Altitude Illnesses — MCQs
Which drug is given to prevent acute mountain sickness?
Which of the following is not done in high altitude sickness?
Which physiological adaptation does not happen at high altitudes?
Which is a feature of high-altitude pulmonary edema?
Which of the following is seen in high altitude climbers?
During acclimatization to high altitude, all of the following take place except:
At what altitude is kala azar unlikely to occur?
In which of the following conditions oxygen delivery is least to muscles?
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.
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.
Altitude Illnesses Indian Medical PG Practice Questions and MCQs
Question 1: Which drug is given to prevent acute mountain sickness?
- A. Acetazolamide (Correct Answer)
- B. Diltiazem
- C. Digoxin
- D. Dexamethasone
Explanation: ***Acetazolamide*** - This drug is a **carbonic anhydrase inhibitor** that acidifies the blood and causes compensatory hyperventilation, increasing oxygenation. - It is the **first-line prophylactic agent** for acute mountain sickness (AMS) and is best started 24-48 hours before ascent. - Most effective and widely recommended for AMS prevention. *Digoxin* - This is a **cardiac glycoside** used to treat heart failure and irregular heartbeats. - Its mechanism of action is unrelated to the physiological changes that cause acute mountain sickness. *Diltiazem* - This is a **calcium channel blocker** primarily used for hypertension, angina, and certain arrhythmias. - It has no known role in the prevention or treatment of acute mountain sickness. *Dexamethasone* - While **dexamethasone** can be used for AMS prophylaxis, it is typically reserved as an **alternative agent** when acetazolamide is contraindicated or not tolerated. - It is more commonly used for **treatment** of severe altitude illness including **High Altitude Cerebral Edema (HACE)** and **High Altitude Pulmonary Edema (HAPE)**. - **Acetazolamide remains the preferred first-line prophylactic agent** due to its mechanism of action that directly addresses the underlying pathophysiology of AMS.
Question 2: Which of the following is not done in high altitude sickness?
- A. Rapid descent
- B. Acetazolamide
- C. Oxygen
- D. Digoxin (Correct Answer)
Explanation: ***Digoxin*** - **Digoxin** is a cardiac glycoside used for heart conditions like **atrial fibrillation** and **heart failure**. It has no role in the treatment of high altitude sickness. - Its primary actions are to increase **myocardial contractility** and decrease heart rate, which are not beneficial in addressing the hypobaric hypoxia of high altitude. *Rapid descent* - **Rapid descent** is the most effective and often immediate treatment for severe forms of high altitude sickness, such as **High Altitude Cerebral Edema (HACE)** or **High Altitude Pulmonary Edema (HAPE)** [2]. - It involves moving the affected individual to a significantly lower altitude to alleviate the effects of **hypoxia** [2]. *Acetazolamide* - **Acetazolamide** is a **carbonic anhydrase inhibitor** commonly used for the prevention and treatment of high altitude sickness [2]. - It works by inducing a **metabolic acidosis**, which stimulates **respiration** and increases **oxygenation**. *Oxygen* - Administering **supplemental oxygen** is a crucial treatment for high altitude sickness, especially in more severe cases [2]. - It directly counteracts the **hypoxia** experienced at high altitudes, improving symptoms and preventing progression [1], [2].
Question 3: Which physiological adaptation does not happen at high altitudes?
- A. Pulmonary vasoconstriction
- B. Respiratory acidosis (Correct Answer)
- C. Hypoxia
- D. Polycythemia
Explanation: ***Respiratory acidosis*** - At high altitudes, the primary physiological response to **hypoxia** is to increase ventilation, leading to a decrease in **arterial PCO2**. - This reduction in **PCO2** causes **respiratory alkalosis**, not acidosis, as the body tries to compensate for the lower oxygen levels. *Pulmonary vasoconstriction* - This is a significant physiological response to **hypoxia** at high altitudes, leading to an increase in **pulmonary artery pressure**. - Its purpose is to divert blood flow to better-ventilated areas of the lung, but it can also contribute to **pulmonary hypertension**. *Hypoxia* - Reduced **atmospheric pressure** at high altitudes directly results in a lower partial pressure of oxygen (**PO2**), leading to **hypoxia**. - This low **PO2** is the primary trigger for most other physiological adaptations seen at high altitudes. *Polycythemia* - Prolonged exposure to **hypoxia** stimulates the kidneys to release **erythropoietin (EPO)**, which in turn increases **red blood cell production**. - This adaptive increase in **red blood cell count** and **hemoglobin concentration** aims to enhance the oxygen-carrying capacity of the blood.
