Question

What would be the heart rate of a person if the cardiac output is 5 L, blood volume in the ventricles at the end of diastole is 100 mL and at the end of ventricular systole is 50 mL?

• A. 125 beats per minute
• B. 50 beats per minute
• C. 75 beats per minute
• D. 100 beats per minute

Answer 1

The correct option is D

100 beats per minute

Given:

Cardiac output $=5\mathrm{L}=5000\mathrm{mL}$

Blood volume in the ventricles at the end of diastole$=100\mathrm{mL}$

Blood volume in the ventricles at the end of ventricular systole$=50\mathrm{mL}$

Formulae used:

1. Stroke volume$=$Blood volume in the ventricles at the end of diastole$-$Blood volume in the ventricles at the end of ventricular systole
2. Cardiac output$=$Stroke volume$\times$Heart rate

Calculate the stoke volume as follows:

Stroke volume$=$Blood volume in the ventricles at the end of diastole$-$Blood volume in the ventricles at the end of ventricular systole

Substitute $100\mathrm{mL}$ for the blood volume in the ventricles at the end of diastole and $50\mathrm{mL}$ for the blood volume in the ventricles at the end of ventricular systole. Thus,

Stroke volume$=100\mathrm{mL}-50\mathrm{mL}$

Stroke volume$=50\mathrm{mL}$

Calculate the heart rate as follows:

Cardiac output$=$Stroke volume$\times$Heart rate

Substitute $5\mathrm{L}=5000\mathrm{mL}$ for the cardiac output of human heart and $50\mathrm{mL}$ for the stroke volume. Thus,

$5000\mathrm{mL}=50\mathrm{mL}\times$Heart rate

Thus,

Heart rate$=\frac{5000\mathrm{mL}}{50\mathrm{mL}}$

Heart rate$=100$ beats per minute.

Thus, the heart rate of a person if the cardiac output is 5 L, blood volume in the ventricles at the end of diastole is 100 mL and at the end of ventricular systole is 50 mL is 100 beats per minute.

Thus, Option D is correct.