Question

What would be the heart rate of a person if the cardiac output is 5L, blood volume in the ventricles at the end of diastole is 100 ml and at the end of ventricular systole is 50 ml?
A) 50 beats per minute
B) 75 beats per minute
C) 100 beats per minute
D) 125 beats per minute

Answer 1

Hint: Cardiac output is the measure of the amount of blood ejected by the left ventricle each minute. It can be measured by the product of stroke volume and heart rate. Stroke volume can be calculated by subtracting volume of diastole and systole. Stroke volume is equal to the volume of blood ejected from the left ventricle.

Complete answer:
Cardiac cycle is the complete cycle in which blood pumps in and out of the heart. It involves systole and diastole. It takes 0.8 seconds for the complete cardiac cycle. The volume of the blood pumped from left ventricles per beat gives the stroke volume.
Cardiac cycle is equal to the product of stroke volume and heart rate.
Given cardiac output = 5L or 5000 Ml
Blood volume present in the ventricles at the end of diastole = 100 ml
Blood volume in the ventricles at the end of systole = 50 ml
Remaining blood or Stroke volume = 100 – 50 = 50ml
 When we put all the values in the formula we get,
5000ml = 50 ml $\times$ Heart rate
Heart rate = 5000 ml/50ml
Heart rate = 100 beats per minute.

So, the correct answer is option C.

Note: The heart rate of an adult is between 60 and 100 beats per minute (bpm) in resting position. It depends on the person’s physical health condition and age. The normal resting heart rate of a child is between 70 and 100 bpm. Measurement of stroke volume can be done by using echocardiograms. Each ventricle has generally equal stroke volume. It is also used to calculate ejection fraction. Cardiac function is directly related to stroke volume.