A patient's left ventricular end-diastolic volume is acutely raised by a fluid bolus. On the pressure-volume loop, the end-diastolic point moves rightward along the same end-diastolic pressure-volume relationship, and the end-systolic pressure-volume relationship (ESPVR) is unchanged. Which statement about the new steady state is correct?
- A The slope of the ESPVR has increased, indicating enhanced contractility
- B The slope of the ESPVR is unchanged, and stroke volume has increased purely by the Frank-Starling mechanism ✓
- C The ESPVR has shifted leftward, indicating reduced contractility
- D Both the slope and the x-intercept of the ESPVR have increased
Correct answer: B. The slope of the ESPVR is unchanged, and stroke volume has increased purely by the Frank-Starling mechanism
Explanation
The ESPVR is relatively load insensitive: its slope (end-systolic elastance) is an index of contractility and does not change with acute preload alteration. A pure preload increase moves the operating point along the same ESPVR, enlarging the loop width, so stroke volume rises by the Frank-Starling mechanism without any change in contractility. A steeper slope, option A, requires a genuine inotropic intervention such as sympathetic stimulation.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
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