Main Heart Volumes
During blood ejection, the volume of the ventricles never drops to zero — it decreases only to its minimum value. Special parameters are used to assess the efficiency of this process.
End-Systolic Volume (ESV) is the portion of blood that physiologically remains in the ventricular cavity immediately after the completion of systole (contraction). Normally, this minimum value is about 60 ml.
Stroke Volume (SV) represents the amount of blood that the ventricle ejects into the vascular bed during one contraction cycle. It is important to remember a strict hemodynamic law: the right ventricle into the pulmonary trunk and the left ventricle into the aorta always eject the exact same volume of blood.
Stroke Volume is calculated as the difference between the End-Diastolic Volume (EDV) and the End-Systolic Volume (ESV). According to the classical formula, if EDV is 125 ml and ESV is 60 ml, then the stroke volume will be: 125 ml − 60 ml = 65 ml.
The Heart as a Piston Pump
Anatomical and functional features allow the heart to combine the properties of three different types of pumps at once. The first of these is the piston pump.
The base of the ventricles is rigidly fixed to the surrounding connective tissue structures, while the rest of the heart muscle remains mobile. Because of this, a specific mechanics arises:
- During the filling phase, the length of the heart increases.
- During muscle contraction, the length of the ventricles sharply decreases.
This translational movement anatomically and functionally strongly resembles the classical stroke of a piston in a medical syringe when mechanical fluid ejection occurs.
Centrifugal and Peristaltic Mechanisms
Centrifugal Pump Blood inside the heart chambers does not move in a straight line, but performs complex rotational movements. This effect of blood "spinning" in the cavity before ejection itself arises from two main reasons:
- The specific relief and structure of the inner surface of the ventricles themselves.
- Rotation, i.e., the turning of the ventricles around their longitudinal axis at the moment of their contraction.
Peristaltic Pump -The third mechanism is that the ejection of a portion of blood occurs not by a simultaneous spasm, but due to wave-like muscular contractions of the myocardium. The direction of this contractile wave is strictly predetermined: it always spreads from the apex of the heart to its base, smoothly "squeezing" blood into the great vessels.