Definitions of stroke volume, preload definition & Factors influencing stroke volume

• Stroke volume is directly correlated with cardiac output-the greater the stroke volume the greater the cardiac output. • Stroke volume represents the difference in the amount of blood between: • the volume in the ventricles at the end of diastole (end-diastolic volume EDV); • the volume after systole (end-systolic volume ESV). • Normal resting stroke volume is 70 ml. • Three factors affect stroke volume: • Preload is the amount of stretch of ventricular muscle before the contraction starts • Contractility is the forcefulness of ventricular muscle contraction. • Afterload is the pressure that must be overcome before ventricles can eject blood. • Preload is the degree of stretch of cardiac muscles cells prior to contraction. • The amount of stretch is related to the end-diastolic volume[EDV]. • Increased return blood flow from the veins increases end-diastolic volume. Cardiac muscle sarcomeres stretch and lengthen. • Contraction of the cardiac it muscle sarcomeres during ventricular systole provides the force needed to eject blood from the heart.

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