Ventilation and Diffusion Flashcards
What is atmospheric pressure? (at sea level)
760mmHg or 101.325 kPa
What is partial pressure
The pressure a gas would exert if it occupied the volume of space on its own
What percentage of the air is nitrogen?
78.08% (593mmHg)
What percentage of the air is oxygen?
20.95% (159mmHg)
What percentage of air is CO2?
0.039% (0.29mmHg)
What will happen to partial pressure when underwater?
It will increase the deeper you are
What can be used to replace high levels of oxygen?
- Trimix: nitrogen-oxygen-helium
- Heliox: Oxygen and helium
What does Henry’s law relate to?
Gases dissolving into and out of the plasma
How will the gas move if the partial pressure in the liquid is higher than in the air?
The gas will move out of the liquid
What is the most soluble gas?
CO2
How much more soluble is CO2 in the blood than Oxygen?
20x more
How much N2 is in the blood at atmospheric pressure and why?
Negligble amounts because it is very poorly soluble
What does the total amount of gas in the liquid include?
The amount dissolved in solution plus what is dissolved and chemically bound in solution (e.g bicarbonate)
What differences are there in composition between the atmospheric air and alveolar air?
- O2 is lower (104 mmHg)
- CO2 is higher (40mmHg)
- Water vapour is higher
- Proportion of N2 is lower
What is the water vapour pressure?
47 mmHg
What is the rate of diffusion of oxygen proportional to?
- Surface area
- Solubility
- Concentration gradient (difference in partial pressure)
- Inversely to tissue thickness
- Inversely to sqroot molecular mass
What is the surface area of the lungs?
50 - 100 m^2
How many alveoli are there on average?
500 million
What is the thickness of the alveoli?
0.2 - 0.5 um
What is the conc difference of O2 between the venous blood and alveolar air?
104 mmHg and 40 mmHg
64 mmHg
How quickly does it take at rest for blood to pass through pulmonary capillaries?
1 second
What is the difference in concentration of PCO2 in alveoli and venous blood?
- 40 mmHg in alveoli
- 45 mmHg in venous blood
What must the gas go through in order to reach the blood?
- Must dissolve in aqueous layer
- Must diffuse across the membrane
- Must enter the blood
What can reduce gas exchange as a result of decreasing surface area?
Emphysema
What increases the thickness of respiratory membranes which can reduce gas exchange?
Pulmonary oedema
How does gas move in the tissues?
- Partial pressure gradients are reversed
- Movement if gases in opposite direction than in the lungs
- CO2 moves into blood from tissues
- O2 moves out of blood from tissues
How does increased altitude affect the gas exchange?
- PO2 is reduced
- Increase in release of EPO
- Hb levels increase
How much does atmospheric pressure increase by every 10m in depth?
760 mmHg (1 atmosphere)
Name some of the problems associated with N2 bubbles?
- Can form lethal emboli
- Bubbles in the pulmonary circulation
- In joints - extremely painful
- In brain - stroke
- Decompression sickness
What can rapid ascension without exhaling cause?
- Atmospheric pressure decreases when coming up to surface
- Volume of air in lungs increases
- Causes rupture of alveoli and gas bubbles enter circulation (arterial gas embolism)
- Usually lodge in cerebral circulation
- Can cause seizures, fits, unconsciousness etc.
