Question

A healthy young man living on the coast at sea level attempts to climb the Himalayan Mountains, which of the following changes are expected?

A) Decreased 2,3 BPG levels which will cause a rightward shift of oxygen-hemoglobin dissociation curve to facilitate O₂ loading hemoglobin.

B) The alveoli PO₂ decreases because of the thinner air and lower O₂ composition (< 21%) in high altitude.

C) A lower pulse oximeter reading because of a reduction in the arterial PO₂.

D) Decreased hemoglobin/hematocrit due to chronic hypoxia.

E) Decreased firing of the peripheral chemoreceptors.

Answer 1

Physiological changes of high altitude

1.After ascending to high altitudes, Oxygen transport can be affected by hypoxia which lead to metabolic syndrome exhibit an increase in erythropoietin and shift of the oxygen-hemoglobin dissociation curve to the right. After ascending to high altitude, 2,3-diphosphoglycerate (2,3 DPG) is increased, and decreased affinity of Hb to oxygen and increased Oxygen release occurs.

- Option A is false ( correct answer is 2,3 DPG increased, Right shift and increased oxygen release)

2.As the altitude increases, barometric pressure decreases. This decrease in barometric pressure affects the partial pressure of alveolar oxygen (PAO2). The percentage of oxygen remains stable at about 21%.

Option B false (correct answer - alveolar partial pressure of oxygen decreased due to decrease in barometric pressure.

PAO2 is calculated by using the alveolar gas equation, as follows:

PAO2 = FiO2 (PB - PH2 O) - PACO2 [FiO2 + (1 - FiO2/R)],

In this equation, FiO2 is the fraction of inspired oxygen, PB is the ambient barometric pressure, PH2 O is the pressure exerted by water vapor at body temperature, PACO2 is the alveolar partial pressure of carbon dioxide, and R is the respiratory exchange quotient. The decrease in barometric pressure with increasing altitude reduces PAO2.

3.Decrements in PAO2 due to altitude result in proportionate decreases in the partial pressure of oxygen (PaO2). As a result, arterial oxygen saturation (SaO2   ) decreased. So pulse oximeter show low reading.

Option C - True

4.order to compensate for the low partial pressure of oxygen at altitude, the human body undergoes a number of physiological changes. A vital component in this process is the increase in the concentration of circulating haemoglobin. The role of Hypoxia inducible factor 1( HIF‐1α) erythropoietin and red blood cells in this acclimatisation process is described, together with the fall in plasma volume that increases the concentration of haemoglobin / hematocrit in the early stages of hypoxic exposure.

Option D - false ( correct answer is increased Hb)

5.Acid–base imbalance and other complex metabolic disturbances Lead to hyperventilation, which activate peripheral chemoreceptor organs along the aorta and the carotid sinus. The carotid body is a highly vascularized cluster of neuron-
like glomus cells (type-I) surrounded by sustentacular type-II
cells located at the bifurcation of the common carotid arteries.The glomus cells are sensitive to changes in arterial O2 partialpressure and the raised CO2 partial pressure, and signal to the respiratory centres in the central nervous system to increase the rate and depth of ventilation. In response to peripheral chemoreceptors, the respira-
tory centre is triggered in cerebral pons and medulla and the signals are relayed to the diaphragm, intercostal muscles and
stretch receptors of the lungs to facilitate ventilation.

Option E - false ( correct answer - activate chemoreceptors)

Option C is right answer