Spirometry
 
Accurate spirometry is crucial in making the diagnosis. Most primary care practices now have spirometers that record in real time FEV1 and FVC. This is important as it identifies poor spirometry. All practitioners who perform spirometry should have passed a competency based assessment and follow the guidelines set out in the ATS/ERS taskforce: Standardisation of lung function testing. (1)

In new guidelines published by NICE the post-bronchodilator FEV1 no longer has to be < 80% predicted (but the patient has to have a history consistent with COPD and symptoms) with an FEV1/FVC ratio of <70%. FEV1 grades the severity but does not always correlate with the degree of breathlessness. COPD is graded as follows.
FEV1/FVC Ratio FEV1 Stage
Post Bronchodilator Post Bronchodilator  
<0.7 80% Mild
<0.7 50-79% Moderate
<0.7 30-49% Severe
<0.7 <30% Very Severe

Contraindications to lung function testing are controversial but tend to include recent MI, recent abdominal surgery, stress incontinence, confusion and dementia.

The patient should be positioned appropriately:

  1. Testing may be performed either in the sitting or standing position
  2. Sitting is preferable for safety reasons
  3. Obese subjects, or those with excessive weight at the mid-section, will frequently obtain a deeper inspiration when tested in the standing position
  4. A nose clip should always be applied

Record the height, weight, age and current inhaled medication. The patient should try and avoid smoking within 1 hour of the test, alcohol within 4 hours, exercise within 30 minutes and a large meal within 2 hours.

The time volume curve

After spirometry the time volume curve is viewed initially to confirm that a good quality blow has been achieved and a plateau has been reached to record an accurate FVC. A short blow will underestimate the level of obstruction and often misleads practitioners into diagnosing restrictive defects. The best of 3 blows should be used.

Expiratory Flow Loop

Modern spirometers allow a more accurate diagnosis by providing an expiratory flow loop. Patient with COPD have expiratory airflow obstruction which can be viewed as a ‘scalloping’ out of the top curve, as shown below.

(1) Eur Respir J 2005; 25: 153-161

Learn More:

History
COPD vs. Asthma

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