What is the equation for partial pressure of gas?
Pgas = PATM x Fractional Concentration of Gas
What is henry’s law?
Partial Pressure = Concentration of Dissolved Gas / Solubility Coefficient
Which is more soluble: CO2 or O2?
CO2
Gas Exchange at the Respiratory
Membrane Depends on…
- Transport rate through
the respiratory membrane. - The rate of alveolar
ventilation
The rate of gas diffusion across the respiratory membrane depends
on…
- Difference in Partial Pressures Across the Membrane (ΔP )
- Solubility of Gas in Fluid (S)
- Cross-Sectional Area of Membrane (A)
- Distance of Diffusion (d)
- Molecular Weight of Gas (MW)
A tissue with high metabolic activity will have a _____ PO2, creating a larger partial pressure gradient.
lower
What are the components of respiratory membrane?
- Surfactant
- Alveolar Epithelium
- Alveolar Basement Membrane
- Interstitial Space
- Endothelial Basement Membrane
- Capillary Endothelium
Average width of respiratory membrane is…
0.6 µm
What is diffusing capacity of the lung used for?
Measures respiratory membrane’s functional integrity
What is the ideal gas for diffusing capacity of the lung (DL)
carbon monoxide
What decreases gas diffusion?
- decrease surface area
- increased distance of the diffusion barrier
What can an abnormally low diffusing capacity (DL) carbon monoxide indicate?
- Thickening of the Barrier
– Interstitial edema or fibrosis - Decreased Surface Area
– Emphysema
– Low Cardiac Output
– Tumors
– Ventilation-Perfusion Mismatch - Decreased Uptake
– Anemia
– Decreased blood volume in pulmonary capillaries
What is the average value of the respiratory quotient (RQ)?
0.8
What is the normal A-a gradient for a young, non-smoker?
5-10 mmHg
The A-a gradient increases by ___ mmHg for each decade
1
How easy is it to measure PAO2?
NOT
PAO2 is predicted based on:
- The partial pressure of O2
inspired - The PaCO2
- The ratio of CO2 produced/O2
consumed— the respiratory quotient
