Spirometry and Lung Disease Overview

Introduction to Spirometry

• Spirometry is a test to monitor lung function.
• It measures lung volumes and capacities.
• Graph Components:
  • X-axis: Time
  • Y-axis: Lung Volume

Lung Volumes

• Tidal Volume (TV): Typical value is 500 mL or 0.5 liters.
• Inspiratory Reserve Volume (IRV): Volume of maximal deep breath in.
• Expiratory Reserve Volume (ERV): Volume after maximal expiration.
• Residual Volume (RV): Air remaining in lungs after maximal expiration.

Lung Capacities

• Vital Capacity (VC): Maximum air expired from fully inflated lungs (TV + IRV + ERV).
• Functional Residual Capacity (FRC): Air remaining after normal expiration (RV + ERV).
• Total Lung Capacity (TLC): Sum of all lung volumes (~6 liters in adult males).
• Forced Vital Capacity (FVC): Largest amount of air expired after maximal inspiration.

Spirometry and Lung Function Graphs

• Normal Lung:
  • Total Lung Capacity: 6 liters
  • Forced Vital Capacity: 5 liters
• FEV1 (Forced Expiratory Volume in 1 second):
  • Ratio FEV1/FVC = 0.8 or 80% (normal value).

Obstructive Pulmonary Disease (COPD)

• Characteristics:
  • Gas trapping and obstruction of airways.
  • Increased Total Lung Capacity and Residual Volume.
  • Vital Capacity may remain the same or decrease.
  • FEV1/FVC ratio < 0.7 or 70%.
• Spirometry Findings:
  • Characteristic 'kink' in flow-volume loop due to obstruction.

Restrictive Lung Disease

• Conditions Include: Pneumoconiosis, Sarcoidosis, etc.
• Characteristics:
  • Lung compliance is impaired due to fibrosis.
  • Decrease in IRV, ERV, RV, and TLC.
  • Overall decrease in lung volumes and capacities.
• Spirometry Findings:
  • FEV1/FVC ratio is typically normal or slightly affected.
  • Example: FEV1 = 3 liters, FVC = 4 liters (FEV1/FVC = 0.75 or 75%).

Conclusion

• Important Ratios:
  • FEV1/FVC ratio helps determine the type and severity of lung disease.
  • Differentiates between obstructive (COPD) and restrictive lung diseases.

Note: Understanding spirometry is crucial for diagnosing and managing lung diseases efficiently.