So the subject of this lecture is asthma,
which is one of the common forms of airways
disease that affects respiratory patients.
When we talk about airways disease, we mean
diseases that affect the conducting airways, the
trachea, the major bronchi, and the bronchioles
going down as far as the terminal bronchioles.
We don’t mean diseases affecting the alveoli.
These airways diseases, in general, will present
with some form of airways obstruction.
And that will be recordable when you do lung function
test as obstructive lung function changes.
They don’t tend to show many abnormalities
on a chest X-ray. That is because the bronchi
are not readily detectable on X-ray, and the
changes we’re talking about are relatively
small changes in multiple different parts of
the airways rather than a single mass lesion
as if you have a cancer, for example. There
are a range of potential airways diseases.
However, this subject is dominated by two
airways disease; asthma and chronic obstructive
pulmonary disease. COPD, this is a subject
to the next lecture as really a smoking-related
lung disease. In this lecture, I will
on asthma. In addition, I will cover post-infective
bronchial hyperactivity. At third lecture,
we'll discuss other airways diseases, the causes
of large airway obstruction, bronchiectasis,
and allergic bronchopulmonary aspergillosis.
A major thing about airways disease is that
the obstruction that occurs can be described
as reversible or irreversible. So the prevention
of effective airflow can be reversed, in reversible
disease, can be improved of treatment, whereas,
with irreversible disease, it can’t be.
That’s the broad distinction.
There are of course patients in between with
partially reversible airways disease, where
the obstruction can be partially reversed
but doesn’t get as good as normal.
Largely speaking, asthma is a reversible airways disease,
whereas, COPD is an irreversible airways disease.
Another important thing about airways disease is
that expiration is always worse than inspiration
with the lower airways obstruction problems. As a
consequence, that means if you have significant
lower airways obstruction, then you’ll end
up with a degree of air trapping and accumulation
of air in the lungs increasing the volume
of the lungs, increasing the residual volume
specifically, and making the lungs hyperexpanded.
So, to talk about reversibility in a bit more
detail as this is a fundamental concept for
airways obstruction. What we mean by reversibility
is that if there’s a 15% increase in your
forced expiratory volume in one second, a
measure of airflow on expiration, and that’s
at least 200 ml, then there is a degree of
reversibility present. Now, if that reversibility
of treatment actually improves your FEV1 to
the expected level for somebody of your age, sex,
and height, then that will be a fully reversible
situation. But if it only goes apart of the
way to what you might expect to have as your
FEV1, then that’s partially reversible.
And that shown by this diagram on the right-hand
side of this slide, the patient’s pre-treatment,
pre-bronchodilator data, given FEV1 of 1.2.
Then the patient is given some salbutamol and the
FEV1 increases by 700 ml, and by over 50%
to 1.9. SO that's a substantial degree
of reversibility. However, because of the
age, sex, and height of this patient, the
FEV1 is expected to be closer to three about
2, 2.8. And yet, they’ve only achieved
1.9 of the bronchodilation. So that’s a
partially reversed situation. Now, reversibility
in asthma is often clinically
very obvious. The patient may come into hospital
in exacerbation, be terribly breathless,
and then two weeks later, be back running
their five kilometers a day. So that clearly
shows somebody who has an airways disease
which can be very severe, they end up in
hospital. But when they’re well, it can
actually allow them to function at a very
high level. The treatment that we use to
test for reversibility
is usually just some inhaled bronchodilator,
a beta2 agonist such as salbutamol, and that
can be inhaled using a normal inhaler or a
nebulizer. Sometimes, when we really want
to test whether somebody is reversible, we
increase the power of the treatment by giving
them oral prednisolone, corticosteroids for
three weeks potentially, and potentially giving
them a nebulised salbutamol over that time.
That’s the real test for full reversibility
in patients where it’s not clear that their
lung function can return to normal with just
taking an inhaled bronchodilator. Now, as I
mentioned already, asthma is largely
a reversible airways disease. And COPD is
largely an irreversible airways disease. But
there’s such a large range of types of asthma
and COPD that there is an overlap. Some patients
with COPD have degree of reversibility. And
some patients with asthma, especially those
patients who had the disease for a very long
period of time or poorly controlled disease,
will develop irreversible components as well.
So there is an overlap between the two.
Another airways disease, for example, bronchiectasis,
can also have reversible and irreversible
and a partially reversible patients with the
airways obstruction. And there are less common
causes of airways obstruction, which, in general,
tend to cause largely irreversible airways
disease. And I’ll talk about those a little
in the second lecture. So, it’s quite easy
to get confused between reversible and irreversible
airways disease in asthma and COPD. But the
basic concept is relatively straightforward.
Reversibility indicates asthma. Irreversibility
suggests COPD, but there’s more to that.
Patients with COPD need to have a smoking
history. But there are patients who do
overlap in the
middle. For example, if you have an asthmatic
who’s been asthmatic since childhood but
has been smoking since the age of 20, at the
time they get to 50, actually, they may acquire
a significant degree of airways obstruction
which is irreversible, and that would be COPD
because of the smoking on the background of
asthma. So, asthma is the commonest chronic