The Rise and Dwell Time for Peak Expiratory Flow in Patients with and without Airflow Limitation

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Abstract
The response of peak expiratory flow (PEF) meters may be affected by the magnitude of PEF, the time taken to get to PEF, and the duration that the peak is sustained. We undertook a retrospective study to define the 10 to 90% rise time (RT) and dwell time for flow above 90% (DT90) and 95% (DT95) of PEF. Blows were analyzed that had been recorded using a pneumotachograph from 912 patients older than 17 yr of age (556 men) who routinely attended a lung function laboratory. For each subject, that blow with the largest PEF was used to derive the PEF, FEV 1 , FVC, RT, DT90, and DT95. The values for RT, DT90, and DT95 were negatively skewed with the median values for men of 58, 29, and 19 ms, respectively, being significantly shorter than those for the women of 67, 49, and 31 ms. From the 912 subjects, there were 277 (153 men) who had all their spirometric indices within the normal range, and 305 (220 men) had both PEF and FEV 1 more than 1.645 SD below predicted, indicating airflow limitation. For subjects with airflow limitation the median RT was significantly smaller than in the normal subjects (men: 46 versus 72 ms, women: 50 versus 72 ms), and the same was found for DT90 (men: 22 versus 40 ms, women: 27 versus 56 ms) and DT95 (men: 15 versus 26 ms, women: 18 versus 34 ms). We conclude that the dwell times for PEF are shorter in men, and the rise and dwell times are shorter in patients with airflow limitation. Profiles used to test PEF meters should encompass the range of rise and dwell times found in subjects most likely to be using PEF meters, that is, those with airflow limitation. Miller MR, Pedersen OF, Quanjer PH. The rise and dwell time for peak expiratory flow in patients with and without airflow limitation. AM J RESPIR CRIT CARE MED 1998;158:23-27. Since the effect of rise time to peak expiratory flow (PEF) was first suggested as possibly affecting the performance of PEF meters (1), it has been important to determine how the shape of the flow-time profiles in the region of PEF varies in the nor- mal and the diseased populations. The American Thoracic So- ciety has recently proposed a new range of human flow-time profiles specifically for testing PEF meters, and these profiles include a range of rise times to PEF (2) ( see Table 1). We have recently published the range of rise and dwell times found among normal subjects when recording their PEF with a pneumotachograph (3), but data from patients with airflow limitation have not yet been presented. Patients with severe chronic obstructive pulmonary disease often have a very brief ill-sustained peak on their flow-volume curves, and so it seems likely that the dynamic characteristics of the way they achieve their PEF may be different from those of normal subjects. We have therefore undertaken a retrospective analysis of blows recorded from patients attending a lung function labo- ratory in order to establish the 95% confidence limits for these indices in patients. METHODS

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