Question 4: Which is a feature of high-altitude pulmonary edema?
- A. Associated with low cardiac output
- B. Exercise has no effect
- C. Associated with pulmonary hypertension (Correct Answer)
- D. Occurs in both acclimatized and unacclimatized persons
Explanation: ***Associated with pulmonary hypertension*** - **High-altitude pulmonary edema (HAPE)** is characterized by **exaggerated hypoxic pulmonary vasoconstriction**, leading to significantly increased pulmonary artery pressures. - This **pulmonary hypertension** drives fluid extravasation into the alveolar spaces, causing non-cardiogenic pulmonary edema. *Associated with low cardiac output* - HAPE is typically associated with **normal or elevated cardiac output** in response to hypoxia, not low cardiac output. - Low cardiac output suggests conditions like cardiogenic shock or severe myocardial dysfunction, which are not primary features of HAPE. *Exercise has no effect* - **Physical exertion at altitude** is a significant risk factor and can worsen HAPE due to increased cardiac output and pulmonary blood flow, exacerbating pulmonary hypertension. - Rest and reduced activity are crucial components of preventing and treating HAPE, indicating that exercise does indeed have an effect. *Occurs in both acclimatized and unacclimatized persons* - HAPE primarily affects **unacclimatized individuals** or those who ascend rapidly to high altitudes. - While rare, it can occur in previously acclimatized individuals returning to altitude after a period at lower elevations or in those with predisposing factors, but it is predominantly a disease of the unacclimatized.
Question 5: Which of the following is seen in high altitude climbers?
- A. Hyperventilation
- B. Pulmonary edema
- C. Decreased PaCO2
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - High altitude climbers experience **hypoxia**, which triggers several physiological responses as the body tries to compensate. - **Hyperventilation**, **pulmonary edema**, and **decreased PaCO2** are all common occurrences in individuals exposed to high altitudes. *Hyperventilation* - **Hypoxia** at high altitudes stimulates the peripheral chemoreceptors, leading to an increased respiratory rate and depth. - This increased ventilation is a compensatory mechanism to try and increase **oxygen intake**. *Pulmonary edema* - **High-altitude pulmonary edema (HAPE)** is a potentially life-threatening condition caused by exaggerated hypoxic pulmonary vasoconstriction. - This leads to increased pulmonary arterial pressure, capillary leakage, and **fluid accumulation in the lungs**. *Decreased PaCO2* - The increased respiratory rate due to **hyperventilation** causes an excessive exhalation of carbon dioxide. - This results in a **decreased partial pressure of arterial carbon dioxide (PaCO2)**, leading to respiratory alkalosis.
Question 6: During acclimatization to high altitude, all of the following take place except:
- A. Increase in minute ventilation
- B. Increase in the sensitivity of carotid body to hypoxia
- C. Shift in the oxygen dissociation curve to the left (Correct Answer)
- D. Increase in 2,3-BPG levels in red blood cells
Explanation: ***Shift in the oxygen dissociation curve to the left*** - Acclimatization to high altitude involves a **right shift** in the oxygen dissociation curve, not a left shift. This right shift, facilitated by an increase in 2,3-bisphosphoglycerate (2,3-BPG), allows for **improved oxygen unloading** to tissues at lower partial pressures of oxygen. - A left shift would mean that hemoglobin has a **higher affinity for oxygen**, hindering its release to the tissues, which would be detrimental in a low oxygen environment. - Note: Acute exposure causes a temporary left shift due to respiratory alkalosis, but chronic acclimatization produces a right shift. *Increase in minute ventilation* - A primary response to high altitude is an **increase in minute ventilation** (the total volume of air inhaled or exhaled per minute). - This increased breathing rate and depth helps to counteract the **lower partial pressure of oxygen** in the atmosphere, thereby maintaining alveolar oxygen levels. *Increase in the sensitivity of carotid body to hypoxia* - During acclimatization, the **carotid body's sensitivity to hypoxia** increases, leading to a stronger ventilatory response to low oxygen levels. - This enhanced sensitivity helps in maintaining adequate oxygenation by **stimulating increased breathing**. *Increase in 2,3-BPG levels in red blood cells* - Acclimatization leads to increased production of **2,3-bisphosphoglycerate (2,3-BPG)** in red blood cells. - This facilitates the **right shift of the oxygen dissociation curve**, promoting oxygen release to tissues at high altitude where oxygen partial pressure is low.
