39 Questions
Which gas has the fastest equilibration between alveolar partial pressure and partial pressure in blood?
Nitrous oxide
What factor limits the diffusion of carbon monoxide from the alveolus to the pulmonary capillary blood?
Diffusivity in the barrier
Why does the partial pressure of carbon monoxide in the pulmonary capillary blood not match that of the alveoli?
Chemical combination with hemoglobin
Why is carbon monoxide transfer considered diffusion-limited rather than perfusion-limited?
Chemical combination with hemoglobin
At resting cardiac outputs, how long does blood typically spend in a pulmonary capillary?
0.75 second
What contributes to the decrease in velocity of bulk flow as air approaches the alveoli during inspiration?
Increased total cross-sectional area in distal airways
How does oxygen primarily move through the alveoli according to its partial pressure gradient?
By diffusion
According to Henry's law, what determines the amount of a gas absorbed by a liquid with which it does not chemically combine?
The partial pressure of the gas and its solubility in the liquid
What determines the rate of diffusion of gas through the alveolar-capillary barrier according to Fick's law for diffusion?
Surface area, diffusivity, and barrier thickness
How does an increase in capillaries recruited during exercise impact the surface area available for diffusion?
Increases surface area for diffusion
What factor can increase the transfer of nitrous oxide from a particular alveolus to its pulmonary capillary?
Increasing the time blood stays in the pulmonary capillary
At what point does oxygen transfer from alveolus to pulmonary capillary become perfusion-limited?
When the partial pressure of oxygen in the blood rises to that in the alveolus
What happens to the partial pressure gradient across the alveolar-capillary membrane when oxygen is chemically bound to hemoglobin?
It becomes negligible
What effect does exercise have on the time blood spends in the pulmonary capillary?
It decreases, allowing less time for gas exchange
How does increasing cardiac output affect nitrous oxide transfer in pulmonary capillaries?
It increases nitrous oxide transfer by decreasing equilibration time
What is the relationship between solubility and diffusion through the alveolar-capillary barrier?
Directly proportional
According to Graham's law, what is the relative rate of diffusion of two gases inversely proportional to?
The square roots of their molecular weights
Which factor is NOT a component that limits the movement of a gas through the alveolar-capillary barrier according to Fick's law for diffusion?
Molecular weight of the gas
Why is the partial pressure gradient of a gas across the barrier considered a major determinant of its rate of diffusion?
It determines how gases move from mixed venous blood to pulmonary capillaries
What is the main difference between gas movement by diffusion and gas movement through conducting airways?
Gas movement by diffusion is based on partial pressure gradients, while gas movement through conducting airways is based on differences in total pressure.
Why does gas transfer during diffusion depend on temperature?
Temperature influences molecular movement, with higher temperatures leading to increased molecular movement.
How does gas transfer occur in a static situation?
Gas transfer stops as equilibrium is reached, and no partial pressure differences exist for any gases.
Why does the net movement of gas during diffusion depend on the partial pressure difference?
The area with higher partial pressure has proportionately more random 'departures', leading to a net movement towards lower partial pressure.
How does Fick's Law describe oxygen transfer into the alveoli?
Oxygen is brought into the alveoli by bulk flow through the conducting airways.
What contributes to the increased total oxygen transfer during exercise?
Recruitment of previously unperfused capillaries
When might a person experience diffusion limitation of oxygen transfer?
During normal rest with an extremely abnormal alveolar-capillary barrier
What sets the upper limit for the end-capillary blood PO2?
Low alveolar PO2
In a normal person, why is carbon dioxide transfer typically perfusion-limited?
Normal partial pressure gradient for carbon dioxide
What is the diffusing capacity of the lung?
The rate of gas uptake per unit pressure gradient
What does the diffusing capacity of the lung depend on?
Both diffusing capacity of the membrane and reaction with hemoglobin
Why is carbon monoxide most frequently used in determinations of the diffusing capacity?
Its mean pulmonary capillary partial pressure is virtually zero at nonlethal alveolar partial pressures
What happens to the DLCO in conditions causing interstitial or alveolar fibrosis?
It decreases
Which conditions lead to a decrease in the surface area available for diffusion?
Emphysema and tumors
What happens to the DLCO in conditions leading to ventilation-perfusion mismatch?
It decreases
What does DM represent in determining the diffusing capacity of the lung?
Diffusing capacity of the membrane
The diffusing capacity of the lung is solely determined by the diffusing capacity of the membrane, DM.
False
Carbon monoxide diffusion is considered perfusion-limited rather than diffusion-limited.
False
The DLCO decreases in conditions associated with decreased surface area available for diffusion, such as emphysema.
True
Ventilation-perfusion mismatch can lead to an increase in the surface area available for diffusion.
False
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