In high altitude mountain sickness, feature of pulmonary edema isa) Decreased pulmonary capillary permeabilityb) Increased pulmonary capillary pressurec) Normal left atrial pressured) Increases left ventricular back pressure

**Core Concept**
High-altitude pulmonary edema (HAPE) is a life-threatening condition that occurs when individuals ascend to high altitudes too quickly, causing damage to the lungs and leading to fluid accumulation in the pulmonary capillaries.

**Why the Correct Answer is Right**
Pulmonary edema in HAPE is primarily caused by increased pulmonary capillary pressure, which is a result of hypoxic vasoconstriction. At high altitudes, the decrease in oxygen levels triggers vasoconstriction in the pulmonary arteries, leading to an increase in pulmonary capillary pressure. This increased pressure causes fluid to leak from the capillaries into the alveoli, resulting in pulmonary edema. The mechanism is closely related to the pathophysiology of hypoxic pulmonary vasoconstriction (HPV).

**Why Each Wrong Option is Incorrect**
* **Option A:** Decreased pulmonary capillary permeability is incorrect because the actual issue in HAPE is increased permeability, allowing fluid to leak into the alveoli.
* **Option C:** Normal left atrial pressure is incorrect because HAPE is characterized by increased pulmonary capillary pressure, which can lead to increased left atrial pressure as the fluid accumulates.
* **Option D:** Increased left ventricular back pressure is incorrect because the primary issue in HAPE is not left ventricular dysfunction but rather increased pulmonary capillary pressure.

**Clinical Pearl / High-Yield Fact**
HAPE is often preceded by symptoms such as cough, chest tightness, and shortness of breath, and can be diagnosed using chest X-rays showing bilateral interstitial edema.

**Correct Answer:** B. Increased pulmonary capillary pressure