**Question:** During acclimatization to high altitude all of the following takes place except

A. Increased cardiac output
B. Hypoxic pulmonary vasoconstriction
C. Increased respiratory rate
D. Pulmonary hypertension

**Core Concept:** Acclimatization to high altitude is the body's response to hypoxia (low oxygen levels) that occurs when moving from low altitude to high altitude. The body adapts to hypoxia by initiating various physiological changes to improve oxygen delivery and utilization.

**Why the Correct Answer is Right:** Option D (Pulmonary hypertension) is not a part of the process of acclimatization to high altitude. While acclimatization involves several physiological changes, pulmonary hypertension refers to an increase in blood pressure in the pulmonary arteries, which is primarily a response to chronic hypoxia and is unrelated to the initial phase of acclimatization.

**Why Each Wrong Option is Incorrect:**

A. Increased cardiac output: This is a correct response during the initial phase of acclimatization, as the body aims to increase the amount of oxygen delivered to tissues.

B. Hypoxic pulmonary vasoconstriction: This is also a correct response, as it is a protective mechanism that narrows the pulmonary arteries in the hypoxic lung areas, allowing better oxygenation of the remaining lung tissue.

C. Increased respiratory rate: This is a correct response, as the body increases ventilation to compensate for the decreased oxygen content in the inspired air at high altitudes.

**Clinical Pearl:**

Acclimatization to high altitude is a critical process that helps maintain homeostasis in the face of decreased oxygen levels. The correct physiological responses include increased cardiac output, hypoxic pulmonary vasoconstriction, and increased respiratory rate, while pulmonary hypertension is a response to chronic hypoxia and not part of the initial adaptation processes. Understanding these responses and their significance is essential for medical professionals, especially in areas with high altitude populations or for those involved in mountaineering and altitude travel.