Deck 11: Gas Exchange and Transport

Question 1

The lowest PO₂ would normally be found in what location?

A)arterial blood
B)atmospheric air
C)cells
D)venous blood

Answer 1

C

Question 2

A normal person breathing 100% oxygen at sea level would have PAO₂ of about what level?

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

Answer 2

B

Question 3

A 70-kg male patient has a $\dot { V }$ CO₂ of 200 ml/min and a $\dot { V }$ _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 $\dot { V }$ _A is abnormally low.
C)The patient will have a lower than normal PACO₂.
D)The patient will have a higher than normal PACO₂.

Answer 3

The patient will have a lower than normal PACO₂.

Question 4

The highest PCO₂ levels are found in what location?

A)arterial blood
B)atmospheric air
C)cells
D)venous blood

Question 5

The PAO₂ depends on which of the following factors?
I.ambient (atmospheric) pressure
II.fractional concentration of inspired oxygen
III.level of $\dot { V }$ _A
IV.types of fuels burned (fat, protein, carbohydrate)

A)I, II, and III
B)I and II
C)III only
D)I, II, III, and IV

Question 6

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

Question 7

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 about 30 mm Hg
B)PAO₂ to fall by about 40 mm Hg
C)PAO₂ to rise by about 30 mm Hg
D)PAO₂ to rise by about 40 mm Hg

Question 8

What is the primary determinant of the PAO₂?

A)body's $\dot { V }$ CO₂
B)metabolic rate of the body tissues
C)PaO₂
D)PO₂ in the inspired gas

Question 9

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 10

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 $\dot { V }$ _A
C)if $\dot { V }$ _A decreases relative to carbon dioxide production
D)when the patient is febrile

Question 11

Which of the following are true regarding the PACO₂?
I.directly proportional to whole-body carbon dioxide production
II.inversely proportional to alveolar ventilation ( $\dot { V }$ _A)
III.normally maintained at about 35 to 45 mm Hg

A)II and III
B)I, II, and III
C)I and II
D)I and III

Question 12

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 13

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 14

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

A)air
B)carbon dioxide
C)oxygen
D)nitrogen

Question 15

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 16

Assuming a constant FIO₂ and carbon dioxide production, which of the following statements are correct?

A)An increased PACO₂ will result in and increased PAO₂.
B)Increased FIO₂ blows off carbon dioxide
C)Increases in $\dot { V }$ _A decrease the PACO₂ and increase the PAO₂.
D)The PAO₂ varies proportionally with the PACO₂.

Question 17

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

Question 18

Which of the following "layers" must be traversed by gases moving across the alveolar-capillary membrane?
I)alveolar epithelial membrane
II)capillary endothelial membrane
III)interstitial space
IV)transbronchial radial tethering mechanisms

A)I, II, and III
B)I, II, and IV
C)II and III
D)I, II, III, and IV

Question 19

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 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

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

A)as bicarbonate ion (HCO₃)
B)as carbamino compounds
C)chemically combined with Hb
D)in physical solution

Question 22

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

A)Bohr effect on the RBC
B)cellular consumption of oxygen
C)Haldane effect on the RBC
D)increased carbon dioxide in blood decreases Hb affinity for oxygen

Question 23

Breathing room air, a normal PAO₂ - PaO₂ of 5 to 10 mm Hg exists due to which of the following?
I.anatomical shunts in the pulmonary and cardiac circulations
II.normal limitations to oxygen diffusion in the lung
III.regional differences in pulmonary ventilation and blood flow

A)I and III
B)III and IV
C)I, II, and III
D)I and II

Question 24

At body temperature, how much oxygen 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 25

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 $\dot { V }$ / $\dot { Q }$ .
C)Most blood flows through the bases of the lung.
D)Most ventilation goes to the apexes of the lung.

Question 26

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

A)The apexes receive about 20 times more blood flow than the bases.
B)The bases receive about 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 27

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 28

An area of the lung has no blood flow but is normally ventilated. Which of the following statements are true about this area?
I .The alveolar gas is like air (PO₂ = 150; PCO₂ = 0).
II.The area represents alveolar dead space.
III.The $\dot { V }$ / $\dot { Q }$ is elevated.

A)I and II
B)I and III
C)II and III
D)I, II, and III

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

What occurs in the bases of the upright lung?

A)The PAO₂ is higher than normal.
B)The respiratory exchange ratio is elevated.
C)There is significant deadspace under normal conditions
D)The $\dot { V }$ / $\dot { Q }$ is lower than the average.

Question 31

As the amount of oxygen 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 32

An area of the lung has no ventilation but is normally perfused by the pulmonary circulation. Which of the following statements are correct?
I .Blood exiting the pulmonary capillary will have a PO₂ = 40 and a PCO₂ = 46.
II.The area represents an alveolar shunt.
III.The $\dot { V }$ / $\dot { Q }$ is 0.

A)II and III
B)I and III
C)II only
D)I, II, and III

Question 33

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 34

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 35

Under normal physiologic circumstances, how many milliliters of oxygen 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 36

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

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

Question 37

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 ( $\dot { V }$ / $\dot { Q }$ ) should rise.

Question 38

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

A)functional residual capacity (FRC)
B)inspired oxygen concentration
C)level of V_A
D)rate of pulmonary blood flow

Question 39

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?
I .The PACO₂ should fall.
II.The PAO₂ should fall.
III.The $\dot { V }$ / $\dot { Q }$ ratio should rise.

A)III only
B)I and II
C)I and III
D)I, II, and III

Question 40

Carbon dioxide diffuses across the alveolar-capillary membrane about how many times faster than oxygen?

