ATS Pulmonary Function Laboratory Manual

chapter  8

3. Interpretation of lung volume data when test acceptability criteria are not met, or only one measurement should be done with caution. 3.1. When acceptability criteria are not met, data should be reported with the warning that the data are sub-optimal. 3.2. When only one FRC N2 or FRC He is obtained, interpretation should be made with caution. 4. Choice of reference equations may affect the final interpretation. 5. Multiple-breath gas dilution/washout FRC is usually underestimated in individuals with moderate to se- vere airflow limitation and air trapping. 6. FRC pleth will be overestimated in patients with severe airway obstruction, or induced bronchospasm unless a slow panting speed (i.e., approximately 1 cycle per second) is maintained. 7. Physical and mental impairment, or other conditions may limit the patient’s ability to adequately perform the test in an acceptable and reproducible manner. 8. Non-panting measurements (i.e., occlusion during quiet breathing) have been suggested for use in children or other individuals who have difficulty mastering the panting maneuver (14). However, an inspiratory effort that is too slow will not assure adiabatic conditions are maintained in the plethysmograph. Non- panting maneuvers that do not have the rapid inspiratory maneuver in plethysmographs with built-in thermal leaks may invalidate FRC pleth measurements (15). 9. Computer-derived pressure/volume slopes may be inaccurate if the system calculates slopes using a best-fit regression, as erroneous data may be included (16, 17). Technologists should review the computer selection of fit-line to assure correctness. 10. Excessive abdominal gas or panting techniques using accessory muscles may slightly increase the measured FRC pleth value, due to compression effects (18). 11. Patient leaks may not be apparent during the FRC He test. 12. If a bacterial filter is used, and with children especially, the added volume needs to be subtracted from the FRC. Changes in pressure in the lungs are isothermal but in the filter, adiabatic, so efforts to keep the dead volume (e.g., filter and connectors before the body box shutter) as small as possible are important. References 1. Wanger J, Clausen JL, Coates A, Pedersen OF, Brusasco V, et al . Standardization of the measurement of lung volumes. Eur Respir J 2005;26:511–522. 2. Quanjer PH, Tammeling GJ, Cotes JE, et al . Lung volumes and forced ventilatory flows. Report of working party of European Community for Steel and Coal. Eur Respir J 1993;6(Suppl. 16): 5–40. 3. Miller MR, Hankinson J, Brusasco V, Burgos F, Casaburi R, et al . Standardisation of Spirometry. Eur Respir J 2005;26:319–338. 4. Miller MR, Crapo R, Hankinson, J, Brusasco V, Burgos F, et al . General considerations for lung func- tion testing. Eur Respir J 2005;26:153–161. 5. Burki NK. The effects of changes in functional residual capacity with posture on mouth occlusion pressure and ventilatory pattern. Am Rev Respir Dis 1977;116:895–900. 6. Parot S, Chaudun E, Jacquemin E. The origin of postural variations of human lung volumes explained by the effects of age. Respiration 1970;27:254–260.

81