4. SPIROMETRY
■ Measures how much air can be exhaled
after a maximal inspiration
■ VITAL CAPACITY (VC) inspiratory
capacity plus expiratory reserve volume
■ In short ask the pt to breathe in as far as
they can then blow out into the spiromwtry
until no more air at all can be breathed out
5. FORCED VITAL CAPACITY
(FVC)
■ VC is measured after the pt has blown as
hard and as fast as possible into the
spirometry
■ In normal lung VC is equal to FVC
■ In copd compression of lungs during
forced expiration leads to closure of
airway earlier than usual
■ FVC maybe less than VC
6. Forced expiratory volume(FEV1)
• The graph on the
side shows a
representation of
spirometry
• Time in seconds on
x axis and liters in y
axis
• Thus it assess the
FVC
7. Forced expiratory volume(FEV1)
• FEV1 is the volume of air in the first
second of a forced expiration
• In a normal lung it is more than 70% of the
FVC
• In obstruction as seen in COPD the time
taken to expire is longer thus the ration of
FEV1 to FVC is reduced
• Seen the graph next
8. Forced expiratory volume(FEV1)
• The FEV1/FVC ration is the FEV1
expressed as a percentage of the FVC (or
VC if that is greater) i.e the proportion of
the vital capacity exhaled in the first
second.
• It distinguishes between reduced FEV1
due to restricted lung volume and that due
to obstruction.
• Obstruction is defined as an FEV1/FVC
ratio of <70%
9. Obstructive ventilatory pattern
FVC = 3.50 litres
(98% predicted)
FEV1 = 1.80 litres
(58% predicted)
FEV1/FVC =51%
FVC normal or
reduced
FEV1 reduced <80%
FEV1/FVC ratio
reduced
