This information consists of BEV (back extrapolated volume), PEF rise time, and hesitation time.
Back extrapolated volume is used to determine the start of exhalation during a forced expiratory vital capacity maneuver and is measured in mL. It being excessive is usually an indication of hesitation or a false start.
To ensure that the FEV1 value comes from a maximal effort, the BEV must be less than 5% of the FVC or 0.100 L, whichever is greater.
PEF Rise Time
Peak expiratory flow is the maximum flow that a patient can reach during a forced expiration that starts from a lung inflated to its maximum point.
This time being shorter shows the patient has an airflow limitation.
This parameter is defined as the time from the point of maximal inspiration to Time 0 (meaning the delay time between the end of maximal inspiration and the start of forced expiration), and it should be 2 seconds or less for the test to be acceptable and usable.
Time 0 is found by drawing a line with a slope equal to peak flow through the point of peak flow on the volume–time curve and setting Time 0 to the point where this line intersects the time axis.
- "Lung Function in Cooperative Subjects", Pediatric Respiratory Medicine (Second Edition), 2008.
- "The Rise and Dwell Time for Peak Expiratory Flow in Patients with and without Airflow Limitation", American Journal of Respiratory and Critical Care, 1997.
- "Standardization of Spirometry 2019 Update", An Official American Thoracic Society and European Respiratory Society Technical Statement, 2019.