The Technique - How To Do It and Common Pitfalls and Problems

How to Do It

To ensure an acceptable result, the FVC manoeuvre must be performed with maximum effort immediately following a maximum inspiration; it should have a rapid start and the spirogram and flow-volume curve should be a smooth continuous curve.

To achieve good results, carefully explain the procedure to the patient, ensuring that he/she is sitting erect with feet firmly on the floor (the most comfortable position, though standing gives a similar result in adults, but in children the vital capacity is often greater in the standing position). Apply a nose clip to the patient's nose (this is recommended but not essential) and urge the patient to:

• breathe in fully (must be absolutely full)

• seal his/her lips around the mouthpiece

• immediately blast air out as fast and as far as possible until the lungs are completely empty

• breathe in again as forcibly and fully as possible (if inspiratory curve is required and the spirometer is able to measure inspiration).

If only peak expiratory flow is being measured then the patient need only exhale for a couple of seconds.

Essentials are:

• to breathe in fully (must be absolutely full)

• a good seal on the mouthpiece 

• very vigorous effort right from the start of the manoeuvre and continuing until absolutely no more air can be exhaled

• no leaning forward during the test

• obtain at least 3 acceptable tests that meet repeatability criteria (see below)

Remember, particularly in patients with airflow obstruction, that it may take many seconds to fully exhale. It is also important to recognise those patients whose efforts are reduced by chest pain or abdominal problems, or by fear of incontinence, or even just by lack of confidence. There is no substitute for careful explanation and demonstration - demonstrating the manoeuvre to the patient will overcome 90% of problems encountered and is critical in achieving satisfactory results. Observation and encouragement of the patient's performance are also crucial.

At least three technically acceptable manoeuvres should be obtained, ideally with less than 0.15 L variability for FEV₁ (and FVC) between the highest and second highest result.  

Each individual test is acceptable if it meets the following acceptability and repeatability criteria.

Acceptability Criteria

• The patient followed instructions
• A continuous maximal expiratory manoeuvre throughout the test (i.e. no stops and starts) was achieved and was initiated from full inspiration
• There was no evidence of hesitation during the test
• The test was performed with a rapid start
• The PEF has a sharp rise (flow-volume)
• No premature termination, i.e. expiration continued until there was no change in volume and the patient had blown for ≥3 seconds (children aged <10 years) or for ≥6 seconds (patients aged ≥10 years). However, the patient or practitioner can terminate the blow if the patient cannot or should not continue
• There were no leaks
• No cough (note FEV₁ may be valid if cough occurs after the first second)
• No glottis closure (Valsalva)
• No obstruction of the mouthpiece (e.g. by the tongue or teeth)
• No evidence that the patient took an additional breath during the expiratory manoeuvre

Repeatability Criteria

• Obtain 3 acceptable tests, i.e. each test should meet the stated acceptability criteria
• The two largest values for FVC should agree to within 0.15L
• The two largest values for FEV₁ should agree to within 0.15L

Obtain additional tests if these repeatability criteria are not met.

Results to Report

• FEV­­₁ - report the largest value
• FVC - report the largest value
• PEF - report the largest value
• FEF_25-75% - report the value from the test with the highest sum of FEV₁ + FVC

It is important that the acceptability criteria be applied and unacceptable tests discarded before assessing repeatability, as the latter is used to determine whether additional tests from the three acceptable ones already obtained are required. These criteria (together with a properly maintained and calibrated spirometer) help to ensure the quality of your results.

Tests that do not fully meet the acceptability criteria may still be useful. For example, FEV₁ may still be valid if cough or premature termination of the blow occurs after the first second. The report should state when the results are obtained from manoeuvres that do not meet acceptability and repeatability criteria.

Figures 3 (a) and 3 (b) show some problematic examples compared with well-performed manoeuvres.

Patient-Related Problems

The most common patient-related problems when performing the FVC manoeuvre are:

1. Submaximal effort

2. Leaks between the lips and mouthpiece

3. Incomplete inspiration or expiration (prior to or during the forced manoeuvre)

4. Hesitation at the start of the expiration

5. Cough (particularly within the first second of expiration)

6. Glottic closure

7. Obstruction of the mouthpiece by the tongue

8. Vocalisation during the forced manoeuvre

9. Poor posture.

Once again, demonstration of the procedure will prevent many of these problems, remembering that all effort-dependent measurements will be variable in patients who are uncooperative or trying to produce low values.

Glottis closure should be suspected if flow ceases abruptly during the test rather than being a continuous smooth curve. Recordings with cough, particularly if this occurs within the first second, or hesitation at the start should be rejected. Vocalisation during the test will reduce flows and must be discouraged - performing the manoeuvre with the neck extended often helps.

The vigorous effort required for spirometry is often facilitated by demonstrating the test yourself.

Instrument-Related Problems

These depend largely on the type of spirometer being used. On volume-displacement spirometers look for leaks in the hose connections; on flow-sensing spirometers look for rips and tears in the flowhead connector tube; on electronic spirometers be particularly careful about calibration, accuracy and linearity. Standards recommend checking the calibration at least daily and a simple self-test of the spirometer is an additional, useful daily check that the instrument is functioning correctly.