Chapter 19.9, Problem 37WDL

What is the cardiac output at rest and during exercise, and the cardiac reserve if (a) the heart rate is 75 beats per minute and stroke volume is 70 mL at rest, and (b) if the heart rate is 150 beats per minute and stroke volume is 100 mL during exercise?

Summary Introduction

To determine:

The cardiac output at rest and during exercise, and the cardiac reserve if (a) the heart rate is 75 beats per minute and stroke volume is $\text{70}\text{mL}$ at rest, and (b) if the heart rate is 150 beats per minute and stroke volume is $\text{100}\text{mL}$ during exercise.

Concept introduction:

The amount of blood, which is pumped by either ventricle in one minute, is known as “cardiac output” ( $CO$). The unit of cardiac output is liters per minute ( $L/min$). The increase in cardiac output by its level is known as cardiac reserve. The “cardiac reserve” is equal to difference of “cardiac output during exercise” and “cardiac output at rest”.

To determine:

The cardiac output at rest and during exercise and the cardiac reserve if the heart rate is 75 beats per minute and stroke volume is $\text{70}\text{mL}$ at rest.

Explanation of Solution

The product of stroke volume and heart rate is called cardiac output. The heart rate ( $HR$) is the number of “heartbeats” per minute ( $bpm$). The blood ejected out during contraction of ventricles is referred to as stroke volume ( $SV$). The heart rate is $75\text{beats}\text{per}\text{minute}$ and the stroke volume is $70\text{mL}$ at rest. The cardiac output is calculated as follows:

$\begin{array}{c}\text{CO}\\ \text{mL}\text{ejected}\text{per}\text{minute}\end{array}=\begin{array}{c}\text{HR}\\ \text{Beats}\text{per}\text{minute}\end{array}\times \begin{array}{c}\text{SV}\\ \text{mL}\text{ejected}\text{per}\text{beat}\end{array}$

$\begin{array}{c}\text{CO}=\frac{75\text{beats}}{\min }\times \frac{70\text{mL}}{\min }\\ \text{CO}=\text{5250}\text{mL}/\min \\ =5.25L/min\end{array}$

The cardiac reserve cannot be determined because the body is at rest and has not performed exercise.

Summary Introduction

To determine: The cardiac output at rest and during exercise and the cardiac reserve if the heart rate is 150 beats per minute and stroke volume is $\text{100}\text{mL}$ during exercise.

Explanation of Solution

The product of stroke volume and heart rate is called cardiac output. The heart rate ( $HR$) is the number of “heartbeats” per minute ( $bpm$). The blood ejected out during contraction of ventricles is referred to as stroke volume ( $SV$).

The heart rate is $75\text{beats}\text{per}\text{minute}$ and the stroke volume is $70\text{mL}$ at rest. The cardiac output is calculated as follows:

$\begin{array}{c}\text{CO}\\ \text{mL}\text{ejected}\text{per}\text{minute}\end{array}=\begin{array}{c}\text{HR}\\ \text{Beats}\text{per}\text{minute}\end{array}\times \begin{array}{c}\text{SV}\\ \text{mL}\text{ejected}\text{per}\text{beat}\end{array}$

$\begin{array}{c}\text{CO}=\frac{75\text{beats}}{\min }\times \frac{70\text{mL}}{\min }\\ \text{CO}=\text{5250}\text{mL}/\min \\ =5.25L/min\end{array}$

The heart rate is $150\text{beats}\text{per}\text{minute}$ and the stroke volume is $\text{100}\text{mL}$ during exercise. The cardiac output is calculated as follows:

$\begin{array}{c}\text{CO}\\ \text{mL}\text{ejected}\text{per}\text{minute}\end{array}=\begin{array}{c}\text{HR}\\ \text{Beats}\text{per}\text{minute}\end{array}\times \begin{array}{c}\text{SV}\\ \text{mL}\text{ejected}\text{per}\text{beat}\end{array}$

$\begin{array}{c}\text{CO}=\frac{150\text{beats}}{\min }\times \frac{100\text{mL}}{\min }\\ \text{CO}=1500\text{0}\text{mL}/\min \\ =15.00L/min\end{array}$

The “cardiac reserve” is equal to difference of “cardiac output during exercise” and “cardiac output at rest”. The cardiac reserve is calculated as follows:

$\begin{array}{c}\text{Cardiac}\text{reserve}=\text{Cardiac}\text{output}\text{during}\text{exercise}-\text{Cardiac}\text{output}\text{at}\text{rest}\\ =15.00\text{L}/\min -05.25\text{L}/\min \\ =09.75L/min\end{array}$

Conclusion

The cardiac output at rest is $5.25L/min$ and the cardiac reserve cannot be determined because the body does not perform any exercise.

The cardiac output during exercises is $15.00L/min$ and the cardiac reserve is $09.75L/min$.