45 Questions
Which factor is inversely proportional to the diffusion of gas to tissue?
Thickness of the membrane
Which gas diffuses more rapidly through the alveolar-capillary barrier?
Carbon dioxide (CO2)
Which gas is affected more by changes in the thickness of the diffusion barrier?
Oxygen (O2)
Which factor is more likely to change due to respiratory pathologies involving the thickness of the diffusion barrier?
Partial pressure of oxygen in the arterioles (PaO2)
Which medical condition is NOT associated with a decrease the area for diffusion?
Fibrosis
Which medical condition can NOT increase the thickness of the diffusion membrane?
Bronchial obstruction
Which factor can reduce the partial pressure difference for oxygen (O2)?
Both altitude and hypoventilation
Which factor can increase the thickness of the diffusion barrier?
Fluid accumulation
Which factor is NOT directly related to the diffusion of gas to tissue?
Thickness of the membrane barrier
Which equation represents the diffusion coefficient (D)?
D = S/√MW
Which gas is used to trace the diffusion in place of O2 in the Single Breath Diffusing Capacity Test (DLCO)?
CO2
Which gas in the special gas mixture used in the Single Breath Diffusing Capacity Test (DLCO) is used to measure the alveolar volume?
Helium
Which component does NOT influence THE COMPLETE 'EFFICIENCY' OF THE LUNGS (DLCO)?
Volume of CO diffused
What does a decreased DLCO indicate?
Emphysema
What does an increased DLCO indicate?
Polycythemia
What does an decreased DLCO indicate
Left to right shunt
Which type of gas exchange is characterized by incomplete equilibration and a slow rate of gas diffusion across the alveolar membrane?
Diffusion-limited gas exchange
What is the main limiting factor in diffusion-limited gas exchange?
Rate of diffusion being slow
Which type of gas exchange is characterized by complete equilibration and can only be increased by increasing pulmonary blood flow?
Perfusion-limited gas exchange
What determines the binding of oxygen to hemoglobin?
Partial pressure of oxygen
What does an increase in P50 reflect?
Decrease in the affinity of hemoglobin for oxygen
What is the P50?
Partial pressure of oxygen at which hemoglobin is 50% saturated
What does a decrease in P50 reflect?
Increase in the affinity of hemoglobin for oxygen
Which type of gas exchange is found for normal oxygen and carbon dioxide across the alveolus?
Perfusion-limited gas exchange
What increases the rate of gas transfer from the lung in perfusion-limited gas exchange?
Pulmonary blood flow
The exchange of N20 is considered ________?
Perfusion limited
During maximal exercise, what can happen to the diffusion of oxygen (O2) across the blood alveolus interface?
It becomes diffusion-limited
Which medical condition can lead to diffusion-limited gas exchange?
All of the above
What determines the rate of gas exchange in perfusion-limited systems?
Cardiac output
Which gas has a higher affinity for hemoglobin than oxygen (O2), binds to Hb 240x more?
Carbon monoxide (CO)
What can decrease the area available for diffusion in the lungs?
All of the above
Which gas is transported in blood in three forms?
Carbon dioxide
What is the shape of the oxygen-hemoglobin dissociation curve?
Sigmoidal
What happens during hyperventilation?
More carbon dioxide is eliminated than the body can produce
What happens to the alveolar partial pressure of carbon dioxide during hyperventilation?
Decreases
What happens to the alveolar partial pressure of oxygen during hyperventilation?
Increases
What happens to the oxygen content in the blood during hyperventilation?
Remains relatively the same
Which gas in the arterial blood within end pulmonary capillary blood is decreased significantly during hypoventilation?
Oxygen (O2)
Which gas in the alveolar gas is increased during the hypoventilation?
Carbon dioxide (CO2)
What happens to the O2 content in the blood when PCO2 is increased by hypoventilation?
It significantly decreases
What happens to the CO2 content in the blood when PO2 is decreased by hypoventilation?
It significantly increases
What happens to the diffusion of CO2 in impaired diffusion?
It remains the same
What happens to the O2 pressure in arterial gas within end pulmonary capillary blood during impaired diffusion?
It is reduced
How can the O2 diffusion rate be increased in impaired diffusion?
By increasing the O2 concentration of inspired air
What tends to keep the partial pressure of CO2 (PaCO2) near normal during impaired diffusion?
Reflex adjustments
Study Notes
Factors Affecting Gas Diffusion
- Thickness of the diffusion barrier is inversely proportional to the diffusion of gas to tissue.
- Oxygen and carbon dioxide diffuse across the alveolar-capillary barrier, with carbon dioxide being more rapid.
Diffusion Coefficient and Equation
- The diffusion coefficient (D) is represented by the equation: D = (KA × A × (P1 - P2)) / (T × V)
Single Breath Diffusing Capacity Test (DLCO)
- Carbon monoxide (CO) is used to trace the diffusion in place of O2 in the Single Breath Diffusing Capacity Test (DLCO).
- Helium (He) is used to measure the alveolar volume in the Single Breath Diffusing Capacity Test (DLCO).
Interpretation of DLCO
- A decreased DLCO indicates impaired diffusion of gas to tissue.
- An increased DLCO indicates increased efficiency of the lungs.
Gas Exchange Types
- Diffusion-limited gas exchange is characterized by incomplete equilibration and a slow rate of gas diffusion across the alveolar membrane.
- Perfusion-limited gas exchange is characterized by complete equilibration and can only be increased by increasing pulmonary blood flow.
Limiting Factors
- The main limiting factor in diffusion-limited gas exchange is the thickness of the diffusion barrier.
- In perfusion-limited gas exchange, the rate of gas exchange is determined by pulmonary blood flow.
Oxygen Binding and P50
- The binding of oxygen to hemoglobin is determined by the P50, which is the partial pressure of oxygen at which hemoglobin is 50% saturated.
- An increase in P50 reflects a decrease in the affinity of hemoglobin for oxygen.
- A decrease in P50 reflects an increase in the affinity of hemoglobin for oxygen.
Gas Transport and Affinity
- Carbon dioxide is transported in blood in three forms: dissolved, bicarbonate, and carbaminohemoglobin.
- Carbon monoxide has a higher affinity for hemoglobin than oxygen, binding to Hb 240 times more.
Oxygen-Hemoglobin Dissociation Curve
- The oxygen-hemoglobin dissociation curve is sigmoid-shaped.
Effects of Hyperventilation and Hypoventilation
- During hyperventilation, the alveolar partial pressure of carbon dioxide decreases, while the alveolar partial pressure of oxygen increases.
- During hypoventilation, the alveolar partial pressure of carbon dioxide increases, while the alveolar partial pressure of oxygen decreases.
- During hyperventilation, the oxygen content in the blood increases.
- During hypoventilation, the oxygen content in the blood decreases.
Impaired Diffusion
- In impaired diffusion, the diffusion of CO2 is increased, while the O2 pressure in arterial gas within end pulmonary capillary blood is decreased.
- The O2 diffusion rate can be increased in impaired diffusion by increasing the pulmonary blood flow or the surface area for diffusion.
Test your knowledge on pathological changes that can affect the dynamics of gas diffusion. Explore concepts such as decreased alveolar surface area, increased alveolar membrane thickness, and increased diffusion distance between alveoli and blood. Also, get familiar with Fick's Equation and understand how gas diffusion to tissue is influenced by various factors.
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