Altitude and Diving Physiology Practice Questions

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: 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.

Q: All are symptoms of acute mountain sickness except?

Tachycardia. **Explanation:** Acute Mountain Sickness (AMS) is a clinical syndrome that occurs in unacclimatized individuals shortly after ascending to high altitudes (usually above 2500m). It is primarily caused by **hypobaric hypoxia**, leading to cerebral vasodilation and mild cerebral edema. **Why Tachycardia is the correct answer:** While tachycardia (increased heart rate) is a common **physiological compensatory response** to hypoxia at high altitudes, it is **not** considered a diagnostic symptom of AMS itself. In the context of high-altitude medicine, tachycardia is a sign of acclimatization or a response to physical exertion, whereas AMS is defined by a specific constellation of neurological and gastrointestinal symptoms. **Analysis of Incorrect Options:** * **Headache (Option A):** This is the **hallmark symptom** and a mandatory criterion for diagnosing AMS. It is typically bilateral, throbbing, and worsens with exertion. * **Dyspnoea (Option B):** Shortness of breath on exertion is a common feature of AMS. However, dyspnoea at rest may indicate progression to High-Altitude Pulmonary Edema (HAPE). * **Light-headedness (Option D):** Dizziness and light-headedness are frequent neurological manifestations of AMS, alongside fatigue, insomnia, and anorexia. **High-Yield Clinical Pearls for NEET-PG:** * **Lake Louise Scoring System:** Used to diagnose AMS (Headache + at least one of: GI upset, fatigue, dizziness, or sleep disturbance). * **Drug of Choice (Prophylaxis):** Acetazolamide (Carbonic anhydrase inhibitor), which induces metabolic acidosis to stimulate ventilation. * **Drug of Choice (Treatment):** Dexamethasone (to reduce cerebral edema). * **Gold Standard Treatment:** Immediate descent and supplemental oxygen. * **Complications:** If untreated, AMS can progress to **HACE** (High-Altitude Cerebral Edema) or **HAPE** (High-Altitude Pulmonary Edema).

Q: Decompression sickness is seen in all of the following conditions except:

High altitude climbing. **Explanation:** The core concept behind **Decompression Sickness (DCS)**, also known as "the bends," is **Henry’s Law**, which states that the solubility of a gas in a liquid is proportional to its partial pressure. **Why High Altitude Climbing is the Correct Answer:** In high altitude climbing, the body moves from sea level (1 atm) to a lower atmospheric pressure. While this can cause hypoxia or Acute Mountain Sickness, it does **not** cause DCS. DCS requires a transition from a state of **high pressure** (where tissues are supersaturated with nitrogen) to a **lower pressure**. In climbing, the starting pressure is already low, so there is no excess nitrogen dissolved in the tissues to form bubbles upon further ascent. **Analysis of Incorrect Options:** * **Diving (A):** This is the classic cause. At high depths, the increased pressure forces nitrogen to dissolve into body tissues. If the diver ascends too rapidly, the pressure drops quickly, and nitrogen comes out of solution as bubbles in the blood and tissues. * **Aviation (B):** Pilots or passengers in unpressurized aircraft can experience DCS if they ascend rapidly from sea level to high altitudes (usually above 18,000 ft). The rapid drop from 1 atm to low atmospheric pressure causes pre-existing dissolved nitrogen to form bubbles. * **Both Diving and Aviation (C):** This is incorrect because DCS occurs in both, but not in climbing. **High-Yield Clinical Pearls for NEET-PG:** * **Henry’s Law:** Governs the pathophysiology of DCS. * **Nitrogen:** The primary gas responsible for DCS due to its high lipid solubility. * **Type I DCS:** "The Bends" (joint pain) and "The Niggles" (skin itching). * **Type II DCS:** "The Chokes" (pulmonary edema/dyspnea) and neurological deficits. * **Treatment:** 100% Oxygen and **Hyperbaric Oxygen Therapy** (recompression). * **Prevention:** Slow ascent and "decompression stops" to allow nitrogen to be exhaled gradually.

Question 1

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 2

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 3

Natural acclimatization in high altitude is due to what primary physiological change?

Accepted Answer

Decreased partial pressure of oxygen

Answer

Increased ventilation

Answer

Increased oxygen utilization

Answer

Increase in chest size and decrease in abdominal circumference

Question 4

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

Question 5

As part of a space-research program, a physiologist was asked to investigate the effect of flight-induced stress on blood pressure. The blood pressure of cosmonauts was to be measured twice: once before takeoff and once after the spacecraft entered the designated orbit around the earth. For a proper comparison, in which position should the pre-flight blood pressure be recorded?

Accepted Answer

The lying down position

Answer

The sitting position

Answer

The standing position

Answer

Any position, as long as the post-flight recording is made in the same position

Question 6

All are symptoms of acute mountain sickness except?

Accepted Answer

Tachycardia

Answer

Headache

Answer

Dyspnoea

Answer

Light headedness

Question 7

Decompression sickness is seen in all of the following conditions except:

Accepted Answer

High altitude climbing

Answer

Diving

Answer

Aviation

Answer

Both diving and aviation

Question 8

Which of the following adaptations will be most effective in increasing work capacity at high altitude?

Accepted Answer

Decreasing workload, increasing duration of exercise

Answer

Increasing workload, decreasing duration of exercise

Answer

Increasing workload, increasing duration of exercise

Answer

Decreasing workload, decreasing duration of exercise

Question 9

In high-altitude mountain sickness, which feature is characteristic of pulmonary edema?

Accepted Answer

Increased left ventricular back pressure

Answer

Decreased pulmonary capillary permeability

Answer

Increased pulmonary capillary pressure

Answer

Normal left atrial pressure

Question 10

A mountaineer ascends to 18,000 feet in 2 days without supplemental oxygen. At the height of ascent, what changes are observed?

Accepted Answer

Decreased inspired O2 concentration

Answer

Increased PaCO2

Answer

Decreased barometric pressure

Answer

Decreased PaO2

Altitude and Diving Physiology — MCQs

Altitude and Diving Physiology — MCQs

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