Altitude and Diving Physiology Practice Questions

Q: Ascent to high altitude may cause all of the following except:

Cerebral palsy. **Explanation:** The physiological changes at high altitude are primarily driven by **hypobaric hypoxia** (low partial pressure of oxygen). **Why Cerebral Palsy is the correct answer:** Cerebral palsy is a non-progressive clinical syndrome resulting from an insult to the **developing fetal or infant brain** (typically due to birth asphyxia, infection, or trauma). It is a developmental neurological disorder and is not an acute or chronic manifestation of high-altitude exposure in adults or children. **Analysis of incorrect options:** * **Cerebral Edema (HACE):** High Altitude Cerebral Edema occurs due to hypoxia-induced cerebral vasodilation and increased capillary permeability (vasogenic edema). It is a life-threatening emergency. * **Pulmonary Edema (HAPE):** Hypoxia causes **hypoxic pulmonary vasoconstriction (HPV)**. When this is uneven or severe, it leads to increased pulmonary capillary hydrostatic pressure and leakage of fluid into the alveoli. * **Venous Thrombosis:** High altitude increases the risk of thromboembolism due to a "Virchow’s triad" effect: **Hemoconcentration** (increased hematocrit due to erythropoietin release), dehydration, and relative stasis during cold-induced inactivity. **High-Yield Clinical Pearls for NEET-PG:** * **HAPE** is the most common cause of death related to high altitude. * **Acetazolamide** (a carbonic anhydrase inhibitor) is the drug of choice for prophylaxis of Acute Mountain Sickness (AMS) as it induces metabolic acidosis, stimulating ventilation. * **Nifedipine** is used for the prevention/treatment of HAPE by reducing pulmonary artery pressure. * **Dexamethasone** is the drug of choice for HACE.

Q: Monge's disease refers to:

High Altitude Erythrocytosis. **Explanation:** **Monge’s Disease**, also known as **Chronic Mountain Sickness (CMS)**, is a condition that develops in long-term residents of high altitudes (usually above 3,000 meters). **Why the correct answer is right:** The hallmark of Monge’s disease is **High Altitude Erythrocytosis**. Due to chronic exposure to low partial pressure of oxygen ($FiO_2$), the body overproduces erythropoietin, leading to an excessive increase in red blood cell mass (hematocrit often >65%). This results in extreme blood hyperviscosity, leading to symptoms like cyanosis, fatigue, headache, and right-sided heart failure (cor pulmonale). **Why the incorrect options are wrong:** * **Primary Familial Polycythemia:** This is a genetic condition caused by mutations in the erythropoietin receptor; it is not triggered by altitude. * **Spurious Polycythemia (Gaisbock’s Syndrome):** This occurs when plasma volume decreases (e.g., dehydration or stress), making the RBC count appear high relatively, though the total RBC mass remains normal. * **Polycythemia Vera:** This is a myeloproliferative neoplasm (primary polycythemia) caused by a mutation in the **JAK2 gene**, leading to autonomous RBC production regardless of oxygen levels. **High-Yield Clinical Pearls for NEET-PG:** * **Treatment:** The definitive treatment for Monge’s disease is **descent to lower altitudes**. Periodic phlebotomy can provide symptomatic relief. * **Acetazolamide:** Often used for Acute Mountain Sickness (AMS), it works by inducing metabolic acidosis, which stimulates ventilation. * **Key Distinction:** Unlike Acute Mountain Sickness or HAPE, Monge’s disease is a **chronic** maladaptation to altitude.

Q: Which of the following is seen in high altitude climbers?

Decreased PaCO2. **Explanation:** The primary physiological challenge at high altitude is the decrease in barometric pressure, which leads to a lower partial pressure of inspired oxygen ($PiO_2$). This results in **hypoxia**. **Why B is the correct answer:** In response to hypoxia, peripheral chemoreceptors (carotid and aortic bodies) are stimulated, leading to **hyperventilation**. While hyperventilation (Option A) is a physiological *process* that occurs, the question asks what is *seen* (the biochemical result) in the climber. Increased ventilation causes excessive "washing out" of Carbon Dioxide from the lungs. This leads to **Hypocapnia** (Decreased $PaCO_2$) and subsequent respiratory alkalosis. This decrease in $PaCO_2$ is a hallmark finding in acute altitude exposure. **Analysis of Incorrect Options:** * **A. Hyperventilation:** While this occurs, it is the *mechanism* rather than the resultant laboratory/blood gas finding. In many competitive exams, if both a process and its direct chemical result are listed, the specific biochemical change ($PaCO_2$) is often the preferred answer. * **C. Pulmonary Edema:** High Altitude Pulmonary Edema (HAPE) is a pathological complication, not a universal finding in all climbers. It occurs due to uneven hypoxic pulmonary vasoconstriction. * **D. Hypertension:** Systemic hypertension is not a standard finding; however, **Pulmonary Hypertension** occurs due to hypoxic pulmonary vasoconstriction. **High-Yield Clinical Pearls for NEET-PG:** * **Oxygen Dissociation Curve:** Initially shifts to the **right** (due to increased 2,3-BPG) to favor oxygen unloading at tissues. * **Polycythemia:** Chronic exposure stimulates Erythropoietin (EPO) release from the kidneys, increasing RBC count. * **Acetazolamide:** The drug of choice for Acute Mountain Sickness (AMS); it inhibits carbonic anhydrase, causing bicarbonate diuresis and metabolic acidosis, which counteracts the respiratory alkalosis and stimulates breathing.

