Stroke volume (SV) refers to the amount of blood ejected by the left ventricle during each heartbeat. It is a key determinant of cardiac output and reflects the heart’s efficiency in circulating blood throughout the body. It plays a crucial role in determining cardiac output (CO), which is essential for maintaining adequate blood circulation.
Formula for Stroke Volume:
SV=EDV−ESVSV = EDV – ESVSV=EDV−ESV
Where:
- EDV (End-Diastolic Volume): Blood volume in the ventricle before contraction (~120 mL).
- ESV (End-Systolic Volume): Blood remaining in the ventricle after contraction (~50 mL).
- Normal SV Range: ~60–100 mL per beat.
Factors Affecting Stroke Volume:
- Preload: Ventricular filling before contraction (↑ preload = ↑ SV).
- Afterload: Resistance the heart must pump against (↑ afterload = ↓ SV).
- Contractility: Strength of heart muscle contraction (↑ contractility = ↑ SV).
Clinical Relevance:
- Heart Failure: Low SV leads to poor tissue perfusion.
- Exercise: SV increases to meet higher oxygen demand.
- Shock States: Low SV can indicate hypovolemia or cardiogenic shock.