Question

question 45 (0.5 points)
a decrease in which of the following is an indicator of increased cardiac output?
sympathetic nervous system activity
cardiac force of contractility
end systolic volume
venous return

Explanation:

1. Recall the formula for cardiac output (CO): \( CO = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)} \), and stroke volume is \( SV = \text{End - Diastolic Volume (EDV)} - \text{End - Systolic Volume (ESV)} \).
2. Analyze each option:

• Sympathetic nervous system activity: An increase in sympathetic activity increases heart rate and contractility, thus increasing cardiac output. So a decrease in it would not indicate increased cardiac output.
• Cardiac force of contractility: An increase in contractility increases stroke volume and thus cardiac output. A decrease in it would not indicate increased cardiac output.
• End - systolic volume (ESV): If ESV decreases, since \( SV=EDV - ESV \), stroke volume (SV) increases (assuming EDV is constant or changes minimally). And since \( CO = SV\times HR \), an increase in SV (due to decreased ESV) leads to an increase in cardiac output. So a decrease in ESV is an indicator of increased cardiac output.
• Venous return: An increase in venous return increases end - diastolic volume (EDV), which increases stroke volume and thus cardiac output. A decrease in venous return would not indicate increased cardiac output.

Answer:

C. End systolic volume