CSAN

Review of Principles

Daltons law and Partial Pressure

In a mixture of gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume.

The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture- (exercise to explain

this)

Henry’s Law

At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

The effect of Temperature on GasesThe solubility of gases DECREASES at higher temperatures

Henry’s LawThe effect of partial pressure on solubility of gases

At pressure of a few atmospheres or less, solubility of gas in solution follows Henry Law. This states that the amount of dissolved gas in solution is directly proportional to the amount of pressure above (or around) the solution.

Henry’s Law & Soft Drinks

Soft drinks contain “carbonated water” – water with dissolved carbon dioxide gas.

The drinks are bottled with a CO2 pressure greater than 1 atm or sea level (Approx 1 bar).

We live at or above sea level, therefore-

When the bottle is opened, the pressure on CO2

decreases and the solubility of CO2 also decreases,

according to Henry’s Law-

bubbles of CO2 escape from solution.

Henry’s Law Application

At sea level 1 atm or roughly 1 .00 Bar (or 100 kilopascals)

Nitrogen that is breathed in is not well absorbed into the blood and tissues

If some-one dives below sea level then to over 30 metres (3 Bar) then their body are subject to higher pressures.

Gases are more likely to be absorbed into the blood and tissues under higher pressures.

If they surface quickly, the pressure on them drops quickly ad gases bubble out of tissues into the blood.

Effects of Henry and Daltons Law with Diving

Henry’s Law also explains the reasons why divers are asked to not to take hot baths after a dive, or asked to abstain from doing strenuous activities or exercise.

The increase in temperature caused by the exercise or hot bath may cause the nitrogen they have breathed in to become less soluble and increase the release of absorbed nitrogen into the blood stream, possibly causing Decompression Sickness ‘the bends’

Boyles Law- relationship between pressure and volume Boyle's law describes the inversely proportional relationship between

the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system.

I.e the thorax

Glenn Educational Programs Office Digital Learning Network

 

Boyles Law-

Revise the mechanics of chest movements and the changes in intra-thoracic and intra-pleural pressure that allows for ventilation.

Law of Laplace Imagine yourself blowing up a balloon.

The harder you blow, the higher the air pressure inside the balloon becomes and the greater the pressure difference between the outside and inside of the balloon.

Since the pressure difference rises, the tension in the rubber walls of the balloon also rises, and this is what causes the balloon to stretch?

Law of Laplace

Now think about the beginning in getting a balloon to inflate.

A white substance is on the inside of the balloon and this lowers surface tension

If lungs volumes are low, surface tension is diverted inwards

Because of internal surface tension

If lung volumes are high, then water particles on the outside

of the alveolus create a pressure pulls internal water

particles towards them – what is this pressure called

Surface tension

The surface tension acts at the air-water interface and tends to make the bubble smaller (by decreasing the surface area of the interface).

In the lungs water is on both sides so surface tension work in both ways

Surfactant on the inner wall also reduces surface tension on the inside, helping to keep the alveolus open

Law of Laplace

. Because surface tension on the inner aspect of each sphere is pulling the bubble inwards, the pressure to inflate the large bubble is much less than that required to inflate the small bubble

If these bubbles were Alveoli then they would be coated on the inside with Surfactant

This lowers the surface tension so that is becomes easier to inflate the small bubble