Altitude and Diving Physiology Practice Questions

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: Caisson's disease is:

Gas embolism. **Explanation:** **Caisson’s disease**, also known as decompression sickness (DCS) or "the bends," occurs due to a rapid decrease in environmental pressure (e.g., a diver ascending too quickly). **Why Gas Embolism is Correct:** According to **Henry’s Law**, the solubility of a gas in a liquid is proportional to its partial pressure. At high pressures (deep underwater), large amounts of nitrogen dissolve into the blood and tissues. If decompression occurs rapidly, the nitrogen cannot stay dissolved and forms **bubbles** in the blood and tissues. These nitrogen bubbles act as **gas emboli**, obstructing blood flow and triggering inflammatory responses. **Analysis of Incorrect Options:** * **B. Fat Embolism:** Typically occurs after long bone fractures (e.g., femur) where fat globules from the bone marrow enter the circulation. * **C. Amniotic Fluid Embolism:** A rare obstetric emergency where amniotic fluid enters the maternal circulation during labor or delivery. * **D. Tumor Embolism:** Occurs when clusters of cancer cells break off from a primary tumor and enter the bloodstream, potentially leading to metastasis. **High-Yield Clinical Pearls for NEET-PG:** * **The Bends:** Joint and muscle pain caused by bubbles in local capillaries. * **The Chokes:** Shortness of breath and cough due to bubbles in pulmonary capillaries. * **Neurological symptoms:** Can include paralysis or sensory loss if bubbles form in the spinal cord. * **Treatment:** The definitive treatment is **Hyperbaric Oxygen Therapy (HBOT)**, which forces the nitrogen bubbles back into solution. * **Prevention:** Following decompression tables to allow for gradual "off-gassing."

Q: Which of the following is NOT a component of acclimatization?

Decreased concentration of 2,3 DPG in RBC. ### Explanation Acclimatization refers to the physiological adjustments the body makes to survive in a low-oxygen environment (hypoxia) at high altitudes. **Why Option B is the Correct Answer:** At high altitudes, the body experiences **increased** levels of **2,3-Diphosphoglycerate (2,3-DPG)** in Red Blood Cells. 2,3-DPG binds to hemoglobin, decreasing its affinity for oxygen and shifting the Oxygen-Dissociation Curve (ODC) to the **right**. This facilitates the "unloading" of oxygen from hemoglobin into the tissues where it is needed most. Therefore, a *decrease* in 2,3-DPG is not a component of acclimatization; it is the opposite of what occurs. **Analysis of Incorrect Options:** * **A. Hyperventilation:** This is the immediate response to hypoxia. Low $PO_2$ stimulates peripheral chemoreceptors, increasing the rate and depth of breathing to bring in more oxygen. * **C. Increased Erythropoiesis:** Hypoxia stimulates the kidneys to release **Erythropoietin (EPO)**. This increases RBC production and hematocrit, enhancing the blood's oxygen-carrying capacity over days to weeks. * **D. Kidneys excrete more alkali:** Hyperventilation causes a "washout" of $CO_2$, leading to respiratory alkalosis. To compensate and normalize pH, the kidneys excrete excess bicarbonate ($HCO_3^-$). **High-Yield Clinical Pearls for NEET-PG:** 1. **ODC Shift:** Acclimatization causes a **Right Shift** (due to increased 2,3-DPG). 2. **Acid-Base Balance:** The primary acid-base disturbance at high altitude is **Respiratory Alkalosis**. 3. **Pulmonary Circulation:** Hypoxia causes **Hypoxic Pulmonary Vasoconstriction**, which can lead to Pulmonary Hypertension and High-Altitude Pulmonary Edema (HAPE). 4. **Acetazolamide:** This drug is used for prophylaxis; it inhibits carbonic anhydrase, forcing bicarbonate excretion and inducing a mild metabolic acidosis to stimulate ventilation.

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

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 2

Caisson's disease is:

Accepted Answer

Gas embolism

Answer

Fat embolism

Answer

Amniotic fluid embolism

Answer

Tumor embolism

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

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 5

Which of the following is NOT a component of acclimatization?

Accepted Answer

Decreased concentration of 2,3 DPG in RBC

Answer

Hyperventilation

Answer

Increased erythropoiesis

Answer

Kidneys excrete more alkali

Question 6

The type of hypoxia present at high altitudes is:

Accepted Answer

Hypoxic Hypoxia

Answer

Anemic Hypoxia

Answer

Stagnant Hypoxia

Answer

Histotoxic Hypoxia

Question 7

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 8

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

Question 9

What is the additional amount of oxygen transported in 100 ml of blood in a subject breathing 100% oxygen under hyperbaric conditions of 4 ATA compared to normobaric conditions (1 ATA)?

Accepted Answer

6 ml

Answer

9 ml

Answer

3 ml

Answer

0.3 ml

Question 10

Which of the following illnesses is NOT associated with high altitude?

Accepted Answer

Hypoventilation

Answer

Cerebral edema

Answer

Venous thrombosis

Answer

Refractory cough

Altitude and Diving Physiology — MCQs

Altitude and Diving Physiology — MCQs

On this page

Practice by Chapter

Want unlimited practice?