What is the primary pathophysiological mechanism underlying benign prostatic hypertrophy (BPH)?

A. In symptomatic heart failure, it is physiologically impossible for the LVEDP to remain within a normal range because the heart cannot effectively empty. The residual volume after systole increases, which naturally raises the pressure at the end of the next filling phase. Maintaining a normal pressure range would imply that the heart's pumping efficiency is still preserved.

B. Heart failure is characterized by decreased ventricular compliance and impaired relaxation, which leads to an increase in pressure for any given volume. Compliance refers to the ability of the heart chamber to stretch; in failure, the walls become stiff or overstretched. Therefore, LVEDP rises significantly as the ventricle resists the incoming blood flow from the left atrium.

C. While LVEDP and cardiac output are related through the Frank-Starling mechanism, saying they are strictly inversely proportional is a physiological oversimplification. In the failing heart, the curve flattens, meaning that increasing LVEDP no longer results in an increased cardiac output. Eventually, the heart reaches a point where higher filling pressures actually lead to a further decline in stroke volume.

D. LVEDP increases because the weakened myocardium cannot eject blood efficiently, leading to high pressures that back up into the pulmonary veins. This increased hydrostatic pressure forces fluid into the alveolar spaces, which is the primary mechanism for pulmonary congestion and edema. Elevated LVEDP is a central hemodynamic finding that explains the shortness of breath in heart failure.

A. Increased compliance of the myocardium: A reduced ejection fraction is typically associated with a decrease in myocardial compliance or an overstretched, dilated ventricle. Increased compliance would suggest a ventricle that is overly distensible, which is not a primary indicator of systolic pumping failure. In systolic heart failure, the muscle wall is often weakened and unable to maintain the structural integrity required for force. This choice contradicts the hallmark of a failing, non-compliant cardiac pump.

B. Inability of the heart to effectively pump blood: The ejection fraction represents the percentage of blood the left ventricle pumps out with each contraction. A reduced EF, typically defined as < 40%, indicates a failure of myocardial contractility, also known as systolic heart failure. This means the heart cannot generate sufficient force to meet the metabolic demands of the body. It is the primary measurement used to quantify the severity of systolic ventricular dysfunction in clinical practice.

C. Elevated diastolic filling pressures: While elevated filling pressures are often present in heart failure, they are a consequence or a secondary finding rather than what the EF specifically measures. High pressures can occur in both systolic and diastolic failure. The ejection fraction is a strictly volumetric measurement of systolic output compared to the total end-diastolic volume. Therefore, pressure readings are distinct hemodynamic parameters that provide different information than the ejection fraction percentage.

D. Impaired relaxation of the ventricle: Impaired relaxation is the defining characteristic of diastolic heart failure, also known as heart failure with preserved ejection fraction (HFpEF). In these cases, the ejection fraction usually remains within a normal or near-normal range because the pump can still contract well. The problem in HFpEF is that the ventricle is too stiff to fill properly during diastole. A reduced ejection fraction specifically points to a contraction problem rather than a relaxation problem.