Physics Relevant to Respiratory Physiology Flashcards
What is Boyle’s Law?
Pressure exerted by a gas is inversely proportional to its volume. Gases (singly or in mixtures) move from areas of high pressure to low pressure.
For any given constant temperature the pressure of any gas can be predicted from its mass and the volume of the chamber it occupies
Using Boyle’s law, explain how air moves into the lungs during inspiration
The diaphragm contracts and descends, and the external intercostal and scalenes contract, increasing the volume of the thoracic cavity by pulling the ribs upwards and outwards.
This increases the volume of the lungs (which are stuck to thoracic wall), thus decreasing the pressure within the lungs to 1 mmHg below atmospheric pressure. This creates a pressure gradient with the external environment, causing a movement of air into the lungs.
Using Boyle’s law, explain why air moves out of the lung during expiration
Somatic motor neurons stop stimulating muscles, allowing the diaphragm, external intercostal and scalenes to relax. Elastic recoil of the lungs and the thoracic cavity causes the everything to return to its relaxed position.
This means that alveolar pressure increases to about 1 mmHg above atmospheric pressure, creating a pressure gradient. This causes the movement of air down the pressure gradient and out of the lungs.
What is the law of LaPlace?
The pressure (P) exerted on the centre of a bubble encapsulated by a fluid film is a function of surface tension of the fluid (T) and the radius of the bubble (r)
P=2T/r
What is Dalton’s law?
States that the total pressure of a gas mixture is the sum of the pressures of the individual gases. This can be applied to the partial pressures of important gases in air such as
What is Charles Law?
States that the volume occupied by a fixed mass of gas at a constant pressure is is directly related to the absolute temperature (V/T=k)
What is Henry’s Law?
States that the amount of gas dissolved in a liquid is determined by the pressure of the gas and it’s solubility in the liquid. Can be applied to gases dissolved in plasma.
What is the definition of the partial pressure of a gas?
The pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture . Each gas contributes to the total pressure of the mixture.
The partial pressure is the pressure the gas would have if the gas were in the same volume and temperature by itself.
What is Gay-Lussac’s Law?
The pressure of a fixed mass of gas at constant volume is directly proportional to its absolute temperature (P/T = k).
What is Avogadro’s law?
The volume occupied by an ideal gas is proportional to the number of moles of gas.
Equal volumes of gases at the same temperature and pressure contain the same number of molecules (6.023 × 1023, Avogadro’s number).
What is the universal (ideal) gas law?
The state of a fixed mass of gas is determined by its pressure, volume and temperature(PV = nRT)
Where
- P is the pressure of the gas
- V is the volume of the gas
- n is the number of moles of the gas
- R is the Universal Gas Constant (8.314)
- T is the absolute temperature of the gas in Kelvin.
What is Graham’s Law?
The rate of diffusion or effusion of a gas is inversely proportional to the square root of the mass of its particles
In most circumstances, the mass of the particles and the density of the gas are sufficiently correlated to one another that an approximation can be made:
Rate of diffusion = 1/squarerootdensity
Thus, if a gas had particularly large particles, or is particularly dense, it will mix more slowly with other gases, and ooze more slowly out of containers.
What is Dalton’s law?
The total pressure of a mixture of gases is equal to the sum of the partial pressure of all of the constituent gases
What is the definition of partial pressure?
How is the solubility of a gas influenced by temperature?
For any given partial pressure of a gas, the solubilithy will be inversely proportional to temperature - in other words, increasing temperature results in decreased solubility
Due to dissociation of a gas in water is exothermic reaction - heat energy is released as gas molecules occupy potential spaces between molecules of solvent. This is more relevant to polar solvents such as water, which can form hydrogen bonds with dissolved gases. This process is different in organic solvents which don’t form hydrogen bonds.
What is the definition of dissolved gas tension?
Gas tension of a solution is the partial pressure of a gas with which that solution is in equilibrium
Why are dissolved gases not described in terms of partial pressure, but gas tension?
A dissolved gas does not exert pressure in the same way a gaseous mixture does, and cannot be described in terms of manometry. However, using Henry’s law, the dissolved fraction exists in equilibrium with the gaseous fraction, and therefore for every tension, there is a corresponding partial pressure. By convention gas tension of a solution as the partial pressure of a gas with which that solution is in equilibrium.
What is the main influencer of gas difssuion between body fluid compartments?
Partial pressure gradient, which is in turn affected by the solubility of a gas in each compartment
Concentration gradient is largely irrelevant
How is the amount of given gas in a solution influenced by solubility?
If one compartment contains a solvent where a gas is highly soluble, and an adjacent compartment contains a solvent where a gas is poorly dissolved, how will the gas distribute between the 2 compartments?
Gas will diffuse out of poor solvents compartment into good solvents compartment, until the partial pressure is the same in both liquids. The concentration of gas in the good solvent will, however, be much higher. This is a case of diffusion occurring against a concentration gradient.
What is the boiling point temperature?
The temperature at which vapour pressure equals atmospheric pressure. A lower atmospheric pressure will result in a lower boiling point
What is the critical point of a gas?
The point of minimum pressure and maximum temperature at which both a gaseous and a liquid phase of a given compound can co-exist
Why can the vapour pressure of a substance be used to describe how volatile a substance is?
Following initial boiling of liquid gas, vapour will fill the unoccupied volume of the chamber. The entire volume of the liquid gas will not be expected to turn into vapour - the rate of vapourisation will slow down. As this happens, part of vapourised gas will start to condesate. The rates of these two processes will work towards a point of equilibrium. When this equilibrium point is reached, this is known aws saturation vapoour pressure
A gas which has a very high vapour pressure is more volatile, i.e. its tendency to be a gas exceeds its tendency to be a liquid. The saturation vapour pressure of a volatile anaesthetic agent at room temperature may be quite high.
How does temperature affect saturation vapour pressure?
As temperature increases, so does vapour pressure - increasing the energy of the molecules of the liquid by heating them allows more of those molecules to lift off from the surface of the liquid.
What is the difference between a gas and a vapour?
Vapour is used to describe an evaporated substance whish is beow its critical temperature (i.e. still has the option of becoming a liquid if pressure increases). A gass is specifically used to describe a substance which is above its critical temperature (i.e. no matter what pressure does it will never liquify)
How much energy is required to convert 1 kg water into 1 kg steam at body temperature?
2.42 MJ - the lower the starting temperature, the more energy/latent heat is required. As temperature increases, less latent heat of vapourisation is required
How does heat and humidity of air change as it enters the respiratory system?
On the way towards the alveolus, gas becomes heated by airway structures to a point where it becomes the same temperature as the rest of the body, and at the same time the relative humidity increases to 100%. This occurs anatomically somehwere just past the carina (5cm distal to it, or in 2nd-4th generation bronchi according to the variable position given by different textbooks).
How does ambient air temperature influence the reclamation of moisture by the respiratory tract?
The hot air on the way into the lungs would therefore have warmed the respiratory mucosa, preventing the normal expiratory condensation of dew from taking place.
