Cardiac output is the volume of blood expelled from a heart ventricle during one minute. As a rule, cardiac output is the same for both ventricles.
Cardiac output (Q) is given by the product of systolic output (SV) and heart rate (HR); in order not to confuse the two terms, it is often preferred to speak of cardiac output.
Systolic output is the volume of blood pumped from a ventricle during a single contraction; it is sometimes called pulsatory throw.
Systolic output is measured in milliliters per heartbeat and corresponds to the following equation:
Heart rate expresses the number of heartbeats in one minute and is measured in bpm.
Cardiac output is expressed in dm3 / min (where 1 cubic decimeter equals one thousand cm3 or one liter). In resting conditions, the cardiac output of an average size man is equal to about 5 L / min, while during an incremental maximal physical effort the cardiac output can rise up to 20 L / min (35-40 L / min in professional athletes).
At rest, the systolic output is around 70 mL and can increase up to 90-100 mL during physical activity. Therefore, if we try to calculate the resting cardiac output with these data we obtain:
Cardiac output = 70 mL x 70 bpm = 4900 mL / min (approximately 5 L / min)
Therefore, in conditions of rest, each ventricle pumps all the blood present in the organism into circulation within a minute.
Pulse output in women is normally 25% lower than the corresponding value in men; this difference is explained by the greater dimensions of the male heart. Finally, in athletes, this parameter is higher than sedentary ones and is - already at rest - around 100 mL, while under effort it can even double.
These data clearly show that maximum cardiac output is higher in athletes than in sedentary; this increase concerns above all the systolic range, which in the athlete is about double.
The following graphs show the trend of heart rate, systolic output and cardiac output in the gradual transition from rest to increasingly intense exercise. Note how the range and heart rate increase in proportion to exacerbation of effort, while the maximum systolic range is already reached around 40-45% of VO2max (around 120 - 140 bpm).
