If afterload increases while preload remains constant, what happens to stroke volume?

If afterload increases while preload remains constant, what happens to stroke volume?

• A. Stroke volume increases
• B. Stroke volume decreases
• C. Stroke volume remains unchanged
• D. Stroke volume becomes unpredictable

Answer: (B)

When afterload rises, the heart has to generate more pressure to eject blood, while the amount of blood in the ventricle at the start of contraction (preload) stays the same. If contractility hasn’t increased to meet the tougher resistance, the ventricle can push out less blood. As a result, more blood remains after systole, so end-systolic volume goes up. Since stroke volume is the difference between how much blood is in the ventricle at end-diastole and end-systole (SV = EDV − ESV), increasing ESV while EDV stays constant reduces stroke volume. So the stroke volume decreases.

When afterload rises, the heart has to generate more pressure to eject blood, while the amount of blood in the ventricle at the start of contraction (preload) stays the same. If contractility hasn’t increased to meet the tougher resistance, the ventricle can push out less blood. As a result, more blood remains after systole, so end-systolic volume goes up. Since stroke volume is the difference between how much blood is in the ventricle at end-diastole and end-systole (SV = EDV − ESV), increasing ESV while EDV stays constant reduces stroke volume. So the stroke volume decreases.