Pathophysiology Quiz: Oxygen Transport And Hemoglobin
20 questions · exam conditions
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Oxygen Transport And HemoglobinQuestion 1 of 20

A 68-year-old male with severe COPD has chronic compensated respiratory acidosis and elevated 2,3-DPG levels. He is admitted with acute bacterial pneumonia, presenting with a fever of 39°C and a superimposed acute lactic acidosis. How will this acute presentation most likely alter his baseline oxyhemoglobin dissociation curve?

His baseline curve is already right-shifted; the acute fever and acidosis will cause a further significant shift to the right.
The acute infection will cause a leftward shift, counteracting his chronic rightward shift and normalizing his P50.
His baseline curve is left-shifted due to chronic hypoxia; the acute illness will shift it to the right, towards a normal position.
The competing factors of chronic 2,3-DPG elevation (right shift) and acute hypoxemia (left shift) will result in no net change.
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Pathophysiology Quiz

Pathophysiology Quiz: Oxygen Transport And Hemoglobin

Practice Oxygen Transport And Hemoglobin in Pathophysiology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Oxygen Transport And Hemoglobin, giving you a quick way to practice the rules, question types, and explanations that matter most for Pathophysiology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A 68-year-old male with severe COPD has chronic compensated respiratory acidosis and elevated 2,3-DPG levels. He is admitted with acute bacterial pneumonia, presenting with a fever of 39°C and a superimposed acute lactic acidosis. How will this acute presentation most likely alter his baseline oxyhemoglobin dissociation curve?

  1. His baseline curve is already right-shifted; the acute fever and acidosis will cause a further significant shift to the right. (correct answer)
  2. The acute infection will cause a leftward shift, counteracting his chronic rightward shift and normalizing his P50.
  3. His baseline curve is left-shifted due to chronic hypoxia; the acute illness will shift it to the right, towards a normal position.
  4. The competing factors of chronic 2,3-DPG elevation (right shift) and acute hypoxemia (left shift) will result in no net change.
Explanation: When you encounter oxyhemoglobin dissociation curve questions, focus on identifying all factors that affect oxygen-hemoglobin binding and determine whether each shifts the curve right (decreased affinity, easier O₂ release) or left (increased affinity, tighter O₂ binding). This COPD patient has a chronically right-shifted curve due to elevated 2,3-DPG levels, which develop as a compensatory mechanism for chronic hypoxemia. The right shift facilitates oxygen unloading to tissues despite lower blood oxygen levels. Now he develops acute pneumonia with fever (39°C) and lactic acidosis - both additional right-shifting factors. Fever increases metabolic demand and reduces hemoglobin's oxygen affinity, while acidosis (lower pH) enhances the Bohr effect, further promoting oxygen release to meet increased tissue demands. Choice A correctly identifies that his baseline right-shifted curve will shift even further right due to the acute fever and acidosis. Choice B incorrectly suggests infection causes a leftward shift - there's no physiologic basis for this. Choice C mischaracterizes his baseline as left-shifted when chronic COPD with elevated 2,3-DPG actually causes a right shift. Choice D mentions "acute hypoxemia causing a left shift," but hypoxemia doesn't directly shift the curve left - it's the compensatory response (increased 2,3-DPG) that shifts it right. Study tip: Remember the classic right-shifting factors with "CADET, face Right" - CO₂ (acidosis), Altitude (2,3-DPG), DPG, Exercise, Temperature. Multiple right-shifting factors are additive, creating a more pronounced rightward shift.