Question 7: At what altitude is kala azar unlikely to occur?
- A. 400 meters
- B. 500 meters
- C. 600 meters (Correct Answer)
- D. 200 meters
Explanation: ***600 meters*** - Kala-azar, or **visceral leishmaniasis**, is primarily found in **low-lying areas** and is rarely reported at altitudes above 600 meters due to the specific ecological requirements of its **sand fly vector**. - The **Phlebotomus argentipes sand fly**, the main vector in the Indian subcontinent, prefers warm, humid climates and **lower altitudes**. *400 meters* - This altitude is within the **typical endemic range** for kala-azar, especially in regions like the Indian subcontinent. - The environmental conditions at 400 meters are generally conducive for the **survival and breeding** of the sand fly vector. *500 meters* - Similar to 400 meters, 500 meters is still considered within the **favorable altitude range** for kala-azar transmission. - The **sand fly vector** can thrive in the climate often found at this elevation. *200 meters* - This altitude represents a **highly endemic zone** for kala-azar, as it provides optimal conditions for the sand fly vector. - Lower altitudes are typically associated with increased **humidity and warmth**, favoring vector density and parasite transmission.
Question 8: In which of the following conditions oxygen delivery is least to muscles?
- A. Marathon runner at sea level
- B. Person with carbon monoxide poisoning (Correct Answer)
- C. Person inhaling 100 percent oxygen at the top of Mount Everest
- D. Person with anemia at sea level
Explanation: ***Person with carbon monoxide poisoning*** - **Carbon monoxide (CO)** binds to **hemoglobin** with an affinity 200-250 times greater than oxygen, forming **carboxyhemoglobin (COHb)**. This significantly reduces the **oxygen-carrying capacity** of the blood. - CO poisoning also shifts the **oxygen-hemoglobin dissociation curve** to the left, meaning that even the oxygen that *is* bound to hemoglobin is less readily released to the tissues, leading to severe **tissue hypoxia**. - **Dual mechanism** of impairment (reduced carrying capacity + impaired unloading) makes CO poisoning the most severe condition for oxygen delivery. *Marathon runner at sea level* - While a marathon runner at sea level experiences high oxygen demand, their **cardiovascular system** is highly adapted to deliver oxygen efficiently to the muscles. - The **partial pressure of oxygen** in the atmosphere is optimal, allowing for maximum oxygen saturation of hemoglobin and effective delivery. - Increased cardiac output and enhanced oxygen extraction compensate for high metabolic demands. *Person inhaling 100 percent oxygen at the top of Mount Everest* - Although the **atmospheric pressure** at the top of Mount Everest is very low, inhaling 100% oxygen significantly increases the **partial pressure of oxygen** in the inspired air. - This allows for a greater **driving pressure** for oxygen to enter the bloodstream and maintain higher oxygen saturation compared to breathing ambient air at altitude, mitigating the effects of hypoxia. - While not optimal, supplemental 100% O₂ can maintain adequate oxygen delivery despite low barometric pressure. *Person with anemia at sea level* - In anemia, there is a reduced **hemoglobin concentration**, which decreases the **oxygen-carrying capacity** of the blood. - However, unlike CO poisoning, the **oxygen-hemoglobin dissociation curve** remains normal, allowing for normal oxygen unloading to tissues. - Compensatory mechanisms include increased cardiac output and increased oxygen extraction, making it less severe than CO poisoning.
Question 9: 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.
