step answer:
- The stroke volume (SV) is a derivative of the cardiac output and is the volume of blood ejected by the left ventricle in one contraction or beat.
- Stroke volume for the average human being with 70 kg weight is 70 ml.
- It is calculated from an echocardiogram, which is an ultrasound of the heart. Here, ventricle volume is measured and the volume of the blood in the ventricle at the end of a beat is subtracted.
So, the correct answer is ‘70 ml’.

Additional information:
- Stroke volume is an important determinant of the cardiac output, which is the product of stroke volume and heart rate - the speed of heartbeat measured by beats per minute.
- Cardiac output is defined as the volume of blood being pumped by the left and right ventricle of the heart, per unit time.
- It is also used to calculate the ejection fraction, which is the volume of fluid ejected with each contraction. It is calculated by stroke volume divided by end-diastolic volume.
- The factors affecting the preload are distinguished as preload, contractility, and afterload.

Note:
- Stroke volume is 5 litres/min and 300 litres/hr.
- The volume increases during exercise.
- Men generally have higher stroke volumes than women due to the larger size of their heart.