Altitude and Diving Physiology Practice Questions

Q: What is the earliest symptom of acute mountain sickness?

Headache. **Explanation:** **Acute Mountain Sickness (AMS)** is a syndrome caused by the body's failure to acclimatize to high altitudes (typically above 2,500m). **Why Headache is the Correct Answer:** Headache is the **earliest, most common, and hallmark symptom** of AMS. It is typically described as bifrontal or occipital and is throbbing in nature. The underlying pathophysiology involves **hypoxia-induced cerebral vasodilation** and a mild increase in intracranial pressure. According to the Lake Louise Scoring System (the clinical standard for diagnosis), a headache is mandatory for the diagnosis of AMS. **Analysis of Incorrect Options:** * **A. Blurring of vision:** This is not a primary symptom of AMS. Visual disturbances may occur in severe cases of High-Altitude Cerebral Edema (HACE) due to papilledema, but it is not the earliest sign. * **B. Fever:** Fever is not a feature of AMS. If present at high altitude, it usually indicates an underlying infection or High-Altitude Pulmonary Edema (HAPE). * **C. Nausea and vomiting:** These are common symptoms of AMS, but they typically develop **after** the onset of the headache. **High-Yield NEET-PG Pearls:** * **Lake Louise Criteria:** Diagnosis of AMS = Recent ascent + Headache + at least one other symptom (Nausea/Vomiting, Fatigue, Dizziness, or Insomnia). * **Drug of Choice (Prophylaxis):** Acetazolamide (Carbonic anhydrase inhibitor). It works by inducing metabolic acidosis, which stimulates ventilation. * **Definitive Treatment:** Immediate descent and supplemental oxygen. * **Cheyne-Stokes Respiration:** This is the most common breathing pattern seen during sleep at high altitudes.

Q: A person unacclimatized develops pulmonary edema at high altitude after how many days?

2-3 days. **Explanation:** High Altitude Pulmonary Edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that typically occurs in unacclimatized individuals who ascend rapidly to altitudes above 2,500 meters (8,000 ft). **Why 2-3 days is correct:** The pathophysiology of HAPE involves **hypoxic pulmonary vasoconstriction (HPV)**. Upon arrival at high altitude, low alveolar oxygen levels trigger a reflex constriction of pulmonary arterioles to redirect blood flow. In susceptible individuals, this constriction is uneven and excessive, leading to high capillary hydrostatic pressure in non-constricted areas. This "stress failure" of the blood-gas barrier causes fluid leakage into the alveoli. This process typically takes **48 to 72 hours (2-3 days)** to manifest clinically after the initial ascent. **Analysis of Incorrect Options:** * **6-7 days:** By this time, the initial acute phase of HAPE has usually either peaked or the body has begun early compensatory mechanisms. Most acute altitude illnesses (AMS and HAPE) manifest within the first 72 hours. * **19-21 days / 2nd-3rd month:** These timeframes are associated with **chronic** altitude exposure. Problems occurring at this stage would be related to Polycythemia or Monge’s Disease (Chronic Mountain Sickness), not acute pulmonary edema. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Prevention/Treatment:** **Nifedipine** (a calcium channel blocker) is used to reduce pulmonary artery pressure. * **Gold Standard Treatment:** Immediate descent to a lower altitude and supplemental oxygen. * **Key Sign:** Early HAPE often presents as a dry cough and decreased exercise tolerance, progressing to central cyanosis and pink frothy sputum. * **Acetazolamide:** Used primarily for Acute Mountain Sickness (AMS) prevention by inducing metabolic acidosis to stimulate ventilation; it is less effective for HAPE than nifedipine.

Q: Which of the following is NOT a feature of chronic mountain sickness?

