Myocardial oxygen demand depends upona) Preloadb) Afterloadc) Intramyocardial tensiond) Blood Hb concentration
**Core Concept**
Myocardial oxygen demand is a critical factor in cardiac physiology, influenced by several key determinants. The main factors affecting myocardial oxygen demand include **preload**, **afterload**, **heart rate**, and **contractility**. Understanding these factors is essential for managing cardiac conditions.
**Why the Correct Answer is Right**
The correct answer is related to the factors that directly influence myocardial oxygen demand. **Preload** (the initial stretching of the cardiac myocytes prior to contraction) and **afterload** (the resistance against which the heart must pump blood) are primary determinants. **Intramyocardial tension**, which is directly related to the contraction force and thus to afterload and preload, also plays a role.
**Why Each Wrong Option is Incorrect**
**Option D:** Blood Hb concentration affects oxygen delivery but is not a direct determinant of myocardial oxygen demand.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that myocardial oxygen demand increases with increased **afterload** and **preload**, as well as with increased **heart rate** and **contractility**. This is crucial for understanding how to manage conditions like hypertension and heart failure.
**Correct Answer:** B. afterload