Deck 12: Gas Exchange and Transport

Question 1

Which of the following values corresponds most closely to the normal PO₂ and PCO₂ in the mixed venous blood returning to the lungs from the right side of the heart?

A) PO₂ = 40 mm Hg; PCO₂ = 46 mm Hg
B) PO₂ = 40 mm Hg; PCO₂ = 100 mm Hg
C) PO₂ = 100 mm Hg; PCO₂ = 40 mm Hg
D) PO₂ = 100 mm Hg; PCO₂ = 46 mm Hg

Answer 1

A
Explanation: Venous blood returning to the lungs has a lower PO₂ (40 mm Hg) than alveolar gas. Thus the pressure gradient for O₂ diffusion into the blood is approximately 60 mm Hg (100 mm Hg - 40 mm Hg). Therefore, as blood flows past the alveolus, it takes up O₂, leaving the capillary with a PO₂ close to 100 mm Hg. Because venous blood has a higher PCO₂ than alveolar gas (46 mm Hg vs. 40 mm Hg), the pressure gradient for carbon dioxide causes diffusion of carbon dioxide in the opposite direction, from the blood into the alveolus.

Question 2

Which of the following gases would diffuse fastest across the alveolar-capillary membrane?

A) Air
B) Carbon dioxide
C) O₂
D) Nitrogen

Answer 2

B
Explanation: Carbon dioxide diffuses approximately 20 times faster across the alveolar-capillary membrane than does O₂, because of its much higher solubility in plasma.

Question 3

On what does the movement of gases between the lungs and the body tissues mainly depend?

A) Active transport
B) Gaseous diffusion
C) Membrane dialysis
D) Membrane transport

Answer 3

B
Explanation: Gas movement between the lungs and tissues occurs by simple diffusion.

Question 4

A healthy person breathing 100% O₂ at sea level would have PAO₂ of approximately what level?

A) 149 mm Hg
B) 670 mm Hg
C) 713 mm Hg
D) 760 mm Hg

Question 5

Assuming a constant FiO₂ and carbon dioxide production, which of the following statements is correct?

A) An increased PACO₂ will result in and increased PAO₂.
B) Increased FIO₂ blows off carbon dioxide.
C) Increases in alveolar ventilation (V_A) decrease the PACO₂ and increase the PAO₂.
D) The PAO₂ varies proportionally with the PACO₂.

Question 6

Under what conditions will the alveolar PACO₂ rise above normal?

A) If both metabolic rate and ventilation increase (e.g., through exercise)
B) If carbon dioxide production decreases relative to V_A
C) If V_A decreases relative to carbon dioxide production
D) When the patient is febrile

Question 7

What is the highest PAO₂ one could expect to observe in an individual breathing room air at sea level?

A) 90 to 100 mm Hg
B) 110 to 120 mm Hg
C) 640 to 670 mm Hg
D) 710 to 760 mm Hg

Question 8

Which of the following is/are true regarding the PACO₂?
1) Directly proportional to whole-body carbon dioxide production
2) Directly proportional to alveolar ventilation (V_A)
3) Normally maintained at approximately 35 to 45 mm Hg

A)2 and 3 only
B)3 only
C)1 and 2 only
D)1 and 3 only

Question 9

Which of the following conditions must exist for gas to move between the alveolus and pulmonary capillary?

A) Adequate alveolar ventilation (V_A)
B) Difference in partial pressures (pressure gradient)
C) Normal central nervous system (CNS) control mechanism
D) Sufficient amount of blood hemoglobin (Hb)

Question 10

Calculate the approximate PAO₂ given the following conditions (assume R = 0.8): FiO₂ = .40, P_B = 770 mm Hg, PACO₂ = 31 mm Hg

A) 100 mm Hg
B) 135 mm Hg
C) 250 mm Hg
D) 723 mm Hg

Question 11

In a person breathing room air (and with all else being normal), if the alveolar PCO₂ rises from 40 to 70 mm Hg, what would you expect?

