What change would lead to an increase in cardiac output during exercise?

• A. Increased heart rate
• B. Decreased sympathetic nervous system activity
• C. Increased parasympathetic nervous system activity
• D. Decreased stroke volume

Answer: (A)

Verified step by step guidance

1. Understand the concept of cardiac output, which is the volume of blood the heart pumps per minute. It is calculated as the product of heart rate (HR) and stroke volume (SV). The formula is: $\mathrm{Cardiac} \mathrm{Output}=\mathrm{HR}\times \mathrm{SV}$.
2. Recognize that during exercise, the body requires more oxygen and nutrients, which necessitates an increase in cardiac output to meet these demands.
3. Identify the factors that can increase cardiac output: an increase in heart rate or an increase in stroke volume, or both.
4. Evaluate the options given: Increased heart rate would directly increase cardiac output as per the formula. Decreased sympathetic nervous system activity would typically reduce heart rate and stroke volume, thus decreasing cardiac output. Increased parasympathetic nervous system activity would also decrease heart rate, reducing cardiac output. Decreased stroke volume would lower cardiac output.
5. Conclude that the change leading to an increase in cardiac output during exercise is an increased heart rate, as it directly contributes to a higher cardiac output according to the formula.