**Core Concept**
Peripheral resistance in arteries refers to the opposition to blood flow that occurs due to the viscous nature of blood and the elastic properties of arterial walls. This resistance is crucial in regulating blood pressure and flow to various tissues and organs.

**Why the Correct Answer is Right**
The peripheral resistance is primarily measured by the formula: Peripheral Resistance (PR) = Mean Arterial Pressure (MAP) / Cardiac Output (CO). However, the most accurate and direct measure of peripheral resistance is obtained using the Ohm's law analogy, where PR is equivalent to resistance in an electric circuit. The correct answer is based on this analogy, where peripheral resistance is directly measured using the ratio of pressure drop to flow.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because peripheral resistance is not directly measured by cardiac output alone. While cardiac output affects peripheral resistance, it is not a direct measure.
**Option B:** This option is incorrect because peripheral resistance is not measured by blood pressure alone. Blood pressure is a result of the interplay between cardiac output, peripheral resistance, and vascular compliance.
**Option C:** This option is incorrect because peripheral resistance is not measured by vascular compliance alone. Vascular compliance affects blood pressure, but it is not a direct measure of peripheral resistance.

**Clinical Pearl / High-Yield Fact**
Peripheral resistance is a key determinant of blood pressure, and its measurement can help in assessing the severity of vascular diseases, such as hypertension and atherosclerosis. A high peripheral resistance can lead to increased blood pressure, which can cause damage to organs like the kidneys and brain.

**Correct Answer: D. The ratio of mean arterial pressure to cardiac output.**