Pulmonary Function Tests (PFTs) are critical in diagnosing, monitoring, and managing childhood asthma. They help assess the degree of airflow limitation, airway hyperresponsiveness, and reversibility. PFTs also provide objective measures to evaluate asthma severity and response to treatment.
Key Pulmonary Function Tests in Childhood Asthma
1. Spirometry
- Purpose: Primary tool to assess lung function in children aged ≥ 5 years.
- Parameters Measured:
- Forced Vital Capacity (FVC): Total volume of air that can be forcefully exhaled.
- Forced Expiratory Volume in 1 Second (FEV₁): Volume of air exhaled in the first second of a forced exhalation.
- FEV₁/FVC Ratio: Differentiates between obstructive and restrictive lung diseases.
- Asthma typically shows a reduced FEV₁/FVC ratio (< 85% in children).
- Peak Expiratory Flow (PEF): Maximum flow rate during forced expiration.
- Asthma Indications:
- Obstruction: Reduced FEV₁ and FEV₁/FVC ratio.
- Reversibility: FEV₁ improvement by ≥ 12% and ≥ 200 mL after bronchodilator administration indicates reversible airway obstruction.
2. Bronchodilator Reversibility Test
- Purpose: Confirms reversible airway obstruction characteristic of asthma.
- Procedure:
- Perform spirometry before and 10–15 minutes after administering a short-acting beta-agonist (e.g., albuterol).
- Positive Test:
- Increase in FEV₁ by ≥ 12% and ≥ 200 mL from baseline indicates reversible obstruction.
3. Peak Expiratory Flow (PEF) Monitoring
- Purpose: Monitors asthma control over time.
- Procedure:
- Child uses a peak flow meter to measure maximum expiratory flow rate.
- Interpretation:
- PEF Variability: Daily variability > 10% suggests poor asthma control.
- PEF Zone System:
- Green Zone (80–100% of personal best): Well-controlled.
- Yellow Zone (50–79%): Increased symptoms, need intervention.
- Red Zone (< 50%): Emergency.
4. Impulse Oscillometry (IOS)
- Purpose: Measures airway resistance; suitable for children < 5 years who cannot perform spirometry.
- Advantages: Non-invasive, requires minimal cooperation.
- Interpretation: Increased resistance in small airways is consistent with asthma.
5. Fractional Exhaled Nitric Oxide (FeNO)
- Purpose: Biomarker for airway inflammation (eosinophilic).
- Procedure: Measures nitric oxide levels in exhaled air.
- Interpretation:
- High FeNO levels (> 35 ppb in children) suggest uncontrolled eosinophilic inflammation.
- Useful for monitoring ICS adherence and effectiveness.
6. Methacholine or Exercise Challenge Test
- Purpose: Identifies airway hyperresponsiveness when baseline spirometry is normal.
- Methacholine Challenge:
- Child inhales methacholine (bronchoconstrictor).
- A ≥ 20% decline in FEV₁ (PC₀₁) confirms airway hyperresponsiveness.
- Exercise Challenge:
- Assess for exercise-induced bronchospasm.
- A ≥ 10–15% decline in FEV₁ post-exercise indicates asthma.
7. Plethysmography
- Purpose: Measures lung volumes to assess hyperinflation or air trapping.
- Indications: Severe or refractory asthma.
- Findings: Increased residual volume (RV) or total lung capacity (TLC) suggests air trapping and hyperinflation.
Use of PFTs in Asthma Management
- Diagnosis:
- Confirm airway obstruction and reversibility.
- Differentiate asthma from other conditions (e.g., chronic bronchitis, vocal cord dysfunction).
- Monitoring:
- Assess lung function over time to detect deterioration.
- Evaluate the effectiveness of treatment (e.g., ICS adherence).
- Risk Stratification:
- Identify poorly controlled asthma based on PEF variability or low FEV₁.
- Decision-Making:
- Determine the need for step-up or step-down therapy.
- Predict exacerbation risk using FeNO or PEF trends.
Challenges in Pediatric PFTs
- Age Limitations: Spirometry requires cooperation and is usually feasible only in children ≥ 5 years.
- Variability: Lung function in children can vary based on growth, technique, and effort.
- Alternative Methods: For younger children, tools like impulse oscillometry and symptom monitoring are critical.
Summary
Pulmonary function tests are integral to diagnosing and managing childhood asthma, with spirometry being the cornerstone in children ≥ 5 years. For younger or less cooperative children, alternative methods like FeNO, IOS, or peak flow monitoring provide valuable insights into asthma control and treatment response.
