A diagnosis of asthma can
sometimes go beyond symptoms,
such as coughing, chest
tightness, wheezing, and dyspnea.
It can go even beyond those
signs and symptoms
that worsen at night and
improve with treatment.
Diagnosis may require certain tests,
including pulmonary function tests,
or PFTs, and peak expiratory
flow, or PEF measurements.
Asthma symptoms can be reversed
by rapid-acting beta agonist,
such as albuterol, and they can
be measured by spirometry.
A bronchial challenge
test is a medical test
used to assist in the diagnosis of asthma.
So, pulmonary function tests.
These are also known as spirometry,
and these measure the airflow
and the lung volumes
during a forced expiratory
maneuver from full inspiration.
Spirometry can help the
clinician assess lung function
by measuring the total volume of air
that the patient can expel from the
lungs after a maximal inhalation.
And it can also be used to see if
airway constriction can be reversed,
and this is called reversibility testing.
Think of an 8-lane highway
that's being squished down
and reduced into 4 lanes
due to road construction.
The traffic is going to take a lot longer
to travel through that stretch of highway.
In the same way, if your airway is narrower
and narrower and narrower than normal,
it will take you longer to
empty your lungs of air.
It can also compare that result to how
much air you breathed out altogether,
and this ratio tells how much
your airways are blocked.
So, asthma, it's an obstructive
This means that the air flows out of
your lungs more slowly than it should.
The patients will wear a nose clip
to control their nasal air movement.
And this spirometry is going to
record the entire breathing loop;
the inspiration and the expiration.
And again, this is useful
for reversibility testing.
Usually, medication is more
effective if you have asthma
because the airways are going
to react to the medication.
In pulmonary function testing, we're
looking at a few different values.
The first is the forced vital
capacity, or the FVC.
This is the volume of air which is forcibly
and maximally exhaled out of the lungs
after taking the deepest breath possible.
The next is the forced expiratory
volume in 1 second, or the FEV1.
And this is the volume of air which can
be forcibly exhaled from the lungs
in the first second of a
forced expiratory maneuver.
The last is a ratio and this indicates
what percentage of the total
FVC is expelled from the lungs
during the first second of
total forced exhalation.
Now, let's talk about peak expiratory
flow tests, also known as peak flows.
A peak flow meter is an
handheld device for those with asthma
that is used to measure how well the
air moves in and out of the lungs.
This measure is called a
peak expiratory flow.
If a patient tracks their peak flows
every day at the same time every day,
the tool can be really useful to predict
when a narrowing might be
happening or a prodrome.
Sometimes, this can happen hours or days
before their asthma symptoms present
and a patient can be proactive
about their treatment measures.
Usually, a patient will measure their
peak flow at least once a day,
usually in the morning before they
take their asthma medications.
To perform this test well and consistently,
the patient needs to have good
and consistent technique.
Before the patient blows into the meter,
they will want to be able to
fully expand their chest cavity,
so they need to stand up.
Next, they'll take a full deep breath.
They'll close their lips
around the mouthpiece
and blow out hard and fast in a single blow.
Now, in a patient with asthma,
this can really trigger a cough
and assure your patient that's okay.
They can recover between the attempts.
Your patient's going to repeat this about
3 times and record the highest number
and that's the peak flow that
they're going to use for that day.
Finally, let's talk about the
bronchial challenge test.
This is where the clinician tries to see
if they can cause an asthma
attack in a patient,
and this can assist in the diagnosis.
During this test, the patient
is going to breathe
in nebulized methacoline
So this test can be called a methacoline
challenge or a histamine challenge.
In a controlled clinical environment,
the patient's going to inhale methacoline
aerosols in increasing concentrations.
Various protocols can be used.
Spirometry is performed before
and after each dose,
and the results are reported
as a decrease in FEV1
from baseline for each step of the protocol.
Methacoline is going to irritate the airway
and cause a narrowing in susceptible people.
And this can cause a severe
hyperinflation, and severe coughing.
The patient's airway is basically
being forced into an asthma attack.
The challenge is considered
positive if the methacoline causes
a 20% or greater decrease in the
patient's breathing ability
when compared to their baseline.
A positive test suggests that
the airways are reactive
and a diagnosis of asthma
should be considered.
A negative test means the
diagnosis of asthma is unlikely.
The procedure is generally well-tolerated
and respiratory symptoms in patients
who react to the methacoline
typically reverse promptly
in response to bronchodilators.
While, this is a pretty common test,
it should be performed in a setting
equipped to deal with acute bronchospasm,
and with personnel trained in resuscitation.
Informed consent should be obtained
and recorded in the medical record
after a detailed explanation of the risks
and benefits of this
procedure are discussed.