Cosinor Analysis of Circadian Rhythm of Peak Expiratory Flow in Young Adults

ABSTRACT

Introduction: Peak expiratory flow (PEF), exhibit a 24 hour circadian rhythm with nadir in the early morningand peak in the evening. This diurnal variability gets accentuated in asthmatics. Rhythm characteristics ofsuch time series data can be better explained using Cosinor analysis by fitting a cosine curve. Also itmakes easier to compare data even when there is a difference in sampling time points. Data of PEFcircadian rhythms in Indian population with Cosinor analysis is lacking making it difficult to frame guidelineto diagnose asthma.Methods: PEF was recorded from 249 subjects using Wright’s portable Peak Flow Rate meter at 500, 800,1100, 1400, 1700, 2000, and 2300 hours for one day. Cosinor analysis was done and rhythm characteristicswere determined for individual subjects.Results: The mean PEF values after a minimum in morning at 0500 hours tend to increase throughout theday peaking in afternoon and there is a regular fall in PEF levels after 1700 hours till 0500 hours. Meandiurnal variation expressed as amplitude percent mean (A%M)is 8.81±4.8. With Cosinor analysis significantrhythms were detectable in 64% of subjects. For this population MESOR (Midline Estimate Statistic ofRhythm) is 528.49 L/min, Amplitude is 8.2% and acrophase is 15.49 Hours.Conclusion: Results are comparable with the data published in other studies for other populations. Thevariability (amplitude) in normal subjects is lesser than that of smokers and asthmatics. Amplitude andacrophase characteristics will help unifying the data and guide in deciding the cut-off values for diagnosingasthma