In the described activity, which variable was altered?

In the described activity, which variable was altered?

• A. Stroke volume
• B. Heart rate
• C. Blood pressure
• D. Cardiac output

Answer: (A)

The central idea being tested is how much blood the heart ejects with each beat, known as stroke volume, and how altering that per-beat amount changes what the heart delivers per minute. In the described activity, the setup was aimed at changing the amount pumped per beat—by tweaking preload or contractility—while keeping the heart rate constant. That directly makes stroke volume the variable being modified. If the focus were on heart rate, we’d be adjusting how often the heart beats rather than how much blood is moved each beat; blood pressure can shift as a downstream result, and cardiac output is the product of heart rate and stroke volume, so it would change as a consequence rather than being the primary manipulated variable. Therefore, stroke volume is the best answer.

The central idea being tested is how much blood the heart ejects with each beat, known as stroke volume, and how altering that per-beat amount changes what the heart delivers per minute. In the described activity, the setup was aimed at changing the amount pumped per beat—by tweaking preload or contractility—while keeping the heart rate constant. That directly makes stroke volume the variable being modified. If the focus were on heart rate, we’d be adjusting how often the heart beats rather than how much blood is moved each beat; blood pressure can shift as a downstream result, and cardiac output is the product of heart rate and stroke volume, so it would change as a consequence rather than being the primary manipulated variable. Therefore, stroke volume is the best answer.