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Introduction:
Unfortunately Ireland has a high prevalence
of lung disease. A recent epidemiological
survey on the prevalence of asthma put
Ireland in 4th place out of the 30 countries
included. It is known that Respiratory
disease kills 1 in 5 people in Ireland
today. In fact Ireland has the highest death
rate from Respiratory disease in Western
Europe. COPD (Chronic Obstructive Lung
Disease) is a longstanding lung disease that
mostly affects smokers or ex smokers. It is
thought that by 2020 it will be the third
most common cause of death worldwide.
Respiratory labs play their part by helping
detect any abnormality and assessing the
severity of the illness. Technologist’s work
as part of a team in hospitals and community
clinics, and they use their skills to assist
in making a diagnosis and to monitor the
patient’s response to treatment. The
ultimate gaol is to improvement quality of
life for suffers. Thankfully with the
support and services available it is now
possible for the majority of those suffering
from lung disease to lead otherwise normal
lives.
Technologists make use of a wide variety of
equipment and techniques. All the tests are
carried out under strict regional or
international guidelines and sometimes under
the supervision of a Doctor.
Here are just some of the most common
reasons for undergoing a Lung Function Test:
-
To determine the presence
or absence of lung disease.
-
To assess the severity of
the disease present.
-
To monitor the response
to treatment and document the changes in
lung function over time.
-
To provide an objective
measurement of lung function for
employers occupational health
departments as part of pre- employment
screening.
-
To assess individuals
prior to surgeries or other
interventions that require anesthesia.
-
For population screening,
surveys and other research activities.
Some Common Tests of Respiratory
Function.
When a Doctor sees a new patient he/she will
decide what the most appropriate test or
tests are required. Technologists may be
asked to assess a patient with a full set of
lung function tests. These are often
referred to as full PFT’s or
pulmonary function tests and includes the
measurement of the following:
-
Spirometry
-
Lung Volumes
-
Transfer Factor
Spirometry:
Spirometry is one of the most widely
performed tests used to assess lung
function. It provides very useful
information on the structure of the lungs
and the function of the airways. It is a
very useful tool in the assessment of
COPD. It is the tool of choice to
establish the diagnosis, monitor the
response to treatment and chart the
progression of the disease. COPD is
an example of an obstructive lung disease.
The airways that carry the air into and out
of the lungs become tight making breathing
more difficult. Asthma is another
type of obstructive lung disease.
However with asthma, medication can be taken
through an inhaler resulting in the airways
returning to there normal state. This does
not always happen to the same extent with
COPD and different types of inhalers are
used to treat COPD.
Spirometry is an effort dependant test and
the technologist will provide the patient
with clear instructions on how to do
the test. They will also provide plenty of
encouragement to get the best effort. The
device used to measure the airflow is called
a
Spirometer.
During the test the patient will be asked to
wear
a nose clip so no air can leak through the
nose.
They will be instructed to take a deep
breath in
and blast it out through the spirometer. The
patient must force the air out as hard as
possible. This will be repeated at
least three times to obtain the best and
most consistent results. The technologist
will always be particularly kind and
sympathetic towards elderly and sick
patients.
Some of the measurements recorded
include:
Forced Expiratory Volume (FEV1): the
amount of air that leaves the lungs in the
first second of expiration.
Forced Vital Capacity (FVC): This is
the total amount of air that can be forcibly
expelled form the lungs from a point of
maximum inspiration.
FEV1/FVC ratio: The percentage of the
FVC exhaled in the first second of the
forced expiration.
Before the test the patient will have their
height and weight taken. This information,
along with the patient’s age and sex, is
used to calculate the results that would be
expected from a similar person with healthy,
normal lungs. These values are used for
comparison and are known as the Predicted
Values.
The FEV1 is used to indicate the severity of
airflow obstruction. Narrowed airways reduce
the amount of air that is expelled in the
first second by increasing the resistance on
the air as it flows out of the lungs.
The FVC provides information on the
structure of the lungs. Restrictive lung
disease involves a process that reduces the
volume of the lungs, or the amount of air
that the lungs can hold. The lungs can empty
very quickly usually in 2-3 seconds due to
their smaller size. An example of a
restrictive lung disease would be
Kyphosciolosis. A feature of Kyphoscoliosis
is a curving of the spine in the area of the
ribcage. The lungs are normally very
stretchy and the effect of this process is
to reduce the amount by which the lungs can
expand and so this reduces the amount of air
they can hold.
The FEV1/FVC ratio will indicate whether the
disease present is obstructive or
restrictive in nature. A higher than
expected ratio indicates restriction and a
lower ratio indicates obstruction. Of course
in some cases there may be mixture of both.
