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- 1.2.1 What is a spirometer?
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- 1.2.2 What is a peak flow meter?
Asthma is diagnosed based on a physical examination, personal
history, and lung function tests. The physical examination looks
for typical asthma symptoms such as wheezing or coughing, and the
personal history provides additional clues such as allergies or a
familial tendency towards asthma. Although lung function tests
have not always been used for diagnosis in the past, the NHLBI
Guidelines for the Diagnosis and Management of Asthma state that
"Pulmonary function studies are essential for diagnosing asthma
and for assessing the severity of asthma in order to make
appropriate therapeutic recommendations. The use of objective
measures of lung function is particularly important because
subjective measures, such as patient symptom reports and
physicians' physical examination findings, often do not correlate
with the variability and severity of airflow obstruction."
Lung function tests may be as simple as measuring peak flow with
a peak flow meter, or using a simple spirometer, or may involve
a battery of spirometry tests in a pulmonary function lab.
A spirometer is a machine for testing lung function that you
breathe in and out of through a hose attached to a mouthpiece.
You are usually given nose clips so that all the air you breathe
goes through the machine. One I've been tested on had a little
expanding tank surrounded by water into which the air goes, and
I could see the top rising and falling as I breathed out and in.
It can measure a fair number of characteristics of your lungs,
including FVC, FEV1, and PEPR. FVC, or forced vital capacity,
is the amount of air that you can exhale forcefully after taking
a deep breath. FEV1, or forced expiratory volume in one second,
is the amount of air that you can be exhale in one second.
Peak flow, or PEPR, is described in section 1.2.2.
The sophisticated spirometers I've seen have a PC attached, and
have neat little curves generated with each breath, which
apparently have characteristic shapes for different respiratory
diseases.
There is a slightly less sophisticated machine that I've blown
into, and I'm not sure if this is also classed as a spirometer or
not, but you take a deep breath and blow into it, much like a
peak flow meter, except that it draws a little graph of how much
volume you've blown out, and I'd imagine that you can get the
FVC and FEV1 off this graph.
For more information, I recommend the book by Drs. Haas,
The Essential Asthma Book,
which goes into more detail about
the various things you can find out from spirometry.
A peak flow meter is a little plastic device which you blow hard
into, after having taken a deep breath. It records the rate at
which you've blown into it in litres exhaled per minute (L/min)
-- this is called the peak expiratory flow rate (PEF or PEFR).
The meter is essentially a cylinder with a mouthpiece at one end,
a place for the air to escape at the other end, and a calibrated
meter along the side. When you blow into it, a marker is pushed
along the scale and comes to rest at a point which indicates your
PEF. Since you want to measure your maximum peak flow, it is
important to take a deep breath and blow as hard and as fast as
you can. Many asthmatics find that their maximum peak flow provides
a good objective measure of how their asthma is doing, so peak flow
meters now are used extensively for self-monitoring of asthma, and
also for monitoring the effectiveness of asthma medications.
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