**Core Concept**
Pulse pressure is the difference between systolic and diastolic blood pressures, reflecting the elastic properties of the arterial system and the force of cardiac contraction. It is an important indicator of arterial stiffness and cardiovascular health.

**Why the Correct Answer is Right**
Pulse pressure is significantly affected by arterial stiffness, as stiffer arteries are less able to cushion the force of the pulse, leading to increased systolic pressure and decreased diastolic pressure. This is due to the reduced compliance of the arterial wall, which is characterized by a lower aortic pulse wave velocity. Additionally, factors such as age, hypertension, and atherosclerosis can also contribute to increased arterial stiffness and altered pulse pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Cardiac output is not a direct determinant of pulse pressure, although it may influence blood pressure levels indirectly through changes in peripheral resistance and cardiac contractility.
**Option B:** Peripheral resistance is a factor in blood pressure regulation, but it does not directly affect pulse pressure, which is primarily influenced by arterial stiffness and cardiac contractility.
**Option C:** Heart rate can influence cardiac output and blood pressure levels, but it does not directly affect pulse pressure, which is more closely related to arterial stiffness and cardiac contractility.

**Clinical Pearl / High-Yield Fact**
Aortic pulse wave velocity is a reliable indicator of arterial stiffness and is closely correlated with pulse pressure. This non-invasive measure can be used to assess cardiovascular risk and monitor the effects of antihypertensive therapy.

**Correct Answer:** D. Arterial stiffness.