Circadian variability in airways characteristics: A spirometric study.
Background: Chronic obstructive pulmonary disease (COPD) and Asthma patients exhibit exacerbation of symptoms in night hours and early morning. Temporal variability in airway caliber have been reported in past using peak expiratory flow rate which represents large airways caliber, while in COPD and Asthma, smaller airways are particularly affected. We studied circadian variability of airway caliber using Forced Expiratory Volume in the First Second (FEV1) and Mid Expiratory Flow rate. Methods: Male volunteers (18-26 years), having similar daily routine were recruited. Spirometry was performed at 5: 00, 8:00, 11:00, 14:00, 17:00, 20:00 and 23:00 h. Data from 104 subjects was analyzed for diurnal variability parameters viz., amplitude percent mean and standard deviation percent of mean. For circadian rhythm Cosinor curve was fitted and rhythm characteristics in terms of MESOR, Amplitude and Acrophase were determined. Results: Repeated measures ANOVA revealed significant differences in spirometric parameters measured at different time points during the day. In general, spirometric parameters follow a sinusoidal pattern and exhibit minimum values during night hours and maximum values during day time. FEV1 Cosinor rhythm was significant in 31% of subjects (Zero amplitude test). The distribution of acrophase revealed interindividual differences in chronophenotypes. Variability was minimum for FEV1% and maximum for FEF75 suggesting dynamic interplay of airway geometry and neuro-chemical influences. Conclusion: The presence of different chronophenotypes in normal subjects suggests that the nocturnal asthma may also be a different phenotype. Availability of portable spirometers and home monitoring thus may be required for ascertaining chronophenotype and tailoring chronotherapeutic interventions.