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Flashcards in Respiratory: Gas Laws Deck (14)
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1
Q

What is the partial pressure of a gas?

A

The individual pressure that the individual gas exerts within a gas mixture. each gas in a mixture exerts a partial pressure equal to the pressure it would exert if it was the only gas present.

2
Q

What is the pO2 in alveolar air, venous blood and atmospheric air?

A

Alveolar pO2 = 13.3 kPa
Venous pO2 = 8kPa
Atmospheric pO2 = 101kPa

Therefore oxygen diffuses from alveolar air to the blood

3
Q

What is saturated vapour pressure?

And what is the value at body temperature? §

A

The pressure exerted by water vapour when it is in the gas phase.
At body temp = 6.28kPa

4
Q

How do you calculate the amount of O2 dissolved in plasma?

A

Solubility coefficient of O2 x pO2

5
Q

Why is the pO2 of alveolar air lower than the pO2 of atmospheric air?

A

The air is humidified as it enters the airways (water vapour ended)
O2 is constantly leaving and CO2 entering due to gas exchange therefore %O2 is lower

6
Q

What is Boyle’s law?

A

The pressure of a gas is inversely proportional to its volume
P = 1/V

7
Q

What is the pCO2 in alveolar air and venous blood?

A

Alveolar air = 5.3 kPa

Venous blood = 6 kPa

8
Q

Why is there still sufficient oxygen supply during exercise?

A

Blood stays in the pulmonary capillaries for 3x longer than it needs to therefore there is a 2/3rd redundancy for exercise.

9
Q

What are some pathologies that affect the rate of gas diffusion?

A

Oedema in the interstitial space - increased thickness of barrier
Fibrotic lungs - increased thickness of barrier
Emphysema - decreases SA

10
Q

What is dead space?

A

Air enters and leaves the lungs - last air in is the first air put
The last air stays in the airways and never reaches the alveoli therefore it is ‘wasted’ (~1/3 of tidal volume)

11
Q

Define serial/ anatomical dead space and give a value

A

The volume of the conducting airways (no gas exchange) - from mouth to terminal bronchioles. Typically ~150m;

12
Q

Define distributive dead space and give a value

A

The volume of the lungs that DOES NOT support gas exchange eg dead/damaged alveoli, alveoli with poor perfusion. Typically ~170ml

13
Q

Define physiological dead space and give a value

A

Anatomical dead space + distributive dead space

Typically ~320ml

14
Q

How do you calculate alveolar ventilation rate?

A

Dead space volume x resp rate

Subtract this from pulmonary ventilation rate (same as CO 5l/min)

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