Evaluation of diurnal variation in peak expiratory flow

Background: Peak expiratory flow rate (PEFR) reflects the strength and condition of respiratory muscles and the degree of airflow limitation in large airways. PEFR shows hour-to-hour variation that follows a specific pattern, which has been identified in both asthmatics and healthy individuals. Adequate data were not available for the diurnal variation in normal individuals who are students in professional courses and lead a sedentary lifestyle. Hence, this study was undertaken to study the diurnal variation in PEFRs in healthy adult male and female subjects in South India.

Materials and Methods: PEFR was recorded in 50 healthy adult male and 50 healthy adult female students aged 18-23 years who were enrolled in professional courses [e.g. Bachelor of Medicine (MBBS), Bachelor of Dental Surgery (BDS), Nursing, and Master of Science (M.Sc.)]. Mini-Wright peak flow meter was used to measure the PEFR. The PEFRs were recorded at 7-8 AM, 10-11 AM, 1-2 PM, 4-5 PM, and 7-8 PM for 2 consecutive days.

Results: On analysis of the PEFR records of individual subjects, it was seen that there was an overall dip in the morning at 7-8 AM PEFR, which increased in the daytime, peaking in the afternoon at 4-5 PM and eventually decreased in the night. The subjects did not show the peak PEFR values at the same time point, 16% of the subjects had a rise in PEFR in the early morning, afternoon (1-2 PM) peak was observed in 22% of subjects, and evening (4-5 PM) peak was observed in 36% of subjects. Only 2% of subjects showed a peak in the night time (7-8 PM) PEFR values.

Conclusion: This study provided the preliminary reference data of diurnal variation of PEFR in healthy adults. There is a variation in the PEFR recorded during different time points of the day; hence, in order to compare the PEFR between individuals it is advisable to record the PEFR at the same time point. The difference in diurnal variation may be due to the difference in the waking up time between the male and the female subjects as the peak PEFR is generally seen at the midtime of the entire duration when the subject is awake.