Altitude and Diving Physiology Practice Questions

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: What is the approximate atmospheric pressure in pounds per square inch at sea level?

13-15. ### Explanation **1. Why the Correct Answer is Right:** Atmospheric pressure is defined as the force exerted by the weight of the air above a given point. At sea level, this pressure is standardized as **1 atmosphere (1 atm)**. In the Imperial system, this is equivalent to approximately **14.7 pounds per square inch (psi)**. In medical physiology, particularly when discussing diving or respiratory mechanics, we often use different units for the same value: * **1 atm = 760 mmHg (or 760 torr)** * **1 atm = 101.3 kPa** * **1 atm = 14.7 psi** (rounded to the range of 13–15 in many clinical texts). **2. Why the Incorrect Options are Wrong:** * **Option A (3 psi) & Option B (7 psi):** These values represent pressures at significantly high altitudes. For instance, at the summit of Mount Everest (approx. 29,000 ft), the atmospheric pressure drops to about 4.4 psi (roughly 1/3rd of sea level pressure). * **Option C (11 psi):** This represents the pressure at an intermediate altitude (approximately 8,000 feet), which is the standard cabin altitude for pressurized commercial aircraft. **3. High-Yield Clinical Pearls for NEET-PG:** * **Diving Physiology (Boyle’s Law):** For every **33 feet (10 meters)** of descent in seawater, the pressure increases by **1 atm (14.7 psi)**. Therefore, at a depth of 33 feet, the total pressure is 2 atm (29.4 psi). * **Alveolar Gas Equation:** Remember that while total atmospheric pressure decreases at altitude, the **fraction of oxygen (FiO2)** remains constant at 21%. Hypoxia at altitude is due to a decrease in the *partial pressure* of oxygen ($PO_2$), not a change in the percentage of oxygen. * **Nitrogen Narcosis:** Often called "Rapture of the Deep," this occurs due to the increased partial pressure of Nitrogen at high psi (usually starting at depths of 100+ feet).

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 is the most severe and persistent symptom of acute mountain sickness?

Headache. **Explanation:** Acute Mountain Sickness (AMS) is a syndrome caused by rapid ascent to high altitudes (typically above 2500m) where the partial pressure of oxygen is low. **Why Headache is the Correct Answer:** Headache is the **cardinal, most common, and most persistent symptom** of AMS. It is typically described as bitemporal or occipital, throbbing in nature, and worsens with exertion or lying flat. The underlying pathophysiology involves **hypoxia-induced cerebral vasodilation** and a breakdown of the blood-brain barrier, leading to mild cerebral edema. This increases intracranial pressure, which manifests primarily as a persistent headache. **Why other options are incorrect:** * **B. Dizziness:** While common in AMS (alongside nausea and fatigue), it is usually transient and less persistent than the headache. * **C. Drowsiness:** This is a "red flag" sign. If drowsiness or lethargy progresses to obtundation, it indicates a transition from AMS to **High-Altitude Cerebral Edema (HACE)**, a life-threatening emergency. * **D. Cyanosis:** This indicates severe hypoxemia. While it may occur at extreme altitudes, it is a clinical sign of respiratory failure or **High-Altitude Pulmonary Edema (HAPE)** rather than a primary symptom of standard AMS. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** AMS is a clinical diagnosis. The **Lake Louise Score** is the gold standard for assessment (Headache + at least one other symptom like GI upset, fatigue, or dizziness). * **Prophylaxis:** **Acetazolamide** (Carbonic anhydrase inhibitor) is the drug of choice; it induces metabolic acidosis, stimulating ventilation. * **Treatment:** The definitive treatment for severe symptoms is **immediate descent**. Dexamethasone is used for HACE, and Nifedipine (or Sildenafil) is used for HAPE.

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.

Q: Sudden decrease in atmospheric pressure in deep sea divers resulting in "bends" and "chokes" are features of which condition?

Air embolism. **Explanation:** The clinical scenario describes **Decompression Sickness (DCS)**, also known as "Caisson disease." This condition occurs due to **Henry’s Law**, which states that the solubility of a gas in a liquid is proportional to its partial pressure. 1. **Why Air Embolism is correct:** When a diver is deep underwater, high atmospheric pressure causes large amounts of Nitrogen to dissolve into the blood and tissues. If the diver ascends too rapidly (sudden decrease in pressure), the Nitrogen comes out of solution and forms **gas bubbles** in the blood and tissues. These bubbles act as **air emboli**, obstructing blood flow. * **"The Bends":** Bubbles in the joints and muscles causing severe pain. * **"The Chokes":** Bubbles in the pulmonary capillaries causing shortness of breath, chest pain, and cough. 2. **Why other options are incorrect:** * **Fat embolism:** Typically occurs after long bone fractures (e.g., femur) where marrow fat enters the circulation; it is not related to atmospheric pressure changes. * **Aspiration pneumonia:** Caused by inhaling foreign material (vomit/food) into the lungs, leading to inflammation/infection. * **Gangrene:** This is tissue death due to lack of blood supply or infection. While severe DCS can lead to necrosis (e.g., dysbaric osteonecrosis), it is a late complication, not the immediate mechanism of "bends and chokes." **NEET-PG High-Yield Pearls:** * **Nitrogen Narcosis:** Occurs at depth (high pressure) due to the anesthetic effect of nitrogen; often called "Rapture of the Deep." * **Treatment:** The definitive treatment for Decompression Sickness is **Hyperbaric Oxygen Therapy (HBOT)** in a recompression chamber. * **Helium-Oxygen (Heliox):** Used by deep-sea divers to prevent nitrogen narcosis because helium is less soluble and diffuses faster.

Question 1

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 2

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 3

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 4

What is the approximate atmospheric pressure in pounds per square inch at sea level?

Accepted Answer

13-15

Answer

3

Answer

7

Answer

11

Question 5

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 6

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 7

What is the most severe and persistent symptom of acute mountain sickness?

Accepted Answer

Headache

Answer

Dizziness

Answer

Drowsiness

Answer

Cyanosis

Question 8

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 9

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

Question 10

Sudden decrease in atmospheric pressure in deep sea divers resulting in "bends" and "chokes" are features of which condition?

Accepted Answer

Air embolism

Answer

Fat embolism

Answer

Aspiration pneumonia

Answer

Gangrene

Altitude and Diving Physiology — MCQs

Altitude and Diving Physiology — MCQs

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