A) PAO₂ to fall by approximately 30 mm Hg
B) PAO₂ to fall by approximately 40 mm Hg
C) PAO₂ to rise by approximately30 mm Hg
D) PAO₂ to rise by approximately 40 mm Hg

Question 12

The PAO₂ depends on which of the following factors?
1) Ambient (atmospheric) pressure
2) Fractional concentration of inspired O₂
3) Level of V_A
4) Types of fuels burned (fat, protein, and carbohydrate)

A)1, 2, and 3 only
B)1 and 2 only
C)3 only
D)1, 2, 3, and 4

Question 13

Which of the following "layers" must be traversed by gases moving across the alveolar-capillary membrane?
1) Alveolar epithelial membrane
2) Capillary endothelial membrane
3) Interstitial space
4) Transbronchial radial tethering mechanisms

A)1, 2, and 3 only
B)1, 2, and 4 only
C)2 and 3 only
D)1, 2, 3, and 4

Question 14

When is the rate of gaseous diffusion across a biological membrane decreased?

A) The diffusion distance is small.
B) The gas diffusion constant increases.
C) The partial pressure gradient is low.
D) The surface area is large.

Question 15

The highest PCO₂ levels are found in what location?

A) Arterial blood
B) Atmospheric air
C) Cells
D) Venous blood

Question 16

Which of the following best represents the partial pressures of all gases in the normally ventilated and perfused alveolus when breathing room air at sea level?

A) PO₂ = 40 mm Hg; PCO₂ = 100 mm Hg; PN₂ = 573 mm Hg; PH₂O = 47 mm Hg
B) PO₂ = 100 mm Hg; PCO₂ = 40 mm Hg; PN₂ = 573 mm Hg; PH₂O = 47 mm Hg
C) PO₂ = 100 mm Hg; PCO₂ = 40 mm Hg; PN₂ = 713 mm Hg; PH₂O = 47 mm Hg
D) PO₂ = 149 mm Hg; PCO₂ = 40 mm Hg; PN₂ = 573 mm Hg; PH₂O = 47 mm Hg

Question 17

A 70-kg male patient has a CO₂ of 200 ml/min and a V_A of 9 L/min. From this information, what can you infer?

A) The patient's carbon dioxide production is abnormally low.
B) The patient's _A is abnormally low.
C) The patient will have a lower than normal PACO₂.
D) The patient will have a higher than normal PACO₂.

Question 18

The lowest PO₂ would normally be found in what location?

A) Arterial blood
B) Atmospheric air
C) Cells
D) Venous blood

Question 19

What is the primary determinant of the PAO₂?

A) Body's CO₂
B) Metabolic rate of the body tissues
C) PaO₂
D) PO₂ in the inspired gas

Question 20

What is the approximate normal level of carbon dioxide production (CO₂) for an adult?

A) 200 ml/min
B) 250 ml/min
C) 4200 ml/min
D) 6000 ml/min

Question 21

Under normal physiologic circumstances, how many milliliters of O₂ are capable of combining with 1 g of Hb?

A) 0.003 ml
B) 0.450 ml
C) 0.820 ml
D) 1.340 ml

Question 22

The time available for diffusion in the lung is mainly a function of which of the following?

A) Functional residual capacity (FRC)
B) Inspired O₂ concentration
C) Level of V_A
D) Rate of pulmonary blood flow

Question 23

Regarding pulmonary blood flow in the upright lung, which of the following statements is true?

A) The apexes receive approximately 20 times more blood flow than the bases.
B) The bases receive approximately 20 times more blood flow than the apexes.
C) The greatest blood flow is found at the apexes of the lungs.
D) The pulmonary circulation is a high-pressure system.

Question 24

As the amount of O₂ that dissolves in the plasma increases, what is it directly proportional to?

A) Its partial pressure
B) Its solubility coefficient
C) Minute ventilation
D) Temperature

Question 25

An area of the lung has no blood flow but is normally ventilated. Which of the following statements are true about this area?
1) The alveolar gas is like air (PO₂ = 150; PCO₂ = 0).
2) The area represents alveolar dead space.
3) The / is elevated.

