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• Measurements usually taken on a gas

  • Volume
  • Temperature
  • Pressure
  • Mass
• Boyle's law

  Keep mass and temperature fixed. As pressure increases, volume decreases. Pressure is inversely proportional to volume. P1V1 = P2V2
• Charles's law

  Volume vs. temperature (keep pressure and mass fixed). Volume increases as temperature increases. Temperature and volume are directly proportional. V2/V1 = T2/T1
• If one reduces the temperature low enough, both pressure and volume is 0 (absolute zero) at 273K or 0°C
• T(K)

  T(C) + 273.15
• Ideal gas law

  PV = nRT ((P1V1)/T1 = (P2V2)/T2). R = 8.314 J mol-1K-1
• Dalton's law

  The total pressure of a mixture of gases is equal to the partial pressure of the gases if they were present separately
• Pressure


  The greater the height, the lower the pressure (P = ρgh)
• 1 kPa = 9.8 x 10-3 atm = 7.5 mmHg (for every 10m of water the ground level pressure increases by 1 atm)
• Partial pressure of a gas in a mixture

  % of the gas in the mixture x total pressure of the gas mixture
• Gases move

  From areas of higher to lower partial pressures, and the greater the difference in pressure between two points, the greater the rate of gas movement
• Henry's law

  At constant temperature, the concentration of a gas dissolved in a liquid is equal to the partial pressure of that gas over the liquid x solubility coefficient - Conc O2 = ppO2 x solubility coefficient
• The solubility of a gas in a liquid can increase when the partial pressure of that gas also increases
• Laplace's law

  Relates the tension/radius of a membrane to the pressure on either side (ΔP = 2T/R) - for the same pressure, if the radius decreases, the tension also decreases
• Respiration

  Air enters through the nose → pharynx → trachea → bronchi → bronchioles → alveoli
• There are around 300 million alveoli in the lungs and they are the main respiratory surface
• Ventilation

  1. Inspiration (diaphragm and external intercostal muscles contract, rib cage moves up and out, volume increases, pressure decreases, air flows in)

  2. Expiration (diaphragm and external intercostal muscles relax, rib cage moves down and in, volume decreases, pressure increases, air flows out)
• Forced expiration

  Abdominal and internal intercostal muscles contract, pushing diaphragm upwards and pulling ribs downwards respectively. Volume decreases and pressure increases, therefore pushing air out
• Intrapleural pressure is almost always less than atmospheric pressure
• Lung volumes

  • Tidal volume (0.5L)
  • Inspiratory reserve volume (3L)
  • Expiratory reserve volume (1L)
  • Residual volume (1.5L)
• Pulmonary volume

  The amount of air moving in and out of our lungs per minute - depends on size of each breath (TV) and number of breaths/min (RF - respiratory frequency). PV = TV x RF
• Gas exchange in the alveoli during inspiration

  Pulmonary pressure decreases, volume increases, diaphragm moves down, intercostals move out, tension increases as radius increases. Drop in pleural pressure increases ΔP which increases the radius that then increases the tension in the alveolar wall
• Out of 1L of blood in the lungs, only 70 ml is present in the alveolar capillary beds for less than 1 sec therefore the gas exchange should be fast
• The diffusion process controls the oxygen and carbon dioxide transfer into and out of the blood. It is a passive process that pushes atoms from regions of high concentration to low concentration till equilibrium is reached
• Poiseuille's law

  The volume of a homogenous fluid in a capillary tube is directly proportional to the pressure difference at both ends of the tube to the fourth power of its internal radius, and inversely proportional to the length and viscosity of the fluid
• A small reduction in the airway diameter can cause difficulties breathing - asthma and croup
• Peak Expiratory Flow Rate (PEFR)


  A test that can determine how fast a person can breathe out, which can help to see whether the lungs are functioning. Usually used in patients with asthma. Results vary depending on age, sex and height
• When the airways are blocked the flow rate lessens, so asthma patients may experience low flow rates before having breathing symptoms
• The flow rates range from 120cm = 215L/min to 180cm = 500L/min, increasing by 50L/min for every 10cm increase in height, but 130cm = 260L/min
• Asthma

  Due to inflammation and mucus secretion, the bronchioles airway is blocked leading to a person's ability to breathe becoming difficult. Exercise can increase the airway responsiveness to agents that promote bronchiole constriction
• Croup

  Identified by a harsh, repetitive cough similar to a seal barking, due to swelling around vocal cords and windpipe. Children younger than 5 years are more susceptible as they have small airways to begin with. Croup is not serious and can be treated at home or by some medication