Makindo Medical Notes

Overview of Lung Compliance

Lung compliance refers to the ability of the lungs to stretch and expand in response to changes in pressure. It is a measure of the lung's distensibility and is an essential factor in the mechanics of breathing.

Key Concepts

• Definition:
  • Lung compliance (C) is defined as the change in lung volume (ΔV) per unit change in transpulmonary pressure (ΔP).
  • Formula: C = ΔV / ΔP
• Types of Compliance:
  • Static Compliance: Measured when there is no airflow (i.e., during a breath hold). It reflects the elastic properties of the lung and chest wall.
  • Dynamic Compliance: Measured during active breathing and reflects both elastic properties and airway resistance.

Factors Affecting Lung Compliance

• Elastic Properties of Lung Tissue:
  • The lung tissue's elastic fibers contribute to its ability to stretch and recoil.
  • Diseases affecting lung tissue elasticity, such as pulmonary fibrosis, can decrease compliance.
• Surface Tension:
  • Alveolar surface tension, primarily due to the presence of surfactant, affects compliance.
  • Surfactant reduces surface tension, increasing compliance. Deficiency in surfactant (e.g., in neonatal respiratory distress syndrome) reduces compliance.
• Chest Wall Mechanics:
  • The compliance of the chest wall also influences overall lung compliance.
  • Conditions affecting chest wall mechanics, such as obesity or kyphoscoliosis, can alter compliance.
• Age:
  • Compliance generally decreases with age due to changes in lung and chest wall elasticity.

Clinical Relevance

• Increased Compliance:
  • Seen in conditions such as emphysema where there is loss of elastic tissue, leading to over-distensible lungs.
  • Results in a higher lung volume for a given pressure change.
  • Patients may experience difficulty in exhaling air due to decreased elastic recoil.
• Decreased Compliance:
  • Observed in restrictive lung diseases such as pulmonary fibrosis where stiffening of lung tissue occurs.
  • Results in a lower lung volume for a given pressure change.
  • Patients often experience difficulty in inhaling air, leading to reduced lung volumes and increased work of breathing.

Measurement of Lung Compliance

• Static Compliance:
  • Measured using a spirometer and oesophageal balloon to determine transpulmonary pressure.
  • Involves recording lung volume at different pressures during a breath hold.
• Dynamic Compliance:
  • Measured during normal breathing cycles using a spirometer.
  • Reflects both lung elasticity and airway resistance.

Summary

Lung compliance is a crucial parameter in respiratory physiology, reflecting the lung's ability to stretch and expand. It is influenced by the elastic properties of lung tissue, surface tension, chest wall mechanics, and age. Changes in lung compliance are significant in various respiratory conditions, affecting both the ability to inhale and exhale effectively. Understanding and measuring lung compliance can aid in diagnosing and managing pulmonary diseases.