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

Question 41

What is the approximate normal CaO₂ - C $\over{V}$ O₂ in a healthy adult at rest?

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

Question 42

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 43

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

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

Question 44

Compared to normal levels, a shift in the HbO₂ curve to the right has which of the following effects?
I .The affinity of Hb for oxygen decreases.
II.The Hb saturation for a given PO₂ falls.
III.The Hb saturation for a given PO₂ rises.

A)I only
B)I and II
C)II and III
D)I, II, and III

Question 45

What role does the Bohr effect play in oxygen transport?

A)describes the affect of varying enzyme levels on Hb and oxygen affinity
B)diminishes tissue oxygenation due to electrolyte imbalances
C)enhances oxygen delivery to tissues and oxygen pickup at lungs
D)explains the affect that oxygen levels have on carbon dioxide transport

Question 46

Given the following blood parameters, compute the total oxygen 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 47

A patient has a whole-body oxygen consumption of 320 ml/min and a measured CaO₂ - C $\over{V}$ O₂ 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 48

The oxidation of the Hb molecule's iron ions to the ferric state (Fe³⁺) results in which of the following?
I.form of anemia called sickle cell anemia
II.formation of methemoglobin (metHb)
III.inability of metHb to bind with oxygen

A)I and II
B)I and III
C)II and III
D)I, II, and III

Question 49

According to the Bohr effect, when the pH drops (blood becomes more acidic), what happens?
I .The affinity of Hb for oxygen decreases.
II.The Hb saturation for a given PO₂ falls.
III.The Hb saturation for a given PO₂ rises.

A)I and II
B)II only
C)II and III
D)I, II, and III

Question 50

Which of the following does NOT increase the affinity of Hb for oxygen?

A)decreased 2,3-DPG
B)decreased PCO₂
C)increased pH
D)increased temperature

Question 51

What happens when the temperature of the blood rises?
i.The Hb saturation for a given PO₂ falls.
II.The HbO₂ curve shifts to the right.
III.The affinity of Hb for oxygen increases.

A)I and II
B)I and III
C)II only
D)I, II, and III

Question 52

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 53

Given the following blood parameters, compute the total oxygen 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 54

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

A)decreased affinity of Hb for oxygen
B)higher than normal Hb saturation for a given PO₂
C)increased affinity of Hb for oxygen
D)normal position in the HbO₂

Question 55

In which of the following forms is carbon dioxide transported by the blood?
I.chemically combined with proteins
II.ionized as bicarbonate (HCO₃^-)
III.simple physical solution

A)II only
B)III only
C)II and III
D)I, II, and III

Question 56

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

A)decrease in the CaO₂ - C $\over{V}$ O₂
B)increase in the CaO₂
C)increase in the CaO₂ - C $\over{V}$ O₂
D)decrease in the C $\over{V}$ O₂

Question 57

Which of the following are 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 oxygen to tissues at low PaO₂ than normal Hb.
D)It has a higher P₅₀ than normal Hb.

Question 58

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

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

Question 59

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

A)decreases the availability of oxygen to the tissues
B)increases the affinity of Hb for oxygen
C)increases the availability of oxygen to the tissues
D)shifts the HbO₂ dissociation curve to the left

Question 60

Which of the following applies to the following reaction: Prot-NH₂ + CO₂ $\leftrightarrow$ Prot-NHCOO^- + H⁺?

A)About 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 HCO₃^-.

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 oxygen made available to them best describes which of the following?

A)diffusion hypoxia
B)dysoxia
C)hemic hypoxia
D)physiologic shunt

Question 63

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 oxygen delivery is inadequate to meet cellular needs.

Question 64

What is the most common cause of hypoxemia?

A)diffusion defect
B)hypoventilation
C)right-to-left shunt
D) $\dot { V }$ / $\dot { Q }$ mismatch

Question 65

The conversion of HbO₂ to deoxygenated Hb does which of the following?
I)decreases blood carbon dioxide content
II)enhances carbon dioxide loading on Hb
III)helps buffer H⁺ ions

A)II and III
B)I and II
C)III only
D)I, II, and III

Question 66

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

Question 67

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) $\dot { V }$ / $\dot { Q }$ imbalance

Question 68

Under which of the following conditions may carbon dioxide removal be impaired?
I.when a $$\dot { V }$$ / $\dot { Q }$ imbalance exists
II.when the dead space ventilation/min is increased
III.when the minute ventilation is inadequate

A)I and II
B)I and III
C)II and III
D)I, II, and III

Question 69

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

A)forms H₂CO₃ 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 70

When Hb saturation with oxygen 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 71

Which of the following are potential causes of hypoxia?
I)decrease in arterial PO₂
II)decrease in available Hb
III)decrease in cardiac output

A)I and II
B)I and III
C)II and III
D)I, II, and III

Question 72

When oxygen 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

In the presence of an acutely reduced arterial oxygen content (hypoxemia), normal oxygen 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 74

A patient breathing 40% oxygen 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) $\dot { V }$ / $\dot { Q }$ imbalance

Question 75

Which of the following would you expect to find with "oxygen debt"?
I)accentuated in diseases such as sepsis
II)oxygen demand exceeds oxygen delivery
III)oxygen excess usage results in debt

A)I, II, and III
B)I and II
C)II only
D)II and III

Question 76

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

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

Question 77

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

A)arterial oxygen content /cardiac output
B)arterial oxygen content * cardiac output
C)cardiac output + arterial oxygen content
D)cardiac output * vascular resistance

Question 78

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

A)dissolved oxygen in ml/dl
B)HCO₃^-
C)Hb
D)PaO₂

Question 79

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 80

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.