Chapter 11: Gas Exchange and Transport

Test Bank

MULTIPLE CHOICE

1.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

ANS: B

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

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2.The lowest PO2 would normally be found in what location?

a. arterial blood

b. atmospheric air

c. cells

d. venous blood

ANS: C

The intracellular PO2 (approximately 5 mm Hg) provides the final gradient for oxygen diffusion into the cell.

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3.The highest PCO2 levels are found in what location?

a. arterial blood

b. atmospheric air

c. cells

d. venous blood

ANS: C

The partial pressure of carbon dioxide (PCO2) is highest in the cells (approximately 60 mm Hg).

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4.Which of the following are true regarding the PACO2?

1. directly proportional to whole-body carbon dioxide production

2. inversely proportional to alveolar ventilation ( A)

3. normally maintained at about 35 to 45 mm Hg

a. 2 and 3

b. 1, 2, and 3

c. 1 and 2

d. 1 and 3

ANS: B

PACO2 varies directly with the body’s production of carbon dioxide (CO2) and inversely with alveolar ventilation ( A). Under normal conditions it is maintained at about 35 to 45 mm Hg.

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5.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

ANS: A

In a healthy individual the normal CO2 of is about 200 ml/min.

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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  A

c. if  A decreases relative to carbon dioxide production

d. when the patient is febrile

ANS: C

The PACO2 will increase above this level if carbon dioxide production increases while alveolar ventilation remains constant or when alveolar ventilation decreases while CO2 remains constant.

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7.A 70-kg male patient has a  CO2 of 200 ml/min and a  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.

ANS: C

When the  CO2 is normal while the  A is elevated, the PACO2 must be lower then normal. Likewise, the PACO2 will fall if carbon dioxide production decreases or alveolar ventilation increases.

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8.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

ANS: D

Many factors determine the alveolar partial pressure of oxygen (PAO2). Most important is the inspired partial pressure of oxygen, or PIO2.

DIF: Application REF: p. 250 OBJ: 2

9.The PAO2 depends on which of the following factors?

1. ambient (atmospheric) pressure

2. fractional concentration of inspired oxygen

3. level of  A

4. types of fuels burned (fat, protein, carbohydrate)

a. 1, 2, and 3

b. 1 and 2

c. 3 only

d. 1, 2, 3, and 4

ANS: D

PAO2 = FIO2  (PB – 47) – PACO2  0.8

where FIO2 is fraction of inspired oxygen, PB is barometric pressure, 47 is water vapor tension (in mm Hg) at 37° C, PACO2 is alveolar PCO2, and 0.8 is normal respiratory exchange ratio (R). As the  A is the primary determinant of PACO2 any changes in  A will affect the PAO2. Likewise the fuel source will determine the RQ which is normally 0.8.

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10.Calculate the approximate PAO2 given the following conditions (assume R = 0.8): FIO2 = .40, PB = 770 mm Hg, PACO2 = 31 mm Hg

a. 100 mm Hg

b. 135 mm Hg

c. 250 mm Hg

d. 723 mm Hg

ANS: C

PAO2 = FIO2 (PB – 47) – PACO2  0.8

where FIO2 is fraction of inspired oxygen, PB is barometric pressure, 47 is water vapor tension (in mm Hg) at 37° C, PACO2 is alveolar PCO2, and 0.8 is normal respiratory exchange ratio (R).

PAO2 = 0.4(770 – 47) – (31/0.8)

PAO2 = 250.45 mm Hg

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11.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

ANS: B

If the FIO2 is 1.0, the PB is 760 mm Hg, and the PACO2 is 40 mm Hg, the alveolar partial pressure of oxygen can be estimated as follows:

PAO2 = 1  (760 mm Hg – 47 ) – (40 mm Hg  0.8) = 663 mm Hg

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12.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

ANS: B

Nitrogen is inert and plays no role in gas exchange. However, nitrogen does occupy space and exert pressure. According to Dalton’s law, the partial pressure of alveolar nitrogen must equal the pressure it would exert if it alone were present. Thus, to compute the partial pressure of alveolar nitrogen, subtract the pressures exerted by all the other alveolar gases, as follows:

PAN2 = PB – (PAO2 + PACO2 + PH2O)

PAN2 = 760 mm Hg – (100 mm Hg + 40 mm Hg + 47 mm Hg)

PAN2 = 760 mm Hg – 187 mm Hg

PAN2 = 573 mm Hg

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13.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

ANS: A

Based on the alveolar air equation, if the FIO2 remains constant, then the PAO2 must vary inversely with the PACO2.

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14.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  A decrease the PACO2 and increase the PAO2.

d. The PAO2 varies proportionally with the PACO2.

ANS: C

With a constant carbon dioxide production, a decrease in  A simultaneously raises the PACO2 and lowers the PAO2.

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15.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

ANS: B

Neural control mechanisms and the increased of work breathing prevent decreases in PACO2 much below 15 to 20 mm Hg. Thus, whenever a patient is breathing room air at sea level, the respiratory therapist should not expect to see a PaO2 any higher than 120 mm Hg during hyperventilation.

DIF: Application REF: p. 250 OBJ: 2