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Interstitial Lung Diseases: Chapter Two

Charles S. Dayton, R.Ph., Richard A. Helmers, M.D., Gary W. Hunninghake,
M.D., David A. Schwartz, M.D., M.P.H. University of Iowa Department of
Internal Medicine Peer Review Status: Internally Peer Reviewed Creation
Date: Unknown Last Revision Date: April 2002 by Gary W. Hunninghake,
M.D. and Thomas J. Gross, M.D.


Diagnostic Tests and Procedures Used in Interstitial Lung Diseases

Pulmonary Function Testing

You will frequently in the management of your illness be asked to
undergo pulmonary function testing. Spirometry measures how much air a
patient can blow out in one second and also with a full exhalation. This
will be decreased if the lungs have a significant amount of fibrosis. As
the lung gets progressively scarred, less air can be drawn into the
lungs and therefore less can be blown out. Lung volumes are another set
of tests done inside what is called a "body box". This examines
essentially how large or how much volume of air the lungs can hold. With
interstitial fibrosis, the lungs may shrink or contract down and the
lung volumes will then be smaller. Diffusing capacity is the test which
looks at how well oxygen moves into your bloodstream and the diffusing
capacity will be measured to be less. The last test usually done is an
arterial blood gas. Blood is drawn from an artery (the blood vessels
which take blood away from the heart) rather than a vein (the blood
vessels which bring blood back to the heart) for this because blood in
the arteries has just passed through the lungs. Usually the artery in
the wrist is used. This blood is ****yzed for oxygen level and carbon
dioxide level. The better the lungs function, the more oxygen and less
carbon dioxide there is in arterial blood. Pulmonary function tests are
quick, easy, and safe to perform and can easily be compared from one
physician visit to the next. They are the most commonly used tests to
monitor the course of interstitial lung disease.

Chest X-ray and CT Scans

Interstitial fibrosis can usually be detected by a routine x-ray of your
chest. X-ray beams cannot pass as easily through scarred tissue as
normal tissue and scarring will look more "white" on an x-ray than
normal tissue. However, this is not always the case, as between 5-10% of
patients with significant interstitial fibrosis will have a normal chest
x-ray. Also, once the diagnosis has been made, we know chest x-rays are
not a good way to monitor these diseases over time. The disease may get
significantly worse with no change in chest x-ray or the chest x-ray may
improve or appear worse when the disease is actually stable. Chest
x-rays, then, are not usually obtained as frequently as pulmonary
function tests.

CT scans, or CAT scans, are fancy x-rays that give us a better look at
the lung tissue that may be damaged from interstitial lung diseases. The
images are sharper and more detailed than plain film chest x-rays. We do
them to help better characterize the extent of your lung disease.

Bronchoscopy

When a doctor finds a patient's pulmonary function tests or chest x-ray
is abnormal and characteristic of interstitial lung disease, in order to
make the diagnosis with certainty, a biopsy or small sample of lung
tissue is needed. This is usually done by using a flexible fiberoptic
bronchoscope to do a procedure called bronchoscopy. This is done with
the patient awake but slightly sedated. The mouth and throat are numbed
up or "frozen" with a local anesthetic until all cough and gag reflexes
are gone. The doctor then passes this flexible scope through the mouth
and into the lungs and with a small instrument called a biopsy forceps,
takes several small tissue samples or biopsies. These biopsies obtained
by the bronchoscopy are then processed and examined under the
microscope. Bronchoscopy is safe and often times done on an outpatient
basis. Because of the small size of samples obtained in this manner,
though, in some cases a firm diagnosis cannot be made by the pathology
doctors. But because of the ease and safety of this test, and the fact
that it may not involve hospitalization and does not require general
anesthesia (being totally put to sleep), it is usually considered the
best test to begin the diagnostic evaluation of a patient with
interstitial lung disease.

