Quiz 105 · Alveolar Ventilation and Gas Exchange in Lungs

15 questions on chapter 105. Pick one answer for each, then save. Your answers stay in this browser, and the right ones are shown at the top of the next quiz.

1. In the single-breath nitrogen test, the subject breathes out after a breath of pure O₂. Why does the first N₂ in the expired air mark the end of the dead space?

N₂ diffuses from the blood into the airways during expirationThe airway lining releases stored N₂ once the O₂ is used upThe dead space holds only O₂, so any N₂ must be alveolar gasN₂ appears only when the expiratory muscles contract hard

2. On the single-breath nitrogen curve, the change from dead-space air to alveolar air is S-shaped rather than sharp because:

Some alveolar gas mixes with the dead-space gasThe inspired breath of O₂ is not quite pureExpiratory flow pauses briefly halfway throughThe airway lining absorbs part of the N₂

3. When the nitrogen curve is analysed with a planimeter, the dead space is found from:

The peak N₂ concentration divided by the tidal volumeThe slope of the alveolar plateau multiplied by the breathing rateThe dead-space area as a fraction of the total area, applied to the volume expiredThe time N₂ takes to reach the alveolar plateau

4. Tidal volume is 500 mL, dead space 150 mL and respiratory rate 12/min. What is the alveolar ventilation?

4200 mL/min5850 mL/min1800 mL/min6000 mL/min

5. Two people have the same minute ventilation. One breathes rapidly and shallowly, the other slowly and deeply. The rapid, shallow breather has:

The same alveolar ventilation, as minute ventilation is equalLower alveolar ventilation, with hypoxia but a low PCO₂Lower alveolar ventilation, with hypoxia and hypercapniaHigher alveolar ventilation, with a low PCO₂

6. In the pulmonary function laboratory, alveolar ventilation is calculated as:

CO₂ expired per minute ÷ fractional CO₂ in alveolar gasCO₂ expired per minute × fractional CO₂ in alveolar gasTidal volume × rate ÷ fractional CO₂ in alveolar gasFractional CO₂ in alveolar gas ÷ CO₂ expired per minute

7. If alveolar ventilation is halved, the alveolar PCO₂:

Rises by about a quarterHalvesDoublesStays the same

8. Which of these causes peripheral rather than central hypoventilation?

Opiate overdoseBarbiturate overdoseMyasthenia gravisHead injury

9. The normal thickness of the alveolar-capillary membrane is:

0.2–0.5 µ0.02–0.05 µ20–50 µ2–5 µ

10. Which of these is NOT one of the six layers of the alveolar-capillary membrane itself?

Interstitial fluidRed cell membraneSurfactant liningCapillary basement membrane

11. In your book's table of partial pressures, venous blood has a PO₂ and PCO₂ of about:

100 and 40 mmHg116 and 32 mmHg95 and 40 mmHg40 and 46 mmHg

12. The diffusion gradient for O₂ across the alveolar-capillary membrane is about:

6 mmHg60 mmHg160 mmHg100 mmHg

13. A patient with heart failure develops interstitial edema of the lungs. Which blood-gas picture does this diffusion defect typically produce?

Normal PO₂ with a low PCO₂Normal PO₂ with a raised PCO₂Low PO₂ with a markedly raised PCO₂Low PO₂ with little change in PCO₂

14. Why is carbon monoxide the gas used to measure the lung's diffusing capacity?

Its uptake is flow-limited, so it tracks pulmonary blood flow closelyIts uptake is diffusion-limited, and its capillary partial pressure stays near zeroIt is present in venous blood at a steady, known concentrationHemoglobin binds it less strongly than it binds oxygen

15. The uptake of nitrous oxide (N₂O) from the alveoli is flow-limited because:

Hemoglobin binds N₂O 210 times more strongly than O₂Blood equilibrates with alveolar N₂O within 0.1 sN₂O is 20 times more soluble in water than CO₂N₂O never equilibrates within the 0.75 s transit time

Save my answers