Question 2

The bar-headed goose migrates over the Himalayas at altitudes where the partial pressure of oxygen (PO₂) is extremely low. Their hemoglobin has evolved to be highly efficient in this environment. Compared to human hemoglobin, the oxyhemoglobin dissociation curve for the bar-headed goose would most likely be:

  1. Shifted to the right, with a higher P50, to maximize oxygen unloading to powerful flight muscles.
  2. Identical in position but with a much steeper slope, indicating stronger and more efficient cooperative binding.
  3. Shifted to the left, with a lower P50, to allow for more effective oxygen loading in a severely hypoxic environment. (correct answer)
  4. Flatter and more hyperbolic, indicating a loss of the sigmoidal shape to maintain saturation across a wide range of low PO₂ values.
Explanation: For an animal adapted to a chronically hypoxic environment, the primary challenge is loading a sufficient amount of oxygen onto hemoglobin in the lungs (or gills). A leftward-shifted curve, characterized by a lower P50, indicates a higher affinity of hemoglobin for oxygen. This allows hemoglobin to become more saturated at the very low partial pressures of oxygen found at high altitudes, ensuring adequate oxygen uptake from the atmosphere.

Question 3

A patient is brought to the emergency department with accidental, severe hypothermia, having a core body temperature of 30°C. What is the most significant pathophysiological consequence of this temperature on tissue oxygenation?

  1. Increased hemoglobin-oxygen affinity, which impairs the unloading of oxygen from hemoglobin in peripheral tissues. (correct answer)
  2. Decreased hemoglobin-oxygen affinity, leading to excessive oxygen release and potential cellular oxidative stress.
  3. A reduction in the total oxygen-carrying capacity of the blood due to cold-induced hemolysis of red blood cells.
  4. A direct suppression of cellular respiration, which makes changes in oxygen transport clinically insignificant.
Explanation: Decreased temperature causes a leftward shift of the oxyhemoglobin dissociation curve. This shift indicates an increased affinity of hemoglobin for oxygen. While this facilitates oxygen loading in the lungs, it significantly impairs the unloading of oxygen from hemoglobin to the peripheral tissues, potentially leading to tissue hypoxia despite adequate arterial oxygen saturation. This effect is particularly dangerous during rewarming when metabolic demand increases.

Question 4

Consider two patients, both with a normal PaO₂ of 100 mmHg. Patient A has severe anemia (Hb = 7.5 g/dL, SaO₂ 100%). Patient B has carbon monoxide poisoning (Hb = 15 g/dL, 50% COHb, 50% SaO₂). Which statement accurately compares their oxygen transport status?

  1. Patient A has a lower arterial oxygen content, but Patient B has a more severe impairment of oxygen unloading.
  2. Both patients have a similar, severely reduced arterial oxygen content, but Patient B has a more profound impairment of oxygen unloading in the tissues. (correct answer)
  3. Both patients have a similar reduction in arterial oxygen content and a compensatory rightward shift of the oxyhemoglobin curve.
  4. Patient B has a lower arterial oxygen content and a leftward shift, while Patient A has a normal oxygen content but impaired unloading.
Explanation: Both patients have a similar, severely reduced oxygen content (CaO₂ ≈ (1.34 * 7.5 * 1.0) ≈ 10 mL/dL for Patient A; CaO₂ ≈ (1.34 * 15 * 0.5) ≈ 10 mL/dL for Patient B). However, their ability to deliver this oxygen is different. Patient A (anemia) has a normal oxyhemoglobin curve. Patient B (CO poisoning) has a left-shifted curve, which increases hemoglobin's affinity for oxygen and severely impairs its release to the tissues. Therefore, for a similar level of oxygen content, Patient B's tissue hypoxia is more profound.

Question 5

A 25-year-old female with type 1 diabetes presents with diabetic ketoacidosis (DKA) and has a concurrent diagnosis of pernicious anemia (Hb 8 g/dL). Her arterial blood pH is 7.15. What is the net effect of these two conditions on her systemic oxygen delivery?

