Hind Leys Biology
F211
Exchange surfaces 4.4
Measuring lung capacity
Objectives
 Explain the meanings of the terms tidal volume and vital capacity.
 Describe how a spriometer can be used to measure vital capacity, tidal volume,
breathing rate and oxygen uptake.
 Analyse and interpret data from a spirometer.
Breathing
Most people breathe in and out, when resting,
about 12 times per minute. Each breath
refreshes some of the air in your lungs and
carries away some of the carbon dioxide
generated by your body. During exercise, or
if you are frightened, you breathe more deeply,
and more quickly. This gets more oxygen-rich air
into your lungs and removes more carbon
dioxide-rich air from your lungs.
Examiner tip
Don’t confuse inspiration and
expiration with respiration.
The former terms describe the
process of breathing whilst the
latter describes the cellular process
which releases energy from
glucose.
Also, muscle contracts and elastic
fibres recoil.
The spirometer and lung volumes
We can measure the different volumes of air moved in and out during breathing using a
spirometer. This consists of a chamber filled with oxygen that floats on a take of water.
A person breathes from a disposable mouthpiece attached to a tube connected to the
chamber of oxygen. Breathing in takes oxygen from the chamber, which then sinks down.
Breathing out pushes air into the chamber, which then floats up. The movements are
recorded on a trace called a kymograph.
Figure 1 Using a spirometer
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Hind Leys Biology
F211
Exchange surfaces 4.4
The subject can breathe normally at rest, take deep breaths or forced expirations, or do some exercise
so that different breathing patterns can be recorded.
Different elements of lung volume
Volume/dm3
Residual
volume
~ 1.5 dm3
Exspiratory
reserve volume
~ 1.5 dm3
Total
lung
capacity
~ 6-7 dm3
Tidal
volume
~ 0.5 dm3
Inspiratory
reserve volume
~ 2.5 dm3
Vital
capacity
~ 5 dm3
Figure 2 A typical spirometer trace showing different lung volumes
 Tidal volume- the volume of air moved in and out with each breathe when at
rest. About 0.5 dm3 which provide enough oxygen to the body and removes
CO2 to maintain safe levels.
 Vital capacity- the largest volume of air that can be moved in and out of
the lungs in any one breath. About 5 dm3 but varies between men and
women, size. age and fitness level.
 Residual volume- the volume of air that always remains in the lungs, even
after biggest expiration. About 1.5 dm3.
 Dead space- air in the bronchioles, bronchi and trachea. No gas exchange
here.
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Hind Leys Biology
F211
Exchange surfaces 4.4
 Inspiratory reserve volume- how much more air can be breathed in over and
above tidal volume. Called on during exercise.
 Expiratory reserve volume-how much more air that can be breathed ou over
and above tidal volume.
Measuring oxygen uptake
If someone breathes in and out of a spirometer for some time, the levels of carbon
dioxide could become dangerously high. To prevent this, soda lime is used to absorb
exhaled carbon dioxide. Therefore, the total volume of gas in the spirometer will
decrease. Since the volume of carbon dioxide exhaled is the same as the volume of
oxygen inhaled, then the reduction in volume of the spirometer is the volume of oxygen
used by the subject. We can then compare oxygen use under different conditions.
Worked example
1. Measure the tidal volume and breaths per minute on the trace.
666 cm3, 12 breaths/min
2. Calculate the ventilation rate in dm3 per minute
0.666 x 12 =8 dm3 min-1
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Hind Leys Biology
F211
Exchange surfaces 4.4
3. Measure the maximum tidal volume and breaths per minute during exercise.
1500 cm3, 24 breaths/min
4. Calculate the exercising ventilation rate.
1,5 x 24 = 36 dm3 min-1
5. Calculate the oxygen uptake per minute during exercise.
1.66 dm3 min-1
1. What process is responsible for oxygen moving into the blood from the alveoli?
2. a) The spirometer trace shown in Figure 3 shows the breathing of a man at rest
and during exercise. It also shows a forced expiration and a deep inspiration. Use
the letters A-E to identify the actions of the subject.
b) What is the tidal volume of the man at rest?
c) How many breaths per minute does he take at rest?
d) Calculate the ventilation rate of the man at rest.
e) What was the maximum volume of a single breath while exercising?
f) What is the vital capacity of this man?
g) What is the total lung capacity, including the residual volume, that cannot be
expired?
Figure 3 Graph to show the changes in rate and depth of breathing at rest and during exercise
This work can be reinforced using pages 58-60 in your textbook.
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