00:00
So, for this second lecture on airways disease,
I'm going to talk about Chronic Obstructive
Pulmonary Disease, COPD. Now, COPD, is the
second commonest chronic lung disease after
asthma. There's an estimated 65 million people
in the world who have moderate to severe COPD,
it's incredibly common, and there's even an
estimate that 6% of the US population have
COPD, although that's scarcely believable.
It's very undiagnosed. About 25% of the patients
with COPD actually have the diagnosis, the
rest having mild disease, which they just
put down to aging and making them more breathless,
and therefore don't actually seek doctors
to get the diagnosis made. In general, COPD is
commoner in men, although women, with their
increased smoking, as it has occurred in
women, it is also very common in women as well,
and is largely a disease of the middle aged
and the elderly. What's the pathogenesis?
Well, in COPD, an
inhaled agent, cigarette smoking, most patients
in industrialized countries causes chronic
inflammation of the airways, which over a
long time leads to a variety of pathological
changes. These include mucous hypersecretion,
increased numbers and expansion of their secretory
capacity of the mucous glands leading to a
lot of chronic mucous production.
01:22
Inflammation of the small airways, the bronchioles, and
that eventually leads to small airways obstruction.
01:28
And then, sometimes you get alveolar destruction.
Now, that's called emphysema, where the alveoli,
instead of forming a large number of small
units are destroyed and form one larger unit.
01:41
And with that, you get something called dynamic
airways collapse, which I'll describe in a
bit more detail later on. The upshot of these
pathologies is that you have a largely irreversible,
slowly progressive airways obstruction occurring,
largely in the small airways. And, unlike
asthma, where the inflammation in asthma responds
well to corticosteroid therapy, the inflammation
that occurs in COPD, responds very poorly to
corticosteroid therapy. Which of the three
major pathologies the patient has actually
varies, and the ratio between them varies
between patients. So, you do get patients
who have emphysema as the dominant problem
with very little record of airways obstruction
elsewhere. You have patients where in fact
the main problem is mucous gland hyperplasia
or chronic bronchitis and very little airways
obstruction, and you get a mix of all three.
This leads to the sort of the variation in
the phenotype that the patient might present with.
What's the cause of the airways inflammation?
Well, cigarette smoking. It causes almost all of
the disease that you may see in industrialized
countries. However, there are inhaled agents
that occur elsewhere in the world, which may
be relevant. So, use of solid fuel fires is
thought to be a very big driver for developing
COPD in sub-Saharan Africa for example. In
addition, coal workers breathing coal dust
that can lead to airways obstruction, purely
from the coal dust by itself without smoking.
03:12
Although many coal workers have smoked as well, so
it's quite hard to tease out the combination
of the two. And then recreational drugs,
crack, cocaine,
or injected drugs such as heroine. They also
contribute and lead to airways obstruction.
03:26
Though, again, many of those patients do smoke
cigarettes as well. An important point here,
is that not everybody who smokes will develop
airways disease. And it's thought to be 1 in 4
patients who smoke will develop COPD, and
that suggests there must be other genotypic
and phenotypic predispositions in those quarter
of smokers that allows the airways inflammation
to progress to airways obstruction. So other
predisposing factors that were recognized is
low birth weight and poor lung development, that
will make your overall lung volume smaller,
and therefore loss of lung volume will precipitate
symptoms at a faster rate, than perhaps somebody
who has well developed lungs. Low socioeconomic
status is also related to airways obstruction,
as is poor nutrition, and there are the occasional
rare patients with genetic and inherited deficiencies
or alpha-1-antitrypsin. Now what that means
is that alpha-1-antitrypsin is an enzyme that
prevents trypsin, an enzyme released by neutrophils
from digesting lung tissue. So what happens
in these patients is that the smoking promotes
neutrophil infiltration into the lungs, the
neutrophils release their trypsin, that starts
to digest the lung. But there is no balancing
alpha-1-antitrypsin around to prevent that. And
therefore, those patients with alpha-1-antitrypsin
deficiency who smoke, will end up with very
rapidly progressive early onset basal emphysema.
05:07
This diagram is a sort of overview of what
may happen with lung function with age and
smoking. So for example, you start off with a
certain level of FEV1, and this diagram is not entirely
accurate, because in fact you reach peak FEV1
around age 20. It then gradually falls with
age in normal people. And somebody who smokes
cigarettes who's not susceptible to the development
of COPD, it will fall at a similar rate. However,
if you smoke cigarettes and you have the susceptibility
to developing COPD, then the rate at which
the FEV1 falls over time will increase.
05:47
And that means the gradient of this deterioration
will be more rapid, it will be steeper.
05:53
And the patient will end up developing disease,
symptoms of airways obstruction, and then
eventually, if it carries on with the deterioration
in the FEV1, they'll get severe respiratory
disease with respiratory failure and death
potentially. In theory, if the patient stops
smoking, that accelerated decline in FEV1 stops,
and the patient achieves a lower decline
in their FEV1 and that will prolong their
stage of disease in the milder stages and
hopefully prevent them developing respiratory
failure and death. The normal loss of FEV1
each year with age is about 30 mls. If you
smoke, that is often increased to 50 mls,
and in many patients can go up as far as 100
mls. You can see how that can rapidly lead
to a fall, so if you have an FEV1 of 3 Litres for
example and you're losing a 100 mls a year,
in 10 years your FEV1 will be 2 Litres, in 10
years more it will be 1 Litre, and you won’t
have another 10 years because your FEV1 will
fall to a level where it doesn't sustain life.
07:12
And this is how airways disease behaves overtime.
And it is also why FEV1 is one of the main measures
that we use for monitoring patients to seeing
how they are doing. So how do patients with