Investigations

Question 1

Define:

FVC?
FEV1?
FEV1/FVC?
PEFR?

Answer 1

FVC = The volume breathed out during the forced expiration.
FEV1 = The volume breathed out during the first second
FEV1/FVC = The proportion of the FVC that is breathed out in the first second
PEFR = The Peak Expiratory Flow Rate –the gradient of the graph at time 0, which corresponds to the highest rate of flow of air from the lungs

Question 2

Normal Spirometry?
Restrictive spirometry?
Obstructive?
Mixed obstructive and restrictive picture?

Answer 2

Normal spirometry –a normal FEV1, FVC and FEV1/FVC ratio
Restrictive spirometry –a reduced FVC but with a normal FEV1/FVC ratio.
Obstructive spirometry –a normal FVC but with a reduced FEV1 and hence FEV1/FVC ratio. In obstruction, the PEFR is also reduced
A ‘mixed obstructive and restrictive picture’ –the FVC is reduced AND the FEV1/FVC ratio is reduced.

The FEV1/FVC ratio is normally greater than 70%. Any value less than this suggests airflow limitation

Question 3

What is bronchodilator reversibility?

Interpret the results

What is the cut off for adults and children indicative of asthma?

Answer 3

Bronchodilator reversibility typically involves repeating spirometry testing 20 –30 mins after administering a dose of bronchodilator (typically Salbutamol 2 x 200mcg puffs, ideally via a large volume spacer).

If there is ‘reversible’ airways obstruction, there will bean improvement in the FEV1/FVC ratio.

In adults, an improvement in FEV1 of 12% or more, together with an increase in volume of at least 200 mL in response to beta-2 agonists or corticosteroids is regarded as a positive result. An improvement of greater than 400 mL in FEV1 is strongly suggestive of asthma.
In children, an improvement in FEV1 of 12% or more is regarded as a positive result.

Question 4

PEFR monitoring

How often would you ask patients to take a measurement?

What would be regarded as a positive result?

Answer 4

PEFR measures the maximum flow of air during expiration, which happens at the beginning of expiration.
The Peak Flow Meter can be used to spot changes in peak flow (which correspond to changes in the degree of airflow obstruction).
During diagnosis of asthma, it is common to ask patients to monitor their peak flow at last twice daily for 2 –4 weeks.
As part of long term monitoring, it is common to ask patients to check their PEFR regularly.
20% variability after monitoring at least twice daily for 2-4 weeks is regarded as a positive result

Question 5

Exhaled Nitric Oxide Test (FeNO)
How useful is this test?
What is the cut-off for a positive test?

Answer 5

Measures Nitric Oxide levels in exhaled breath. These levels are increased when there is active airways inflammation.
However, the levels may be affected by smoking and inhaled corticosteroids (which tend toreduce the level); and it is not always raised in people with asthma.
NICE suggests that approximately 1 in 5 people with a negative FENO result will have asthma and approximately 1 in 5 people with a positive FENO result will not have asthma

FeNO level of 40 parts per billion (ppb) or higher is considered a positive result in adults.
A FeNO level of 35ppb is considered a positive result in 5-16 yr olds

Question 6

Lung Volumes

Answer 6

TV- amount of air inspired or expired in a normal breath at rest
IRV - maximal amount of air that can be inspired beyond the TV
ERV - maximal amount of air that can be expired beyond the normal TV expiration
RV - volume of air that remains in the lungs after a forced, maximal expiration
IC - maximal amount of air that can be inspired
FRC - air remaining in the lungs after normal exhalation
VC - volume of air exhaled during forced exhalation
TLC - TV+IRV+ERV+RV