Circadian rhythms in peak expiratory flow rate in workers exposed to cotton dust.

One hundred and sixty two people working in various departments of cotton spinning and weaving mills measured and recorded their own peak expiratory flow rate (PEFR) at two hourly intervals during Monday, Wednesday, and Thursday of the same work week, from waking in the morning throughout the day until going to bed and a last time the following morning after waking. The circadian rhythm in PEFR was computed by the Halberg program. The mean amplitude of the rhythm in the group was found to be 3.3% and the acrophase fell approximately in the middle of the waking hours. Older workers and those claiming to suffer from symptoms of chronic bronchitis were found to have an amplitude significantly higher (4.1% and 3.9% respectively) than their younger or symptom free counterparts (2.6% and 2.9% respectively; p less than 0.03). The amplitude of cardroom workers (2.4%), workers with byssinosis (2.7%), and those with much exposure to airborne cotton dust (3.3%) and bacteria (2.9%) tended to be lower than that of less exposed groups such as office staff (3.9%), though the difference was significant only in the case of cardroom workers (p less than 0.04). This may be due to airborne contaminants in the working environment.