Pulmonary
function testing is used by physicians on a daily basis to evaluate
and follow diseases affecting heart function, lung function, the effects
of environmental exposures, for pre-employment physicals, and as an
assessment of lung function for surgery. There are broad ranges of
tests that physicians have available to them, however the most commonly
used technique is referred to as Spirometry. Spirometry is commonly
used to assess diseases affecting millions of individuals including
asthma, bronchitis and emphysema. These tests are typically carried
out in a physician's office and are neither invasive nor painful.
In addition they can be repeated at intervals to assess trends in
disease or response to therapy. In the following paragraphs the indications
for, interpretation of and significance of Spirometry will be detailed.
The most common indication for pulmonary function testing is to evaluate
a patient with unexplained shortness of breath or wheezing. Two very
common diseases, asthma and emphysema, can be diagnosed and followed
based on the results of Spirometry. In addition unexplained chest
pain, poor oxygenation of the blood, or the effect of a non-lung disease
on the lung can be evaluated. In addition patients undergoing surgery
can be evaluated to determine how much lung reserve they have before
surgery so physicians may take the necessary precautions when preparing
for surgery.
|
Following
are some essential steps that a patient needs to follow:
|
- Take
a full breath before the start of the test;
-
That the patient give maximum effort;
- The
test lasts at least 6 seconds;
- There
is no leaking of air around the mouthpiece;
- That
the patient does not cough or hesitate during the test.
|
Spirometry
itself is very simple to perform. The patient begins by fully inhaling
a breath of air to maximal capacity. Then he or she inserts a small
piece of sterile tubing into the mouth and forms an airtight seal
with the lips. The nasal passages are then clamped closed with a small
rubber padded clip to prevent leakage of air through the nose. The
patient then forcibly exhales all of the air in the lungs until they
can no longer force any air out. The patient then takes a full inhalation
without letting go of the mouthpiece. At the end of this inhalation
a full breath cycle has been completed and the test is over. Typically
the test is repeated three times and the results are averaged to provide
the most accurate test result. In order to assure that the test is
an accurate assessment of lung function the individual administering
the test must insure that several criteria have been met.
The results from the test are then compared to "normal" individuals
of the same age, sex, height and weight. (Testing individuals with
no known heart or lung disease and using them as comparison models
determine the "normal" values). It is this information that guides
the physician to appropriate diagnoses and treatment, or in particular
cases indicates the need for further testing.
The information that Spirometry provides can be quite valuable. The
Spirometry machine records both the amount of air moved over a certain
period of time, (referred to as flow rate), as well as the volume
of air being moved by the individual during breathing. A graph of
these variables tells the physician several things e.g. an individual
with asthma has an obstruction in the airways of the lung caused by
mucous and constriction of the lower lung passageways. This decreases
the flow rate of the air being exhaled. For instance, imagine trying
to blow air through a garden hose and then repeating the exercise
by trying to blow air through a straw. The narrowness of the straw
will prevent you from exhaling air rapidly and thus will increase
the length of time to move the same amount of air through the hose.
This is essentially what is happening inside of the lungs in individuals
with diseases such as asthma and emphysema. It is this phenomenon
that allows a physician to follow the severity of the lung disease.
The more severe the lung disease, there will be more difficulty in
forcing the air out of the lungs, just as the small diameter straw
will make it more difficult to blow air.
As mentioned earlier the results of this testing are compared to "normal"
controls. The further away an individual is from "normal" the more
severe their disease. Once again asthma provides us with a good example.
If an individual's results on Spirometry are >70 percent of normal
they are considered to have mild disease. If however they have 60-70
percent of normal values they are considered to have moderate disease
and so forth. By testing individuals over time the physician can determine
if a particular disease is improving or increasing in severity and
adjust treatment accordingly. In addition Spirometry can reveal several
other indicators of lung function such as poor compliance of the chest
wall or if the capacity of the lungs is decreased. All of these variables
can be used to diagnose a broad range of diseases.
In conclusion, Spirometry is a simply non-invasive method of evaluating
lung function that can be done in the office setting with no discomfort
to the patient. In addition it can be repeated over time to reliably
follow the course of a disease and direct treatment.
Feature Archives