Gaseous Diffusion & Transport #2 Flashcards
(40 cards)
What is pO2, PCO2 + PH2O of atm air?
- pO2: 21
- PCO2: 0
- PH2O: variable
What is mixed expired air + what is PO2, PCO2 + PH2O?
- mix of alveolar + dead space gas
- pO2: 16 (inbetween 13.5 + 21)
- pCO2: 3.5 (inbetween 0 + 5.3)
- pH2O: variable
What is pO2, PCO2 + PH2O of air in trachea during insp?
- pO2: 20 (trachea moist so take way H2O vapour so PO2 dec from 21 to 20)
- pCO2: 0
- pH2O: 6.3
What is pO2, PCO2 + PH2O of alveolar gas?
- breathe in O2 + give out CO2
- pO2: 13.5
- pCO2: 5.3 (CO2 comes in to replace O2)
- pH2O: 6.3
What happens to P from atm to alveoli?
falls
How does blood get oxy?
- goes from RA —> pul artery —> pul cap - O2 enter from alveolus down PP gradient —> pul vein —> L atrium
How does pO2 differ from blood in alveoli + cap?
- alveolar pO2 higher than pO2 in venous blood entering pul cap into lung from rest of body
What drives diffusion of O2 from alveoli to pul cap?
- PP gradient through large SA of alv epi, ISF + cap endo
How quick is diffusion from alveoli to pul cap?
v. quick as at rest, pul cap pO2 = alv pO2 by 1/3 of way along pul cap
What does rate of transfer of gas through sheet of tissue prop to?
- A x (P1-P2)/T
- A = area, T = thickness, (P1-P2) = alveolar - mean cap pul P
- A + T can be combined to give DLg (transfer factor) of lungs for any gas so rate of transfer of gas (g) = DLg x (PA - Pc)
What affects diffusion rate across mem?
- greater area, greater diffusion rate
- greater PP gradient, greater diffusion rate
- greater thickness, slower diffusion rate
When does diffusion limitation occur?
if alv-cap unit disrupted by resp disease esp if pul blood F inc during exercise bc dec amount of time blood spends in cap as have inc CO so might not reach alv levels
Why is diffusion at rest not an issue in abnormal lung?
bc blood fully oxy by time it leaves cap
Compare diffusion between normal + grossly abnormal lung e.g. COPD
- normal: pO2 met alv levels in pul cap blood in 0.25sec
- abnormal: never reach level
What is consequence of changing alv cap mem SA in emphysema?
- dec SA of gas exchange surface
What is consequence of changing alv cap mem SA in lung resection?
- lung removed so dec SA
What is consequence of changing alv cap mem SA when dec venous return?
- e.g. heart failure, pul hypertension
- dec SA
What is effect in inc thickness of alv-cap mem in gas transfer?
- dec efficiency of putting O2 in blood = dec gas transfer
What inc alv-cap mem thickness?
- interstitial/alv fibrosis
- collagen vas diseases e.g. scleroderma, lupus stc
- congestive heart failure (IS oedema)
What is diffusivity + what is it prop/inversely prop to?
- measure of how diffusible gas is
- directly prop to sol
- inv prop to MW
How does CO2 compare to O2 diffusion across alv cap exchange surface?
- rapidly at approx 85% of rate of O2
- has higher MW (larger) so diffuses slower but sol coefficient = 0.7 ml/L/mmHg - much higher than O2 (0.3 ml/L/mmHg)
- sp CO2 23x more so for any given PP gradient + diffuse 20x faster (23x0.8) than O2 which outweighs it being larger
- CO2 equ rapidly across alv-cap exchange surface despite having lower PP gradient
What is alveolar + arterial pCO2 important marker of?
- efficiency of alv ventilation
- if breathing efficiently, low levels of PACO2 but CO2 builds up of stop breathing enough so PACO2 inc
What is tidal vol (vol of inspired are) equal to?
- alv vol + dead space vol
What is minute ventilation?
- TV x freq
- at rest: 500ml x 15 = 7500ml/min or 7.5L/min
