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Respiratory > Gas Transport > Flashcards

Gas Transport Flashcards

1
Q

What is P?

A

partial pressure (kPa or mmHg)

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2
Q

What is F?

A

fraction (% or decimal)

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3
Q

What is S?

A

Hb saturation (%)

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4
Q

What is Dalton’s Law?

A

pressure of a gas mixture is equal to the sum of the partial pressures of gases in that mixture
(N, O then other)
Pgas mixture = ΣPgas1 + Pgas2 + … + Pgasn

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5
Q

What is Ficks Law?

A

molecules diffuse from high [] region to low [] at rate proportional to [] gradient (P1-P2), the exchange SA (A), diffusion capacity of the gas (D) and inversely proportional to the thickness of the exchange surface (T)

e.g. movement from alveolar space to blood

Vgas = A X D X (P1-P2) / T

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6
Q

What is Henry’s Law?

A

at constant T, [] of gas that dissolves in given type/V of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid and solubility of the gas

CDgas = agas x Pgas

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7
Q

What is Boyle’s Law?

A

at constant T, V of gas is inversely proportional to the pressure of the gas

P proportional to 1/Vgas

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8
Q

What is Charles’ Law?

A

at constant P, volume of gas proportional to T

Vgas proportional to Tgas

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9
Q

What is the composition of the air that we breathe in?

A

N - 78%
O - 21%
Ar - 0.9%
CO2 - 0.04%

oxygen therapy - increased O2
smoke (house fire) - increased CO2, CO
high altitude - lower barometric pressure, reduced oxygen intake (same proportion)

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10
Q

How do we modify inspiratory gases?

4 steps

A

warmed, humidified, slowed and mixed passing down the respiratory tree .

dry air at sea level
(PO2 = 21kPa, PCO2 = 0kPa)

conducting airways
(PO2 reduced slightly due to mixing - 20)
PH2O = 6.3 kPa

respiratory airways
PO2 = 13.5
PCO2 = 5.3
PH2O = 6.3
greater mixing effect - O2 diluted
CO2 higher as moving out of blood to be cleared
saturated with water to facilitate gas exchange

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11
Q

Why is gas slowed down by generation 23?

A

to facilitate gas exchange by increased cross sectional cumulative area at each generation

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12
Q

How to find total O2 delivery at rest hypothetically?

A

CDgas = agas x pgas
= 0.32mL/dL diffused across alveoli
CO is 5L/min therefore approx total oxygen delivery is 16mL/min (VO2) at rest

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13
Q

How is O2 delivered in reality?

A

but resting VO2 is 250mL/min so cannot rely on oxygen alone to deliver O2 to tissues

use haemoglobin

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14
Q

What haemoglobin?

A

monomers with ferrous iron (Fe2+ haem) at centre of tetrapyrole porphyrin ring that is connected to protein chain globin
covalently bonded at proximal histamine molecule

all haemoglobin has 2 alpha monomers

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15
Q

HbA?

A

Hb alpha and beta

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16
Q

HbA2?

A

Hb alpha and delta

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17
Q

HbF?

A

Hb alpha and gamma

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18
Q

How does haemoglobin work?

A
  1. Low O2 affinity initially when no O2 bound
  2. Binding of O2 increases oxygen affinity of Hb via COOPERATIVE BINDING
    4th subunit has increased affinity for O2 of x3000
  3. Increased affinity relaxed state opens extra binding site for 2,3-DPG
  4. 2,3-DPG binding pushes relaxed Hb into a tense state by causing O2 to be ejected
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19
Q

What behaviour does Hb exhibit?

A

allosteric behaviour
= binding of oxygen to one of the subunits is affected by its interactions with the other subunits causing structural changes

These cause increase affinity of Hb for O2 - COOPERATIVE BINDING

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20
Q

What is methaemoglobin?

A

MetHb is 0.5-1% of haemoglobin at one point
- constant flux between MetHb and Hb
Fe3+ instead
does not bind O2

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21
Q

What does Hb do to the skin?

A

provides us with colour

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22
Q

Describe foetal haemoglobin?

A

higher affinity for O2 than adult Hb

O2 dissociation curve it has a left shift

  • greater affinity for O2
  • lower partial pressure of O2 required to generate 50% Hb saturation
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23
Q

What is given in surgical scenario if MetHb too high

A

Methylene blue -

24
Q

What is the intrinsic enzyme to reduce MetHb?

A

MetHb reductase -

25
Q

Why are linear O2 dissociation curves no good?

A

too great variability in binding in lungs

small binding range systemically to offload (no sufficient access to reserve O2)

26
Q

How to track changes in oxygen dissociation curves?

A

P50
Find partial pressure of O2 at 50% saturation
This is assuming normal Hb [] of 150g/L

27
Q

What causes right shift?

A

increased temp
acidosis
increase 2,3-DPG
hypercapnia

all lead to decrease affinity for O2 –> at given partial pressure less O2 bound to Hb

28
Q

What causes left shit?

A

decreased T
alkalosis
decreased 2,3-DPG
hypocapnia

increased affinity (loading)

29
Q

What causes upwards shift?

