Lecture on Lung Compliance and Elasticity

Introduction to Compliance

• Mathematical definition: Compliance = change in volume/change in pressure
• Simplified: Measure of stretchability (distensibility)
• High compliance: Easily stretched (e.g., rubber band)
• Lungs: Naturally compliant but also have elasticity

Compliance vs. Elasticity

• Compliance: Ease of stretching
• Elasticity: Resistance to stretch, desire to recoil
• Compliance formula: Change in volume is directly proportional to compliance, change in pressure inversely proportional
• Elasticity formula: Change in pressure is directly proportional to elasticity, change in volume inversely proportional

Factors Affecting Lung Compliance

1. Elasticity of the Lungs
   • Lungs are generally compliant with the right amount of elasticity
   • Pulmonary fibrosis: Scar tissue increases elasticity, decreases compliance
   • Emphysema: Decreases elasticity, increases compliance
2. Surface Tension in Alveoli
   • Tension at air-water interface tries to shrink alveoli
   • Respiratory distress syndrome: High surface tension decreases compliance
   • Surfactant: Reduces surface tension, increases compliance
3. Elasticity of the Chest Wall
   • Chest wall generally compliant, outward recoil
   • Disorders (ankylosing spondylitis, kyphosis, scoliosis) can decrease compliance
   • Aging affects cartilage, reducing compliance
4. Neuromuscular Factors
   • Diaphragm or intercostal muscle paralysis decreases compliance
   • ALS affects neuron signals, reducing muscle function and compliance
5. Airway Obstructions
   • Mucus buildup decreases compliance by limiting airflow
   • Pneumothorax: Air in pleural cavity increases pressure, decreases compliance

Effects of Pressure Changes

• Transpulmonary vs. Trans-thoracic Pressure
  • Lungs: Transpulmonary pressure
  • Chest wall: Trans-thoracic pressure
• Pneumothorax: Atmospheric air equalizing intrapleural pressure leads to lung collapse (atelectasis), reducing compliance

Conclusion

• Compliance is influenced by various factors including elasticity, surface tension, neuromuscular components, and airway integrity.
• Pathological conditions like pneumothorax and pulmonary disorders demonstrate changes in compliance and elasticity.
• Understanding compliance and elasticity is crucial for assessing respiratory health and mechanics.