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How does the preload affect cardiac output?

A.

Decreased preload increases cardiac output.

B.

Increased preload decreases cardiac output.

C.

Increased preload increases cardiac output.

D.

Preload has no effect on cardiac output.

Answer and Explanation

The Correct Answer is C

A. Decreased preload increases cardiac output:
 Decreased preload reduces ventricular filling, leading to lower stroke volume and reduced cardiac output.

B. Increased preload decreases cardiac output:
 Increased preload generally increases stroke volume via the Frank-Starling mechanism, so it does not decrease cardiac output under normal physiological conditions.

C. Increased preload increases cardiac output:
 According to the Frank-Starling law, greater ventricular filling (preload) stretches cardiac fibers, resulting in a stronger contraction and higher stroke volume, thus increasing cardiac output.

D. Preload has no effect on cardiac output:
 Preload directly affects ventricular filling and stroke volume, which are critical determinants of cardiac output.


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Related Questions

Correct Answer is C

Explanation

A. S3:
S3 occurs during rapid ventricular filling in early diastole and may indicate volume overload or heart failure. It is not related to valve closure.

B. S1:
S1 corresponds to the closure of the atrioventricular (mitral and tricuspid) valves at the beginning of systole.

C. S2:
S2 occurs at the closure of the semilunar valves (aortic and pulmonic) at the end of systole, marking the onset of ventricular diastole. It is best heard at the base of the heart and is the normal “dub” sound.

D. S4:
S4 occurs during atrial contraction at the end of diastole and is associated with a stiff or hypertrophic ventricle. It is not a normal sound and does not correspond to semilunar valve closure.

Correct Answer is C

Explanation

A. Peripheral edema:
Peripheral edema is a hallmark of right ventricular failure, resulting from systemic venous congestion. While left ventricular failure may eventually lead to right-sided symptoms if chronic, it is not the initial manifestation.

B. Jugular venous distention:
Jugular venous distention indicates right-sided heart congestion due to elevated venous pressure, not left ventricular failure.

C. Pulmonary congestion:
Left ventricular failure causes fluid backup in the pulmonary circulation, leading to pulmonary edema, dyspnea, orthopnea, and crackles on auscultation. This occurs because the left ventricle cannot efficiently pump blood to the systemic circulation, raising pulmonary venous pressure.

D. Hepatomegaly:
Hepatomegaly occurs with right-sided heart failure, as venous congestion affects the liver. It is not a primary symptom of left ventricular dysfunction.

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