A 
polycythaemia
- tumour secreting erythropoietin 
- increase [] RBCs in blood 
increased O2 carrying capacity
saturation same
30
Q

What causes downwards shift?

A

anaemia
impaired oxygen carrying capacity
less O2 in blood
saturation same!

31
Q

What causes downwards and leftwards shift?

A

increase HbCO

decreased capacity for release, increased affinity (cannot release O2 already bound)

32
Q

Describe myoglobin O2 dissociation curve?

A

steeper - provide O2 for early stages of exercise
increased affinity to store O2

Myoglobin has an increased affinity than adult HbA to extract O2 from circulating blood and store it

33
Q

Saturation of Hb in capillary after returning to lungs? What is the PO2 in capillary and alveolar space?

A 
75%
PO2 capillary = 5.3kPa 
lung = 13.5kPa
HbO2 = 15ml/dl
dissolved O2 lower (0.14)
34
Q

How is oxygen transported in the lungs?

A

O2 moved to capillary along [] gradient till plasma PO2 = 13.5kPa
Some binds to Hb so SO2 (saturation) is 100% but some dissolved (0.34)
HbO2 = 20.1 ml/dl

35
Q

Why does blood arriving at tissues have lower PO2 than in lungs?

A

lung tissue has 2 circulations

- some bronchial drainage from bronchial circulation drains into pulmonary veins to provide haemodilution

36
Q

How do values change at the tissues?

A

PO2 decreased - 12.7
SO2 slightly decreased
HbO2 - 20 (down slightly)
dissolved O2 content slightly decreased

37
Q

What does sigmoidal curve mean?

A

despite large decrease in PO2 entering and leaving tissues

the saturation of O2 decreased by a much smaller %

38
Q

What is oxygen flux?

A

difference between the total dissolved and Hb bound O2 entering and leaving the tissues

(unloaded O2)

= HbO2 leaving - HbO2 entering (negative _ mL/dL)

39
Q

What are the standard values for oxygen flux?

A

delta = -5mL/dL
multiplied by cardiac output (5L/min) (x50)
gives -250ml O2/ min

this is the resting VO2 as well as oxygen flux

40
Q

What does [CO2] equal?

A

[H+]

41
Q

What is tissue PCO2?

A

6.3 kPa

42
Q

Where is CO2 converted to H2CO3?

A

in RBC

by carbonic anhydrase

43
Q

How is HCO3- removed from RBC?

A

by AE1 transporter
via chloride shift
to maintain RMP of RBC

44
Q

How is CO2 transported in the blood?

What is major form?

A
  1. solution
  2. as bicarbonate
  3. bound to Hb

AS BICARBONATE

45
Q

Where does CO2 bind on Hb?

A

to amine end of globin chains
4 CO2 / Hb
to form carbaminohaemoglobin

46
Q

How is increased in RBC H+ addressed?

A

negatively charged amino acids on globin chain of Hb (especially histadine) bind to protons to avoid lowering pH dramatically

47
Q

What are the significant changes in PCO2 across tissue?

A

less significant increase in PCO2 compared to decrease in PO2

not sigmoidal shape as O2 dissociation curve

48
Q

What is the CO2 flux?

A

difference between total dissolved/bicarbonate CO2 (leaving - entering)

52 - 48 = +4 mL/dL
+200mL CO2 / min

49
Q

Overall consumption of O2 and CO2?

A

200 ml of CO2 released for 250 ml of O2 used / min

50
Q

What is the Haldane effect?

A

oxygenation of blood in the lungs displaces carbon dioxide from haemoglobin which increases the removal of carbon dioxide

oxygenated blood has a reduced affinity for carbon dioxide

when Hb bound 4 O2 (100% saturated) will not bind any CO2

51
Q

What is the pulmonary transit time?

A

amount of time that blood is in contact with the respiratory exchange surface

0.75s / erythrocyte
time for PO2 to equilibrate between alveolus and plasma

gas exchange time (0.25s for PCO2 to equilibrate between tissue and plasma)

52
Q

What happens if CO increases?

A

more pulmonary capillary beds recruited

if very intense exercise, blood flows through capillary beds faster

53
Q

Explain the regional differences in ventilation in the lung?

A
  • Airways at top of lung more stretched, larger and less compliant due to reduced gravity effect
  • Ppl more negative (-8cmH2O) so greater transmural pressure gradient
    LESS VENTILATION
  • greater pressure required to inflate alveoli more

-At bottom alveoli are smaller and more compliant
- Smaller gradient (Ppl is less negative at -2cmH2O)
MORE VENTILATION

54
Q

Explain regional differences in perfusion of lung?

A 
TOP
Lower intravascular pressure (gravity effect)
less recruitment
more resistance
lower flow
BOTTOM
Higher intravascular pressure
more recruitment
less resistance 
higher flow rate
55
Q

Are the difference in ventilation and perfusion the same? Why?

A

No
Greater impact on perfusion than ventilation
Blood flow is denser and so more susceptible to effects of gravity

56
Q

What is V/Q?

A

ventilation-perfusion ratio
at base tends toward 0, at apex tends towards infinity

at base there is wasted perfusion because there not as much ventilation, at apex there is wasted ventilation because there is not as much perfusion

IDEAL - where lines cross

Respiratory (7 decks)

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