title: Longer duration of asthma is significantly associated with increased RV/TLC ratio.
abstract: Although 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.
  
  
  
  Patients 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.
  
  
  
  Among 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).
  
  
  
  RV/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.
authors.affiliation: Division of Pulmonary/Critical Care, UCSF-Fresno, USA; East Carolina University, Greenville, NC, USA.
authors.forename: Anupama
authors.initials: A
authors.lastname: Tiwari
authors.affiliation: Department of General Internal Medicine, UCSF-Fresno, USA.
authors.forename: Kazi
authors.initials: K
authors.lastname: Rahman
authors.affiliation: Division of Occupational Medicine, UCSF-Fresno, USA.
authors.forename: Belayneh
authors.initials: B
authors.lastname: Abejie
authors.affiliation: Division of Pulmonary/Critical Care, UCSF-Fresno, USA.
authors.forename: Vipul V
authors.initials: VV
authors.lastname: Jain
authors.affiliation: Division of Pulmonary/Critical Care, UCSF-Fresno, USA. Electronic address: jjoseph@fresno.ucsf.edu.
authors.forename: Jose Joseph
authors.initials: JJ
authors.lastname: Vempilly
mesh_terms: D000328:Adult; D000368:Aged; D001249:Asthma / Q000175:diagnosis / Q000208:ethnology / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012115:Residual Volume / Q000502:physiology*; D012129:Respiratory Function Tests / Q000379:methods*; D012720:Severity of Illness Index; D013147:Spirometry / Q000379:methods; D014109:Total Lung Capacity / Q000502:physiology*; D014797:Vital Capacity / Q000502:physiology
keywords: Duration of asthma; FEV1/FVC ratio; General linear model; RV/TLC ratio