ATS Pulmonary Function Laboratory Manual

chapter  9

Review and Reporting Results 1. The reported Raw and related indices 1.1.

Should be calculated from the ratio of open- and closed-shutter tangents for each maneuver (14). 1.2. Should be averaged from three to five separate, acceptable maneuvers (which may require as many as 8 to 10 trials) (15). 1.3. Should have the open shutter tangent ( ˙ V /Pbox) measured between flows of +0.5 to −0.5 L/s (4). For loops that display hysteresis, the inspiratory limbs may be used and the report should contain a comment noting this (14). 2. Report of test results should contain a technologist’s statement about test quality, patient’s understanding of testing process, and, if appropriate, which criteria were not achieved (4, 8, 9, 16). Various miscellaneous factors may affect this test. 1.1. Certain pathologic conditions can cause a leak in the lung measurement system (e.g., leak around mouthpiece). 1.2. Diurnal variations in lung function may cause differences (particularly in the patient with asthma). Thus, if serial measurements are to be performed, the time of day that measurements are made should be held constant (16). 1.3. Raw measurements should precede forced expiratory maneuvers, which may cause bronchospasm and alter resting values. 1.3.1. Other confounding factors that could influence resting Raw values include exposure to environmental pollution, cold air, allergen, exercise, or the type of medication the patient is taking (e.g., bronchodilators and steroids). 1.4. The patient with asthma should refrain from performing deep inspirations, which could alter Raw values (17, 18). 1.5. Physical and mental impairment, or other conditions, may limit the patient’s ability to perform the test adequately in an acceptable and repeatable manner (4). 1.5.1. Claustrophobia may be aggravated by entering the plethysmograph cabinet (4). 2. Some patients are unable to perform the necessary panting maneuver required for Raw determination. 3. Choice of reference equations may affect the final interpretation (1, 19). 3.1. Interpretation of test data that are not acceptable should be reported with a warning that data are suboptimal. 4. Non-panting measurements have been suggested for use in children or others who have difficulty master- ing the panting maneuver (20). Non-panting maneuvers in plethysmographs with built-in thermal leaks may invalidate thoracic gas volume (TGV) measurements (21). In addition, non-panting (tidal breathing) technique has been reported to overestimate sRaw compared to panting in children (23). 5. Computer-derived TGV slopes may be inaccurate if the system calculates slopes using a best-fit regression, as erroneous data may be included (22). 6. Bacterial filters cause a small difference in Raw in children, but it is not considered clinically significant (24). Pediatric Considerations As a tidal breathing maneuver, sRaw may be measured as young as the preschool years, though commercial devices generally lack incentives to aid the child in breathing gently and regularly. A parent may accompany the child into Procedure Notes 1.

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