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Obstructive Lung Diseases |

RV/TLC Ratio Is a Better Criterion for Diagnosing Obstructive Ventilatory Defect in Asthma

Ali Rashidian*, MD; Dale Claes, RT; Andres Escobar, MD; Thitiwat Sriprasart, MD; Cathleen Mueller, BS; Tim Tyner, MS; Jose Joseph Vempilly, MD
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UCSF-Fresno, Fresno, CA


Chest. 2012;142(4_MeetingAbstracts):705A. doi:10.1378/chest.1388905
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Abstract

SESSION TYPE: Asthma Posters

PRESENTED ON: Wednesday, October 24, 2012 at 01:30 PM - 02:30 PM

PURPOSE: The diagnosis of obstructive ventilatory defect in asthma is currently based on FEV1/FVC ratio <75%. The accuracy of this criterion has been questioned. In a retrospective analysis, we observed that abnormal RV/TLC ratio was a better predictor for obstruction. However, the reversibility of lung volumes following bronchodilator administration has not been well documented. Therefore we prospectively investigated the utility of lung volume measurements before and after bronchodilator administration in a cohort of physician-diagnosed subjects with asthma.

METHODS: Adult subjects with physician-diagnosed asthma that met inclusion criteria were recruited prospectively after obtaining an informed consent. Patients completed a questionnaire before spirometry and lung volume testing and following administration of bronchodilators with repeat pulmonary function tests (PFT). Symptom score and PFT values were compared using paired t test. Correlation between FEV1 reversibility and RV reversibility were done using Pearson’s test.

RESULTS: The 29 subjects were recruited, consisting of 62% women. Sixty-nine percent of subjects were Caucasian, 24% Hispanic, 3% African American and 3% Indian American. There were 3% smokers. The mean subject age was 50 ± 14.4 years. The median duration of asthma was 6 years. FEV1/FVC ratio <75% was observed in 34%, while RV/TLC ratio >35% was observed in 55% of subjects. A significant reversibility was observed in 24% based on ATS criteria. While all spirometry values improved significantly following bronchodilator administration, total lung capacity (p=0.78) and residual volume (p=0.18) did not improve after bronchodilator administration. Furthermore, there was no correlation between FEV1 reversibility and RV reversibility (r=0.1, p=0.3).

CONCLUSIONS: Abnormal RV/TLC ratio was a superior criterion for diagnosing obstruction in asthma. While FEV1 improvement with bronchodilator may be a function of large airway reversibility, lack of significant RV reversibility may indicate small airway closure that is non-reversible.

CLINICAL IMPLICATIONS: FEV1/FVC ratio underestimates obstruction in asthma. Increased residual volume and RV/TLC ratio indicate unresolved obstruction in small airways associated with inflammation. Lung volume measurement may be a better tool to assess asthma severity.

DISCLOSURE: The following authors have nothing to disclose: Ali Rashidian, Dale Claes, Andres Escobar, Thitiwat Sriprasart, Cathleen Mueller, Tim Tyner, Jose Joseph Vempilly

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UCSF-Fresno, Fresno, CA

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