Q: Which of the following metabolic changes are observed in acclimatization?

Respiratory alkalosis. **Explanation:** The primary physiological challenge at high altitude is the decrease in the partial pressure of oxygen ($PO_2$), leading to **hypoxia**. **1. Why Respiratory Alkalosis is Correct:** In response to hypoxia, peripheral chemoreceptors (carotid and aortic bodies) are stimulated, leading to **hyperventilation**. This increased rate and depth of breathing "wash out" carbon dioxide ($CO_2$) from the blood. According to the Henderson-Hasselbalch equation, a decrease in $PCO_2$ (hypocapnia) raises the blood pH, resulting in **Respiratory Alkalosis**. This is the hallmark initial acid-base change in altitude acclimatization. **2. Why other options are incorrect:** * **Metabolic Alkalosis (A):** This would involve an increase in bicarbonate ($HCO_3^-$), which does not occur. In fact, the kidneys compensate for respiratory alkalosis by *excreting* bicarbonate. * **Metabolic Acidosis (B):** While the compensatory phase involves a decrease in bicarbonate (mimicking a metabolic acidosis pattern), the primary driving change is respiratory. * **Respiratory Acidosis (D):** This occurs when $CO_2$ is retained (e.g., COPD or hypoventilation), which is the opposite of what happens at altitude. **High-Yield Clinical Pearls for NEET-PG:** * **Bicarbonate Compensation:** After 24–48 hours, the kidneys increase the excretion of $HCO_3^-$ to normalize pH. This is why **Acetazolamide** (a carbonic anhydrase inhibitor) is used for prophylaxis; it forces bicarbonate excretion, creating a mild metabolic acidosis that stimulates ventilation. * **Oxygen Dissociation Curve:** Initially, alkalosis shifts the curve to the **left** (increasing $O_2$ affinity). However, with prolonged stay, 2,3-BPG levels increase, shifting the curve back to the **right** to facilitate oxygen unloading at tissues. * **Polycythemia:** Hypoxia stimulates Erythropoietin (EPO) release, leading to increased RBC production over weeks.

Q: High-altitude acclimatization may be facilitated by all of the following except?

Growth of new skeletal muscle fibers. **Explanation:** The physiological response to high altitude is centered on overcoming **hypoxia** (decreased oxygen availability). Acclimatization involves mechanisms that improve oxygen delivery and utilization at the cellular level. **Why Option D is the correct answer:** Acclimatization does **not** involve the growth of new skeletal muscle fibers (hyperplasia). In fact, prolonged exposure to high altitude often leads to a **decrease in muscle fiber diameter** (atrophy). This reduction in muscle mass is an adaptive mechanism that decreases the distance oxygen must travel from the capillaries to the mitochondria, thereby improving diffusion efficiency. **Analysis of Incorrect Options:** * **A. Increased RBC production:** Hypoxia stimulates the kidneys to release **Erythropoietin (EPO)**, which increases red blood cell production (polycythemia). This increases the oxygen-carrying capacity of the blood. * **B. Increased alveolar ventilation:** Low partial pressure of oxygen ($PO_2$) stimulates peripheral chemoreceptors, leading to hyperventilation. This helps blow off $CO_2$ and increases the alveolar $PO_2$. * **C. Growth of new blood vessels:** Chronic hypoxia triggers **Angiogenesis** (increased capillary density) in tissues, particularly in the heart and skeletal muscles, to shorten the diffusion path for oxygen. **NEET-PG High-Yield Pearls:** 1. **2,3-BPG:** Acclimatization leads to an increase in 2,3-Bisphosphoglycerate, which shifts the Oxygen-Dissociation Curve (ODC) to the **right**, facilitating oxygen unloading at the tissues. 2. **Acid-Base Balance:** Hyperventilation causes **Respiratory Alkalosis**. The kidneys compensate by increasing bicarbonate excretion (Acetazolamide can be used to speed up this process). 3. **Pulmonary Hypertension:** Hypoxia causes pulmonary vasoconstriction, which can lead to Right Ventricular Hypertrophy and High-Altitude Pulmonary Edema (HAPE).