A)1 and 2 only
B)1 and 3 only
C)2 and 3 only
D)1, 2, and 3

Question 26

Carbon dioxide diffuses across the alveolar-capillary membrane approximately how many times faster than O₂?

A) 10
B) 20
C) 30
D) 40

Question 27

Even in healthy young subjects, regional differences in pulmonary ventilation and blood flow result in the PaO₂ being lower than the PAO₂. Why is this so?

A) Most blood flows through the apexes of the lung.
B) Most blood flows through areas with high.
C) Most blood flows through the bases of the lung.
D) Most ventilation goes to the apexes of the lung.

Question 28

What is the minimum amount of time that blood must take for pulmonary capillary transit for equilibration of O₂ to occur across the alveolar-capillary membrane?

A) 0.15 sec
B) 0.25 sec
C) 0.35 sec
D) 0.45 sec

Question 29

During normal inspiration, which of the following occurs?

A) Alveoli at the apexes expand less than those at the bases.
B) Alveoli at the apexes expand more than those at the bases.
C) Alveoli at the bases and apexes expand almost equally.
D) Alveoli at the bases expand less than those at the apexes.

Question 30

In order to assess the events occurring at the tissue level, especially tissue oxygenation, what parameter would you sample and measure?

A) Coronary sinus blood
B) Left-sided heart blood
C) Systemic arterial blood
D) Systemic mixed venous blood

Question 31

What is the primary factor that maintains the pressure gradient that drives O₂ from the capillaries into the interstitial spaces and into the cells?

A) Bohr effect on the RBC
B) Cellular consumption of O₂
C) Haldane effect on the RBC
D) Increased carbon dioxide in blood decreasing Hb affinity for O₂

Question 32

At body temperature, how much O₂ will physically dissolve in plasma at a PO₂ of 40 mm Hg?

A) 0.12 ml/dl
B) 0.20 ml/dl
C) 0.30 ml/dl
D) 1.34 g/dl

Question 33

What occurs in the bases of the lung when a person is standing upright?

A) The PAO₂ is higher than normal.
B) The respiratory exchange ratio is elevated.
C) There is significant dead space under normal conditions.
D) Theis lower than the average.

Question 34

What is the normal range of PAO₂ - PaO₂ for healthy young adults breathing room air?

A) 5 to 10 mm Hg
B) 10 to 20 mm Hg
C) 20 to 30 mm Hg
D) 50 to 60 mm Hg

Question 35

Which of the following would you expect to occur if ventilation to an area of the lung remained constant but perfusion to this same area decreased?
1) The PACO₂ should fall.
2) The PAO₂ should fall.
3) The ratio should rise.

A)3 only
B)1 and 2 only
C)1 and 3 only
D)1, 2, and 3

Question 36

An area of the lung has no ventilation but is normally perfused by the pulmonary circulation. Which of the following statement(s) is/are correct?
1) Blood exiting the pulmonary capillary will have a PO₂ = 40 and a PCO₂ = 46.
2) The area represents an alveolar shunt.
3) The is 0.

A)2 and 3 only
B)1 and 3 only
C)2 only
D)1, 2, and 3

Question 37

How is the vast majority of O₂ carried in the blood?

A) As bicarbonate ion (HCO₃)
B) As carbamino compounds
C) Chemically combined with Hb
D) In physical solution

Question 38

If the total hemoglobin content (Hb + HbO₂) of a sample of blood is 20 g/dl and the oxyhemoglobin (HbO₂) content is 15 g/dl, what is the HbO₂ saturation?

A) 17%
B) 50%
C) 75%
D) 83%

Question 39

Which of the following would you expect to occur if perfusion to an area of the lung remained constant, but V_A to this same area decreased?

A) The PACO₂ should fall.
B) The HCO₃^- will fall.
C) The PAO₂ should fall.
D) The ventilation/perfusion ratio () should rise.

