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Chapter 3: Respiratory procedures 95

Litres
FVC
FVC After bronchodilators (normal)
FEV 1 Before bronchodilators

FEV 1

1 2 3 4 5 6
Figure 3.1 Spirometry in reversible Seconds
obstructive airways disease.

out as hard and fast as they can into a peak flow meter, both values preserving the FEV 1 /FVC ratio whereas
with a good seal around the tube with their lips. The in obstructive airways disease, although both may be
best of three tries is recorded. This is compared with a reduced, the FEV 1 falls proportionately more and the
predicted value for age, sex and height, although there is FEV 1 /FVC ratio is reduced.
considerable individual variation. Other useful testing which can be done by the bedside
It is most useful in monitoring disease patterns, e.g. includes pulse oximetry to measure oxygen saturations,
the day-to-day and diurnal variation in asthma, and for exercise testing (timed 6 minute walk with PEF, pulse
rapid objective assessment and response to treatment. oximetry and even arterial blood gases pre- and post-
Howeveritis limited in that it only measures the peak exertion).
expiratory flow, is effort dependent, and can be relatively
preserved despite the presence of severe lung disease. Laboratory testing
Spirometry: This is now possible with bedside elec- More comprehensive tests can be performed in the pul-
tronic spirometers, which are more portable and con- monary function laboratory, but the equipment requires
venient than the older Vitalograph models. The patient aspecialisttechnician,isexpensive,time-consumingand
takes a deep breath to full inspiration, then blows as hard patients with severe chronic airflow limitation find some
as they can and must continue to blow into the spirom- of the tests difficult to perform, claustrophobic or ex-
eter until the lungs can be emptied no further (≥6sec- hausting.
onds in normal people but may require 15–20 seconds These include the assessment of the following:
in obstructive airways disease). In reversible obstructive 1 Flow–volume loops: These can localise the site of
airways disease this gives the graph shown in Fig. 3.1. airflow limitation to extra-thoracic, large airways or
On this (or calculated by the machine) can be plotted smaller airways.
the forced expiratory volume in 1 second (FEV 1 ) and the 2 Lung volumes: Tidal volume and vital capacity can be
forced vital capacity (FVC). Normal values are related to measured. A total body plethysmograph can be used
age, sex and height. to measure total lung capacity (TLC) and residual vol-
1 The FEV 1 falls particularly with airflow limitation, i.e. ume (RV) (see Fig. 3.2). It is characteristic in em-
obstructive airways disease and with reduced lung vol- physema for the TLC and RV to be increased due to
umes in restrictive disease. air trapping, although the FVC is decreased. In re-
2 The FVC falls with reduced lung volumes, i.e. restric- strictive lung disease, the FVC and TLC are decreased
tive lung disease and more severe obstructive airways together.
disease. 3 Transfer factor: This measures the diffusing capacity
3 The FEV 1 /FVC ratio is normally ∼75%. In restric- of the lungs across the alveolar-capillary membrane by
tive lung disease there is a proportionate reduction in indirectly measuring the uptake of carbon monoxide