Bronchodilator Response:
Bronchodilators (sometimes called relievers)
are inhaled medicines that are used to treat
obstructive lung diseases. They act on the
muscles in the airway causing them to relax.
The effect of this is to let the air leave
the lungs more easily. When the
Bronchodilator response is indicated on the
request the technologist will give this
medicine to the patient after the Spirometry
test. It is necessary to wait for at least
15mins before repeating the test.
The doctors will be looking to see if the
medicine improved the values of the
spirometry by a significant amount, and so
helping them to decide if the patient would
benefit from their use.
Transfer Factor:
Transfer testing is carried out to determine
how well the lungs are absorbing oxygen into
the blood.
The airways inside in the lungs get smaller
and smaller as they approach their end. They
also branch many times greatly increasing
the size of lungs and the number of airways
available to carry the air. Each airway ends
with a small sac called the alveoli of the
lungs. These are so small they can only be
seen under a microscope. These are covered
in blood vessels that absorb the oxygen out
of the alveoli so it can be taken around the
body.
The primary function of the lungs is to add
oxygen to the blood and remove Carbon
Dioxide, a waste product produced by the
cells of the body. To determine how well the
lungs do this job we measure the transfer
factor or diffusing capacity of the lungs.
The patient is asked to breath in a special
medical gas. The important ingredient of
this mixture is carbon monoxide (CO). (You
are correct in thinking that carbon monoxide
is a dangerous gas. However we use a special
medical gas mixture. In this mixture it is
present in a very small and controlled
amount. So only when under these
circumstances, it will not be harmful.) We
assess how well this gas is taken up by the
lungs in order to determine the diffusing
capacity of the lungs for CO per minute.
CO behaves in a very similar way to Oxygen
and gets into the blood through the same
pathway as oxygen does. It does this much
faster though and the test can be carried
out in a 10 second period.
It
Is performed using the 10-second single
breath hold method. To use oxygen would take
much longer and nobody would be able to hold
their breath long enough to measure the
amount of oxygen absorbed.
A specialised machine is used to measure
this process and the test is usually only
available in hospitals.
LUNG VOLUMES
It is not possible to measure the total size
of the lungs directly. No matter how hard
you try to blow out you will not be able to
empty all the air from your lungs. The
amount of air that remains in the lungs is
known as the Residual Volume (RV). This is
the amount of air that stays in the lungs at
the end of expiration to keep them inflated.
If this did not happen your lungs would
collapse and you would not be able to take
another breath in!
To measure the RV the technologist will get
the patient to breath 100% oxygen through a
spirometer until all the room air in the
lung has been replaced by oxygen. It is
referred to as the washout method. The
amount or concentration of room air at the
start and end of the test is measured. The
amount of oxygen used is also measured and
time taken to remove all the room air and
replace it with oxygen. Calculations are
then made and from these the Total Lung
Capacity (TLC) or size of the lung is
determined as well as the RV.
Restrictive lung disease reduces the TLC and
can therefore confirm the presence of this
defect. In obstructive lung diseases a
greater amount of air can sometimes remain
in the lung than is normal. This is a
process called air trapping. This is seen as
an increase in the RV for somebody of his or
her age, height and weight.
Sleep breathing disorders:
Clinical measurement scientists are also
involved in taking measurements during
sleep. Respiratory technologists play an
important role in the diagnosis of sleep
breathing disorders.
Obstructive Sleep Apnoea is an
example of one such disorder. This can be
described in very simple terms as a series
of repeated cessations in breathing during
sleep. Suffers are often noted for their
snoring and another common feature is
daytime sleepiness. It affects between 2-4%
of the population but many doctors feel it
affects many more people but goes unnoticed.
At the moment in Ireland there is almost
5000 people diagnosed with Sleep Apnoea.
Traditionally the investigation of Sleep
breathing disorders has being managed by the
respiratory service in hospitals.
It is often a job for the Respiratory or
Sleep Technologist to carry out overnight
sleep studies. Overnight sleep studies range
from a simple device worn on the finger to
monitor oxygen levels during sleep
(Overnight Oximetry) to a comprehensive
study known as a Polysomnogram (PSG). A PSG
monitors sleep quality using electrodes
attached on the scalp (an EEG), airflow
through the mouth and nose, breathing
efforts, oxygen levels and heart rate.
Additional monitors maybe attached to the
patient depending on the Doctors request and
what he/she feels is causing the patient
problems in their sleep.
Depending on the course of treatment offered
the Technologist may be asked to assist in
providing the patient with treatment and to
carry out tests to monitor the response to
the chosen therapy.
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