Question 40

Breathing room air, a normal PAO₂ - PaO₂ of 5 to 10 mm Hg exists due to which of the following?
1) Anatomical shunts in the pulmonary and cardiac circulations
2) Normal limitations to O₂ diffusion in the lung
3) Regional differences in pulmonary ventilation and blood flow

A)1 and 3 only
B)2 and 4 only
C)1, 2, and 3
D)1 and 2 only

Question 41

In which of the following forms is/are carbon dioxide transported by the blood?
1) Chemically combined with proteins
2) Ionized as bicarbonate (HCO₃^-)
3) Simple physical solution

A)2 only
B)3 only
C)2 and 3 only
D)1, 2, and 3

Question 42

Given the following blood parameters, compute the total O₂ content (dissolved + HbO₂) of the blood in ml/dl: Hb = 18; PO₂ = 40 mm Hg; SO₂ = 73%.

A) 16.5 ml/dl
B) 17.7 ml/dl
C) 18.6 ml/dl
D) 19.5 ml/dl

Question 43

Why is it necessary to keep the patient's PaO₂ greater than 60 mm Hg?

A) A level of 60 mm Hg marks the beginning of the steep part of O₂Hb dissociation curve.
B) Below the 60 mm Hg level, tissue hypoxia is ensured.
C) Oxygen deprivation will cause severe cerebral vasoconstriction below 60 mm Hg.
D) The PaCO₂ will start to rise precipitously if the PaO₂ falls further.

Question 44

In which of the following conditions will erythrocyte concentration of 2,3-DPG be decreased?

A) Anemia
B) Banked blood
C) High pH
D) Hypoxemia

Question 45

At a PaO₂ of 65 mm Hg, what is the approximate saturation of Hb with O₂?

A) 73%
B) 80%
C) 90%
D) 97%

Question 46

Compared to normal levels, a shift in the HbO₂ curve to the right has which of the following effects?
1) The affinity of Hb for O₂ decreases.
2) The Hb saturation for a given PO₂ falls.
3) The Hb saturation for a given PO₂ rises.

A)1 only
B)1 and 2 only
C)2 and 3 only
D)1, 2, and 3

Question 47

The affinity of Hb for carbon monoxide (CO) is approximately how many times greater than its affinity for O₂?

A) 10 to 50 times greater
B) 50 to 90 times greater
C) 100 to 190 times greater
D) 200 or greater

Question 48

Given the following blood parameters, compute the total O₂ content (dissolved + HbO₂) of the blood in ml/dl: Hb = 16; PO₂ = 625 Hg; SO₂ = 100%.

A) 17.8 ml/dl
B) 19.4 ml/dl
C) 21.4 ml/dl
D) 23.3 ml/dl

Question 49

Which of the following is true regarding fetal hemoglobin (HbF)?

A) It has a reduced level of 2,3-DPG.
B) It is replaced in the first month of life.
C) It delivers more O₂ to tissues at low PaO₂ than normal Hb.
D) It has a higher P₅₀ than normal Hb.

Question 50

Which of the following increases the affinity of Hb for O₂?
1) Decreased 2,3-DPG
2) Decreased PCO₂
3) Increased pH
4) Increased temperature

A)1, 2, and 3 only
B)1, 2, and 4 only
C)3 and 4 only
D)3 and 4 only

Question 51

What is the effect of an elevated intracellular 2,3-DPG concentration?

A) Decreases the availability of O₂ to the tissues.
B) Increases the affinity of Hb for O₂.
C) Increases the availability of O₂ to the tissues.
D) Shifts the HbO₂ dissociation curve to the left.

Question 52

The oxidation of the Hb molecule's iron ions to the ferric state (Fe³⁺) results in which of the following?
1) Form of anemia called sickle cell anemia
2) Formation of methemoglobin (metHb)
3) Inability of metHb to bind with O₂

A)1 and 2 only
B)1 and 3 only
C)2 and 3 only
D)1, 2, and 3

Question 53

A patient has a whole-body O₂ consumption of 320 ml/min and a measured CaO₂ - CO₂ of 8 ml/dl. What is the cardiac output?