- A. Alkalosis shifting the oxygen-hemoglobin dissociation curve leftward
- B. Decreased plasma volume reducing stroke volume and cardiac output
- C. Incomplete respiratory compensation reducing oxygen delivery
- D. Reduced oxidative enzyme activity in skeletal muscle mitochondria
- E. Inadequate time for erythropoietin-stimulated red blood cell production (Correct Answer)
Explanation: ***Inadequate time for erythropoietin-stimulated red blood cell production*** - While **erythropoietin (EPO)** levels rise within hours of altitude exposure, a significant increase in **red blood cell mass** and **hemoglobin** takes approximately 2 to 3 weeks to occur. - At 2 days, the athlete has decreased **arterial oxygen content (CaO2)** due to the lower partial pressure of oxygen (hypoxia) without the compensatory increase in **oxygen-carrying capacity** provided by polycythemia. *Alkalosis shifting the oxygen-hemoglobin dissociation curve leftward* - **Respiratory alkalosis** (pH 7.46, PaCO2 32 mmHg) causes a **left shift**, increasing hemoglobin's affinity for oxygen and slightly hindering oxygen unloading at the tissues. - This is not the primary limiting factor, as the body eventually compensates for this shift by increasing **2,3-BPG** levels to shift the curve back to the right. *Decreased plasma volume reducing stroke volume and cardiac output* - Early altitude exposure leads to **diuresis** and a decrease in **plasma volume**, which can reduce **stroke volume**. - However, this is largely offset by an initial increase in **heart rate** via sympathetic activation to maintain **cardiac output** during exercise. *Incomplete respiratory compensation reducing oxygen delivery* - The ABG results show **hyperventilation** (decreased PaCO2) which is the immediate and most important respiratory compensation for hypoxemia. - **Respiratory compensation** is functioning as expected for 2 days of acclimatization; the fundamental limitation is the fixed **hypobaric hypoxia** of the environment. *Reduced oxidative enzyme activity in skeletal muscle mitochondria* - High-altitude acclimatization actually leads to an increase in **mitochondrial density** and **oxidative enzyme activity** over long periods. - These metabolic adaptations in the **skeletal muscle** occur much later and are not the cause of an acute performance decline after only 2 days.
Question 10: 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.
- A. Decreased plasma volume reducing stroke volume and cardiac output
- B. Alkalosis shifting the oxygen-hemoglobin dissociation curve leftward
- C. Incomplete respiratory compensation reducing oxygen delivery
- D. Inadequate time for erythropoietin-stimulated red blood cell production (Correct Answer)
- E. Reduced oxidative enzyme activity in skeletal muscle mitochondria
Explanation: ***Inadequate time for erythropoietin-stimulated red blood cell production*** - While **erythropoietin (EPO)** levels rise within hours of arrival at altitude, significant **polycythemia** and increased red cell mass take **2-4 weeks** to develop. - After only 2 days, the athlete has a lower **PaO2** without the increased **hemoglobin (Hb)** needed to restore total **arterial oxygen content (CaO2)**, limiting her aerobic capacity. *Decreased plasma volume reducing stroke volume and cardiac output* - **Plasma volume** does decrease shortly after reaching altitude, which can lower **stroke volume**, but this is typically a secondary factor compared to the oxygen-carrying deficit. - At 2400m, the primary limitation at submaximal exercise is the **hypoxia** rather than a failure of the **frank-starling mechanism**. *Alkalosis shifting the oxygen-hemoglobin dissociation curve leftward* - The **respiratory alkalosis** (pH 7.46) causes a **left shift**, which increases oxygen affinity in the lungs but may hinder **unloading** at tissues. - This effect is often self-limiting as levels of **2,3-BPG** rise within days to shift the curve back to the right, mitigating this as a primary performance limiter. *Incomplete respiratory compensation reducing oxygen delivery* - The ABG shows a **PaCO2 of 32 mmHg**, indicating that **hypoxic ventilatory response** and respiratory compensation are already active and functioning well. - The primary issue is not the lack of breathing effort but the low **ambient PIO2** and the time-lag for the body to produce more **oxygen carriers**. *Reduced oxidative enzyme activity in skeletal muscle mitochondria* - Changes in **oxidative enzyme activity** and mitochondrial density are slow-onset **peripheral adaptations** that occur over much longer periods of altitude training. - This factor reflects a chronic adaptation rather than an acute limiting factor for performance after only **48 hours** of exposure.
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