Diagnostic Evaluation
A
wide range of diagnostic studies, described on the following pages, may be
performed in patients with respiratory conditions.
PULMONARY FUNCTION TESTS
Pulmonary function tests (PFTs) are routinely used in patients with chronic respiratory disorders. They are performed to assess respiratory function and to determine the extent of dysfunction. Such tests include measurements of lung volumes, ventilatory function, and the mechanics of breathing, diffusion, and gas ex-change (Table 21-7).
PFTs
are useful in following the course of a patient with an established respiratory
disease and assessing the response to ther-apy. They are useful as screening
tests in potentially hazardous industries, such as coal mining and those that
involve exposure to asbestos and other noxious fumes, dusts, or gases. They are
useful for screening patients scheduled for thoracic and upper abdominal
surgery, and symptomatic patients with a history suggesting high risk.
PFTs generally are performed by a
technician using a spirom-eter that has a volume-collecting device attached to
a recorder that demonstrates volume and time simultaneously. A number of tests
are carried out because no single measurement provides a complete picture of
pulmonary function. The most frequently used PFTs are described in Table 21-7.
Technology is available that allows for more complex assessment of pulmonary
function. Methods include exercise tidal flow-volume loops, negative
expi-ratory pressure, nitric oxide, and forced oscillation. These assess-ment
methods allow for detailed evaluation of expiratory flow limitations and airway
inflammation ( Johnson, Beck, Zeballos & Weisman, 1999).
PFT results are interpreted on the basis
of the degree of devi-ation from normal, taking into consideration the
patient’s height, weight, age, and gender. Because there is a wide range of
normal values, PFTs may not detect early localized changes. The patient with
respiratory symptoms (dyspnea, wheezing, cough, sputum production) usually
undergoes a complete diagnostic evaluation, even though the results of PFTs are
“normal.” Trends of results provide information about disease progression as
well as the pa-tient’s response to therapy.
Patients with respiratory disorders may
be taught how to mea-sure their peak flow rate (reflects maximal expiratory
flow) at home using a spirometer. This allows them to monitor the progress of
therapy, to alter medications and other interventions as needed based on
caregiver guidelines, or to notify the health care provider if there is
inadequate response to their own inter-ventions.
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