COSINOR ANALYSIS OF CIRCADIAN PEAK EXPIRATORY FLOW VARIABILITY IN NORMAL SUBJECTS, PASSIVE SMOKERS, HEAVY SMOKERS, PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE AND PATIENTS WITH INTERSTITIAL LUNG-DISEASE

Peak expiratory flow (PEF) presents a circadian rhythm with a maximum in the afternoon, and a significant variability in its diurnal variati ons has been reported in normal subjects and in chronic obstructive pu lmonary disease (COPD). In order to investigate whether passive smokin g, active tobacco smoking, COPD and interstitial lung disease (ILD) ar e associated with changes in the circadian rhythm of PEF, five groups of adult male subjects, comparable for age, weight and height, were st udied: group A: 30 clinically healthy subjects who never smoked, group B: 30 subjects passively exposed to tobacco smoking, group C 30 heavy smokers (>20 cigarettes daily for at least 5 years), group D: 30 pati ents with nonasthmatic COPD (emphysema and/or chronic bronchitis), and group E: 15 patients with ILD (pneumoconiosis). Active tobacco smokin g and exposure to passive smoking were assessed by the determination o f the urinary cotinine concentration. A portable spirometer was used t o measure PEF over a whole day, at 0.00, 6.00, 8.00, 10.00, 12.00, 14. 00, 16.00, 18.00, 20.00, 22.00, and 24.00 h, all subjects leading a no rmal life. The 'mean cosinor' method was used for statistical analyses ; the PEF variability was evaluated by the amplitude percent mesor (da ily mean). All groups showed diurnal fluctuations in PEF values with s ignificant (p < 0.05) circadian rhythms. The peaks of PEF rhythms occu rred in the early afternoon, without significant (p > 0.05) difference s between the groups. The cosinor mean was significantly (p < 0.05) lo wer in heavy smokers, in passive smokers, and in COPD patients than in controls. Controls, passive smokers, heavy smokers, COPD and ILD pati ents presented a PEF amplitude percent mesor (95% confidence limits) o f 6.26% (range 4.57-7.95), 7.79% (range 5.07-10.51), 12.60% (range 7.6 1-17.59), 17.19% (range 10.18-23.50), and 3.98% (range 2.09-5.87), res pectively, with significant differences (p < 0.05) between all groups, except between controls and passive smokers. These data suggest that tobacco smoke, both passive and active, does not modify the circadian peak of PEF, but modifies significantly its mesor and amplitude. Tn th is respect, heavy smokers have the same pattern of COPD: lower mesor a nd greater amplitude; passive smokers present an intermediate situatio n. An increased diurnal variability in PEF could be considered as an e arly index of tobacco smoke damage and of developing COPD. When studyi ng diurnal PEF variability, active and passive smoking habits should b e considered.