Respiratory: Gas Laws Flashcards
What is the partial pressure of a gas?
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.
What is the pO2 in alveolar air, venous blood and atmospheric air?
Alveolar pO2 = 13.3 kPa
Venous pO2 = 8kPa
Atmospheric pO2 = 101kPa
Therefore oxygen diffuses from alveolar air to the blood
What is saturated vapour pressure?
And what is the value at body temperature? §
The pressure exerted by water vapour when it is in the gas phase.
At body temp = 6.28kPa
How do you calculate the amount of O2 dissolved in plasma?
Solubility coefficient of O2 x pO2
Why is the pO2 of alveolar air lower than the pO2 of atmospheric air?
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
What is Boyle’s law?
The pressure of a gas is inversely proportional to its volume
P = 1/V
What is the pCO2 in alveolar air and venous blood?
Alveolar air = 5.3 kPa
Venous blood = 6 kPa
Why is there still sufficient oxygen supply during exercise?
Blood stays in the pulmonary capillaries for 3x longer than it needs to therefore there is a 2/3rd redundancy for exercise.
What are some pathologies that affect the rate of gas diffusion?
Oedema in the interstitial space - increased thickness of barrier
Fibrotic lungs - increased thickness of barrier
Emphysema - decreases SA
What is dead space?
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)
Define serial/ anatomical dead space and give a value
The volume of the conducting airways (no gas exchange) - from mouth to terminal bronchioles. Typically ~150m;
Define distributive dead space and give a value
The volume of the lungs that DOES NOT support gas exchange eg dead/damaged alveoli, alveoli with poor perfusion. Typically ~170ml
Define physiological dead space and give a value
Anatomical dead space + distributive dead space
Typically ~320ml
How do you calculate alveolar ventilation rate?
Dead space volume x resp rate
Subtract this from pulmonary ventilation rate (same as CO 5l/min)
