So I’m going to concentrate largely on lung-function
tests in this lecture. And these include the
peak flow, the spirometry, lung volumes and
transfer factor. They describe how good the
patient’s lungs are at getting oxygen into
the blood, how good – how large the lungs
are, how much air can be moved during inspiration
They are largely dependent on patient effort.
So if the patient can cooperate and do the
test well, you’ll get much more accurate
results. And one of the major problems with
lung-function tests is that people are not
able to do them effectively and therefore
you can’t get data from them.
We normally use the best-of-three attempts
for each type to get the most appropriate
answer as to the patient’s lung function.
If they’re normal, that largely excludes
significant respiratory function impairment.
So they’re very useful in patients presenting
with breathlessness of unknown cause. And
if you do full lung-function testing and they’re
all normal, then you can probably say it’s
not a lung problem.
And also they are the essential method for
monitoring chronic lung disease such as COPD
or interstitial lung disease over time.
The values that you get from lung-function
tests are expressed in two ways: one is an
absolute value – the absolute number. But
also they’re expressed as a percentage of
expected. And that is because your lung-function
value depends on your age, sex and height.
A young man who is 6ft4 will have considerably
different lung volumes to an 80-year-old woman
who is 5ft2, for example. So you need to have
a feel for what the expected values will be
for each person’s age, sex and height. And
those are available in tables.
As I said, the normal values are altered by
age, your sex, your height and also they’re
affected by ethnicity. But the data for that
are poor and there’s no clear indication
about the effects of ethnicity on lung function.
So the first lung-function test is the peak
flow. This is measured using a handheld portable
device. Therefore you can use it frequently.
You can repeat it multiple times within a
day if necessary. And what it measures is
the maximum flow measured in litres per minute
on a forced expiration. It identifies patients
with airways obstruction, whether it’s upper
airways or lower airways.
Because it’s portable and can be used repeatedly,
it’s actually very good for people to take
home and therefore you can use it to identify
people with variable airflow obstruction.
That means they have asthma. And indeed the
peak flow correlates with the severity of
asthma and it’s very useful for monitoring
how they’re doing with their treatment and
how severe they are when they present with
an exacerbation. It’s not so good for patients
with other forms of airflow obstruction such
as COPD because it doesn’t vary much even
with the patient’s condition varying. It’s
also good for identifying patients with large
So an example: this is a 30-year-old man.
He has asthma. His best peak flow is 650 L/min.
He comes to hospital because he’s having
an exacerbation of asthma with increased cough
and wheeze. If you measure his peak flow and
it’s 450 L/min, that’s fallen by 200.
That’s a pretty major deterioration but
it’s not life threatening. So this is a
moderately severe attack. With treatment – with
bronchodilators – he should get better and
should be able to either return home that
evening or, perhaps, stay in for a short period
However, if you do the peak flow and it’s
150 L/min, that puts him immediately into
a very severe attack and a potentially life-threatening
situation. And you would not let that patient
go home until his peak flows have been stable
for a day or two at least.
If he comes back to outpatients after having
been in hospital for a while and he shows
you the peak flows he’s been recording at
home and you see that actually in the morning
it’s 500-550 and in the evening it’s 600-650,
that’s quite a big difference. That’s
100 L/min difference between morning and evening.
And that’s what we call diurnal variation.
And that indicates that his asthma is not
well controlled and that he may need increasing
health therapy to try and iron out that difference
between the morning and the evening result
and therefore show that the disease is better
So the other simple lung-function test we
do is spirometry. This requires however a
handheld or a lab-based machine. It’s a
bit more difficult to do. It requires a forced
manoeuvre where people breathe out as hard
as they can for as long as they can. And it’s
not therefore very readily reproducible to
be repeated several times a day for example.
