Regarding calculation of stroke volume, NOT true is
**Core Concept**
Stroke volume (SV) is the amount of blood ejected by the left ventricle in one contraction, representing the volume of blood pumped from the ventricle into the aorta per beat. It is a critical determinant of cardiac output, which is the total volume of blood pumped by the heart per minute. The calculation of stroke volume involves understanding the relationship between ventricular volume and pressure.
**Why the Correct Answer is Right**
Stroke volume can be calculated using the formula: SV = (End-diastolic volume - End-systolic volume) / Heart rate. This formula represents the change in ventricular volume from the end of diastole (when the ventricle is fully relaxed) to the end of systole (when the ventricle is fully contracted). The correct answer will relate to this fundamental principle of cardiac physiology.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the formula for calculating stroke volume. The correct formula involves the difference between end-diastolic and end-systolic volumes, not just the end-diastolic volume.
**Option B:** This option is incorrect because it introduces an irrelevant factor. The calculation of stroke volume does not involve the measurement of systemic vascular resistance.
**Option C:** This option is incorrect because it misrepresents the relationship between stroke volume and heart rate. Heart rate affects cardiac output, not stroke volume directly.
**Clinical Pearl / High-Yield Fact**
A key point to remember when calculating stroke volume is that it is affected by the preload, afterload, and contractility of the heart. The Frank-Starling mechanism describes how an increase in preload (end-diastolic volume) leads to an increase in stroke volume, assuming the heart's contractility remains constant.
**Correct Answer: B. Systemic vascular resistance is not a factor in the calculation of stroke volume.**