This document compares and contrasts spirometry and peak expiratory flow rate (PEFR) tests used in pulmonary function testing. Spirometry measures inhaled and exhaled lung volumes and airflow over time, providing key metrics like FVC, FEV1, and their ratio. It is useful for diagnosing COPD and asthma. PEFR only measures maximum exhaled airflow and is affected by inspiration depth, airway caliber, and effort. It primarily assesses large airways. Both tests can help distinguish obstructive disorders like asthma from restrictive disorders.

1. Spirometry vs. Peak
Expiratory Flow Rate
Pulmonary Function Tests

2. What is Spirometry?
• Is the most important diagnostic test for COPD & asthma.
• It measures the volume of air inhaled, the volume exhaled and the
rate at which the patient exhale.
• May be used periodically to assess effectiveness of medications.
• Most important variables:
• FVC: “forced vital capacity”-the total exhaled volume
• FEV₁: “forced expiratory volume in one second”
• FEV₁/FVC ration: their ratio
• The slow vital capacity can be measured which collect data for at least
30 seconds.
• Useful when FVC is reduced & airway obstruction is present.
• Values expressed as L/sec

3. Factors Affecting Results:
• Age:
• Lung function generally increases with age up to ~25yrs, then declines with
increasing age afterwards.
• Sex:
• Pre-pubescent males & females have same lung function
• Post-puberty, growth of thorax is greater in males
• Height:
• The taller the person, the bigger the lungs.
• Weight:
• Increasing weight causes increasing lung function until obesity is reached.
• Ethnic origin
• Smoking:
• Cause a more rapid decline in lung function.

4. Peak Expiratory Flow Rate:
• Is the maximal(how fast & hard) rate at which a person can exhale
after full inspiration.
• Is affected by the fullness of:
• Fullness of the preceding inspiration
• Caliber of the large airways
• Expiratory muscle strength
• Voluntary effort
• Predominantly assesses large airway caliber & can underestimate the
effects of asthma in the small airways.
• Validity dependent on maximal effort.
• Normal value: 10L/s (600mL/min) in healthy adult.
• Device used is called a Peak Flow Meter.
• Values expressed as L/min

5. Steps in Measuring PEFR:
• Step 1: Move marker to 0
• Step 2: Patient to stand or sit up straight
• Chin slightly elevated & look straight ahead
• Step 3: Empty lungs (as much as possible)
• Step 4: Breathe in (deeply)
• Step 5: Put mouthpiece between lips
• Between teeth & close lips tightly.
• Do NOT PUT TONGUE ON MOUTHPIECE
• Step 6: Blow out
• Step 7: Look at meter
• Step 8: Measure peak flow three times
• Record highest number reached
• Called “Personal best peak flow”.

6. PEFR Meter SPIROMETER

7. Obstructive Disorders:
• Characterised by airflow limitation;
• There is a decreased airway caliber through either:
• Smooth muscle contraction
• Inflammation
• Mucus plugging
• Airway collapse in emphysema
• Characterised by:
• Reduced FEV₁
• Normal (or reduced) VC
• Normal (or reduced) FVC
• Reduced FEV₁/FVC ratio
• Concave flow-volume loop

8. Restrictive Disorders:
• Characterised by a loss in lung volume and are much rarer
• Occurs in:
• Pulmonary fibrosis
• Pleural disease
• Chest wall disorders (kyphoscoliosis)
• Neuromuscular disorders
• Pulmonary edema &
• Obesity (to name a few)
• Characterised by:
• Reduced FVC
• Normal to high FEV₁/FVC ratio
• Normal looking shape on spirometry trace
• Possibly a relatively high PEF.