PERV spirometry
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PERV spirometry mnemonics lung volumes
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PERV spirometry FEV FVC interpretation mnemonic medical
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"PERV" spirometry steps interpretation approach
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PERV acronym spirometry "Patient Effort Reproducibility Validity" OR "pattern" interpretation
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PERV is a 4-step mnemonic for systematically interpreting spirometry results. Here is a full breakdown:
PERV - Spirometry Interpretation Mnemonic
| Letter | Step | What to assess |
|---|---|---|
| P | Pattern | Is it obstructive, restrictive, mixed, or normal? |
| E | Extent / Severity | How severe is the impairment? |
| R | Reversibility | Does the pattern reverse with a bronchodilator? |
| V | Validity | Was the test technically acceptable and reproducible? |
P - Pattern
Use the FEV1/FVC ratio and FVC as the core values.
Obstructive pattern:
- FEV1/FVC ratio reduced (< lower limit of normal; often taken as < 0.70)
- FVC normal or mildly reduced (from air trapping)
- FEV1 reduced
- Flow-volume curve shows a "scooped" or concave expiratory limb
- Causes: COPD, asthma, bronchiectasis
Restrictive pattern:
- FEV1/FVC ratio normal or elevated
- FVC reduced (< 80% predicted)
- FEV1 reduced proportionally
- TLC reduced (requires full lung volumes for definitive diagnosis)
- Causes: pulmonary fibrosis, pleural disease, neuromuscular disease, obesity
Mixed pattern:
- FEV1/FVC ratio reduced AND FVC reduced significantly
- Seen in combined obstructive + restrictive disease
Goldman-Cecil Medicine summarises the key patterns as:
| FEV1 | FVC | FEV1/FVC | RV | TLC | |
|---|---|---|---|---|---|
| Normal | Normal | Normal | Normal | Normal | Normal |
| Obstructive | ↓ | Normal to ↓ | ↓ | ↑ | Normal to ↑↑ |
| Restrictive | ↓ | ↓↓ | Normal or ↑ | Normal or ↓ | ↓↓ |
| Weak chest wall | ↓ | ↓↓ | Normal or ↑ | ↑ | Normal or ↓ |
- Goldman-Cecil Medicine, Table 79.2
E - Extent (Severity)
Once a pattern is identified, grade severity based on % predicted FEV1 (ATS/ERS grading):
| Grade | FEV1 % predicted |
|---|---|
| Mild | ≥ 70% |
| Moderate | 60-69% |
| Moderately severe | 50-59% |
| Severe | 35-49% |
| Very severe | < 35% |
Note: use z-scores (z < -1.64 = below lower limit of normal) for more statistically valid classification rather than the 80% cutoff, which misclassifies the young and elderly.
R - Reversibility
After establishing an obstructive pattern, give a short-acting bronchodilator (usually salbutamol/albuterol 400 mcg) and repeat spirometry after 15-20 minutes.
Positive bronchodilator response (significant reversibility):
- FEV1 increases by ≥ 12% AND ≥ 200 mL from baseline
- Suggests asthma (reversible airway obstruction)
- Fixed obstruction with no/minimal response suggests COPD
The flow-volume curve below shows moderate obstruction with bronchodilator response - note the green (post-bronchodilator) curve with slightly higher early peak and improved flow:
- Murray & Nadel's Respiratory Medicine
For asthma, a 20% and 200 mL increase in FVC post-bronchodilator is also suggestive. Additionally, a > 20% fall in FEV1 with methacholine challenge (PC20) supports bronchial hyperresponsiveness when baseline spirometry is normal.
V - Validity (Quality of the Test)
Before interpreting any results, confirm the test is technically acceptable. According to ATS/ERS standards:
- At least 3 acceptable maneuvers must be obtained
- Each blow must show no hesitation at start and last ≥ 6 seconds (plateau for ≥ 1 sec)
- The two largest FVC values must agree within 0.15 L (150 mL)
- The two largest FEV1 values must also agree within 0.15 L
- Up to 8 maneuvers may be attempted to achieve valid, reproducible results
- An irregular or jagged flow-volume curve suggests poor effort or suboptimal coaching
Poor quality invalidates interpretation regardless of the numerical values.
Quick Summary Table
| Step | Key question | Key value |
|---|---|---|
| P - Pattern | Obstructive / Restrictive / Mixed? | FEV1/FVC ratio + FVC |
| E - Extent | How severe? | % predicted FEV1 |
| R - Reversibility | Does it respond to bronchodilator? | ≥12% + ≥200 mL rise in FEV1 |
| V - Validity | Is the test technically reliable? | Repeatability within 150 mL |
Sources:
- Goldman-Cecil Medicine, 26th ed. - Pulmonary Function Tests (Ch. 73 & 79)
- Murray & Nadel's Textbook of Respiratory Medicine - Spirometry and Asthma chapters
- ATS/ERS 2022 spirometry standardization (updated guidelines using LLN and z-scores)
- AAFP stepwise approach to spirometry interpretation
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