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The following graph depicts a set of Frank–Starling curves. Which of the following BEST represents the change that occurs after a fluid bolus is administered to an individual with normal left ventricular function?
Answer: (A) Movement along the curve (arrow A). Read the discussion.
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Discussion
The Frank–Starling law was conceptualized by Otto Frank and Ernest Henry Starling (Figure 1) in the early 20th century. The law states that myocardial performance increases as myocardial muscle is stretched; however, overstretching eventually leads to a decrease in performance. This is an intrinsic property of muscle fibers. In terms of cardiac function, the Frank–Starling Law states that there is a point of cardiac preload where cardiac function is optimal, and that increasing preload beyond this point leads to reduced cardiac performance or even failure. Figure 2 depicts a stylized set of Frank–Starling curves for a cardiac ventricle.
Figure 1. German physiologist Otto Frank (left) and British physiologist Ernest Henry Starling (right), both credited independently with providing knowledge regarding the relationship between end-diastolic volume and stroke volume now known as the Frank–Starling law. Images courtesy of Wikipedia. https://en.wikipedia.org/wiki/File:Otto_frank_physiologist.jpg; https://commons.wikimedia.org/wiki/File:Ernest_Starling_portrait.jpg
Figure 2. Moving from lower to higher, the y-axis represents increasing cardiac performance or stroke volume. Moving from left to right, the x-axis represents increasing myocardial stretch or myocardial filling (left ventricular end-diastolic pressure, or LVEDP). The middle curve (arrow A) is the normal curve. When an inotropic agent is administered, the curve will shift upwards, indicating improved myocardial performance at the same myocardial stretch (arrow B). When myocardial failure develops, the curve shifts downwards, indicating decreased myocardial performance at the same myocardial stretch (arrow C). When fluids are administered, the position of the curve on the graph does not change, but the performance of the ventricle (stroke volume) moves along the curve, according to the LVEDP. Overstretching the myocardial muscle (or overfilling the ventricle) will lead to decreased myocardial performance and manifest as fluid overload. © 2021 American Society of Anesthesiologists.
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