spirometry

Question 1

overview of spirometry

Answer 1

Spirometry measures the FEV1 and FVC of a patient, which are dependent on height, age and sex.
The instrument used is basically a box with a tube coming out of it. The technique involves a maximum inspiration followed by a forced expiration (for as long as possible). Patients with airflow limitation may have a very long forced expiratory time.

You need to say to the patient that this test is different to the peak flow one – “You need to breathe in
as mush air as you can and then breathe out as fast as you can for as long as you can, until there’s
no air left in your lungs”. Do a Sonia – “Keep going, keep going, keep going…”.

The FEV1 expressed as a percentage of the FVC is an excellent measurement of airflow limitation – it
is around 75% in normal subjects.

In obstructive lung disease there is a decreased ratio because the FEV1 falls more than the
FVC

In restrictive lung disease both FEV1 and FVC are reduced so you get a normal ratio (it may even be increased because of elastic recoil) In emphysema and asthma, the total lung capacity may increase, but there is usually a reduction in
the FVC. This is because the small airways cause obstruction to airflow before the normal RV is reached – this traps air in the lung giving an increased RV.

Question 2

define Vital capacity (VC)

Answer 2

The change in volume of air in the lungs from a complete inspiration to the complete expiration. In
patients with lung disease it can be greater than FVC due to air trapping in the manoeuvre.

Question 3

define Forced Expiratory Volume in the First Second (FEV1)

Answer 3

The maximum volume of air expelled from the lungs in the first second of forced expiration, starting
from full inspiration.

Question 4

define Forced Expiratory Ratio (FER)

Answer 4

This is the FEV1 expressed as a percentage of the vital capacity – it is sometimes called the FEV1%
or the FEV1/VC% when expressed as a percentage of the VC, or the FEV1/FVC% when shown as a
percentage of the FVC. In normal subjects it should be over 75% - ie. The subject should be able to
exhale at least three quarters of their vital capacity in the first second.

Question 5

define Peak Expiratory Flow Rate (PEFR)

Answer 5

The maximum flow that can be sustained for 10milliseconds on forced expiration starting from full
inspiration. It is measured in L/min using a peak flow meter.

Question 6

define Forced Expiratory Flow (FEF 25-75%)

Answer 6

The overall forced expiratory flow rate of the middle part of the FVC manoeuvre. It gives an indication
of what is happening in the lower airways and is expressed in L/s. Can be an early warning sign of
disease.

Question 7

Differentiating between COPD and asthma on spirometry:

Answer 7

Differentiating between COPD and asthma on spirometry:

An abnormal FEV1 with little variability in serial PEFR (