Stroke volume
Definition and Overview
Stroke volume (SV) is a term used in cardiology to describe the amount of blood pumped out of the left ventricle of the heart during each contraction or heartbeat. It is a crucial component of the cardiac cycle and is typically measured in milliliters (ml).
Calculation
Stroke volume can be calculated using the formula: SV = EDV - ESV. Here, EDV stands for end-diastolic volume, which is the total volume of blood in the ventricle immediately before a contraction, and ESV stands for end-systolic volume, which is the volume of blood remaining in the ventricle after a contraction.
Factors Influencing Stroke Volume
Several factors can influence stroke volume, including preload, afterload, and contractility.
Preload
Preload refers to the degree of stretch of the heart muscle at the end of diastole, just before contraction. The Frank-Starling law of the heart states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (the end diastolic volume) when all other factors remain constant.
Afterload
Afterload is the pressure that the heart must work against to eject blood during systole. Increased afterload (such as in hypertension) can decrease stroke volume because the heart has to work harder to pump the same amount of blood.
Contractility
Contractility refers to the inherent strength and vigor of the heart's contractions. Increased contractility (such as with sympathetic stimulation) increases stroke volume, while decreased contractility (such as with heart failure) decreases stroke volume.
Clinical Significance
Stroke volume is a critical parameter in cardiovascular physiology and is used to calculate cardiac output, which is the total volume of blood the heart pumps per minute. Abnormalities in stroke volume can lead to various cardiovascular disorders, including heart failure, hypertension, and cardiomyopathy.
Measurement
Stroke volume can be measured using several methods, including echocardiography, cardiac magnetic resonance imaging (MRI), and invasive hemodynamic monitoring.
Conclusion
Understanding stroke volume is crucial for clinicians and researchers in cardiology and critical care medicine. It provides valuable insights into the functioning of the heart and can help in diagnosing and managing various cardiovascular conditions.