Diffusion and Perfusion

• • The pressure of the mixture of gasses is equal to the sum of the individual partial pressures of the gasses in the mixtures.
• PRINCIPLES OF GAS DIFFUSION: DALTON’S LAW

  
• • A bulk of the air that we breathe is composed of:
  • Nitrogen = 78%
  • Oxygen = 20%
  • Water = 0.4%
  • Carbon dioxide = 0.004%
  • Other gases = 0.006%
• Gases would behave as if they are the only one occupying the space.
• The standard atmospheric pressure is equivalent to 760 mmHg.
• PRINCIPLES OF GAS DIFFUSION: HENRY’S LAW

  • States that the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility.
  • The higher the pressure of a gas above a liquid, the more of that gas will dissolve into the liquid.
  • In the lungs, oxygen from the alveoli dissolve to the blood based on the partial pressure difference between the alveolar air and the blood. 
  • If there’s a pressure difference, flow is present.
  • Similarly, carbon dioxide from the blood dissolves to the alveoli to be exhaled based on its partial pressure.
• Diffusion coefficient ; Solubility coefficient

  • Oxygen = 1 ; 0.024
  • Carbon dioxide = 20.3 ; 0.57
• PRINCIPLES OF GAS DIFFUSION: FICK’S LAW

  
• The rate of diffusion is directly proportional to the surface area, diffusion coefficient, and the difference between the partial pressure gradient of the alveoli and capillaries.
• Gases move from areas of high concentration or high partial pressure to areas of low concentration.
• The rate of diffusion is inversely proportional to the membrane thickness.
• • Diffusion coefficient indicates how easily a gas can diffuse through a medium.
  • For nitrogen, its diffusion coefficient is approximately 0.0019.
• Nitrogen has a lower diffusion coefficient than oxygen and carbon dioxide. Thus, it cannot participate in gas exchange.
• Although carbon dioxide has a lower amount than oxygen, it has a greater diffusion coefficient. Therefore, the exchange between carbon dioxide and oxygen is still balanced.
• • The diffusion of a gas is inversely proportional to the square root of the molecular weight.
• Graham’s Law of Diffusion

  
• Gases with a lower molecular weight have a faster rate of diffusion.