Cardiac output is the product of heart rate and what parameter?

• A. Stroke volume
• B. Cardiac stroke rate
• C. Blood pressure
• D. Oxygen content

Answer: (B)

The amount of blood the heart moves per minute is determined by two factors: how fast the heart beats (heart rate) and how much blood is ejected with each beat (stroke volume). Cardiac output is the product of these two, so CO = HR × SV. Stroke volume—the amount of blood expelled from the ventricle with a single contraction—provides the per-beat quantity needed to translate heart rate into total output. Blood pressure is a pressure measure in the arteries, not a per-beat volume, and oxygen content describes how much oxygen is carried in the blood, not how much blood is pumped per minute. So the multiplying factor with heart rate to yield cardiac output is the amount ejected per beat, i.e., stroke volume. For example, with a heart rate of 70 beats per minute and a stroke volume of about 0.07 liters per beat, cardiac output is roughly 4.9 liters per minute.