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MD3001 Respiratory > Ventilation and Diffusion > Flashcards

Ventilation and Diffusion Flashcards

1
Q

What is the volume of dead space?

A

150mls

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2
Q

What is partial pressure?

A

the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own at the same temperature

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3
Q

How would you calculate partial pressure?

A

percentage of the gas (proportion) x atmospheric pressure

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4
Q

What determines how much oxygen will dissolve in water?

A
  • solubility of O2 in water

- PO2

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5
Q

What is the normal partial pressure of PN2, PO2, PCO2 and water vapour?

A
  • PN2 = 593.48 mmHg
  • PO2 = 159.22 mmHg
  • PCO2 = 0.23 mmHg
  • water vapour 47mmHg
    (divide by 7.5 to get to KPa)
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6
Q

What is the alveolar gas composition of PN2, PO2, PCO2?

A
  • PN2 = 556.78 mmHg
  • PO2 = 149.37 mmHg
  • PCO2 = 0.21 mmHg
    (divide by 7.5 to get KPa)
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7
Q

What is Henry’s Law?`

A
  • the concentration of O2 dissolved in water is proportional to the partial pressure in the gas phase
  • [O2]dis = s x PO2
    (s = solubility of O2 in water)
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8
Q

What are the requirements for oxygen for gas exchange to the bloodstream?

A
  • dissolve in the aqueous layer
  • diffuse across the membranes
  • enter the blood
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9
Q

What is rate of diffusion proportional to?

A
  • partial pressure difference (∆P)
  • surface area
  • solubility (D, diffusion coefficient)
  • molecular mass (D, diffusion coefficient)
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10
Q

What is rate of diffusion inversely proportional to?

A
  • tissue thickness (T)
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11
Q

Describe the normal conditions for gas exchange between the alveoli and blood to take place

A
  • surface area of lungs is large
  • large number of alveoli
  • thickness is small
  • concentration gradient is large so diffusion is rapid (PO2 alveolar air is 100 mmHg and PO2 venous blood is 40 mmHg)
  • molecular mass insignificant
  • CO2 20 times more soluble than O2
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12
Q

Describe the conditions and process of the movement of CO2 in gas exchange

A
  • CO2 moves in other direction from capillary to alveoli
  • smaller concentration gradient (alveoli PCO2 is 40mmHg, venous PCO2 is 45mmhg)
  • however greater solubility so CO2 diffuses faster than O2
  • same amount of gas moves
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13
Q

Describe how different disease states can limit gas exchange

A
  • oedema: thickness of barrier increases so transit time through capillar may not be sufficient to complete full gas exchange, gas exchange reduced
  • emphysema: surface area reduced, reducing gas exchange
  • pulmonary fibrosis: tissue thickness increases, reducing gas exchange
  • mucus, inflammation of airways, tumours which reduce gas entry reducing gas exchange
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14
Q

How does altitude affect atmospheric pressure?

A

decreases PO2

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15
Q

What are the physiological adaptations to acute altitude?

A
  • hypoxia sensed by peripheral chemoreceptors
  • ventilatory drive increases initially but blunted by central chemoreceptors that respond to decreased PaCO2 due to increased ventilation
  • CO increases due to suppression of cardioinhibitory centre
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16
Q

What are the physiological adaptations to adaptive altitude?

A
  • central chemoreceptors adapt so ventilation rate continues to increase
  • PaCO2 drops leading to respiratory alkalosis, kidneys compensate by reducing acid secretion blood pH normalises
  • alkalosis stimulates 2,3 DPG production leading to rightward shift of O2 dissociation curve
17
Q

What are the changes to blood in altitude?

A
  • erythropoietin release stimulated

- Hb concentration increases

18
Q

What are the changes to vasculature in altitude?

A
  • hypoxia stimulates angiogenesis

- capillary density increases throughout body

19
Q

What are the changes to the cardiopulmonary system in altitude?

A
  • vascular and ventricular remodelling
  • smooth muscle growth increase vascular wall thickness
  • right ventricle hypertrophies
20
Q

How does diving affect atmospheric pressure?

A

atmospheric pressure increases by 760mmHg every 10m depth

21
Q

What effect does depth have on the blood?

A
  • increase in partial pressure
  • N2 and O2 dissolve into blood at lethal excess
  • volume decreases
22
Q

Describe the gas toxicity associated with diving?

A
  • N2 narcosis: partial pressure of N2 rises and starts to dissolve in body tissues
  • O2 poisoning: high pressure O2 dissolves in blood in excess of buffering capacity of Hb
  • TREATMENT - Heliox: N2 replaced by helium and percentage of O2 tailored to reduce harm
  • less readily dissolves in body tissues and less narcotic

MD3001 Respiratory (38 decks)

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