A 35-year-old woman with asthma undergoes spirometry before and after inhaled albuterol. FEV₁ improves from 68% to 82% predicted. Which is the most common reason for incomplete reversibility of airway obstruction in chronic asthma?

Explanation

## Reversibility and Remodeling in Chronic Asthma **Key Point:** Complete reversibility (FEV₁ return to >90% predicted post-bronchodilator) occurs in mild asthma. Incomplete reversibility (as shown: 68% → 82%, still <85%) indicates airway remodeling—the most common cause in chronic disease. ### Pathophysiology of Incomplete Reversibility **High-Yield:** Chronic asthma with repeated inflammation → airway wall thickening, smooth muscle hypertrophy, collagen deposition, and loss of elastic recoil. This **fixed component** does not respond to beta-2 agonists. **Clinical Pearl:** The degree of irreversible obstruction correlates with: - Duration of asthma - Frequency of exacerbations - Degree of eosinophilic inflammation - Inadequate inhaled corticosteroid use ### Mechanism of Remodeling ```mermaid flowchart TD A[Chronic airway inflammation]:::outcome --> B[Repeated epithelial injury] B --> C[Smooth muscle proliferation] B --> D[Collagen deposition] C --> E[Airway wall thickening]:::outcome D --> E E --> F[Fixed airway narrowing]:::urgent F --> G[Incomplete bronchodilator response]:::outcome ``` **Mnemonic: REMOD** — **R**emodeling, **E**pithelial, **M**uscle, **O**bstruction, **D**uration. **Warning:** Do not confuse reversibility testing with asthma diagnosis. A 12% and ≥200 mL improvement in FEV₁ post-bronchodilator confirms reversibility and supports asthma diagnosis. However, incomplete reversibility does NOT exclude asthma—it indicates chronic remodeling. ### Why Other Options Are Less Common | Cause | Frequency | Why Not Most Common | |-------|-----------|---------------------| | Airway remodeling | Very common (chronic asthma) | **MOST COMMON** | | Acute bronchospasm | Occurs but usually responsive to higher-dose beta-2 agonists | Less common than remodeling | | Incorrect technique | Testing artifact; should be repeated | Not a pathophysiologic cause | | Pulmonary fibrosis | Rare; would show restrictive pattern (low TLC) | Unrelated to asthma reversibility | [cite:Harrison 21e Ch 297]