Study of Diurnal Variation of Pulmonary Function Test

Abstract

Pulmonary function has circadian rhythm in humans proven in diseased in conditions. These variations will contribute to better understanding the relationship between biorhythms and lung physiology for better management of pulmonary diseases.To study PFT in medical students during different time of the day and to study whether there is diurnal variation in PFT. The I MBBS students chosen as subjects were apparently normal and non-smokers. The study group included 113 students. They underwent PFT during different time of the day, i.e. at 6am, 11am, 4pm and 9pm. PFT was done using computerized Spirometer and the parameters studied were FEV1, FVC, FEV1/FVC, PEF, FEF2575% and FEF.2-1.2L. The data was tabulated and statistically analyzed. There were changes in all the PFT parameters recorded during different time of the same day. Mean of FEV1 and FVC were highest in the recording taken at 9:00pm. % change noted was 1.74% and 1.32% respectively, when compared to the recording at 6:00am. Mean of FEV1/FVC ratio also showed diurnal rhythm with highest % at 11:00am and lowest % at 6:00am. The % change noted was 0.76%. Mean of PEFR, FEF25-75% and FEF0.2-1.2L showed diurnal rhythm. They were high in the recording done at 4:00pm and low in the recording done at 6:00am. % change noted in PEFR, FEF25-75% and FEF.2-1.2L were 2.25%, 3.66% and 2.08% respectively. % change noted for each parameter was statistically not significant. The diurnal variation in PFT parameters is noted in healthy subjects. The % change noted is minimal in young healthy individuals. This diurnal rhythm amplitude increase in asthma and bronchitis patients.