  1. A normal arterial oxygen content but severely impaired oxygen unloading due to the combined effects of anemia and acidosis.
  2. A reduced arterial oxygen content due to anemia, which is further worsened by impaired oxygen unloading due to the DKA.
  3. An overall improvement in oxygen delivery, as the rightward curve shift from acidosis fully compensates for the reduced hemoglobin.
  4. A significantly reduced arterial oxygen content due to anemia, partially compensated by enhanced oxygen unloading to tissues due to acidosis. (correct answer)
Explanation: This scenario involves two competing effects on oxygen delivery. The pernicious anemia (low Hb) drastically reduces the total oxygen-carrying capacity and thus the arterial oxygen content (CaO₂). The DKA causes severe acidosis (low pH), which shifts the oxyhemoglobin curve to the right. This rightward shift decreases hemoglobin's affinity for oxygen, enhancing its ability to unload oxygen at the tissue level. Therefore, oxygen delivery is a balance between reduced content (from anemia) and improved unloading efficiency (from acidosis). The compensation is partial, and overall oxygen delivery remains compromised.

Question 6

During strenuous exercise, contracting skeletal muscles produce large amounts of lactic acid and carbon dioxide. How do these local metabolic byproducts facilitate increased oxygen delivery to the muscle tissue?

  1. They lower the local pH and increase PCO₂, which stabilizes the T-state of hemoglobin, reducing its affinity for oxygen. (correct answer)
  2. They increase the local pH and decrease PCO₂, which stabilizes the R-state of hemoglobin, increasing its affinity for oxygen.
  3. They directly compete with oxygen for the same binding site on the heme iron, causing allosteric displacement of oxygen.
  4. They trigger a rapid, localized increase in 2,3-DPG synthesis within red blood cells passing through the muscle bed.
Explanation: This phenomenon is known as the Bohr effect. Increased carbon dioxide and lactic acid (H⁺) in exercising muscle lower the local pH. Both H⁺ and CO₂ are allosteric regulators that bind to hemoglobin (at sites other than the heme iron) and stabilize its deoxygenated, low-affinity T (taut) state. This stabilization promotes the release of oxygen from hemoglobin, enhancing delivery to the tissues that need it most.

Question 7

A trauma patient receives a rapid transfusion of 8 units of packed red blood cells that have been stored under standard blood bank conditions for 28 days. What is the most immediate concern regarding the oxygen-delivering capability of the transfused blood?

  1. The transfused red blood cells have an excess of 2,3-DPG, causing a decreased hemoglobin-oxygen affinity and potential tissue hypoxia from poor loading.
  2. The hemoglobin in stored blood is largely converted to methemoglobin, which is incapable of binding and transporting oxygen.
  3. The transfused red blood cells are depleted of 2,3-DPG, leading to an increased hemoglobin-oxygen affinity and impaired oxygen release to tissues. (correct answer)
  4. The transfused red blood cells have a significantly lower hemoglobin concentration than native blood, reducing the overall oxygen content.
Explanation: During storage, red blood cells metabolize their 2,3-diphosphoglycerate (2,3-DPG) and are unable to replenish it. 2,3-DPG is crucial for reducing hemoglobin's oxygen affinity, allowing for efficient unloading in tissues. When a patient receives a large volume of 2,3-DPG-depleted blood, the transfused hemoglobin has an abnormally high affinity for oxygen (a 'left-shifted' curve), which impairs its ability to release oxygen to peripheral tissues, potentially worsening tissue hypoxia despite restoration of blood volume and hemoglobin levels.

Question 8

A patient with end-stage renal disease has a hemoglobin level of 7 g/dL. Arterial blood gas analysis on room air is otherwise normal (pH 7.40, PaO₂ 98 mmHg, SaO₂ 99%). How does this patient's anemia primarily affect oxygen transport?

  1. It causes a rightward shift of the oxyhemoglobin curve to compensate for the reduced hemoglobin.
  2. It lowers the partial pressure of arterial oxygen (PaO₂) due to impaired gas exchange.
  3. It reduces the total arterial oxygen content (CaO₂) without altering hemoglobin's intrinsic affinity for oxygen. (correct answer)
  4. It decreases the arterial oxygen saturation (SaO₂) because fewer hemoglobin molecules are available to bind oxygen.
Explanation: The primary consequence of anemia is a reduction in the concentration of hemoglobin, which is the main determinant of the blood's oxygen-carrying capacity. This directly reduces the total arterial oxygen content (CaO₂). Anemia itself does not alter the partial pressure of oxygen (PaO₂), the percentage of available hemoglobin that is saturated (SaO₂), or the intrinsic affinity of hemoglobin for oxygen (i.e., it does not cause a curve shift).

