How can I easily learn to perform spirometry for diagnosing asthma in adults?

How to Learn Spirometry Easily

Core Concept: Understanding What You're Measuring

Spirometry measures how much air you can forcefully blow out and how fast you can do it—these two simple measurements (FEV1 and FVC) tell you if airways are obstructed. 1

The key parameters you need to master are:

• FEV1 (Forced Expiratory Volume in 1 second): The volume of air expelled in the first second of forced exhalation 1, 2
• FVC (Forced Vital Capacity): The total volume of air expelled from full inhalation to complete exhalation 1, 2
• FEV1/FVC ratio: This ratio drops below 70-80% in adults (or below 90% in children) when airways are obstructed 1

Step-by-Step Patient Preparation

Position the patient sitting upright in a chair with arms and no wheels for safety reasons. 1

Before starting:

• Loosen tight-fitting clothing for proper chest access 3
• Measure height and weight without shoes 3
• Document smoking history, recent illness, and current medications 3
• Apply a nose clip or manually occlude the nares 1
• Withhold short-acting bronchodilators for >6 hours and long-acting bronchodilators for >12 hours if testing for asthma diagnosis 1

The Maneuver: Coaching is Everything

The most critical skill in spirometry is enthusiastic coaching—you must actively encourage the patient throughout the entire maneuver using phrases like "blast the air out" and "keep going." 1

Inhalation Phase

• Instruct the patient to inhale rapidly and completely to total lung capacity 1
• Pause at full inspiration for only 1-2 seconds maximum (longer pauses reduce FEV1 and PEF) 1

Exhalation Phase

• Tell the patient to "blast," not just "blow," the air from their lungs 1
• Use enthusiastic coaching with appropriate body language throughout 1
• Continue verbal encouragement ("keep going") to ensure complete exhalation to the end 1
• The exhalation should continue until the patient cannot or should not continue further 1

Quality Control: Start and End Criteria

Start of Test (Back Extrapolation Method)

The extrapolated volume (EV) must be <5% of FVC or <0.150 L, whichever is greater, to ensure a proper start. 1

• If you see a hesitant start, terminate the trial early to avoid unnecessary prolonged effort 1
• The equipment should display the EV value for immediate feedback 1
• Peak expiratory flow should occur close to the start of exhalation with a sharp rise 1

Reproducibility Requirements

• Obtain at least 3 acceptable maneuvers 1
• For clinical trials, FEV1 values should be within 100 ml of each other 1
• For general use, values within 150-200 ml are acceptable 1

Interpretation: The Simple Algorithm

Step 1: Check the FEV1/FVC Ratio

• If FEV1/FVC <70-80% (adults) or <90% (children): Obstruction is present 1
• If FEV1/FVC is normal but both FEV1 and FVC are low: Consider restriction (requires lung volume measurement to confirm) 1

Step 2: Assess Bronchodilator Response (if obstruction present)

• Give 400 mcg albuterol (or equivalent) and repeat spirometry after 15 minutes 1
• An increase in FEV1 ≥12% AND ≥200 ml (adults) or ≥12% (children) indicates significant reversibility suggestive of asthma 1, 2

Step 3: Compare to Predicted Values

• Use the lower limit of normal (LLN) or <80% predicted as cutoffs 1
• FEV1 or FEV1/FVC below LLN or <80% supports asthma diagnosis 1

Common Pitfalls to Avoid

Normal spirometry does NOT exclude asthma—asthma is variable and often normal between symptomatic episodes. 1, 2

• Slow or incomplete inhalation: Reduces PEF and FEV1; ensure rapid, complete inhalation 1
• Prolonged pause at TLC: Pauses of 4-6 seconds reduce measurements; keep pause to 1-2 seconds only 1
• Inadequate coaching: Without enthusiastic encouragement, patients won't give maximal effort 1
• Testing while standing: Increases syncope risk; always use a seated position with arms 1
• Fixed ratio cutoffs in elderly: May cause false positives in older adults and false negatives in younger adults 1
• Single test reliance: One-time spirometry has low sensitivity (0.12-0.52) for asthma; serial measurements may be needed 2

Special Populations

Children (Age 5 and Up)

• Create a bright, pleasant atmosphere with age-appropriate toys and reading material 1
• Use detailed but simple instructions without intimidation 1
• Provide visual feedback during teaching 1
• Children as young as 5 years can perform acceptable spirometry with proper coaching 1
• If unsuccessful initially, children often perform better in subsequent sessions 1

When Spirometry is Normal but Asthma is Suspected

• Measure FeNO (≥25 ppb supports asthma diagnosis) 2
• Perform peak flow variability testing over 2 weeks (>10% in adults, >13% in children suggests asthma) 1, 2
• Consider bronchial challenge testing with methacholine (PC20 <8 mg/mL is diagnostic) 1, 2
• Exercise challenge testing (>10% fall in FEV1 post-exercise indicates exercise-induced asthma) 1, 4