Q.101. Which ONE of the following graphs represents the relationship between ventricular enddiastolic volume and cardiac output in a healthy adult individual at rest (solid line) and upon exercise
(dotted line)?
Introduction
The relationship between ventricular end-diastolic volume (EDV) and cardiac output (CO) is a fundamental concept in cardiovascular physiology. It is governed primarily by the Frank–Starling law of the heart, which states that an increase in ventricular filling leads to a stronger contraction and increased stroke volume, up to a physiological limit.
In a healthy adult, this relationship differs between rest and exercise due to changes in:
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Sympathetic stimulation
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Myocardial contractility
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Heart rate
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Venous return
The question asks which graph correctly represents this relationship at rest (solid line) and during exercise (dotted line).
Correct Answer
✅ Option (A) isIght curve shifted upward during exercise
Why Option (A) Is Correct
Option (A) correctly illustrates the Frank–Starling curve:
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At rest (solid line):
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Cardiac output increases with EDV but eventually plateaus.
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During exercise (dotted line):
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The curve shifts upward and to the left.
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For the same EDV, cardiac output is higher.
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Physiological Basis
During exercise:
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Sympathetic stimulation increases myocardial contractility
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Stroke volume and heart rate increase
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Cardiac output rises at any given EDV
This upward shift reflects enhanced pumping efficiency, which is exactly what Option (A) shows.
Explanation of All Options
Option (A): Correct ✅
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Shows a positive, saturating relationship between EDV and cardiac output
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Exercise curve lies above resting curve
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Matches Frank–Starling physiology and real cardiovascular response
Option (B): Incorrect ❌
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Exercise (dotted line) lies below resting curve
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This would imply reduced cardiac output during exercise, which is physiologically impossible in a healthy adult
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Contradicts increased sympathetic tone and contractility
Option (C): Incorrect ❌
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Shows cardiac output decreasing with increasing EDV
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Violates the Frank–Starling law
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Such a pattern may be seen only in severe heart failure, not in healthy individuals
Option (D): Incorrect ❌
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Both curves slope downward
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Suggests increased filling reduces cardiac output
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This is physiologically incorrect and inconsistent with normal or exercise conditions
Key Concept: Frank–Starling Law
Within physiological limits, the heart pumps what it receives.
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Increased venous return → increased EDV
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Increased EDV → increased stroke volume
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Exercise enhances this relationship by increasing contractility
Exam Tip (GATE / NEET / Physiology)
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Always look for an upward-shifted curve during exercise
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Exercise never reduces cardiac output in a healthy heart
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Any graph showing a downward slope is immediately wrong
Final Takeaway
✔ The correct graph is the one where cardiac output increases with ventricular end-diastolic volume, and the exercise curve lies above the resting curve.
