Pulmonary function tests are a single or combination of
tests to help doctors understand more about how a patient's lungs are
functioning. These tests require special equipment, trained technologists to
perform the tests and skills in interpreting the tests. Below will briefly
explain the various parts of a pulmonary function test.
Spirometry - This is used to evaluate how well
air is moving into and out of the lungs. When performing this procedure, the
individual being tested exhales as hard and fast as they can and then inhales
rapidly. From the information gathered with this test we make certain
deductions about what is happening throughout the lung.
Flow volume
loops - By examining the information in
this form, it helps us further understand the way air is moving into and out
of the lungs and will also help identify specific diseases that can otherwise
be very hard to diagnose.
Maximum voluntary
ventilation -- This test is
usually performed whenever spirometry is done. To perform this, the person
being tested breathes in and out as fast as they can for 12 seconds. If people
have weakness in the muscle of breathing this test can help identify these
difficulties.
Bronchodilator
testing with spirometry
-- This
test is performed when an obstruction is identified by the initial spirometry.
A bronchodilator is a medication which will help open up airways which have
bronchoconstriction (the airway is partially closed off). The goal of this
test is to identify how much if any of a patient's obstructive disease can be
reversed. This information is used both to clarifying diagnosis and to help
decide on medications for treatment.
Body
Plethysmography - Lung volume assessment
-
This is another tool used to assess lung function. With this tool, the
volumes of the lung are evaluated. Although the lung would appear to have only
two obvious volumes, empty and full, there are actually four different volumes
and then four combinations of volumes known as capacities that are used to
assess the lung.
Helium dilution -
Lung volume assessment --
Although body plethysmography is the most accurate tool to measure
lung volumes, helium dilution techniques are another tool, which can add to
the information gained from testing lung volumes. Body plethysmography
delineates the total volume in the chest. Using helium dilution only those
volumes that are directly open to the atmosphere are checked. Although these
two volumes would be the same in normal lungs, in a variety of lung diseases,
air becomes trapped in the chest and can no longer move freely from in the
chest and out the mouth to the atmosphere. By looking at the patterns of both
of these volumes in certain situations, even more knowledge can be gained.
This test is not performed in all situations. If the body plethysmography is
normal, there is no need to perform further testing.
Diffusing capacity
(DLCO)-- This test is used
to evaluate how well oxygen moves into and out of the lungs. Certain diseases
will lead to difficulties in getting oxygen from in the alveoli (air sac in
the lung) into the blood where it is carried to the rest of the body.
Identifying problems with this process in the lung can identify people at risk
for needing oxygen. With this additional information, the pulmonary function
test interpretation is also greatly improved.
Arterial blood gas
analysis -- Most blood
tests performed use blood drawn from veins in the arms. An arterial blood gas
is a blood test, which requires taking a sample of blood from the artery,
usually in the wrist. Blood from the artery comes straight from the heart,
after it has been oxygenated (blood which travel through the heart and lungs
gets rid of carbon dioxide which is a waste product it picks up from the body,
and picks up oxygen that will be delivered to the body). The blood sample from
the artery is then analyzed for the amount of oxygen in it, the amount of
carbon dioxide (there is always some, and in some diseases this can be
increased). The pH of the blood, hemoglobin, and carbon monoxide level (which
will be elevated in people smoking) and several other tests are also run on
the blood sample. The information gained by this test will help
determine if a person might require oxygen or help explain other possible
processes occurring.
Pulse oximetry
-- Using light technology we
can determine the oxygen saturation through this test. Oxygen saturation tells
us how much of the hemoglobin is loaded with oxygen in the blood stream.
Unfortunately this test is not nearly as accurate as doing an arterial blood
gas, but will often be more than enough for evaluation of a patient's oxygen
level.
Cardiopulmonary
Exercise Testing -- Most
pulmonary function tests take place while the person being tested is sitting
down and not moving. Real life is a series of activities that link together to
make up each and every day. Most complaints that people have when regarding
their lungs and lung function occur when people are active. Cardiopulmonary
exercise testing is exactly that, a test of the pulmonary system while the
patient is exercising. The test is performed on a special stationary bike.
Monitoring of the heart rate, blood pressure, pulse oximetry, an EKG readout,
and data while the person being tested breaths in and out are collected. This
information is then put together in both number form as well as a series of
graphs. This information is then reviewed by several physicians to determine
any causes for limitations with exercise.
Specialty Testing
Bronchoprovocation
studies -- When the physician
assessing a patient is concerned that they might have asthma, first spirometry
is performed. If no obstruction is identified (see above - spirometry section)
further testing is sometimes required. The Henry Ford Hospital Pulmonary
Function Laboratory uses a medication called methacholine. When the airways of
people with asthma are exposed to this medication, it will stimulate a
response, which can be measured. If there is a positive response, asthma can
be clearly identified and treated appropriately.
Respiratory muscle
forces testing -- There are
diseases that can affect the muscles throughout the body. The muscles of
breathing are the same as those in the leg or the arm. There are groups of
muscles used to inhale and exhale. When these muscles become weak, it can lead
to difficulty breathing. This test is designed to evaluate those muscles of
breathing.
Exercise
desaturation and oxygen dose determination studies--
There are some patients that have normal oxygen levels
at rest, but when they become active and move around their oxygen levels go
below normal. This study requires walking on a treadmill while the oxygen
saturation is watched. If the oxygen level is found to decrease, oxygen is
given to the person being tested at increasing levels until the oxygen
saturation remains normal. This way, oxygen levels can be assessed with
exercise and if necessary, oxygen can be prescribed to stop this from
happening.