Question 9

A patient in septic shock has a core body temperature of 39.5°C and severe lactic acidosis with an arterial pH of 7.20. Which statement best describes the primary alteration in the oxyhemoglobin dissociation curve and its functional consequence in this patient?

  1. A leftward shift occurs, impairing tissue oxygenation despite an adequate arterial oxygen saturation.
  2. A rightward shift occurs, enhancing the unloading of oxygen to metabolically active peripheral tissues. (correct answer)
  3. A decrease in maximal oxygen saturation occurs, reducing total arterial oxygen content independently of affinity changes.
  4. The sigmoidal shape of the curve becomes hyperbolic, indicating a loss of cooperative binding due to acidosis.
Explanation: Increased temperature (fever) and decreased pH (acidosis) are both factors that shift the oxyhemoglobin dissociation curve to the right. A rightward shift signifies a decrease in hemoglobin's affinity for oxygen. This facilitates the release (unloading) of oxygen from hemoglobin to the tissues, which is an adaptive response to the high metabolic demand in conditions like sepsis.

Question 10

A patient with end-stage renal disease has a hemoglobin level of 7 g/dL. Arterial blood gas analysis on room air is otherwise normal (pH 7.40, PaO₂ 98 mmHg, SaO₂ 99%). How does this patient's anemia primarily affect oxygen transport?

  1. It causes a rightward shift of the oxyhemoglobin curve to compensate for the reduced hemoglobin.
  2. It lowers the partial pressure of arterial oxygen (PaO₂) due to impaired gas exchange.
  3. It reduces the total arterial oxygen content (CaO₂) without altering hemoglobin's intrinsic affinity for oxygen. (correct answer)
  4. It decreases the arterial oxygen saturation (SaO₂) because fewer hemoglobin molecules are available to bind oxygen.
Explanation: The primary consequence of anemia is a reduction in the concentration of hemoglobin, which is the main determinant of the blood's oxygen-carrying capacity. This directly reduces the total arterial oxygen content (CaO₂). Anemia itself does not alter the partial pressure of oxygen (PaO₂), the percentage of available hemoglobin that is saturated (SaO₂), or the intrinsic affinity of hemoglobin for oxygen (i.e., it does not cause a curve shift).

Question 11

A patient is brought to the emergency department with accidental, severe hypothermia, having a core body temperature of 30°C. What is the most significant pathophysiological consequence of this temperature on tissue oxygenation?

  1. Increased hemoglobin-oxygen affinity, which impairs the unloading of oxygen from hemoglobin in peripheral tissues. (correct answer)
  2. Decreased hemoglobin-oxygen affinity, leading to excessive oxygen release and potential cellular oxidative stress.
  3. A reduction in the total oxygen-carrying capacity of the blood due to cold-induced hemolysis of red blood cells.
  4. A direct suppression of cellular respiration, which makes changes in oxygen transport clinically insignificant.
Explanation: Decreased temperature causes a leftward shift of the oxyhemoglobin dissociation curve. This shift indicates an increased affinity of hemoglobin for oxygen. While this facilitates oxygen loading in the lungs, it significantly impairs the unloading of oxygen from hemoglobin to the peripheral tissues, potentially leading to tissue hypoxia despite adequate arterial oxygen saturation. This effect is particularly dangerous during rewarming when metabolic demand increases.

Question 12

During strenuous exercise, contracting skeletal muscles produce large amounts of lactic acid and carbon dioxide. How do these local metabolic byproducts facilitate increased oxygen delivery to the muscle tissue?

