Physiological Lung Volumes and Capacities

Jun 6, 2024

Review flashcards

Physiological Lung Volumes and Capacities

Overview

  • Lecture by Amir Hussain, 2nd year student in College of Medicine
  • Focus on lung volumes and capacities

Key Concepts and Definitions

Lung Volumes

  • Tidal Volume (TV): The volume of air inhaled or exhaled in a normal breath (about 500ml).
  • Inspiratory Reserve Volume (IRV): Maximum volume of air inhalable after normal inspiration (up to 3000ml).
  • Expiratory Reserve Volume (ERV): Maximum volume of air exhalable after normal expiration (about 1100ml).
  • Residual Volume (RV): Volume of air remaining in lungs after maximal exhalation (about 1200ml).

Lung Capacities

  • Total Lung Capacity (TLC): Sum of all lung volumes, almost 6000ml.
  • Vital Capacity (VC): Total volume of air that can be exhaled after maximum inhalation (VC = TV + IRV + ERV; typically around 4800ml).
  • Inspiratory Capacity (IC): Maximum volume of air that can be inhaled after a normal exhalation (IC = TV + IRV).
  • Functional Residual Capacity (FRC): Volume of air remaining in the lungs after a normal expiration (FRC = ERV + RV).

Calculations and Procedures

  • Using a spirometer to measure volumes and calculate capacities.
  • Deep Inspiration: Maximum volume an individual can inhale; can reach up to 6000ml.
  • Deep Expiration: Maximum volume an individual can exhale; normal spirometry values critical to determine lung health.
  • Forced Expiratory Volume (FEV1): Volume of air expelled in the first second of a forced exhalation; normal ratio (FEV1/FVC) >80%.

Pathophysiology

  • Obstructive Lung Disease: Increased airway resistance (e.g., asthma, COPD). Lower FEV1 and FEV1/FVC ratio; higher RV due to air trapping.
  • Restrictive Lung Disease: Decreased lung compliance (e.g., fibrosis, sarcoidosis). Reduced lung volumes and capacities, particularly TLC and VC.

Clinical Significance

  • Importance of FEV1 and FVC in diagnosing obstructive and restrictive lung diseases.
  • FEV1/FVC Ratio: Crucial for categorizing different lung diseases:
    • Normal: >80%
    • Obstructive: <70% (e.g., asthma, COPD)
    • Restrictive: May still be normal but lowered total lung volumes
  • Compliance and Elasticity: Determines lung’s ability to expand and recoil:
    • Compliance: Ability to stretch (increased in obstructive diseases due to fibrosis).
    • Elasticity: Tendency to recoil (important for healthy exhalation).

Practical Application

Spirometry Test Components

  1. Breath Normally: Establish baseline (TV).
  2. Deep Inhalation: Measure IRV.
  3. Forced Exhalation: Measure ERV and FEV1.
  4. Calculate Capacities: Using collected volumes construct TLC, FVC, etc.

Typical Patterns in Disease States

  • Asthma: Normal/increased compliance but decreased elasticity due to airway narrowing.
  • Fibrosis: Decreased compliance and preserved/increased elasticity; restrictive pattern.
  • COPD: Increased RV and decreased FEV1/FVC due to airway obstruction.

Summary

  • For accurate lung volume and capacity measurements, understanding the concepts and correct use of spirometry is essential.
  • Proper interpretation is critical for diagnosing and managing various pulmonary conditions effectively.
  • Comparisons with standard values and attention to deviations help identify specific pulmonary issues.

Remember: Practice with these techniques and formulas improves diagnostic accuracy and enhances clinical assessment skills.