- In high altitude, a number of compensatory mechanisms operate over a period of time to increase altitude tolerance in humans which is called acclimatization. The following statements propose these compensatory changes:
A. The initial increase of ventilation is relatively small in high altitude but the ventilation steadily
increases over next few days.
B. Red blood cell 2, 3-DPG is increased.
C. The blood pH becomes more alkaline.
D. The oxygen dissociation curve is shifted to the left.
E. The pH of cerebrospinal fluid is further increased.
Choose the option with both INCORRECT statements:
(1) A and B (2) B and C
(3) C and D (4) D and E
Introduction
Acclimatization to high altitude involves complex physiological adaptations allowing humans to tolerate lower oxygen availability. Typical changes include adjustments in breathing, blood chemistry, and oxygen transport mechanisms. However, not all proposed statements about these adaptations are correct. This article analyzes several statements about high altitude acclimatization and identifies the two that are not true.
Evaluation of Statements
A. The initial increase of ventilation is relatively small in high altitude but ventilation steadily increases over the next few days.
-
True.
Early exposure causes a modest increase in ventilation. Over days, ventilatory acclimatization progressively enhances breathing rate and depth, improving oxygen uptake.
B. Red blood cell 2,3-DPG is increased.
-
True.
2,3-bisphosphoglycerate (2,3-DPG) concentration in erythrocytes rises with prolonged hypoxia, promoting oxygen unloading at tissues by shifting the oxygen-hemoglobin dissociation curve to the right.
C. The blood pH becomes more alkaline.
-
True.
Hyperventilation reduces arterial CO2, causing respiratory alkalosis (alkaline blood pH) initially during ascent to high altitude.
D. The oxygen dissociation curve is shifted to the left.
-
False.
Initially, respiratory alkalosis tends to shift the curve left, increasing hemoglobin’s oxygen affinity. However, with acclimatization, increased 2,3-DPG shifts the curve right to facilitate oxygen release at tissues. The net sustained effect is a rightward shift during acclimatization.
E. The pH of cerebrospinal fluid (CSF) is further increased.
-
False.
Despite respiratory alkalosis in plasma, CSF pH initially rises but then normalizes or decreases through compensatory mechanisms (renal bicarbonate excretion), so sustained increase in CSF pH does not occur.
Summary Table
Statement Correctness Explanation A Correct Ventilation increases progressively over days B Correct 2,3-DPG increases, shifting curve right C Correct Blood initially becomes more alkaline (alkalosis) D Incorrect Sustained right shift occurs due to 2,3-DPG increase E Incorrect CSF pH does not remain elevated, compensates over time
Identifying the Incorrect Statements Combination
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D and E are incorrect
Conclusion
The combination of both incorrect statements regarding acclimatization to high altitude is:
(4) D and E
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1 Comment
Kirti Agarwal
September 19, 2025Statement d and e is incorrect