Question

Which of the following does NOT increase left ventricular stroke volume?

A) Increasing the preload (the stretch of cardiac muscle fibers by increased venous return)
B) Increasing the contractility of cardiac muscle
C) Increasing the peripheral resistance (afterload)
D) The positive inotropic effect of thyroid hormone

Answer 1

Increasing peripheral resistance (afterload) does not increase left ventricular stroke volume; instead, it makes the heart work harder to pump blood, potentially decreasing stroke volume.

Step-by-step explanation:

The option that does NOT increase left ventricular stroke volume is Increasing the peripheral resistance (afterload). Stroke volume (SV) is the amount of blood pumped by the left ventricle of the heart in one contraction. Increasing the preload, which is the stretch of cardiac muscle fibers due to increased venous return, increases the contractility of the cardiac muscle, resulting in a larger SV according to the Frank-Starling mechanism.

Additionally, positive inotropic effects, such as those of thyroid hormone, also increase contractility and thereby SV. However, increasing peripheral resistance (afterload) requires the heart to work harder to overcome the resistance, which can ultimately lead to a decrease in SV.