True about stroke volume is?
## **Core Concept**
Stroke volume (SV) is the amount of blood pumped by the left ventricle of the heart in one contraction, or heartbeat. It is a critical component of cardiac output (CO), which is the total amount of blood pumped by the heart per minute. Stroke volume is directly related to the heart's efficiency in pumping blood.
## **Why the Correct Answer is Right**
The correct answer relates to the definition and physiological determinants of stroke volume. Typically, stroke volume is about 70 mL/beat in a healthy adult and can increase with exercise or decrease in conditions like heart failure. It is influenced by preload (the initial stretching of the cardiac myocytes prior to contraction), contractility (the intrinsic ability of the heart muscle to contract), and afterload (the resistance the ventricles must overcome to eject blood during systole).
## **Why Each Wrong Option is Incorrect**
- **Option A:** Without specific details on option A, we cannot directly address its inaccuracies. However, any statement contradicting basic physiological principles of stroke volume (e.g., suggesting it is directly equivalent to cardiac output, or stating it does not change with exercise) would be incorrect.
- **Option B:** Similarly, without specifics, if option B suggests stroke volume is constant under all conditions or does not vary with changes in preload, contractility, or afterload, it would be incorrect.
- **Option C:** If option C provides an incorrect numerical value for a normal stroke volume or misrepresents how stroke volume relates to cardiac output (CO = SV * heart rate), it would be incorrect.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that stroke volume can be estimated using the formula: SV = end-diastolic volume (EDV) - end-systolic volume (ESV). Clinically, it is also relevant to note that stroke volume index (SVi), which normalizes stroke volume to body surface area, is a valuable measure for assessing left ventricular function on a per-body-size basis.
## **Correct Answer:** . 70 mL/beat.