Ventilation perfusion coupling

• Ventilation perfusion coupling

  • In respiratory physiology the V/Q ratio is measurement used to describe efficiency and adequacy of matching two variables
  • Ventilation – the air which reaches the lungs
  • Perfusion – the blood which reaches the lungs
• V/Q differences in normal lung:

  • The lungs are centered vertically around the heart
  • Part of the lung is superior to the heart and part is inferior
  • This has major impact on the V/Q ratio
  • Lower part of lung is better ventilated and better perfused than apex
• Clinical relevance V/Q

  • For efficient gas exchange there needs to be maximum coupling between ventilation and perfusion
  • Inadequacy of either V or Q will have significant impact on removal of CO2 and oxygenation of blood
  • The V/Q ratio can be measured with a ventilation/perfusion scan
• Maintaining V/Q matching:

  • Vital to maintain V/Q ratio to achieve adequate gas exchange
  • In respiratory disease V/Q mismatch triggers auto-regulatory homeostatic mechanisms to minimise deficit
  • Hypoxic pulmonary vasoconstriction (HPV) or dilation
  • Bronchiole response (constriction or dilation)