A) 3.2 L/min
B) 4.0 L/min
C) 5.0 L/min
D) 7.0 L/min

Question 54

Which of these statements applies to the following reaction: Prot-NH₂ + CO₂ Prot-NHCOO^- + H⁺?

A) Approximately 20% of the total blood carbon dioxide is carried in this form.
B) It is second in importance to only the bicarbonate buffer system.
C) It represents the formation of blood carbamino compounds.
D) The resulting H⁺ ions are buffered by reduced HCO_3.

Question 55

A patient has a P₅₀ value of 29 mm Hg. What does this indicate?

A) Decreased affinity of Hb for O₂
B) Higher than normal Hb saturation for a given PO₂
C) Increased affinity of Hb for O₂
D) Normal position in the HbO₂

Question 56

What role does the Bohr effect play in O₂ transport?

A) Describes the effect of varying enzyme levels on Hb and O₂ affinity.
B) Diminishes tissue oxygenation due to electrolyte imbalances.
C) Enhances O₂ delivery to tissues and O₂ pickup at lungs.
D) Explains the effect that O₂ levels have on carbon dioxide transport.

Question 57

According to the Fick principle, if O₂ consumption remains constant, an increase in cardiac output will manifest itself as which of the following?

A) Decrease in the CaO₂ - CO_2.
B) Increase in the CaO_2.
C) Increase in the CaO₂ - CO_2.
D) Decrease in the CO_2.

Question 58

According to the Bohr effect, when the pH drops, what happens?
1) The affinity of Hb for O₂ decreases.
2) The Hb saturation for a given PO₂ falls.
3) The Hb saturation for a given PO₂ rises.

A)1 and 2 only
B)2 only
C)2 and 3 only
D)1, 2, and 3

Question 59

What is the approximate normal CaO₂ - CO₂ in a healthy adult at rest?

A) 5 ml/dl
B) 15 ml/dl
C) 20 ml/dl
D) 250 ml/dl

Question 60

What happens when the temperature of the blood rises?
1) The Hb saturation for a given PO₂ falls.
2) The HbO₂ curve shifts to the right.
3) The affinity of Hb for O₂ increases.

A)1 and 2 only
B)1 and 3 only
C)2 only
D)1, 2, and 3

Question 61

The largest percentage of carbon dioxide transported in the blood occurs as which of the following?

A) Carbamino-Hb
B) Carbonic acid (H₂CO₃)
C) HCO₃^-
D) Physically dissolved carbon dioxide

Question 62

An abnormal metabolic state in which the tissues are unable to utilize the O₂ made available to them best describes which of the following?

A) Diffusion hypoxia
B) Dysoxia
C) Hemic hypoxia
D) Physiologic shunt

Question 63

A patient breathing 40% O₂ at sea level has a PaO₂ of 50 mm Hg, a PCO₂ of 30 mm Hg, and a PAO₂ - PaO₂ of 250 mm Hg. When the FiO₂ is raised to 0.7, the PaO₂ rises to only 58 mm Hg. Hypoxemia is primarily due to which of the following?

A) Hypoventilation
B) Impaired diffusion
C) Right-to-left shunt
D) imbalance

Question 64

When Hb saturation with O₂ is high, less carbon dioxide is carried in the blood. What is this relationship called?

A) Bohr effect
B) Chloride shift
C) Dissociation constant
D) Haldane effect

Question 65

Which of the following are potential causes of hypoxia?
1) Decrease in arterial PO₂
2) Decrease in available Hb
3) Decrease in cardiac output

A)1 and 2 only
B)1 and 3 only
C)2 and 3 only
D)1, 2, and 3

Question 66

What is the most common cause of hypoxemia in patients with lung disease?

A) Diffusion defect
B) Hypoventilation
C) Right-to-left shunt
D) mismatch

Question 67

A patient with a normal PaO₂ and cardiac output is exhibiting signs and symptoms of tissue hypoxia. What is the most likely cause?

