00:00
The other aspect of
lung function tests that
you need to think about, are the flow volume
loops and the lung volumes. So, the lung volumes
are increased in COPD, the patient has bigger
overall lung volumes than normal. That may
seem surprising but that relates to the air
trapping that we discussed that I mentioned
earlier, and that I'll discuss in more detail
in a second. The reason for the increase in
lung volume is that the residual volume, the
amount of air left in the lung at the end
of expiration, increases. So although the
lung volumes are larger, it's useless volume,
it's not air that shifting during inspiration
and expiration. It's just the residual volume
that's driving the increase in lung volume.
If the patient has emphysema, then they've
lost a lot of surface area for gas exchange
because of the alveolar destruction. And that
means the transfer factor which measures the
ability of oxygen to get in from the lungs
into the blood, goes down. So a low transfer
factor suggest emphysema.
01:11
In addition, the alveolar structures are required
for splinting open the airways, as you breath out.
01:18
So on expiration, there tends to be,
there's a positive pressure in the thoracic cavity,
and that squeezes air out of the lungs, but
it also squeezes the bronchi, taking the air
out of the lungs. And if the bronchi have
lost their structural support, then there'll
be a tendency for them to be closed off by
that pressure, the expiratory pressure.
01:39
And that's called dynamic airways collapse and
occurs in emphysema where the loss and destruction
of the alveoli means the bronchi are not splintered
open and cannot combat the positive pressure
of expiration. And you can see that on a flow
volume loop, which is illustrated here on
the right hand side of the slide. You can see
that the person with emphysema, the solid
blue line, what happens is that as they breathe
out there’s a rapid increase in flow initially,
and then there is a sudden decrease in flow
due to this dynamic airways collapse, and
that’s followed by a prolonged phase of low
flow expiration. The other investigations
you need to do with somebody with COPD, will
clear your chest X rays is useful, but actually
it’s not that abnormal in most patients.
In patients with significant disease, it will
show a degree of hyper-inflation with reduced
lung markings, more visible anterior rib ends
than normal, perhaps flattened diaphragms and
a small heart. You can see bullae on a chest
X ray so some people who have quite expanded
lung cysts due to COPD, that is bullus that
is visible on a chest X ray. And also a chest
X ray is important to identify complications,
pneumonia, pneumothorax, and chronically,
to make sure that they don’t have cancer.
02:52
The CT scan is used to identify patients who
have emphysema, to look for bullae, and perhaps
to look for co-existent bronchiectasis or other
complications. So, these are some examples
of X rays you might see. The X ray on the
left hand side of the slide is somebody with
a hyperexpanded lungs due to COPD and basically
you see black lungs, very long thin lungs,
and the heart is stretched as well, and that’s
a hyperexpanded pair of lungs with oligaemic
lung fields. The middle CT scan shows centrilobular
emphysema, and what you can see a black hole
is where there’s been lung destruction with
the grey material around the outside being
the normal lung. That’s a sort of Swiss cheese
lung, it’s got holes in it. The last scan
is somebody who also has some emphysema but
that’s distributed in a different way, it’s
different in being centrilobular in the middle
of the lung lobules. It’s actually around
the septum, around the edges of the lung lobules,
around the edges of the lung.
What other investigations are useful
in COPD? Well, actually not much. Lung function,
chest X ray, some patients need a CT scan, blood tests,
you may want to measure the alpha-1-antitrypsin
levels to see whether they have early onset
emphysema, if they are relatively young patients,
especially if they have basal emphysema on
their CT scan. Normal blood tests for blood
count, Fbc, U+E, LFT are all normal. Some
patients, you need to do an echocardiogram
and ECG and there’s two reasons for that- one,
the main differential diagnosis for somebody
with COPD would be cardiac breathlessness,
congestive cardiac failure, or a valvular
problem such as aortic cyanosis, and you may need
to exclude that as a cause of their breathlessness.
04:34
And the other reason why you need to do an echocardiogram
and ECGs is those patients with chronic hypoxia
may develop cor pulmonale and you need an echocardiogram
to measure the pulmonary hypertension
that could be present in those circumstances.
Invasive tests such as bronchoscopy or lung biopsy
are not needed for patients with COPD,
they are not needed for diagnosis at all.
04:53
So, how do you recognize patients with COPD?
It’s a combination of gradually worsening
breathlessness on exertion over years or months
with a significant pack year history, 25 to
30 pack year history, therefore, most patients
will be aged over 50 or so. Plus obstructive spirometry.
05:13
The chest X ray often looks normal,
the main differential diagnosis is congestive
cardiac failure, chronic PEs, that will be a
shorter history, and they’ll have an abnormal
transfer factor, and importantly the lung
volumes and spirometry will be normal. Chronic
asthma, there’s no history of smoking, there’s
definitely a past history of asthma in most
of those patients. And pulmonary fibrosis.
And this is where crackles are important,
because if you hear crackles, that’s not due
to COPD, and in addition the lung function
pattern you get with pulmonary fibrosis is different,
it’s a restrictive lung function with an
increased FEV1 to FVC ratio and usually
a fall in transfer factor as well.