Gas Exchange Flashcards
What is Fick’s 1st law?
Flux across a membrane = constant x pressure gradient
V = DL x (P1 - P2)
Carbon dioxide diffuses 20x quicker than oxygen T/F
True
Which gas is perfusion limited in the lungs?
Nitrous oxide - perfuses extremely quickly and reaches 100% in 0.2s
Which gas is diffusion limited in the lungs?
Carbon monoxide
Name two lung conditions which cause problems with diffusion
- COPD (emphysema)
- Interstitial oedema
Altitude increases the partial pressure of oxygen T/F
False, it decreases
What is the alveolar gas equation?
PAO2 = FiO2 (PB - PH2O) - PaCO2/RQ
Where PAO2 is the alveolar oxygen partial pressure, FiO2 is the fraction of inspired oxygen, PB is the barometric pressure, PH2O is the partial pressure of water (47 mm Hg), PaCO2 is the partial pressure of carbon dioxide, and RQ is the respiratory quotient, dependent on metabolic activity and diet and is considered to be about 0.825.
What is the definition of total lung capacity (TLC)?
Gas volume in the lung after maximal inspiration. It is typically 6-8L
What is the definition of residual volume?
The air that remains in the lung after maximal expiration. This is 2-2.5L
What is the definition of vital capacity?
The maximum volume that can be inspired and expired. It is the difference between TLC and RV and is 4 to 6L.
Why is helium used when measuring transfer factor?
Helium doesn’t diffuse into the blood, so after a ten second hold after inspiration, the helium concentration will be the same but the CO concentration won’t be. You can calculate alveolar volume from this, as the helium and CO are diluted initially.
What is VA on pulmonary function tests?
Alveolar volume
What is KCO on pulmonary function tests?
Diffusion of CO which can be affected by blood flow.
What does VA x KCO =
Transfer factor