A) Hemoglobin deficiency
B) Low ambient PO₂
C) Right-to-left shunt
D) Hypoventilation

Question 68

Which of the following statements is true regarding the Haldane effect?

A) At high SaO₂ levels, carbon dioxide more readily forms carbamino compounds.
B) At high SaO₂ levels, the capacity of blood to hold carbon dioxide decreases.
C) At high SaO₂ levels, the capacity of blood to hold carbon dioxide increases.
D) At low SaO₂ levels, the capacity of blood to hold carbon dioxide decreases.

Question 69

The expected PaO₂ for an 80-year-old man who is otherwise in good health and breathing room air is approximately what level?

A) 50 mm Hg
B) 75 mm Hg
C) 80 mm Hg
D) 90 mm Hg

Question 70

The conversion of HbO₂ to deoxygenated Hb does which of the following?
1) Decreases blood carbon dioxide content.
2) Enhances carbon dioxide loading on Hb.
3) Helps buffer H⁺ ions.

A)2 and 3 only
B)1 and 2 only
C)3 only
D)1, 2, and 3

Question 71

Under which of the following conditions may carbon dioxide removal be impaired?
1) When a mismatch exists.
2) When the dead space ventilation/min is increased.
3) When the minute ventilation is inadequate.

A)1 and 2 only
B)1 and 3 only
C)2 and 3 only
D)1, 2, and 3

Question 72

When O₂ uptake by the tissues is abnormally low, as occurs in certain forms of dysoxia, what would you expect to find?

A) Decreased CaO₂
B) Decreased CvO₂
C) Decreased PaO₂
D) Increased CvO₂

Question 73

What is the most important component in the O₂ transport system?

A) Dissolved O₂ in ml/dl
B) HCO₃^-
C) Hb
D) PaO₂

Question 74

In the presence of an acutely reduced arterial O₂ content (hypoxemia), normal O₂ delivery to the tissues can be maintained by which of the following?

A) Hyperventilation (increased V_A)
B) Increased RBC production
C) Increasing the cardiac output
D) Peripheral vasoconstriction

Question 75

Why is the presence of carbonic anhydrase in RBCs so crucial for carbon dioxide transport?

A) Forms H₂CO_3, which is the major buffer for carbon dioxide.
B) Drives the hydrolysis reaction that forms HCO₃^-.
C) Forms H₂CO₃, which is the way the majority of carbon dioxide is transported.
D) Without its formation, carbon dioxide could not be excreted at the lungs.

Question 76

Which of the following would you expect to find with "O₂ debt"?
1) Accentuated in diseases such as sepsis.
2) O₂ demand exceeds O₂ delivery.
3) O₂ excess usage results in debt.

A)1, 2, and 3
B)1 and 2 only
C)2 only
D)2 and 3 only

Question 77

A patient breathing room air at sea level has the following arterial blood gases: PaO₂ = 62 mm Hg; PCO₂ = 75 mm Hg. When the FIO₂ is raised to 0.28, the PaO₂ rises to 95 mm Hg. What is the most likely cause of the hypoxemia?

A) Hypoventilation
B) Impaired diffusion
C) Right-to-left shunt
D) V/Q imbalance

Question 78

Hypoxia is best defined as a condition in which what occurs?

A) Blood Hb levels are less than normal (15 g/dl).
B) The arterial PCO₂ is greater than normal (45 mm Hg).
C) The arterial PO₂ is greater than normal (100 mm Hg).
D) Tissue O₂ delivery is inadequate to meet cellular needs.

Question 79

Which of the following equations best describes O₂ delivery to the tissues?

A) Arterial O₂ content ÷ cardiac output
B) Arterial O₂ content . cardiac output
C) Cardiac output + arterial O₂ content
D) Cardiac output . vascular resistance

Question 80

When a Hb molecule accumulates excessive amounts of HCO₃^-, it is expelled from the cell in exchange for Cl^-. What is this called?

A) Bohr effect
B) Haldane effect
C) Hamburger phenomenon
D) Hydrolysis phenomenon