Decreased mitochondria. **Explanation:** Chronic Mountain Sickness (Monge’s disease) occurs due to long-term exposure to high altitudes, leading to chronic alveolar hypoxia and subsequent physiological maladaptations. **Why "Decreased mitochondria" is the correct answer:** In response to chronic hypoxia, the body undergoes cellular adaptations to maximize energy efficiency. One such adaptation is an **increase in mitochondrial density** and myoglobin content in skeletal muscles. This enhances the cell's ability to utilize limited oxygen for oxidative phosphorylation. Therefore, "decreased mitochondria" is physiologically incorrect and is not a feature of the condition. **Analysis of Incorrect Options:** * **Hyperventilation:** Hypoxia stimulates peripheral chemoreceptors (carotid bodies), leading to a persistent increase in the rate and depth of breathing to improve arterial $PO_2$. * **Increased Erythropoietin:** Chronic hypoxia triggers the kidneys to release erythropoietin (EPO), stimulating the bone marrow to produce more RBCs (Polycythemia). This increases the oxygen-carrying capacity of the blood but also increases blood viscosity. * **Increased $HCO_3^-$ excretion:** Hyperventilation causes respiratory alkalosis (low $PCO_2$). To compensate and normalize pH, the kidneys increase the excretion of bicarbonate ($HCO_3^-$). **Clinical Pearls for NEET-PG:** * **Monge’s Disease:** Characterized by extreme polycythemia (Hematocrit >65%), cyanosis, and pulmonary hypertension leading to right heart failure. * **Acute Mountain Sickness (AMS):** Occurs within hours; primary symptom is headache. * **High Altitude Pulmonary Edema (HAPE):** Caused by uneven hypoxic pulmonary vasoconstriction. * **High Altitude Cerebral Edema (HACE):** Result of hypoxia-induced vasodilation and increased capillary permeability.

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

The cerebral arterial pressure rises.. **Explanation:** In aviation physiology, **Negative G (-Gz)** occurs when acceleration is directed from the feet toward the head (e.g., during a nose-dive or outside loop). This causes a massive shift of blood volume toward the upper body and head. **1. Why the Correct Answer is Right:** In -Gz, the inertial force pushes blood into the head. This results in a significant increase in **cerebral arterial and venous pressure**. To protect the brain, the baroreceptor reflex is triggered, leading to intense bradycardia and peripheral vasodilation; however, the mechanical force of the G-load still keeps the cephalic pressures high. **2. Analysis of Incorrect Options:** * **Option A:** Hydrostatic pressure in the lower limbs **decreases** because blood is forced away from the legs toward the head. (Increased pressure in lower limbs is seen in Positive G). * **Option B:** Cardiac output initially **increases** (or remains stable) due to the massive increase in venous return from the lower body to the heart. * **Option C:** **"Red-out"** occurs, not blackout. Red-out happens because the high pressure forces blood into the retinal capillaries and causes the lower eyelid to be pushed upward, covering the field of vision with a red tint. **Blackout** (loss of vision) is a feature of **Positive G (+Gz)** due to retinal ischemia. **3. Clinical Pearls for NEET-PG:** * **Positive G (+Gz):** Blood moves Head → Feet. Results in: Foot edema, decreased venous return, and **Blackout** (Vision loss) followed by **G-LOC** (G-induced Loss of Consciousness). * **Negative G (-Gz):** Blood moves Feet → Head. Results in: Facial congestion, **Red-out**, and risk of cerebral hemorrhage. * **Tolerance:** The human body is much less tolerant of Negative G (-3 to -4 G) compared to Positive G (+5 to +9 G). * **G-suit:** Designed to prevent blood pooling in the legs during **Positive G**; it is not effective against Negative G.

Q: The type of hypoxia present at high altitudes is:

