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.