Respiratory - from West's 8th ed Chapter 5 - Ventilation-Perfusion Relationships

Question 1

1. A climber reaches an altitude of 4,500 m (14,800 ft) where the barometric pressure is 447 mm Hg. The PO2 of moist inspired gas (in mm Hg) is:
A. 47
B. 63
C. 75
D. 84
E. 98

Answer 1

D

Question 2

2. A man with normal lungs and an arterial PCO2 of 40 mm Hg takes an overdose of barbiturate that halves his alveolar ventilation but does not change his CO2 output. If his respiratory exchange ratio is 0.8, what will be his arterial PO2 (in mm Hg), approximately?

A. 40
B. 50
C. 60
D. 70
E. 80

Answer 2

B

Question 3

3. In the situation described in Question 2, how much does the inspired O2 concentration (%) have to be raised to return the arterial PO2 to its original level?
A. 7
B. 11
C. 15
D. 19
E. 23

Answer 3

A

Question 4

4. A patient with normal lungs but a right-to-left shunt is found at catheterization to have oxygen concentrations in his arterial and mixed venous blood of 18 and 14ml/100ml, respectively. If the O2 concentration of the blood leaving the pulmonary capillaries is calculated to be 20ml/100ml, what is his shunt as a percentage of his cardiac output?
A. 23
B. 33
C. 43
D. 53
E. 63

Answer 4

B

Question 5

5. If a climber on the summit of Mt. Everest (barometric pressure 247 mm Hg) maintains an alveolar PO2 of 34 mm Hg and is in a steady state (R is less than or equal to 1), his alveolar PCO2 (in mm Hg) cannot be any higher than:

A. 5
B. 8
C. 10
D. 12
E. 15

Answer 5

B

Question 6

6. A patient with severe chronic obstructive pulmonary disease, which causes marked ventilation-perfusion inequality, has an arterial PO2 of 50 mm Hg and an arterial PCO2 of 40 mm Hg. The PCO2 is normal despite the hypoxemia because:

A. Ventilation-perfusion inequality does not interfere with CO2 elimination.
B. Much of the CO2 is carried as bicarbonate.
C. The formation of carbonic acid is accelerated by carbonic anhydrase.
D. CO2 diffuses much faster through tissue than O2.
E. The O2 and CO2 dissociation curves have different shapes.

Answer 6

E

Question 7

7. The apex of the upright human lung compared with the base has:

A. A higher PO2.
B. A higher ventilation.
C. A lower pH in end-capillary blood.
D. A higher blood flow.
E. Smaller alveoli.

Answer 7

A

Question 8

8. If the ventilation-perfusion ratio of a lung unit is decreased by partial bronchial obstruction while the rest of the lung is unaltered, the affected lung unit will show:

A. Increased alveolar PO2.
B. Decreased alveolar PCO2.
C. No change in alveolar PN2.
D. Rise in pH of end-capillary blood.
E. Fall in oxygen uptake.

Answer 8

E

Question 9

9. A patient with lung disease who is breathing air has an arterial PO2 and PCO2 of 49 and 48 mm Hg, respectively, and a respiratory exchange ratio of 0.8. The approximate alveolar-arterial difference for PO2 (in mm Hg) is:

A. 10
B. 20
C. 30
D. 40
E. 50

Answer 9

D