  1. They lower the local pH and increase PCO₂, which stabilizes the T-state of hemoglobin, reducing its affinity for oxygen. (correct answer)
  2. They increase the local pH and decrease PCO₂, which stabilizes the R-state of hemoglobin, increasing its affinity for oxygen.
  3. They directly compete with oxygen for the same binding site on the heme iron, causing allosteric displacement of oxygen.
  4. They trigger a rapid, localized increase in 2,3-DPG synthesis within red blood cells passing through the muscle bed.
Explanation: This phenomenon is known as the Bohr effect. Increased carbon dioxide and lactic acid (H⁺) in exercising muscle lower the local pH. Both H⁺ and CO₂ are allosteric regulators that bind to hemoglobin (at sites other than the heme iron) and stabilize its deoxygenated, low-affinity T (taut) state. This stabilization promotes the release of oxygen from hemoglobin, enhancing delivery to the tissues that need it most.

Question 13

A clinician is evaluating two different pathophysiological states affecting oxygen transport. Which of the following correctly pairs a condition with its primary effect on either hemoglobin's oxygen affinity (P50) or the blood's oxygen-carrying capacity?

  1. Iron deficiency anemia primarily alters P50 by changing the allosteric properties of the globin chains.
  2. Carbon monoxide poisoning primarily alters oxygen-carrying capacity by promoting the hemolysis of red blood cells.
  3. Fever primarily alters oxygen-carrying capacity by increasing the metabolic rate and oxygen consumption of red blood cells.
  4. Chronic hypoxemia at high altitude primarily alters P50 through adaptive changes in red blood cell 2,3-DPG levels. (correct answer)
Explanation: Chronic hypoxemia stimulates an increase in the production of 2,3-DPG, which reduces hemoglobin's affinity for oxygen. This causes a rightward shift of the curve and an increase in the P50, facilitating oxygen unloading. Anemia (A) primarily affects carrying capacity, not P50. CO poisoning (B) affects carrying capacity by occupying binding sites and also alters P50, but not through hemolysis. Fever (C) primarily alters affinity (P50), not carrying capacity.

Question 14

The bar-headed goose migrates over the Himalayas at altitudes where the partial pressure of oxygen (PO₂) is extremely low. Their hemoglobin has evolved to be highly efficient in this environment. Compared to human hemoglobin, the oxyhemoglobin dissociation curve for the bar-headed goose would most likely be:

  1. Shifted to the right, with a higher P50, to maximize oxygen unloading to powerful flight muscles.
  2. Identical in position but with a much steeper slope, indicating stronger and more efficient cooperative binding.
  3. Shifted to the left, with a lower P50, to allow for more effective oxygen loading in a severely hypoxic environment. (correct answer)
  4. Flatter and more hyperbolic, indicating a loss of the sigmoidal shape to maintain saturation across a wide range of low PO₂ values.
Explanation: For an animal adapted to a chronically hypoxic environment, the primary challenge is loading a sufficient amount of oxygen onto hemoglobin in the lungs (or gills). A leftward-shifted curve, characterized by a lower P50, indicates a higher affinity of hemoglobin for oxygen. This allows hemoglobin to become more saturated at the very low partial pressures of oxygen found at high altitudes, ensuring adequate oxygen uptake from the atmosphere.

Question 15

A 25-year-old female with type 1 diabetes presents with diabetic ketoacidosis (DKA) and has a concurrent diagnosis of pernicious anemia (Hb 8 g/dL). Her arterial blood pH is 7.15. What is the net effect of these two conditions on her systemic oxygen delivery?