Q: In deep sea divers, decompression illness is mainly due to which factor?

Nitrogen gas. **Explanation:** **Decompression Sickness (Caisson Disease/The Bends)** occurs due to the principles of **Henry’s Law**, which states that the solubility of a gas in a liquid is directly proportional to its partial pressure. 1. **Why Nitrogen is the correct answer:** When a diver descends, the high ambient pressure causes large amounts of **Nitrogen** (a relatively inert gas) to dissolve into the blood and tissues (especially fat). If the diver ascends too rapidly, the ambient pressure drops quickly, and the dissolved nitrogen comes out of solution faster than it can be exhaled. This leads to the formation of **nitrogen gas bubbles** in the blood and tissues. These bubbles cause mechanical obstruction (emboli), joint pain ("the bends"), and neurological symptoms. 2. **Why other options are incorrect:** * **Oxygen narcosis:** High partial pressures of oxygen can be toxic to the CNS (causing seizures), but oxygen is rapidly metabolized by tissues and does not form bubbles during ascent. * **Hypoxia:** This refers to low oxygen levels. While it can occur if gas mixtures are incorrect, it is not the mechanism behind decompression illness. * **Carbon dioxide narcosis:** CO₂ retention can cause respiratory acidosis and narcosis, but it is highly soluble and does not form the bubbles characteristic of decompression sickness. **High-Yield Clinical Pearls for NEET-PG:** * **Henry’s Law:** Governs decompression sickness. * **Haldane’s Principle:** Used to calculate decompression stages. * **Treatment:** 100% Oxygen and **Hyperbaric Oxygen Therapy (HBOT)** to re-dissolve the bubbles. * **Prevention:** Divers use **Helium-Oxygen (Heliox)** mixtures because Helium is less soluble in body tissues and has a lower molecular weight, making it easier to breathe at depth. * **Chokes:** A severe form of decompression sickness involving nitrogen bubbles in the pulmonary capillaries, leading to dyspnea and cough.

Q: Which of the following agents may be used as prophylaxis in high altitude pulmonary edema?

Nifedipine. **Explanation:** **High Altitude Pulmonary Edema (HAPE)** is a non-cardiogenic pulmonary edema caused by exaggerated **hypoxic pulmonary vasoconstriction (HPV)**. This leads to increased pulmonary capillary pressure, causing fluid leakage into the alveoli. **Why Nifedipine is correct:** Nifedipine is a **Calcium Channel Blocker (CCB)** that acts as a potent pulmonary vasodilator. By inhibiting the constriction of pulmonary arterioles, it reduces pulmonary artery pressure and prevents the hydrostatic leakage of fluid. It is the drug of choice for the **prophylaxis and treatment** of HAPE in individuals susceptible to the condition. **Analysis of Incorrect Options:** * **Acetazolamide (CAI):** While it is a Carbonic Anhydrase Inhibitor (CAI), it is the drug of choice for **Acute Mountain Sickness (AMS)** and **High Altitude Cerebral Edema (HACE)**, not specifically for HAPE prophylaxis. It works by inducing metabolic acidosis, which stimulates ventilation. * **Digoxin:** This is an inotropic agent used in heart failure and certain arrhythmias. HAPE is a non-cardiogenic condition; therefore, improving myocardial contractility with Digoxin has no role in its management. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Treatment:** The most effective treatment for all high-altitude illnesses is **immediate descent** and supplemental oxygen. * **HAPE Pathophysiology:** Characterized by patchy pulmonary edema and protein-rich exudate. * **Other Drugs:** **Tadalafil/Sildenafil** (PDE-5 inhibitors) can also be used for HAPE prophylaxis as they decrease pulmonary vascular resistance. **Dexamethasone** is primarily used for HACE and AMS. * **Gamow Bag:** A portable hyperbaric chamber used as a temporary measure when descent is not possible.

