Effect of circadian rhythm on peak expiratory flow rate in healthy young adults

Background: Many human biological systems, including airway calibre, show a circadian rhythm. This may be because the airways are passively influenced by the rhythm of related endogenous systems or because they respond directly to cyclically varying exogenous stimuli. The peak expiratory flow rate (PEFR) is an accepted marker of pulmonary function, primarily reflects large airway flow and depends on the voluntary effort and muscular strength of the patient. Aims and Objective: In the present study an attempt has been made to investigate the effect of circadian rhythm on peak expiratory flow rate in healthy young adults.Method : Peak expiratory flow rate (PEFR) was observed at 5:00 am, 8:00 am, 11:00 am, 2:00 pm, 5:00 pm, 8:00 pm, and 11:00 pm on two consecutive days. The highest value of PEFR from at least three acceptable blows was recorded separately and used for the analysis. Only PEFR readings recorded at 11 pm on first day and all readings on the second day were taken into consideration to rule out the remote possibility of training effect. The Diurnal Variation in PEFR is calculated as the difference between the highest and the lowest PEFR values as a percentage of the mean PEFR on each day. Result: The lowest mean PEFR and mean (%) PEFR value was recorded at 5 am (487.8 L/min) and highest at 5 pm (527.4 L/min) for the study group. The mean PEFR values at different time points were analysed for variation using ANOVA which did not reveal significant rhythm (P>0.5). After normalizing the data, the circadian rhythm of PEFR was statistically significant (P<0.001). The data was also analyzed by comparing mean PEFR values at different time points using repeated measures ANOVA test with Bonferroni’s test which showed that there is significant difference between the mean PEFR values at 11pm on day one and mean PEFR values at 5am, 11am, 2pm, 5pm & 8pm on second day (P value < 0.05). Conclusion: Our study suggests that there is a significant variation in peak expiratory flow rate between morning and evening in healthy young adult population. This is important in understanding the behaviour of airways in producing changes in PEFR. We conclude that a diurnal variation pattern of PEFR exists in healthy population. This knowledge is important for any meaningful interpretation of PEFR recordings used to screen population for asthma.