Altitude and Diving Physiology Practice Questions

Q: What is the earliest physiological change observed at high altitude?

Hyperventilation. **Explanation:** The primary physiological challenge at high altitude is **hypobaric hypoxia** (decreased barometric pressure leading to a lower partial pressure of inspired oxygen, $PiO_2$). **1. Why Hyperventilation is the Correct Answer:** The **earliest** response to high altitude is the **Hypoxic Ventilatory Response (HVR)**. As $PaO_2$ falls below 60 mmHg, peripheral chemoreceptors (primarily in the **carotid bodies**) are stimulated. They send signals to the medulla to increase the rate and depth of breathing. This occurs almost **instantaneously** (within seconds to minutes) upon exposure to low oxygen levels to improve alveolar oxygenation. **2. Analysis of Incorrect Options:** * **Decrease in work capacity (B):** This occurs shortly after arrival due to reduced oxygen delivery to muscles, but it is a consequence of the hypoxia that follows the initial respiratory attempt to compensate. * **Drowsiness (C):** This is a symptom of acute mountain sickness (AMS) or cerebral hypoxia. While it can occur early, it is a sign of compensatory failure rather than the first physiological adjustment. * **Polycythemia (D):** This is a **chronic/acclimatization** change. It takes days to weeks for erythropoietin to stimulate the bone marrow to significantly increase red blood cell production. **3. High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Alkalosis:** Hyperventilation causes a "washout" of $CO_2$ ($PCO_2$ ↓), leading to respiratory alkalosis. This is the most common acid-base disturbance at high altitude. * **Bohr Effect vs. 2,3-BPG:** Initially, alkalosis shifts the Oxygen-Dissociation Curve (ODC) to the **left**. Later, an increase in 2,3-BPG shifts it back to the **right** to facilitate oxygen unloading at tissues. * **Pulmonary Hypertension:** Hypoxia causes **hypoxic pulmonary vasoconstriction**, leading to increased pulmonary artery pressure (the basis for HAPE).

Q: A temporary increase in the number of circulating reticulocytes will most likely result when an individual:

Moves from sea level to a high altitude. **Explanation:** **Correct Option: D (Moves from sea level to a high altitude)** The primary physiological trigger for reticulocytosis (an increase in immature red blood cells) is **hypoxia**. When an individual moves to a high altitude, the partial pressure of oxygen ($PO_2$) decreases. This hypoxic state is sensed by the peritubular interstitial cells of the **kidneys**, which respond by increasing the synthesis and secretion of **Erythropoietin (EPO)**. EPO stimulates the bone marrow to increase erythropoiesis. Within 2–3 days, there is a measurable increase in the reticulocyte count as the body attempts to increase its oxygen-carrying capacity. **Incorrect Options:** * **A & C (Bacterial/Viral Infections):** These typically trigger a **leukocyte** (WBC) response. Bacterial infections usually cause neutrophilia, while viral infections often lead to lymphocytosis. They do not directly stimulate the erythropoietic pathway unless complicated by hemolysis or chronic disease. * **B (Vaccination):** Vaccinations stimulate the adaptive immune system (B and T lymphocytes) to produce antibodies and memory cells. They have no physiological effect on red blood cell production or EPO levels. **NEET-PG High-Yield Pearls:** * **Timeframe:** EPO levels rise within hours of altitude exposure, but reticulocytosis takes **2–5 days** to manifest in peripheral blood. * **Polycythemia:** Chronic exposure to high altitude leads to secondary polycythemia (increased hematocrit), which increases blood viscosity. * **Shift to the Right:** At high altitudes, there is an increase in **2,3-BPG**, which shifts the Oxygen-Dissociation Curve (ODC) to the right, facilitating oxygen unloading at the tissues. * **Alkalosis:** Hyperventilation at altitude causes respiratory alkalosis, which is later compensated by renal excretion of bicarbonate.

Q: During underwater diving, what is the main danger?

Oxygen and nitrogen. **Explanation:** Underwater diving involves breathing air at high ambient pressures, which significantly increases the partial pressure of gases in the blood and tissues. The primary dangers are associated with **Oxygen** and **Nitrogen**. 1. **Nitrogen (Nitrogen Narcosis & Bends):** At depths exceeding 100 feet, nitrogen exerts a narcotic effect on the CNS (often called "Rapture of the Deep"), similar to alcohol intoxication. Furthermore, during rapid ascent, dissolved nitrogen forms bubbles in the blood and tissues, leading to **Decompression Sickness (The Bends)**. 2. **Oxygen (Oxygen Toxicity):** Breathing oxygen at high partial pressures (hyperoxia) leads to the formation of free radicals. This can cause **CNS toxicity (Paul Bert Effect)**, resulting in seizures, and **Pulmonary toxicity (Lorrain Smith Effect)**, leading to lung damage. **Why other options are incorrect:** * **Carbon Monoxide:** This is a pollutant, not a physiological component of diving air. While accidental contamination of tanks can occur, it is not an inherent danger of the diving process itself. * **Oxygen/Nitrogen Only:** These options are incomplete. Both gases pose distinct, life-threatening risks at depth (toxicity and narcosis/decompression, respectively). **High-Yield Clinical Pearls for NEET-PG:** * **Haldane’s Rule:** Used to calculate decompression limits. * **Heliox:** To prevent nitrogen narcosis and reduce airway resistance, deep-sea divers use a mixture of Helium and Oxygen. * **Treatment:** The definitive treatment for Decompression Sickness is **Hyperbaric Oxygen Therapy (HBOT)** in a recompression chamber. * **Deepest Danger:** Nitrogen narcosis typically begins at ~3-4 atmospheres of pressure.

