PHYL 422 Review Questions
Set 7
Modified from Shumaker and Hlastaa’’s Textbooks
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If two gas volumes with different oxygen tensions are separated by a membrane, what effect will increasing the solubility of oxygen in the
membrane have on the rate of equilibration between the compartments?
What processes contribute to the transport of gases from ambient air to the alveolar capilllary membrane?
What are the components of the alveolar- capillary barrier?
Is the transport of oxygen in pulmonary capillaries normally limited by perfusion or diffusion?
What factors might contribute to a decrease in the diffusing capacity measurement for carbon monoxide?
How does exercise affect the carbon monoxide diffusing capacity measurement?
What is the overall the ventilation perfusion ratio and how does this ratio vary form the apex to the base of the lungs.
What happens when the ventilation perfusion ratio decreases?
What is the respiratory quotient when a person’s tissues consume on average 275 ml O2 per minute and produce 195 ml CO2 per
minute?
What is the significance of the calculated ideal alveolar oxygen tension for a lung?
Why does systemic arterial blood PO2 decrease more than arterial PCO2 increases when shunt or ventilation-perfusion inequality is
present?
Why doesn’t ventilation with pure oxygen correct the hypoxemia caused by shunt?
Why is the (A – a)DO2 greater than 0 torr in a normal healthy lung?
Answers
1. Increasing the solubility in the membrane will speed up the rate of equilibration.
2. Convection (bulk flow) carries air from the mouth to the distal airways; diffusion transports gas up to the gas-blood barrier.
3. From the alveolus toward the capillary: surfactant layer, alveolar epithelium, interstitial space, and pulmonary capillary endothelium, plasma. On
average, this barrier is about 0.6 μm in thickness.
4. Oxygen equilibration is normally limited by perfusion, because blood equilibrates with alveolar gas before the end of the pulmonary capillary.
5. Decreased surface area, increased membrane thickness and decreased blood hemoglobin concentration.
6. By increasing the number of perfused capillaries and the volume of blood within alveolar septal capillaries, exercise increased the diffusing
capacity for carbon monoxide.
7. The overall V/Q ratio is 0.8 and it is highest at the apex compared to the base of the lungs in an upright individual
8. Alveolar PCO2 rises and alveolar PO2 decreases.
10. RQ=0.7
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10. The value calculated from the ideal alveolar oxygen equation represents the highest blood P O2 value that could be produced by a given lung.
Thus, the (A – a)DO2 represents the difference between what the lung theoretically could produce and what it actually yielded.
11. When shunt or ventilation – perfusion inequality is present, blood from normally ventilated alveoli admixes with blood from non-ventilated (or
poorly ventilated) lung regions. Because the oxygen partial pressure-content relationship is sigmoidal, excessive ventilation of normal alveoli
cannot significantly augment the oxygen content in the blood leaving them. Because the partial pressure-content relationship for carbon dioxide is
much more linear, excessive ventilation of some alveoli can effectively compensate for the under-ventilation of others, in terms of carbon dioxide
exchange. This difference is often manifested by a low arterial PO2 with a normal PCO2 in many forms of lung disease.
12. Ventilation with pure oxygen cannot fully correct they hypoxemia caused by shunt because the non-ventilated lung regions cannot be directly
affected by a gas that does not ventilate them.
13. Even healthy lungs exhibit a small (A – a)DO2 that is caused largely by small topographical ventilation-perfusion heterogeneity and to a lesser
extent the normal R-L anatomic shunt.