Longer duration of asthma is significantly associated with increased RV/TLC ratio

BackgroundAlthough FEV1/FVC ratio has been shown to be negatively associated with longer duration of asthma; an association between RV/TLC ratio and longer duration of asthma has not been explored.Material and methodsPatients with established asthma for more than a year and met inclusion and exclusion criteria were recruited. Data obtained by questionnaire after informed consent was obtained, Pulmonary function tests and laboratory results were collected through chart review. Correlation and multiple linear regressions were used to analyze the data.ResultsAmong the 93 subjects, 61 were women. The mean age of patients was 58 ± 15 years, and the mean duration of asthma was 21 ± 18 years. The ethnic composition included: Caucasians 64%, Hispanics 28% and other groups 8%. The FEV1/FVC ratio was not significantly associated with duration of asthma (R2 = 0.15, p = 0.05). However, the RV/TLC ratio was significantly associated with duration of asthma (R2 = 0.46, p < 0.001).ConclusionRV/TLC ratio may be a better indicator than FEV1/FVC ratio to detect airway obstruction related to longer duration of asthma. Lung volume measurements should be done in addition to spirometry to detect changes related to airway obstruction in patients with longer duration of asthma.