We read with interest the paper on glutaraldehyde and symptoms in endoscopy nursing staff.1 It is reported that there was an absence of objective evidence of the physiological changes associated with asthma. Peak expiratory flow (PEF) records from 17 cases were analysed by the OASYS-2 computer program, and three of these had OASYS-2 scores less than 2.5. These cases were thought not to show asthma because PEF diurnal variability was less than 15%. We have recently shown that increased diurnal variability is not found in most workers with occupational asthma.2 Part of the explanation may be that the acrophase (time of maximum PEF in a 24 hour period) in normal and asthmatic people occurs at around 1600 with a trough about 12 hours later. Any deterioration in lung function due to exposure in the workplace is superimposed on the normal circadian rhythm. Thus, if a worker starting work in the morning has a fall in PEF that continued throughout the day while at work, the maximum PEF occurring at the time of the acrophase might be reduced. This would tend to reduce the diurnal variability. …

Dr A Vyas AV{at}2moonjxn.freeserve.co.uk