14. Peripheral Lung Disease

• ventilation = driving pressure / airway resistance
• asthma = chronic airway inflammation, bronchoconstriction

  • inflammatory cells activated by allergens -> bronchoconstriction
  • increased mucous secretion
  • decreased alveolar ventilation
  • decreased partial pressure gradients for O2 and CO2
• FEV1 = first second of forced expiration
• in asthma FEV1 is reduced

  • FEV1:FVC ratio is reduced
  • peak expiratory flow is also reduced
• B2 agonists cause bronchodilation by increasing intracellular cAMP -> activated PKA and phosphorylation and inactivation of myosin light chain kinases -> inhibits contraction
• theophylline = phosphodiesterase inhibitor -> increase in cAMP -> enhance sympathetic activity on airway smooth muscle
• anti-muscarinic drugs block vasal effect on airway smooth muscle in asthma
• steroids counteract airway inflammation in asthma
• leukotriene receptor antagonists block actions of bronchoconstricting and pro-inflammatory leukotrienes
• main cause of copd = tobacco smoking
• copd = alveolar obstruction (emphysema) and inflammation

  • airways tend to collapse on expiration
  • residual volume and TLC is increased causing hypoventilation
• chest wall compliance is unchanged in emphysema but lung compliance is increased

  • causes increased system compliance
  • FRC higher and closer to chest wall volume
• COPD = decreased PEFR, FEV1, FEV1:FVC
• classification of COPD is based on FEV1
• in COPD there is a large increase in FRC due to increased lung compliance caused by breakdown of the structure of the alveoli and reduced elastic recoil of the lungs
• increased RV and decreased VT in COPD, TLC is unchanged

  • PEF is reduced
• managing COPD:

  • prevent deterioration - no more smoking
  • bronchodilators to alleviate symptoms and improve exercise capacity
  • long term O2 therapy to increase partial pressure gradient for O2 by increasing PaO2
• fibrosis = increased fibroblast proliferation, increased collagen and elastic -> thickening of alveoli

  • decreased lung compliance
  • increased diffusion barrier
  • dry cough, hypoxaemia and hypocapnia (alveolar ventilation increases to correct hypoxaemia
• CO2 is 20x more diffusable than O2
• fibrosis decreases lung compliance

  • TLC reduced
  • FRC reduced
  • decreased VC
  • no change in FEV1:FVC
  • decrease in FEV1