Spirometry interpretation

Question 1

How to interpret spirometry results?

Answer 1

Results need to be interpreted by a professional trained to ARTP standards

• Age, sex, height & ethnicity needs to be checked as they determine predicted values
• predicted values need to be checked
• if the spirometry test is repeatable/acceptable
• if the shape of the expiratory flow volume curve
• to look at the data and be able to determine the severity

Question 2

Define the Importance of height, sex and age

Answer 2

height is used to calculate predicted values, under/overestimating height can influence the reliability of the predicted value affecting interpretation of results. Always use a patient’s current height. As taller people tend to have greater chest/lung volumes

Age: loss of elastin connective tissue as we age, so less forcefully exhalations

Sex: men tend to have larger lungs then women

Restrictive disorders may be over diagnosed or missed

The severity of obstructive disorders will be incorrect

Question 3

Describe the acceptability criteria

Answer 3

Flow volume curve: stiff peak with a rapid rise, merges with x-axis,

Spirogram: smooth trace that leads to a plateau, greater than 6 seconds

Test should be discarded & repeated if there is air leakage around the mouthpiece or obstruction to mouthpiece, if the patient coughs or gives a poor effort attempt, bad starting manoeuvre & the breath does not last for minimum of 6 seconds

Question 4

How to determine if the spirometry is normal?

Answer 4

1. look at the trace & shape of the curve, are they normal?
2. is FEV1/FVC%>LLN
3. is FEV1 > LLN
4. is FVC > LLN
5. if all are > LLN then spirometry is within normal limits

Question 5

Describe indications of obstruction to flow airways/lungs

Answer 5

Obstruction to flow: volume is normal, but flow is reduced, takes longer to exhale

Reduction in flow
Narrowed airways
e.g., COPD, asthma & bronchiectasis

FEV1 is reduced relative to FVC, so FEV1/FVC % will be reduced

Look at flow volume loop, is it scooped/concaved?, the more scooped the greater the airway obstruction

Question 6

Describe the indications of restriction of volume

Answer 6

Reduction in volume

e.g., ILD, Musco skeletal, neuromuscular, diabetes, pregnancy
Restriction is indicated if the FEV1/FVC is normal or increased, if the FVC & FEV1 are reduced, however poor technique can also cause a reduced FEV1 & FVC

Question 7

How to interpret spirometry

Answer 7

1. Decide if spirometry is normal or abnormal
2. check FEV1/FVC% ratio
   3.If FEV1/FVC% ratio is below LLN then there is an obstruction to the airway

Question 8

Describe the indications of a mixed result

Answer 8

Mixed defect: where both FVC and FEV1 are reduced, FEV1/FVC reduced

Question 9

How do we determine the severity of results of an obstruction

Answer 9

Severity classification is a 2-step process, FEV1/FVC ratio must be lower than the LLN (lower limit number) (z score greater than –1.64) to be classified as obstructive

Severity is graded on the FEV1 z-score

Z score greater than:
-1.64= mild, 1/20 ppl
-2=moderate, 1/40 ppl
-2.5=moderately severe, 1/150
-3=severe, 1/750 ppl
-4+= very severe, 1/30000

Question 10

Describe reversibility testing

Answer 10

Used to assess a patient’s response to an inhaled bronchodilator, (B2 agonist or anticholinergic). Bronchodilators may be given a metered doses or via nebulisers (2.5mg).

Ensure the patient has not taken their inhaler before the test, perform baseline spirometry, administer bronchodilator, wait to allow max bronchodilation, repeat spirometry test. Finally calculate the FEV1 & FVC as a & change from baseline.

Most reversibility tests use salbutamol a short acting B2 agonist (4 puffs) to assess reversibility.
A 12% increase in FEV1 & 200ml increase in volume is a positive response to bronchodilators, Salbutamol reaches max effect after 15-20 minutes, so response is measured 20 mins post inhalation

Question 11

Describe the use of a spacer with an inhaler and it’s effects

Answer 11

A spacer may be used for patients who have never taken a metered dose inhaler as they may have difficulties with the technique.

A spacer acts as a holding chamber for the drug which can be inhaled by the patient through normal breathing.

Question 12

How to calculate the bronchodilator response

Answer 12

(post BD FEV1-pre BD FEV1)/Pre FEV1 x 100

Question 13

What indicates a positive bronchodilator response

Answer 13

If FEV1 increases by 620mls, which is a 62% increase from baseline

FVC increases by 990mls which is an 53% increase from baseline

This is positive as FEV1 has increased by more than both 200mls and 12%