Occupational Asthma Reference

Bright P, Burge PS, Characterisation of laze and learning effects on serial peak flow records, Thorax, 1996;51 Suppl 3:A70,

Keywords: OASYS-NN, laze, learn, PEF

Known Authors

Sherwood Burge, Oasys Sherwood Burge

Phil Bright, Oasys Phil Bright

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Abstract

Serial PEF records plotted as daily maximum, mean and minimum may show longitudinal declines (lazes) or inclines (learns) which are not related to work or medication. If such phenomena represent true laze or learning by the subject then interpretation of the PEF record may be difficult. We have investigated the properties of lazes and learns of PEF records. Subjects investigated for occupational asthma were asked to perform 2-hourly measurements of PEF from waking to sleeping for a minimum of 21 days. Records containing lazes (n=17) and learns (n=26) were identified visually. They were investigated for the slope of the daily maximum, mean and minimum, the number of readings per day, dispersion of readings (lazes only) and diurnal variation (DV % predicted). Comparisons were made between the period of the record affected and the remainder of the record. The impact of removing visually identified laze and learn effects was tested using a computer-based analysis program (OASYS-NN). All lazes had a decline in the daily mean, 14 in the minimum and 15 in the maximum. All learns had a rise in the daily mean, 11 in the minimum and 10 in the maximum. Neither lazes nor learns had a difference in the number of readings/day (paired t-tests, p=0.54 and 0.5 respectively). There was no difference in the dispersion of readings for lazes (paired t test, p=0.30). Lazes had no difference in DV (paired t test, p=0.62), learns did have a higher DV (26.4% vs. 17.65% for the rest of the record (paired t test, p=0.04). All learns started within 2 days of the record start, lazes were equally split between the beginning (8), middle (9) and end (9) of the record. Removal of the learns did not affect the number of records as having definitely no work effect (14), but increased those with a definite work effect from 5 to 7. Removal of lazes decreased the number of records as having no definite work effect from 10 to 8, and increased those with definite work effect from 3 to 5. Apart from characteristic changes in the slope especially in the daily mean, lazes and learns do not have other features that theoretically should be present if they were true lazing and learning. This raises the possibility that other factors may be the cause of the phenomena, e.g. progressive deterioration in PEF due to prolonged recovery from exposure. Removal of lazes particularly can lead to reclassification of records by a computer analysis program, the records tending to become more positive for a work effect.

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