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PPoS > Gaseous Diffusion & Transport #2 > Flashcards

Gaseous Diffusion & Transport #2 Flashcards

1
Q

What is pO2, PCO2 + PH2O of atm air?

A
  • pO2: 21
  • PCO2: 0
  • PH2O: variable
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2
Q

What is mixed expired air + what is PO2, PCO2 + PH2O?

A
  • mix of alveolar + dead space gas
  • pO2: 16 (inbetween 13.5 + 21)
  • pCO2: 3.5 (inbetween 0 + 5.3)
  • pH2O: variable
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3
Q

What is pO2, PCO2 + PH2O of air in trachea during insp?

A
  • pO2: 20 (trachea moist so take way H2O vapour so PO2 dec from 21 to 20)
  • pCO2: 0
  • pH2O: 6.3
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4
Q

What is pO2, PCO2 + PH2O of alveolar gas?

A
  • breathe in O2 + give out CO2
  • pO2: 13.5
  • pCO2: 5.3 (CO2 comes in to replace O2)
  • pH2O: 6.3
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5
Q

What happens to P from atm to alveoli?

A

falls

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6
Q

How does blood get oxy?

A
  • goes from RA —> pul artery —> pul cap - O2 enter from alveolus down PP gradient —> pul vein —> L atrium
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7
Q

How does pO2 differ from blood in alveoli + cap?

A
  • alveolar pO2 higher than pO2 in venous blood entering pul cap into lung from rest of body
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8
Q

What drives diffusion of O2 from alveoli to pul cap?

A
  • PP gradient through large SA of alv epi, ISF + cap endo
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9
Q

How quick is diffusion from alveoli to pul cap?

A

v. quick as at rest, pul cap pO2 = alv pO2 by 1/3 of way along pul cap

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10
Q

What does rate of transfer of gas through sheet of tissue prop to?

A
  • 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)
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11
Q

What affects diffusion rate across mem?

A
  • greater area, greater diffusion rate
  • greater PP gradient, greater diffusion rate
  • greater thickness, slower diffusion rate
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12
Q

When does diffusion limitation occur?

A

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

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13
Q

Why is diffusion at rest not an issue in abnormal lung?

A

bc blood fully oxy by time it leaves cap

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14
Q

Compare diffusion between normal + grossly abnormal lung e.g. COPD

A
  • normal: pO2 met alv levels in pul cap blood in 0.25sec

- abnormal: never reach level

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15
Q

What is consequence of changing alv cap mem SA in emphysema?

A
  • dec SA of gas exchange surface
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16
Q

What is consequence of changing alv cap mem SA in lung resection?

A
  • lung removed so dec SA
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17
Q

What is consequence of changing alv cap mem SA when dec venous return?

A
  • e.g. heart failure, pul hypertension

- dec SA

18
Q

What is effect in inc thickness of alv-cap mem in gas transfer?

A
  • dec efficiency of putting O2 in blood = dec gas transfer
19
Q

What inc alv-cap mem thickness?

A
  • interstitial/alv fibrosis
  • collagen vas diseases e.g. scleroderma, lupus stc
  • congestive heart failure (IS oedema)
20
Q

What is diffusivity + what is it prop/inversely prop to?

A
  • measure of how diffusible gas is
  • directly prop to sol
  • inv prop to MW
21
Q

How does CO2 compare to O2 diffusion across alv cap exchange surface?

A
  • 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
22
Q

What is alveolar + arterial pCO2 important marker of?

A
  • efficiency of alv ventilation

- if breathing efficiently, low levels of PACO2 but CO2 builds up of stop breathing enough so PACO2 inc

23
Q

What is tidal vol (vol of inspired are) equal to?

A
  • alv vol + dead space vol
24
Q

What is minute ventilation?

A
  • TV x freq

- at rest: 500ml x 15 = 7500ml/min or 7.5L/min

25
Q

What is alv vent?

A
  • 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
26
Q

Where is rate of expired CO2 measured as + where can it only come from?

A
  • alv participation in gas exchange
27
Q

What is PACO2 + PaCO2 a good rep of?

A
  • how effectively you’re breathing bc CO2 diffuses rapidly from arterial blood to alveoli
28
Q

What is PACO2 + PaCO2 prop to?

A
  • CO2 prod/alv vent

- if vent inc, dec CO2 prod

29
Q

Why is alv-vent equation important + how does it differ in hyper + hypovent?

A
  • if alv vent halves, PaCO2 2x + vice versa
  • hypervent: alv vent inc + PACO2 dec
  • hypovent: alv vent dec + PACO2 inc
30
Q

What is O2 diffusing capacity?

A
  • O2 uptake from lungs (VO2)/ PACO2 - PcO2 (mean cap PO2 but its unmeasurable)
31
Q

Why can mean pul cap CO be assumed to be 0?

A
  • 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

32
Q

What is CO diffusing capacity (DLCO) equal to?

A

CO uptake from lungs (VCO)/PACO

33
Q

How do you measure CO uptake + PACO from lungs?

A
  • 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
34
Q

What is CO diffusing capacity also known as (DLCO)?

A

transfer factor (TLCO)

35
Q

What is DLCO red by?

A
  • 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
36
Q

What is DLCO inc by?

A
  • inc pul blood vol e.g. exercise (in effective area)

- polycythaemia (too many RBCs)

37
Q

How much pO2 does mito need in tissues?

A

> 1mmHg (0.13kPa)

38
Q

What happens as blood moves through cap?

A
  • tissues take up O2

- O2 moves down PP gradient from 13.3kPa in arterial end to 5.3kPa in venous end

39
Q

What happens if cap pO2 falls too low e.g. due to lung disease?

A
  • rate of diffusion becomes too slow for tissue needs + tissue becomes hypoxic
40
Q

What is sol of O2 in blood + issue?

A
  • 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

PPoS (11 decks)

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