Open Lung Biopsy

In situations where a biopsy obtained by bronchoscopy (trans-bronchial
biopsy) is too small for a definite diagnosis to be made, your doctor
may advise you to undergo an open-lung biopsy. This involves being
admitted to the hospital and undergoing general anesthesia (being put
totally to sleep). A chest surgeon then makes an incision between two
ribs and removes a section of lung about one-half to three-quarters of
an inch long. This is such a small piece of lung tissue that overall
lung function is not affected, but it is many times larger than the
biopsy obtained by bronchoscopy, and in nearly all cases, it is totally
adequate for a pathologist to make a definite diagnosis. After surgery,
patients who have undergone open lung biopsy remain in the hospital for
approximately 4-7 days before discharge. In the first few days to weeks
following surgery, there is pain around the incision site. Overall, open
lung biopsy is a safe procedure, but does involve general anesthesia,
hospitalization, and significantly more discomfort and time than
bronchoscopy. Again, it is utilized only when absolutely necessary.

Bronchoalveolar Lavage

Once a diagnosis of one of the interstitial lung diseases is made, often
your doctor will want to attempt to determine if your disease is
currently in an active stage (with a high risk of more scar formation in
the immediate future) or a non-active stage (with much less risk of
further scar formation). Remember, these diseases can wax and wane
(particularly sarcoidosis) with time, and if in a nonactive state,
treatment may not be helpful, and only result in side effects.
Bronchoalveolar lavage is one test which may help your doctor decide if
your disease is active or not. Bronchoalveolar lavage (BAL) is a simple
extension of fiberoptic bronchoscopy. Instead of taking a biopsy, with
BAL, saline (salt-water) is injected into a section of lung and then
removed immediately by suction. This fluid then contains cells which
were contained in the very small air sacs of the lung (alveoli), where
the inflammation begins in interstitial lung disease. Whereas
transbronchial biopsy samples a section of lung about the size of a
pinhead, and open lung biopsy samples a section of lung about the size
of your thumbnail, BAL samples a section of lung about the size of your
fist. But BAL differs from the biopsy techniques in that it does not
give the kind of information needed to make a specific, definite
diagnosis, but gives information regarding if the disease (in which a
diagnosis has already been made by one of the biopsy techniques) is
active or not. By sampling a larger section of lung in this way, it can
be very informative. At the current time, the number of cells and types
of cells obtained by BAL are used by some institutions to make decisions
regarding treatment of interstitial lung disease.

BAL is a very safe procedure. Because it does not involve taking pieces
of lung tissue but rather injecting and withdrawing fluid, the risk of
any serious complication is very low. It is nearly always performed as
an outpatient procedure and can be performed multiple times over months
or years if necessary without any longlasting adverse effects.

Exercise Testing

Just as patients with interstitial lung disease may have much more
shortness of breath when exerting or exercising than when at rest, your
doctor may wish to assess your breathing ability and lung function with
exercise in addition to the other lung function tests described earlier.
This is done usually on a stationary bicycle or a treadmill. If enough
lung scarring or fibrosis is present, with the stress of exertion or
exercise enough oxygen may not be able to get into your bloodstream and
the blood oxygen level may actually fall with exercise. If this is
serious enough and goes unrecognized, it could potentially over time be
harmful to the heart. If this is detected by exercise testing, your
doctor may prescribe oxygen to use only when you exercise, not when you
are at rest, if it is only when you exercise that the blood oxygen level
is low.

The exact methods used for exercise testing vary from hospital to
hospital. Usually though, blood pressure, heart tracing
(electrocardiogram) and the blood oxygen level (usually by an electronic
clip placed on the ear) are monitored closely, first with minimal
exertion and then with progressively greater stress, such as a faster
pace on a treadmill or a greater resistance on a stationary bicycle. The
test is stopped if your blood oxygen falls, but otherwise is generally
continued until you feel you can not go further. In some instances, your
doctor may wish to obtain more detailed information about your heart and
lungs with exercise and in addition to the above mentioned monitoring
techniques, also have you breathe into a mouthpiece connected to a
computerized lung function machine while you exercise.

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