Which condition best describes the pathophysiological mechanism behind hypertension?

Hypertension is primarily characterized by increased vascular resistance and/or blood volume. The pathophysiological mechanisms involve various factors, including increased systemic vascular resistance due to narrowing of the arteries, increased blood volume from fluid retention, or both.

When vascular resistance rises, the heart must work harder to pump blood through the narrowed or constricted vessels, leading to an elevation in arterial blood pressure. Additionally, conditions that result in increased blood volume can also contribute to hypertension. This might occur through mechanisms such as excessive sodium retention, which draws water into the bloodstream, thereby increasing total blood volume and contributing to higher blood pressure.

Other options do not accurately reflect the primary mechanisms of hypertension. Decreased cardiac output would typically lead to lowered blood pressure rather than hypertension. Decreased blood viscosity is not a common factor in hypertension; in fact, increased viscosity can occur in certain conditions but generally does not relate directly to hypertension itself. Increased heart rate alone may contribute to higher blood pressure, but it is not sufficient as a standalone mechanism to characterize hypertension, which primarily results from increased resistance and/or volume.