Cardiac output is the volume of blood expelled by a cardiac ventricle for one minute. As a rule, cardiac output is the same for both ventricles.
Cardiac output (Q) is given by the product of stroke volume (SV) for heart rate (FC); in order not to confuse the two terms, we often prefer to talk about cardiac output.
| Cardiac output or flow = stroke volume x heart rate |
Systolic range is the volume of blood pumped by a ventricle during a single contraction; sometimes it is called pulsatory range.
Systolic range is measured in milliliters per heartbeat and corresponds to the following equation:
| Systolic range = | ventricular blood volume before contraction | - | residual ventricular blood volume after contraction |
Heart rate expresses the number of heartbeats in a 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 a medium-sized man is about 5 L / min, while during a maximal physical effort of an incremental type the cardiac output can go up to 20 L / min (35-40 L / min in the professional athletes).
At rest, stroke volume is around 70 mL and can increase to 90-100 mL during physical activity. Therefore, if we try to calculate the cardiac output at rest with these data we get:
Cardiac output = 70 mL x 70 bpm = 4900 mL / min (about 5 L / min)
Therefore, in resting conditions, each ventricle circulates all the blood in the body within one minute in a circle.
The pulse range of women is normally 25% lower than the corresponding value in men; this difference is explained by the greater dimensions of the male heart. In athletes, finally, this parameter is superior to the sedentary and stands - already at rest - around 100 mL, while under stress can even double.
These data clearly show that the maximum cardiac output is higher in athletes than in sedentary patients; this increase mainly concerns the systolic range, which is about double in the athlete.
The following graphs show the trend of heart rate, stroke volume and cardiac output in the gradual transition from rest to increasingly intense exercise. Note how the flow rate and heart rate increase proportionally to the exacerbation of the effort, while the maximum systolic range is already reached around 40-45% of VO2max (around 120 - 140 bpm).