Q: Side effects of hyperbaric oxygen therapy include all of the following EXCEPT:

Increased pulmonary compliance. **Explanation:** Hyperbaric Oxygen Therapy (HBOT) involves breathing 100% oxygen at pressures greater than 1 atmosphere. While therapeutic, prolonged exposure to high partial pressures of oxygen ($PO_2$) leads to **Oxygen Toxicity** (Paul Bert and Lorrain Smith effects), primarily affecting the central nervous system and the lungs. **Why Option B is the Correct Answer:** Hyperbaric oxygen **decreases** pulmonary compliance, it does not increase it. High $PO_2$ causes oxidative stress, leading to the inactivation of pulmonary surfactant and damage to type II pneumocytes. This results in "stiff lungs," making them harder to inflate, thereby reducing compliance. **Analysis of Incorrect Options:** * **A. Absorption Atelectasis:** When breathing 100% oxygen, nitrogen (which normally keeps alveoli splinted open) is washed out. Oxygen is rapidly absorbed into the blood; if an airway is even slightly obstructed, the alveolus collapses, leading to atelectasis. * **C. Decreased Vital Capacity:** This is one of the earliest measurable signs of pulmonary oxygen toxicity. It occurs due to a combination of airway congestion, alveolar edema, and the aforementioned atelectasis. * **D. Endothelial Damage:** High levels of reactive oxygen species (ROS) directly damage the pulmonary capillary endothelium, leading to increased permeability, pulmonary edema, and eventually hyaline membrane formation. **High-Yield Clinical Pearls for NEET-PG:** * **Lorrain Smith Effect:** Refers to pulmonary oxygen toxicity (presents as substernal burning, cough, and reduced vital capacity). * **Paul Bert Effect:** Refers to CNS oxygen toxicity (presents as seizures/convulsions when $PO_2$ > 2 atm). * **Other Side Effects:** Myopia (reversible), barotrauma (middle ear squeeze), and retrolental fibroplasia (in neonates). * **Key Contraindication:** Untreated pneumothorax is an absolute contraindication for HBOT.

Question 1

A 25-year-old elite swimmer training at sea level travels to compete at altitude (2400 meters). After 2 days of acclimatization, she experiences decreased performance. Her arterial blood gas shows pH 7.46, PaO2 65 mmHg, PaCO2 32 mmHg, HCO3- 22 mEq/L. Analyze the limiting factor for her current exercise performance at altitude.

Accepted Answer

Inadequate time for erythropoietin-stimulated red blood cell production

Answer

Decreased plasma volume reducing stroke volume and cardiac output

Answer

Alkalosis shifting the oxygen-hemoglobin dissociation curve leftward

Answer

Incomplete respiratory compensation reducing oxygen delivery

Answer

Reduced oxidative enzyme activity in skeletal muscle mitochondria

Question 2

Ascent to high altitude may cause all of the following except:

Accepted Answer

Cerebral palsy

Answer

Cerebral edema

Answer

Pulmonary edema

Answer

Venous thrombosis

Question 3

Monge's disease refers to:

Accepted Answer

High Altitude Erythrocytosis

Answer

Primary Familial Polycythemia

Answer

Spurious Polycythemia

Answer

Polycythemia Vera

Question 4

Which of the following is seen in high altitude climbers?

Accepted Answer

Decreased PaCO2

Answer

Hyperventilation

Answer

Pulmonary edema

Answer

Hypertension

Question 5

Acclimatization to high altitude is associated with which of the following changes?

Accepted Answer

Oxygen dissociation curve shifts to the right

Answer

Hyperventilation

Answer

Polycythemia

Answer

Decreased concentration of systemic capillaries

Question 6

Which of the following metabolic changes are observed in acclimatization?

Accepted Answer

Respiratory alkalosis

Answer

Metabolic alkalosis

Answer

Metabolic acidosis

Answer

Respiratory acidosis

Question 7

High-altitude acclimatization may be facilitated by all of the following except?

Accepted Answer

Growth of new skeletal muscle fibers

Answer

Increased production of red blood cells

Answer

Increased alveolar ventilation

Answer

Growth of new blood vessels

Question 8

In deep sea divers, decompression illness is mainly due to which factor?

Accepted Answer

Nitrogen gas

Answer

Oxygen narcosis

Answer

Hypoxia

Answer

Carbon dioxide narcosis

Question 9

Which of the following agents may be used as prophylaxis in high altitude pulmonary edema?

Accepted Answer

Nifedipine

Answer

CAI

Answer

Acetazolamide

Answer

Digoxin

Question 10

Side effects of hyperbaric oxygen therapy include all of the following EXCEPT:

Accepted Answer

Increased pulmonary compliance

Answer

Absorption atelectasis

Answer

Decreased vital capacity

Answer

Endothelial damage

Altitude and Diving Physiology — MCQs

Altitude and Diving Physiology — MCQs

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