Spirometry: FVC, FEV1, Peak Expiratory Flow
Definition
Pulmonary function test measurements that assess lung capacity and airflow:
- FVC (Forced Vital Capacity) - Total volume of air you can forcibly exhale after maximum inhalation
- FEV1 (Forced Expiratory Volume in 1 second) - Volume exhaled in the first second of forced exhalation
- PEF (Peak Expiratory Flow) - Maximum speed of exhalation
Why It Matters
Spirometry values are essential for: - Asthma diagnosis and monitoring - Detecting airway obstruction - COPD assessment - Measuring disease severity - Treatment effectiveness - Tracking response to medications - Surgical preparation - Assessing respiratory reserve - Occupational health - Monitoring exposure effects
How It's Measured
Spirometry requires specialized equipment: - Clinical spirometer - Laboratory-grade device - Portable spirometers - Home devices (some connect to HealthKit) - Peak flow meters - Simple PEF measurement devices
Technique matters: 1. Maximum deep breath in 2. Seal lips around mouthpiece 3. Blast air out as hard and fast as possible 4. Continue until lungs are empty
Reference Values
Values are expressed as percentage of predicted, based on: - Age - Sex - Height - Ethnicity
| Measurement | Normal Range |
|---|---|
| FVC | ≥80% of predicted |
| FEV1 | ≥80% of predicted |
| FEV1/FVC ratio | ≥70% (or lower limit of normal) |
| PEF | Varies; personal best used as reference |
Key Patterns
| Pattern | FEV1 | FVC | FEV1/FVC |
|---|---|---|---|
| Normal | Normal | Normal | Normal |
| Obstructive (asthma, COPD) | ↓ | Normal or ↓ | ↓ |
| Restrictive (fibrosis) | ↓ | ↓ | Normal or ↑ |
Confounders & Limitations
- Technique-dependent - Poor effort affects results
- Acute conditions - Colds, infections alter baseline
- Medications - Bronchodilators affect readings
- Time of day - Values may vary throughout day
- Device calibration - Home devices less accurate than clinical
Use Cases
- Asthma action plans - PEF zones (green/yellow/red)
- COPD staging - Disease severity classification
- Treatment monitoring - Before/after bronchodilator response
- Long-term trends - Tracking lung function over time