Stroke Volume and Pressure-volume Boxes

In this video, we’ll delve into the intricacies of stroke volume and the use of pressure-volume (PV) boxes to simplify our understanding of cardiac function. Stroke volume is the amount of blood pumped by the left ventricle with each heartbeat, calculated by subtracting the end-systolic volume from the end-diastolic volume. We’ll explore the PV loop, a graphical representation of the changes in pressure and volume in the left ventricle during a cardiac cycle, highlighting its phases: isovolumetric contraction, ejection, isovolumetric relaxation, and filling. The area within this loop, known as stroke work, represents the heart's effort to eject blood.
PV boxes come into play as a simplified method to approximate the PV loop. By converting the complex loop into a rectangular shape, the PV box makes it easier to visualize and calculate stroke work. The height of the box represents the end-systolic pressure, while the width denotes the stroke volume. Although there are slight differences between the actual loop and the box, the overall areas are close enough for practical purposes. We’ll also discuss how changes in contractility, arterial elastance, and preload can alter the size and shape of the PV box, reflecting variations in cardiac function.
Join us as we break down these essential concepts, providing a clear and concise understanding of how the heart pumps blood and how these measurements are used in clinical practice.
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