What happens to the contractile force of the heart in heart failure?
Contractile force increases to compensate for the reduced cardiac output.
Contractile force increases, leading to an increased end systolic volume.
Contractile force is diminished due to damaged cardiomyocytes or cardiomyopathies.
Contractile force is not affected in heart failure.
Contractile force remains the same, but the heart becomes larger.
The Correct Answer is C
A. Contractile force increases to compensate for the reduced cardiac output: In early compensatory phases, the heart may attempt to increase contractility via sympathetic stimulation, but in true heart failure, the myocardium is unable to generate sufficient force due to structural or functional impairment.
B. Contractile force increases, leading to an increased end systolic volume: Increased contractility would reduce, not increase, end-systolic volume because more blood is ejected per beat. In heart failure, contractile weakness leads to higher end-systolic volumes, reflecting incomplete emptying of the ventricles.
C. Contractile force is diminished due to damaged cardiomyocytes or cardiomyopathies: Heart failure results from conditions such as myocardial infarction, chronic hypertension, or dilated cardiomyopathy that impair cardiomyocyte function. This reduces the strength of ventricular contraction, decreasing stroke volume and overall cardiac output.
D. Contractile force is not affected in heart failure: Contractile force is significantly affected in heart failure. The weakened myocardium cannot generate sufficient pressure to maintain normal stroke volume, making this statement inaccurate.
E. Contractile force remains the same, but the heart becomes larger: While ventricular dilation can occur in chronic heart failure as a compensatory mechanism (eccentric hypertrophy), the contractile force per myocyte is reduced. Increased chamber size alone does not preserve effective contraction.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Correct answer: True
During exercise, the sympathetic nervous system stimulates the sinoatrial (SA) node, which is located in the right atrium and functions as the heart’s natural pacemaker, leading to an increase in heart rate. This physiological response enhances cardiac output to meet the increased metabolic demands of skeletal muscles, delivering more oxygen and nutrients while removing carbon dioxide and metabolic waste. After exercise ceases, parasympathetic (vagal) tone gradually predominates, slowing SA node firing and allowing the heart rate to return toward its resting baseline. This recovery reflects normal autonomic regulation of cardiovascular function.
Correct Answer is B
Explanation
Correct answer: False
Preload refers to the degree of stretch of the ventricular myocardial fibers at the end of diastole, just before ventricular contraction. It is influenced by the volume of blood returning to the heart (venous return) and the compliance of the ventricular walls. End-diastolic volume (EDV) is the actual volume of blood present in the ventricle at the end of diastole. While preload is closely related to EDV, it is a functional measure of myocardial fiber stretch rather than a direct measurement of blood volume. Thus, preload describes the mechanical tension on the myocardium, whereas EDV quantifies the volume of blood in the chamber.
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