Hypoxic Hypoxia. **Explanation:** The correct answer is **Hypoxic Hypoxia**. At high altitudes, the total barometric pressure decreases. Although the percentage of oxygen in the air remains constant (21%), the **partial pressure of inspired oxygen ($PiO_2$)** falls significantly. This leads to a decrease in alveolar oxygen tension ($PAO_2$) and a subsequent drop in arterial oxygen tension ($PaO_2$). Since the primary defect is a low arterial $PO_2$ despite normal hemoglobin and blood flow, it is classified as **Hypoxic Hypoxia** (also known as Hypoxemic Hypoxia). **Analysis of Incorrect Options:** * **Anemic Hypoxia:** Occurs when the oxygen-carrying capacity of the blood is reduced due to low hemoglobin levels or carbon monoxide poisoning. Arterial $PO_2$ is typically normal. * **Stagnant (Ischemic) Hypoxia:** Results from inadequate blood flow to tissues (e.g., heart failure or shock). The blood contains enough oxygen, but it isn't reaching the destination fast enough. * **Histotoxic Hypoxia:** Occurs when tissues cannot utilize the oxygen delivered to them, usually due to the inhibition of the cytochrome oxidase enzyme (e.g., Cyanide poisoning). Arterial and venous $PO_2$ are often high. **High-Yield Clinical Pearls for NEET-PG:** * **Immediate response to High Altitude:** Hyperventilation triggered by peripheral chemoreceptors (due to low $PaO_2$), leading to **Respiratory Alkalosis**. * **Chronic Adaptation:** Increased 2,3-BPG (shifts Oxygen-Dissociation Curve to the **Right**) and Polycythemia (increased Erythropoietin). * **High Altitude Pulmonary Edema (HAPE):** Caused by uneven hypoxic pulmonary vasoconstriction leading to pulmonary hypertension. * **High Altitude Cerebral Edema (HACE):** Caused by hypoxic vasodilation of cerebral vessels.

Q: A 31-year-old man is on a scuba diving trip and descends to a depth of 50 m. After 30 minutes, he experiences equipment malfunction and quickly returns to the surface. He develops difficulty breathing within 5 minutes, with dyspnea and substernal chest pain, followed by a severe headache and vertigo. An hour later, he develops severe, painful myalgias and arthralgias. These symptoms abate within 24 hours. Which of the following occluding his arterioles is the most likely cause of his findings?

Nitrogen gas bubbles. ### Explanation **1. Why Nitrogen Gas Bubbles is Correct:** The clinical presentation describes **Decompression Sickness (DCS)**, also known as "the bends" or "caisson disease." According to **Henry’s Law**, the amount of gas dissolved in a liquid is proportional to its partial pressure. At a depth of 50 m (approx. 6 atmospheres), nitrogen from the diver's air tank dissolves into the blood and tissues in high concentrations. When the diver ascends **rapidly**, the ambient pressure drops too quickly for the dissolved nitrogen to be exhaled via the lungs. Instead, the nitrogen comes out of solution as **gas bubbles** in the blood and tissues. * **Chokes:** Bubbles in pulmonary capillaries cause dyspnea and substernal pain. * **Staggers:** Bubbles in the inner ear or CNS cause vertigo and headache. * **Bends:** Bubbles in joints and muscles cause severe arthralgia and myalgia. **2. Why Other Options are Incorrect:** * **A. Fat globules:** These cause *Fat Embolism Syndrome*, typically seen after long bone fractures (e.g., femur), not rapid decompression. * **B. Fibrin clots:** These represent *Thromboembolism*. While DCS can trigger the coagulation cascade, the primary occluding agent in this acute setting is gas. * **D. Platelet thrombi:** While bubbles can activate platelets, the initial and primary cause of vessel occlusion and tissue distension in DCS is the nitrogen gas itself. **3. Clinical Pearls for NEET-PG:** * **Henry’s Law** is the governing physical principle of DCS. * **Treatment:** Immediate **Hyperbaric Oxygen Therapy (HBOT)** to force nitrogen back into solution and improve oxygenation. * **Nitrogen Narcosis:** Occurs *at depth* (not during ascent) due to the anesthetic effect of high-pressure nitrogen; often called "Rapture of the Deep." * **Helium-Oxygen (Heliox) mixtures** are used in deep diving because helium is less soluble in lipids and diffuses faster, reducing the risk of narcosis and DCS.

Q: Which of the following statements is true about High Altitude Pulmonary Edema (HAPE)?