  1. A normal arterial oxygen content but severely impaired oxygen unloading due to the combined effects of anemia and acidosis.
  2. A reduced arterial oxygen content due to anemia, which is further worsened by impaired oxygen unloading due to the DKA.
  3. An overall improvement in oxygen delivery, as the rightward curve shift from acidosis fully compensates for the reduced hemoglobin.
  4. A significantly reduced arterial oxygen content due to anemia, partially compensated by enhanced oxygen unloading to tissues due to acidosis. (correct answer)
Explanation: This scenario involves two competing effects on oxygen delivery. The pernicious anemia (low Hb) drastically reduces the total oxygen-carrying capacity and thus the arterial oxygen content (CaO₂). The DKA causes severe acidosis (low pH), which shifts the oxyhemoglobin curve to the right. This rightward shift decreases hemoglobin's affinity for oxygen, enhancing its ability to unload oxygen at the tissue level. Therefore, oxygen delivery is a balance between reduced content (from anemia) and improved unloading efficiency (from acidosis). The compensation is partial, and overall oxygen delivery remains compromised.

Question 16

A patient in septic shock has a core body temperature of 39.5°C and severe lactic acidosis with an arterial pH of 7.20. Which statement best describes the primary alteration in the oxyhemoglobin dissociation curve and its functional consequence in this patient?

  1. A leftward shift occurs, impairing tissue oxygenation despite an adequate arterial oxygen saturation.
  2. A rightward shift occurs, enhancing the unloading of oxygen to metabolically active peripheral tissues. (correct answer)
  3. A decrease in maximal oxygen saturation occurs, reducing total arterial oxygen content independently of affinity changes.
  4. The sigmoidal shape of the curve becomes hyperbolic, indicating a loss of cooperative binding due to acidosis.
Explanation: Increased temperature (fever) and decreased pH (acidosis) are both factors that shift the oxyhemoglobin dissociation curve to the right. A rightward shift signifies a decrease in hemoglobin's affinity for oxygen. This facilitates the release (unloading) of oxygen from hemoglobin to the tissues, which is an adaptive response to the high metabolic demand in conditions like sepsis.

Question 17

A patient with a baseline P50 of 27 mmHg develops acute metabolic acidosis, causing their arterial pH to drop from 7.40 to 7.20. Their hemoglobin level and PaO₂ remain stable. Which change in oxygen transport dynamics is expected as a direct result of the acidosis?

  1. The P50 will decrease, reflecting an increase in hemoglobin's affinity for oxygen and impairing O₂ delivery to the tissues.
  2. The total arterial oxygen content (CaO₂) will decrease significantly because the acidosis will denature most of the hemoglobin.
  3. The P50 will increase, reflecting a decrease in hemoglobin's affinity for oxygen and enhancing O₂ availability at the tissue level. (correct answer)
  4. The P50 will remain unchanged, but the maximal saturation of hemoglobin at a PaO₂ of 100 mmHg will be substantially reduced.
Explanation: P50 is the partial pressure of oxygen at which hemoglobin is 50% saturated. Acidosis (an increase in H⁺ concentration) causes a rightward shift in the oxyhemoglobin dissociation curve (the Bohr effect). A rightward shift means that a higher partial pressure of oxygen is required to achieve the same level of saturation. Therefore, the P50 will increase. This reflects a decrease in hemoglobin's affinity for oxygen, which facilitates the unloading of oxygen to the tissues.

Question 18

A 68-year-old male with severe COPD has chronic compensated respiratory acidosis and elevated 2,3-DPG levels. He is admitted with acute bacterial pneumonia, presenting with a fever of 39°C and a superimposed acute lactic acidosis. How will this acute presentation most likely alter his baseline oxyhemoglobin dissociation curve?

