Lecture Notes: Obstructive vs Restrictive Lung Diseases

Introduction

• Topic Relevance: Differentiating obstructive vs restrictive lung diseases is a top 5 question for USMLE Step 1.
• Objective: Mastery of key concepts and high-yield facts related to lung diseases.

Types of Lung Diseases

• Two Main Types:
  • Obstructive Lung Disease
  • Restrictive Lung Disease

Obstructive Lung Disease

• Pulmonary Function Tests:
  • FEV1/FVC Ratio: Less than 0.7
  • FEV1: Measures the ability to exhale as much as possible in 1 second.
• Characteristics:
  • Harder to exhale (get air out).
  • Examples include COPD, asthma, chronic bronchitis, and emphysema.
• Mnemonic:
  • O: Out - Harder to get air out
  • B: Below - PFTs are down or below
  • U: Upper - The numerator (FEV1) decreases more than the denominator (FVC).

Restrictive Lung Disease

• Pulmonary Function Tests:
  • FEV1/FVC Ratio: Greater than 0.7
• Characteristics:
  • Harder to inhale (get air in).
  • Examples include interstitial lung disease, environmental pneumoconiosis, ARDS.
  • Pulmonary fibrosis, honeycombing, asbestosis, silicosis.
• Mnemonic:
  • R: R inside - Harder to get air in
  • E: Elevated - PFTs are elevated
  • I: Inferior - The denominator (FVC) decreases more than the numerator (FEV1).

Clinical Application

• Step 1 Questions:
  • Understand patient symptoms and identify the pattern based on the clinical vignette.
  • Identify FEV1, FVC, and FEV1/FVC ratio from given data.
• Common Signs: Hyperresponsiveness, mucus plugging, albuterol relief, and methacholine challenge test for asthma.

Summary

• Key Differences:
  • Obstructive: Decreased FEV1/FVC ratio due to a lower numerator (FEV1).
  • Restrictive: Increased FEV1/FVC ratio due to a lower denominator (FVC).
• Common Diseases:
  • Obstructive: COPD (chronic bronchitis, emphysema), asthma.
  • Restrictive: Interstitial lung disease, pulmonary fibrosis, environmental pneumoconiosis.

Final Thoughts

• Importance of Understanding: Key for USMLE and diagnosing patient patterns.
• High-Yield Areas: Understanding PFT ratios and disease examples.
• Encouragement: Study these mnemonics and patterns to secure free points on exams.

Good luck with your studies!