It gives you two parameters: the forced expiratory
volume in one second – that is a flow rate,
a bit like the peak flow – and the forced
vital capacity – that’s the total volume
expired from the lungs. So that’s basically
the measure of how much air somebody can move
in and out of their lungs when they do a forced
inspiration and a forced expiration. The other
parameter it gives you is the ratio between
the two. Because the FEV1 tends to fall when
you have airways obstruction to a greater
level than the FVC. And therefore the ratio
between the two becomes lower. And that’s
called an obstructive disorder. And the ratio,
if it’s less than 80%, indicates an obstructive
problem with the spirometry. Whereas if it
remains greater than 80% - and in fact with
many diseases it becomes 90-95% - that suggests
a restrictive problem.
If somebody has obstructive spirometry, then
the very important question is whether this
is reversible. So is that abnormality in FEV1
recoverable if the patient is given treatment
with bronchodilators? Because that identifies
patients with reversible airways disease – asthma
– or irreversible airways disease such as
These are three different examples: the spirometry,
the one you can see on the left-hand side
of the slide, is what a normal spirometry
may look like. The middle one is somebody
who has a reversible airways obstruction – so
the black line is where they have no treatment
and you can see that their FEV1 has fallen
quite a lot: it’s 1.2 whereas the estimated
normal would be 3.8 for this patient for example.
But then you give them a bronchodilator and
the FEV1 has improved substantially. So that’s
a bit of reversible airways disease but, importantly,
it hasn’t reversed back up to normal levels.
And the last one shows somebody with restrictive
spirometry. And this is where they have a
chronic lung disease like pulmonary fibrosis
where the lungs are small but the airflow
is maintained. And you can see that the FEV1
and the FVC are very close to each other and
therefore the ratio is about 90-95% in these
So all of the causes of obstructive and restrictive
lung function. Obstructive is as it says:
it’s airways disease with obstruction. So
COPD, a largely irreversible disease. Asthma
would be a largely reversible disease. Other
airways diseases: bronchiectasis, rarer causes
of lower airways obstruction, upper airways
Restrictive lung function: actually anybody
who does not put the full effort in doing
a spirometry manoeuvre will come out with
what looks like a restrictive lung function
result. So poor effort during the test will
leads to what looks like restrictive lung
function but that can be seen when you observe
the patient during the test.
Interstitial lung disease, pulmonary fibrosis,
post-infective scarring of the lung, pleural
effusions, pleural thickening, anything that
affects the chest wall will all cause restrictive
Sarcoidosis and hypersensitive pneumonitis,
they’re both interstitial lung diseases
which cause restrictive changes. But there’s
often an obstructive element causing a mixed
restrictive-obstructive picture. And a mixed
restrictive-obstructive picture also occurs
if you have somebody with more than one disease
present. So, for example, pulmonary fibrosis
commonly occurs in smokers, COPD commonly
occurs in smokers and therefore you often
get patients who have pulmonary fibrosis and
COPD. And their lung function reflects that
by having a mixed restrictive-obstructive
So some examples of how you use spirometry.
This is examples of how you use spirometry
over time because it’s the most useful way
of monitoring how the patient’s lung function
is doing in a chronic lung disease over time.
So, for example, on the left-hand side we
have somebody who’s got stable COPD with
his FEV1 being repeated every six months or
so and showing very similar values. They’re
not deteriorating. They stopped smoking, they’re
on inhalers, they’re doing reasonably well.
The middle patient is somebody with asthma.
And again the FEV1 seems to be stable between
month 1 and month 24. But if you look back
at the results, month 7 it was much lower
and that reflects an exacerbation that occurred
at that time but then they got treated and
the FEV1 came back up to where it should be.
The right-hand side is somebody with progressive
COPD. And the FEV1 starts off at the same
level. It’s a stable patient. But you see
it falls. And it falls by a little bit each
time but that means that, after 24 months,
it’s fallen by 300 ml. That’s 150 ml per
year. And if it carries on falling at that
rate, the patient will be in respiratory failure
within 5 to 6 years.