Q: What amount of dissolved oxygen is transported in 100 ml of plasma in a subject breathing 100% oxygen at 4 ATA?

9 ml. ### Explanation **1. Why Option A (9 ml) is Correct:** The amount of dissolved oxygen in plasma is governed by **Henry’s Law**, which states that the concentration of a dissolved gas is directly proportional to its partial pressure ($P_{O2}$). * At sea level (1 ATA), breathing room air, the $P_{O2}$ is ~100 mmHg, and the dissolved oxygen is **0.3 ml/100 ml** of blood. * The solubility coefficient of oxygen in plasma is **0.003 ml/100 ml/mmHg**. * At **4 ATA** (Atmospheres Absolute), the total pressure is $4 \times 760 \text{ mmHg} = 3040 \text{ mmHg}$. * Breathing **100% oxygen** at this pressure (ignoring water vapor pressure for simplification in exams) makes the $P_{O2} \approx 3000 \text{ mmHg}$. * **Calculation:** $3000 \text{ mmHg} \times 0.003 \text{ ml/mmHg} = \mathbf{9 \text{ ml/100 ml}}$. **2. Why Other Options are Incorrect:** * **Option B (6 ml):** This would be the dissolved oxygen at approximately 3 ATA breathing 100% $O_2$. * **Option C (3 ml):** This is the dissolved oxygen at 1.3 ATA breathing 100% $O_2$, or roughly 4 ATA breathing room air (21% $O_2$). * **Option D (0.3 ml):** This is the physiological "normal" value for dissolved oxygen in a healthy individual breathing room air at sea level (1 ATA). **3. Clinical Pearls & High-Yield Facts:** * **Hyperbaric Oxygen Therapy (HBOT):** At 3–4 ATA, the dissolved oxygen (6–9 ml) is sufficient to meet the body’s resting metabolic needs (approx. 5 ml/100 ml) even without hemoglobin. * **Oxygen Toxicity (Bert Effect):** Breathing 100% $O_2$ at high pressures can lead to CNS toxicity (seizures) due to the oxidation of enzymes and lipid peroxidation. * **Nitrogen Narcosis (Rupture of the Deep):** Occurs at high pressures (usually >4 ATA) due to the high lipid solubility of nitrogen affecting neuronal transmission.

Question 1

Acclimatization does NOT include which of the following?

Accepted Answer

Decreased concentration of 2,3-DPG in RBC

Answer

Hyperventilation

Answer

Increased erythropoiesis

Answer

Kidneys excrete more alkali

Question 2

What is the earliest physiological change observed at high altitude?

Accepted Answer

Hyperventilation

Answer

Decrease in work capacity

Answer

Drowsiness

Answer

Polycythemia

Question 3

In a person who has been acclimatized to high altitude for a long time, which of the following changes is observed?

Accepted Answer

Pulmonary arterial hypertension

Answer

Increased MCHC

Answer

Irregular respiration

Answer

Increased airway resistance

Question 4

A normal, healthy, 25-year-old man lives at sea level. His twin brother has been living in a mountain cabin for the past 2 years. Which of the following indices would be expected to be higher in the man living at sea level?

Accepted Answer

Diameter of pulmonary vessels

Answer

Erythropoietin production

Answer

Mitochondrial density in a muscle biopsy

Answer

Respiratory rate

Question 5

A temporary increase in the number of circulating reticulocytes will most likely result when an individual:

Accepted Answer

Moves from sea level to a high altitude

Answer

Has a bacterial infection

Answer

Received a vaccination against measles

Answer

Has a viral infection

Question 6

Hyperbaric oxygen is dangerous because it:

Accepted Answer

Is toxic to tissues

Answer

Decreases displacement of O2 from hemoglobin

Answer

Decreases respiratory drive

Answer

Causes enzyme damage

Question 7

Nitrogen narcosis is caused due to:

Accepted Answer

Increased solubility of nitrogen in nerve cell membrane

Answer

Nitrogen inhibits dismutase enzyme

Answer

Increase production of nitrous oxide

Answer

Decrease in oxygen free radicals

Question 8

During underwater diving, what is the main danger?

Accepted Answer

Oxygen and nitrogen

Answer

Carbon monoxide and nitrogen

Answer

Oxygen only

Answer

Nitrogen only

Question 9

A pilot in a Sukhoi aircraft is experiencing negative G. Which of the following physiological events will manifest in such a situation?

Accepted Answer

The cerebral arterial pressure rises

Answer

The hydrostatic pressure in veins of the lower limb increases

Answer

The cardiac output decreases

Answer

Blackout occurs

Question 10

What amount of dissolved oxygen is transported in 100 ml of plasma in a subject breathing 100% oxygen at 4 ATA?

Accepted Answer

9 ml

Answer

6 ml

Answer

3 ml

Answer

0.3 ml

Altitude and Diving Physiology — MCQs

Altitude and Diving Physiology — MCQs

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