  1. His baseline curve is already right-shifted; the acute fever and acidosis will cause a further significant shift to the right. (correct answer)
  2. The acute infection will cause a leftward shift, counteracting his chronic rightward shift and normalizing his P50.
  3. His baseline curve is left-shifted due to chronic hypoxia; the acute illness will shift it to the right, towards a normal position.
  4. The competing factors of chronic 2,3-DPG elevation (right shift) and acute hypoxemia (left shift) will result in no net change.
Explanation: When you encounter oxyhemoglobin dissociation curve questions, focus on identifying all factors that affect oxygen-hemoglobin binding and determine whether each shifts the curve right (decreased affinity, easier O₂ release) or left (increased affinity, tighter O₂ binding). This COPD patient has a chronically right-shifted curve due to elevated 2,3-DPG levels, which develop as a compensatory mechanism for chronic hypoxemia. The right shift facilitates oxygen unloading to tissues despite lower blood oxygen levels. Now he develops acute pneumonia with fever (39°C) and lactic acidosis - both additional right-shifting factors. Fever increases metabolic demand and reduces hemoglobin's oxygen affinity, while acidosis (lower pH) enhances the Bohr effect, further promoting oxygen release to meet increased tissue demands. Choice A correctly identifies that his baseline right-shifted curve will shift even further right due to the acute fever and acidosis. Choice B incorrectly suggests infection causes a leftward shift - there's no physiologic basis for this. Choice C mischaracterizes his baseline as left-shifted when chronic COPD with elevated 2,3-DPG actually causes a right shift. Choice D mentions "acute hypoxemia causing a left shift," but hypoxemia doesn't directly shift the curve left - it's the compensatory response (increased 2,3-DPG) that shifts it right. Study tip: Remember the classic right-shifting factors with "CADET, face Right" - CO₂ (acidosis), Altitude (2,3-DPG), DPG, Exercise, Temperature. Multiple right-shifting factors are additive, creating a more pronounced rightward shift.

Question 19

A patient exposed to smoke in a house fire presents with headache and confusion. Co-oximetry reveals a carboxyhemoglobin level of 30%. Which set of findings most accurately describes this patient's oxygen transport status?

  1. Decreased PaO₂, a rightward shift of the oxyhemoglobin curve, and decreased oxygen-carrying capacity.
  2. Normal PaO₂, a leftward shift of the oxyhemoglobin curve, and decreased oxygen-carrying capacity. (correct answer)
  3. Normal PaO₂, a rightward shift of the oxyhemoglobin curve, and normal oxygen-carrying capacity.
  4. Decreased PaO₂, a leftward shift of the oxyhemoglobin curve, and decreased oxygen-carrying capacity.
Explanation: In carbon monoxide (CO) poisoning, CO has a much higher affinity for hemoglobin than oxygen, forming carboxyhemoglobin. This has two major effects: 1) It reduces the number of available binding sites for oxygen, thus decreasing the blood's oxygen-carrying capacity. 2) It causes a leftward shift in the oxyhemoglobin dissociation curve for the remaining functional hemoglobin, impairing the unloading of oxygen to tissues. The partial pressure of dissolved oxygen in the arterial blood (PaO₂) remains normal because gas exchange in the lungs is unaffected.

Question 20

A student having a panic attack is hyperventilating. An arterial blood gas analysis shows pH 7.55, PaCO₂ 25 mmHg, and PaO₂ 110 mmHg. The student reports feeling dizzy and having tingling in their fingertips. How does the patient's acid-base status contribute to these neurological symptoms?

  1. The high PaO₂ creates oxygen toxicity, which directly damages neuronal tissues and causes the symptoms.
  2. The alkalosis and low PaCO₂ cause a leftward shift in the oxyhemoglobin curve, impairing oxygen unloading to cerebral and peripheral tissues. (correct answer)
  3. The alkalosis causes a rightward shift in the oxyhemoglobin curve, leading to excessive oxygen dumping and oxidative stress in the brain.
  4. The low PaCO₂ directly reduces hemoglobin's oxygen-carrying capacity, leading to a state of functional anemia and tissue hypoxia.
Explanation: Hyperventilation leads to respiratory alkalosis (increased pH) and hypocapnia (decreased PaCO₂). Both of these conditions cause a leftward shift of the oxyhemoglobin dissociation curve. This shift increases hemoglobin's affinity for oxygen, making it more difficult for oxygen to be released from hemoglobin to the tissues. The resulting decrease in oxygen availability to the brain and peripheral nerves can cause symptoms like dizziness and paresthesias (tingling).