Variability of lung function and respiratory muscles power in healthy and asthmatic subjects

Abstract

Airway function is one of the many biologic functions that exhibit circadian variability over 24-h periods. Studies of circadian variability of lung function in normal subjects as well as asthmatics are particularly scarce, and those of MEP and MIP are unknown. The aim of this study to determine circadian variation in lung function (FVC, FEV1 and PEFR) and respiratory muscle pressures(MEP and MIP) for measurement of respiratory muscle power at 6:00am (early morning),12:00midday, 6:00pm( evening) and 12:00 midnight in healthy subjects and in patients with mild asthma at 6:00am and 6:00pm , to elaborate on the possibility of using MEP and MIP variability as a new diagnostic test for asthma. This is a cross sectional study performed in Khartoum, the capital of Sudan during December 2010. Thirty healthy, symptoms free non smokers normal subjects aged 20-64 years selected randomly and 15 mild asthmatics, clinically free during the time of study aged 19-49 years were included in the study. There is significant drop in healthy subjects early in the morning compared to 6:00pm, the drop in FVC was 9.75%, in FEV1 was 8.79%, in PEFR was 8.44%, in MEP was 10.04%, and in MIP was 17.57%. There is also significant drop in asthmatics early in the morning in MEP and MIP (21.76%, 27.57% respectively), is comparable to FEV1 (22.56%) and PEFR (23.86%). The sensitivity and specificity of variability for MEP (53%, 77%) and MIP (60%, 63%) comparable to sensitivity and specificity of FEV1 variability (40%, 86%) and PEFR variability (46%, 73%). The obtained comparable results of MEP, MIP variability to FEV1, PEFR variability in normal and asthmatic subjects could imply that MEP & MIP can be used in assessing airway calibre as in asthma. The study concluded that MEP & MIP variability could be sensitive tests to confirm asthma diagnosis.