Basic heart volumes
During blood expulsion, the ventricular volume never drops to zero — it only decreases 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) is the amount of blood that the ventricle ejects into the vascular bed during a single 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 end-diastolic volume (EDV) and end-systolic volume (ESV). According to the classical formula, if EDV is 125 ml and ESV is 60 ml, 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. This gives rise to a specific mechanism:
- During the blood filling phase, the length of the heart increases.
- During muscular contraction, the length of the ventricles sharply decreases.
This translational motion anatomically and functionally strongly resembles the classic stroke of a piston in a medical syringe when mechanical fluid expulsion 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 just before ejection occurs due to 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 expulsion of a portion of blood occurs not by a simultaneous spasm, but through wave-like muscular contractions of the myocardium. The direction of this contractile wave is strictly predetermined: it always propagates from the apex of the heart to its base, smoothly "squeezing" blood into the major vessels.
Briefly: answers to topical questions
What is end-diastolic volume (EDV) and what does it consist of?
End-diastolic volume is the volume of blood contained in the ventricle at the end of the filling period (diastole).
Key characteristics:
- Normal volume — for the left ventricle is 125 ml.
- Volume formation — blood enters from the atrium, and the volume increases from end-systolic to end-diastolic.
The direct addition formula is not provided in the text, however, stroke volume is equal to the difference between end-diastolic and end-systolic volumes. Accordingly, EDV is composed of stroke volume (65 ml) and end-systolic volume (60 ml).
What is cardiac output (CO) and by what formula is it calculated?
Cardiac output (CO) of the heart is an indicator that normally equals the blood flow through the lesser circulation. The formula for calculating CO is absent in the provided sources.
Normative values of the indicator:
- Resting state — is 3.5–5.5 L/min.
- Physical work — increases up to 30–40 L/min.
During moderate physical exertion, cardiac output can increase 2-fold, affecting the pressure in the pulmonary trunk.
To remember the three mechanisms of the pumping function, use the acronym PCP: Piston, Centrifugal, Peristaltic.
Class and exam questions
What is end-systolic volume (ESV)?
This is the volume of blood that remains in the ventricular cavity after the completion of systole. Normally, it is 60 ml.
How to calculate the heart's stroke volume?
Stroke volume is calculated as the difference between end-diastolic (EDV) and end-systolic (ESV) volumes. Normally this is 125 ml − 60 ml = 65 ml.
In what direction does the contraction wave travel across the ventricles?
Wave-like muscular contractions (peristaltic mechanism) are always directed from the apex of the heart to its base.
What else to study on this topic
- Regulation of stroke volume: preload and afterload
- Ejection fraction as a derivative parameter of SV and EDV
- The role of trabeculae in the rotational movement of blood
- The connection of the valve apparatus anatomy with the direction of ejection
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