Associated with pulmonary vasoconstriction. **Explanation:** **High Altitude Pulmonary Edema (HAPE)** is a form of non-cardiogenic pulmonary edema that occurs due to rapid ascent to altitudes typically above 2,500 meters. **Why Option B is Correct:** The primary pathophysiology of HAPE is **Hypoxic Pulmonary Vasoconstriction (HPV)**. At high altitudes, the low partial pressure of alveolar oxygen ($PAO_2$) triggers a reflex contraction of pulmonary vascular smooth muscle. This constriction is often **patchy and uneven**, leading to over-perfusion in non-constricted areas. This results in high capillary hydrostatic pressure (pulmonary hypertension), which causes stress failure of the alveolar-capillary membrane and subsequent leakage of fluid into the lungs. **Analysis of Incorrect Options:** * **Option A:** Exercise **exacerbates** HAPE because it further increases pulmonary artery pressure and cardiac output, worsening the stress failure of capillaries. * **Option C:** While more common in unacclimatized individuals, HAPE can also occur in **acclimatized residents** returning to high altitude after a brief stay at sea level (known as "Re-entry HAPE"). * **Option D:** HAPE is associated with **normal or high cardiac output**; it is a non-cardiogenic process. Low cardiac output is not a primary feature. **NEET-PG High-Yield Pearls:** * **Treatment of Choice:** Immediate descent to lower altitude and supplemental oxygen. * **Pharmacotherapy:** **Nifedipine** (a calcium channel blocker) is used for prevention and treatment as it reduces pulmonary artery pressure. * **Key Sign:** Early symptoms include dyspnea at rest and a dry cough, progressing to pink frothy sputum. * **Radiology:** Characteristically shows patchy, bilateral opacities.

Question 1

What is the earliest symptom of acute mountain sickness?

Accepted Answer

Headache

Answer

Blurring of vision

Answer

Fever

Answer

Nausea and vomiting

Question 2

A person unacclimatized develops pulmonary edema at high altitude after how many days?

Accepted Answer

2-3 days

Answer

19-21 days

Answer

2nd-3rd month

Answer

6-7 days

Question 3

Following acute respiratory response to ascent to high altitude, there is normalization of blood pH. What is the mechanism for this normalization?

Accepted Answer

Increased excretion of HCO3– by the kidneys

Answer

Increased erythropoiesis leads to increased buffering by haemoglobin

Answer

Increased levels of 2, 3–DPG

Answer

Retention of bicarbonate by the kidneys

Question 4

Which of the following is NOT a feature of chronic mountain sickness?

Accepted Answer

Decreased mitochondria

Answer

Hyperventilation

Answer

Increased erythropoietin

Answer

Increased HCO3 excretion

Question 5

Decompression sickness, commonly known as 'the bends', is caused by what phenomenon?

Accepted Answer

Formation of nitrogen bubbles in muscles and joints

Answer

Escape of nitrogen bubbles from the myelin sheath of motor nerves

Answer

Blockage of pulmonary capillaries by nitrogen bubbles

Answer

Blockage of blood vessels in the brain and spinal cord by nitrogen bubbles

Question 6

In a person acclimatized to high altitude, what maintains O2 saturation?

Accepted Answer

More O2 delivery to tissue

Answer

Hemoconcentration

Answer

Decreased CO2 saturation

Answer

Hypoxia

Question 7

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 8

The type of hypoxia present at high altitudes is:

Accepted Answer

Hypoxic Hypoxia

Answer

Anemic Hypoxia

Answer

Stagnant Hypoxia

Answer

Histotoxic Hypoxia

Question 9

A 31-year-old man is on a scuba diving trip and descends to a depth of 50 m. After 30 minutes, he experiences equipment malfunction and quickly returns to the surface. He develops difficulty breathing within 5 minutes, with dyspnea and substernal chest pain, followed by a severe headache and vertigo. An hour later, he develops severe, painful myalgias and arthralgias. These symptoms abate within 24 hours. Which of the following occluding his arterioles is the most likely cause of his findings?

Accepted Answer

Nitrogen gas bubbles

Answer

Fat globules

Answer

Fibrin clots

Answer

Platelet thrombi

Question 10

Which of the following statements is true about High Altitude Pulmonary Edema (HAPE)?

Accepted Answer

Associated with pulmonary vasoconstriction

Answer

Not exacerbated by exercise

Answer

Occurs only in unacclimatized individuals

Answer

Associated with low cardiac output

Altitude and Diving Physiology — MCQs

Altitude and Diving Physiology — MCQs

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