Detection of Circadian Variation in Pulmonary Function Using peak Expiratory Flow and Forced Expiratory Volume Measurements

Abstract

IN the clinical environment, pulmonary function tests are used to monitor the progression of respiratory disorders and the patient's response to treatment. The t w o most commonly used by physiotherapists are those of forced expiratory volume (FEV, and peak expiratory flow rate (PEFR); both of these tests are considered indices of airway resistance. The purpose of this study was to determine whether FEV, and PEFR measurements could detect the presence of a circadian variation in airway resistance in healthy subjects. Circadian variation (variation occurring within a 24-hour period) is considered to be larger than the response of the airways to bronchodilator drugs. Hence an improvement in the results of these two tests may not necessarily reflect an improvement in a patient's condition. Measurements of FEV, and PEFR were recorded by a Vitalograph spirometer and function analyser, and a Wright peak f low meter. The validity and reliability of the equipment were confirmed prior to the main study. Measurements of FEV,, PEFR and oral temperature were recorded from eight healthy subjects at three-hourly intervals over a 24-hour period. This procedure was repeated on three days to determine the reliability of the data. Oral temperature was monitored as it is considered to be one of the main influencing factors on the 'body clock'. The activities and food/drink intake of the subjects was restricted and they were encouraged to maintain their normal sleep/wakefulness patterns. The data were analysed using cosinor analysis and t-tests. The former considers a mathematical model of the rhythm which is best approximated by a sine or cosine wave and tests the fit. The group of subjects demonstrated significant circadian rhythm (p<0.05) in oral temperature on all three days, while the measurements of PEFR and FEV, were non-significant (p<0.05) for each day. The circadian variation in oral temperature, PEFR and FEV, was significant (p<0.05) for the group of subjects on each of the three days. The analysis of the individual results revealed five significant rhythms (p<0.05) in FEV, and three in PEFA during the three days. These rhythms only occurred concomitantly on one day in one subject. This study indicates that airway resistance does vary significantly during the day. An interesting feature is the lack of concomitant rhythms between PEFR and FEV,. It suggests the t w o tests are not measuring the same aspects of pulmonary function. This has many clinical implications and requires further investigation.