## **Core Concept**
The rate of oxygen delivery to tissues at rest is determined by the **arteriovenous oxygen difference** and **cardiac output**. Oxygen delivery is crucial for meeting the metabolic demands of tissues.

## **Why the Correct Answer is Right**
The correct formula for the rate of oxygen delivery to tissues at rest is **DO2 = CO x CaO2**, where **DO2** is the oxygen delivery, **CO** is the cardiac output, and **CaO2** is the arterial oxygen content. However, when considering the extraction and utilization, it can also be related to **VO2 = CO x (CaO2 - CvO2)**, where **VO2** is the oxygen consumption, **CaO2 - CvO2** represents the arteriovenous oxygen difference, and **CO** is cardiac output. At rest, the body maintains a relatively constant oxygen delivery to meet basal metabolic needs.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the relationship between oxygen delivery and the factors influencing it, such as cardiac output and arteriovenous oxygen difference.
- **Option B:** This option is incorrect as it seems to misrepresent or oversimplify the physiological relationship between oxygen consumption, delivery, and utilization at rest.
- **Option D:** This option is incorrect because it inaccurately describes the physiological parameters related to oxygen delivery and consumption.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that at rest, the body's **oxygen extraction ratio** is approximately 25%, meaning that 25% of the oxygen delivered to tissues is extracted and used. This ratio can increase during exercise or in conditions of increased metabolic demand.

## **Correct Answer:** .