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RESP > Gas exchange > Flashcards

Gas exchange Flashcards

1
Q

How O2 travels from alveolar air to capillary blood?

A
  • enters alveoli airspace from atmosphere
  • dissolves in Alevolar Lining Fluid
  • diffuses via alveolar epithelium, basement membrance. capillary endothelial cells
  • dissolves in plasma
  • binds to Hb
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2
Q

Times for 🔴 pass via pul capillary for oxygenation?

A
  1. 75 s

0. 25 s (exercise) due to increased pul blood flow

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3
Q

What’s rate of diffusion determined by?

A

partial p gradient, diffusion distance, SA

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4
Q

rate of diffusion ∝ (alveolar SA/distance²) x (PA - P꜀)

A

(PA - P꜀) : partial p gradient between alveolar air, capillary blood

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5
Q

How specific pathologies affect the rate of gas exchange?

A
  • hypoperfusion type I : ↓P꜀
  • hypoventilation type II : ↓Pa
  • emphysema : ↓SA
  • fibrosis : ↑basement membrane thickness
  • pul oedema : ↑thickness of fluid layer
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6
Q

How to modulate pp gradients?

A

changing rate of V̇a

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7
Q

What’s Hypoventilation?

A

excessive CO2 within arterial blood (PaCO2 < 4.9 kPa).

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8
Q

What’s Hyperventilation?

A

reduced CO2 within arterial blood (PaCO2 > 6.0 kPa)

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9
Q

Effect of increasing ventilation rate?

A

increases alevolar O2 pp (PAO2)

decreases alveolar CO2 pp (PACO2)

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10
Q

Normal ventilation/perfusion ratio?

A

1

because 1L blood carries 200ml O2 + 1L dry air carries 200ml O2

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11
Q

Define dead-space effect

A

ventilation w/o perfusion

V/Q >1

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12
Q

Define physiologic dead-space

A

affected alveoli where inspired O2 ‘wasted’ + no gas exchange due to reduced blood supply

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13
Q

Why doesn’t overall perfusion change when there’s a pul embolism?

A

blood diverted via other pul arteries/capillaries so increased ventilation of these areas compensates for reduction in gas exchange in others

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14
Q

Define pulmonary shunt/shunt-effect

A

Reduced ventilation of alveoli or limits to diffusion
Blood from R to L w/o taking part in gas exchange
V/Q <1

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15
Q

Resting ventilation + perfusion?

A

5L/min

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16
Q

How to reduce ventilation-perfusion mismatching?

A

Hypoxic vasoconstriction of capillaries divert blood from poor to well ventilated alveoli

17
Q

What induces a reflex hyperventilation?

A

↑PACO2

clears excess CO2 but DOESN’T ↑O2

18
Q

eg of physiologic dead-space?

A

heart failure : cardiac arrest
blocked vessels : pul embolism
loss/damage capillaries : emphysema

19
Q

eg of pul shunt?

A

cardiac shunts

pneumonia, acute lung inury, respiratory distress syndrome, atelectasis

20
Q

Dead space effects?

A

V̇a = normal
Q = ↓
V/Q = ↑
Response to O2 therapy = helps

21
Q

Pul shunt effects?

A

V̇a = ↓
Q = normal
V/Q = ↓
Response to O2 therapy = poor

22
Q

Why doesn’t O2 therapy work on pul shunts?

A

cannot increase O2 saturation in well-ventilated lung regions sufficiently to compensate for deoxygenated blood which it will mix with

23
Q

How hypoxic vasoconstriction can pathologically effect COPD?

A
  • from chronic hypoventilation –>prolonged, widespread pul vasoconstriction
  • increases resistance within the pul vasculature
  • pul hypertension–>R heart hypertrophy –> R heart failure
24
Q

How to determine cause of hypoxaemia?

A

PAO2 but invasive so:

F₁O2 + PaCO2

25
Q

Basis of F₁O2 + PaCO2?

A

Alveolar content = O2 inspired - O2 consumed

O2 inspired calculated by determining the O2 p of inspired air (total pressure x molar fraction)
O2 consumption measured indirectly by measuring PaCO2 (similar to PACO2 + quantity of CO2 in expired air)

26
Q

Role of Respiratory Exchange Ratio (RER) + normal value?

A

describes relationship between CO2 production + O2
consumption in metabolism
0.8

27
Q

How’s PaCO2 used to calculate PAO2?

A

dividing PaCO2 by RER indirectly provides measurement of O2 consumption
then Alveolar content = O2 inspired - O2 consumed

28
Q

Alveolar gas equation?

A

PAO2 = F₁O2 x (PB - PH2O) - (PaCO2/RER)

F₁O2 : O2 content of inspired air
PB : 100kPa - sea level
PH2O : 6kPa - humidified air

PAO2 : alevolar content
F₁O2 x (PB - PH2O) : O2 inspired (19.74)
(PaCO2/RER) : O2 consumption

29
Q

How is RER calculated?

A

vCO2 produced/vO2 consumed

assumed 0.8

30
Q

What determines RER?

A

metabolic substrate eg carb = 1, FA = 0.7

31
Q

What’s A-a O2 gradient + values?

A

PAO2-PaO2
normal=<2kPa
F₁O2 x (PB - PH2O) ambient air at sea level=19.74kPa

32
Q

How to investigate decrease PaO2?

A

1) hypo or hyperventilation causing hypoxaemia?
is PaCO2>5kPa? - hypo
is PaCO2<5kPa - V/Q inequality
2) is O2 diffusing into blood at alveoli?
use AGE + ABG readings to calcukate A-a O2 gradient
>2kPa - gas exchange prob due to V/Q mismatch, diffusion defect, shunt

RESP (11 decks)

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