Gaseous Diffusion & Transport #2 Flashcards
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
What is alv vent?
- vol of air that reaches alv where gas exchange can occur that’s physiologically useful (so CO2 comes from there)
= min vent - dead space vent
= 7500 - (150 x 15) = 5250 ml/min
Where is rate of expired CO2 measured as + where can it only come from?
- alv participation in gas exchange
What is PACO2 + PaCO2 a good rep of?
- how effectively you’re breathing bc CO2 diffuses rapidly from arterial blood to alveoli
What is PACO2 + PaCO2 prop to?
- CO2 prod/alv vent
- if vent inc, dec CO2 prod
Why is alv-vent equation important + how does it differ in hyper + hypovent?
- if alv vent halves, PaCO2 2x + vice versa
- hypervent: alv vent inc + PACO2 dec
- hypovent: alv vent dec + PACO2 inc
What is O2 diffusing capacity?
- O2 uptake from lungs (VO2)/ PACO2 - PcO2 (mean cap PO2 but its unmeasurable)
Why can mean pul cap CO be assumed to be 0?
- Hb has approx 240x affinity for CO than for O2
- as CO transferred across alv-cap mem, almost all of it enters chem combo with Hb so its 0 bc its all attached to Hb
What is CO diffusing capacity (DLCO) equal to?
CO uptake from lungs (VCO)/PACO
How do you measure CO uptake + PACO from lungs?
- patient inhales breath containing v. low amount of CO + tracer gas + composition of exhaled gas examined
- measure diff between how much they breathed in + tracer gas
- directly measure how much they breathed out to get PACO2
What is CO diffusing capacity also known as (DLCO)?
transfer factor (TLCO)
What is DLCO red by?
- red in alv cap mem area e.g. emphysema, pul emboli, lung resection
- inc thickness of alv-cap mem e.g. pul oedema
- pul fibrosis - diffusion impaired both by thickening + red area caused by red lung vol
- anaemia
What is DLCO inc by?
- inc pul blood vol e.g. exercise (in effective area)
- polycythaemia (too many RBCs)
How much pO2 does mito need in tissues?
> 1mmHg (0.13kPa)
What happens as blood moves through cap?
- tissues take up O2
- O2 moves down PP gradient from 13.3kPa in arterial end to 5.3kPa in venous end
What happens if cap pO2 falls too low e.g. due to lung disease?
- rate of diffusion becomes too slow for tissue needs + tissue becomes hypoxic
What is sol of O2 in blood + issue?
- at normal arterial pO2 of 13kPa, 0.003ml O2 dissolved in each ml of blood - v. poor
- but resting O2 consumption = 250ml/min
- need CO of 83000 ml/min
