Questions: What is the relationship between heart rate and cardiac output?

The answer is the first one: Cardiac output is the product of heart rate and stroke volume.

Explanation for each option:

1. Cardiac output is the product of heart rate and stroke volume: This is correct. Cardiac output (CO) is calculated by multiplying the heart rate (HR), which is the number of heartbeats per minute, by the stroke volume (SV), which is the amount of blood pumped by the heart with each beat. The formula is CO = HR x SV.

2. Heart rate is irrelevant to cardiac output: This is incorrect. Heart rate is a crucial component in determining cardiac output, as it directly affects the total volume of blood the heart pumps per minute.

3. Cardiac output is only determined by stroke volume: This is incorrect. While stroke volume is a factor in determining cardiac output, heart rate is equally important in the calculation.

4. Cardiac output is the sum of heart rate and stroke volume: This is incorrect. Cardiac output is not the sum but the product of heart rate and stroke volume.

5. Cardiac output is only determined by blood pressure: This is incorrect. Blood pressure is related to cardiac output but does not determine it. Cardiac output is specifically the product of heart rate and stroke volume.

In summary, cardiac output is determined by both heart rate and stroke volume, making the first option the correct answer.