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Respiratory > Gas exchange / ventilation perfusion > Flashcards

Gas exchange / ventilation perfusion Flashcards

1
Q

What is the pressure of O2 and CO2 in artery PA

A 
O2 = 100
CO2 = 40
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2
Q

What is the pressure of O2 and CO2 in alveoli Pa

A 
O2 = 100
CO2 = 40
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3
Q

What is the pressure of O2 and CO2 in venous Pv

A 
O2 = 40
CO2 = 46
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4
Q

What is the difference between partial pressure and o2 content

A 
Content = all 02 in solution 
Partial = solubility
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5
Q

How does gas exchange work

A

Gas moves across permeable membrane down pressure gradient until equilibrium reached

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6
Q

What is the rate of diffusion affected by

A 
Directly proportional to gradient 
Solubility - more soluble = faster
SA - larger = faster (alveoli destroyed in emphysema so decreased SA) 
Distance - smaller = faster 
Molecular weight - smaller = faster
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7
Q

What diffuses faster CO2 or O2

A

CO2

Although O2 is smaller but CO2 is much more soluble

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8
Q

Once O2 is in the blood what happens

A

Binds to haemoglobin = oxyhaemoglobin
Only 3ml O2 dissolves per L plasma so Hg greater increases capacity of O2
Hg = high affinity for O2 so will pull until saturated

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9
Q

Does exercise affect gas exchange

A

No as only takes 0.25s

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10
Q

What type of molecules does haemoglobin bind

A 
92% = HbA (2 alpha and 2 beta) 
8%. = HbF (gamma chains replace beta)
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11
Q

What determines degree of saturation

A

Partial pressure of O2

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12
Q

When does partial pressure of O2 begin to affect saturation

A

Almost 100% saturated at normal PaO2 100mHg
90% if PaO2 60
When PaO2 = 40 very difficult to saturate Hg and deliver O2 to cell

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13
Q

If two individuals with partial pressure of 100 and 80 who has most O2

A

No diff in saturation

Individual with most haemoglobin

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14
Q 
What are variables in oxyhemoglobin dissociation curve 
Acidic 
PCO2
Hyperventilation
Asthma
Temp 
DPG
A

More acidic = more Co2 and less O2 and curve shifts to right (less saturated)
Increase pCo2 = shifts to R
Voluntary hyperventilation = shifts to the L
Asthma = shifts to R as constricted so decreased ventilation
Temp = shifts to R as want oxygen available for exercise
DPG added = shifts to R as produced when No o2 so want o2 to be available

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15
Q

What type of haem molecules have highest affinity for oxygen

A

Myoglobin - as muscles need most
Fetal - 2nd most as want to extract from maternal vblood
HbA has least affinity

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16
Q

Can you have a low partial pressure and normal O2 content

A

No
Partial pressure is what pushes O2 onto haemoglobin
If o2 content low but partial pressure normal then haemoglobin would still be saturated

17
Q

What happens in anaemia

A

Partial pressure is normal
O2 content reduced as not enough RBC to carry O2
Ventilatory drive is normal as PaO2 is normal

18
Q

What happens in CO poisoning

A

CO binds to haemoglobin

Affinity much greater than O2 and dissociates more slowly

19
Q

What are the symptoms of CO poisoning

A 
Hypoxia
Anaemia
Headache
Cherry red skin
Nausea
RR unaffected as PCo2 is normal
20
Q

How is Co2 transported in the blood

A

Only 7% dissolves in plasma
93% diffuse into RBC
Converted to H2CO3 with H20 -> HCO3 + H
Products removed to keep reaction going

21
Q

What enzyme catalyses

A

Carbonic anhydrase

22
Q

What are products exchanged for

A

HCO3 for Cl = chloride shift
H binds to deoxyhaemoglobin to bufer
If CO2 increases not enough Hg = acidosis

23
Q

How does CO2 go back to alveoli

A 
Pco2 alveoli < venous blood 
CO2 diffuses out of RBC
Disturbes Co2-HCO3
H leaves Hg 
CL shift reverses 
Co2 diffuses into alveoli
24
Q

What needs to be matched adequately

A

Ventilation
Perfusion
Usually both 5l/ minute
Ideally ratio would be 1

25
Q

What affects ventilation / perfusion

A

Disruption of blood flow - influenced by Pa (hydrostatic) and PA (alveolar)
Resistance

26
Q

What happens as you move from the apex to base of the lung

A

Ventilation and perfusion rise
Perfusion increases at a greater rate
Pleural pressure greater at base = more compliant and greater ventilation
Hydrostatic pressure is decreased at apex = decreased blood flow and perfusion

27
Q

What happens at the base of the lung

A 
Blood flow high as Pa is higher 
Pa > PA
Low resistance 
Blood flow > ventilation 
V/Q = 0.8
28
Q

What happens at the apex of the lung

A 
Blood flow low as Pa < PA
Alveoli compressed and more compliant
Higher resistance 
Ventilation > blood flow 
V/Q = 3.3
29
Q

What happens when perfusion > ventilation

V/Q <1

A

Po2 falls in the alveoli and Pco2 will rise
Less O2 in alveoli than is being pulled out
Decrease in partial pressure of O2
Increase in partial pressure CO2
Lose gradient so can’t get ri dog CO2 in blood
Shunt form as blood goes from R-L without getting O2

30
Q

What could cause V/Q <1

A 
Low O2 in air 
Poor alveolar ventilation as decreased compliance 
Increased resistance
Drug overdose 
COPD / asthma / pneumonia / IRDS
31
Q

What happens to deal with this

A

Hyperventilation
Blood vessels in lung constrict
Mild bronchial relaxation
Causes hypoxia as reduced ventilation, CO2 can still get out as rest of lung takes over so no hypercapnia = type 1

32
Q

What happens when ventilation > perfusion

V/Q >1

A

Increase in alveolar O2

33
Q

What causes V/Q >1

A

Blood clot / PE

34
Q

What happens to deal with this

A

Pulmonary vasodilatation to well perfused areas so V/Q in this is <1
Bronchial constriction if decrease in PCo2

35
Q

What is type 1 respiratory failure

A

PaO2 <8kPa
PaCO2 normal or low
Problem is with diffusion or exchange so cannot oxygenate haemoglobin
Unaffected part of lung will keep CO2 out

36
Q

What is type 2 respiratory failure

A

PaCO2 >6.5kPA
Respiratory mechanism fails
Not usually primary

37
Q

What is hypoxia

A

Insufficient O2 supply

38
Q

What is hyperaemia

A

O2 arterial supply low

39
Q

What causes hypoxaemia in type 1

A

V/Q mismatch = most common and responds well to increase FIO2
Shunt = no ventilation so respond poorly to FIo2
Alveolar hypoventilation due to reduced res drive - will respond to increase in FIo2
Diffusion impairment if loss of alveoli

Respiratory (23 decks)

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