Detection of upper airway obstruction with spirometry results and the flow-volume loop: a comparison of quantitative and visual inspection criteria.

BACKGROUND: There are important gaps in our understanding of the epidemiology and diagnosis of upper-airway obstruction.
METHODS: We examined the diagnostic value of several criteria for predicting upper-airway obstruction, and we measured the frequency of detecting upper-airway obstruction via quantitative and visual assessment of flow-volume loops. We studied 4 quantitative and 3 visual criteria for their ability to detect upper-airway obstruction. The quantitative criteria were: ratio of forced expiratory volume in the first second (FEV(1)) to maximum expiratory flow (MEF) > 10 mL/L/min; ratio of the flow at the mid-point of the forced expiratory maneuver (MEF(50%)) to the flow at the mid-point of the forced inspiratory maneuver (MIF(50%)) < 0.3 or > 1; MIF(50%) < 100 L/min; and FEV(1)/FEV(0.5) > 1.5. The visual criteria were: presence of a plateau; biphasic shape; and oscillations. The accepted standard tests for diagnosing upper-airway obstruction were bronchoscopy, laryngoscopy, and chest or neck computed tomogram. We considered 979 consecutive flow-volume loops from the Cleveland Clinic's pulmonary function laboratory. We calculated the sensitivity, specificity, and positive and negative predictive values of the individual criteria and an aggregate criterion for predicting upper-airway obstruction.
RESULTS: We excluded 504 flow-volume loops because the workups for those patients did not include any of the accepted standard tests for diagnosing upper-airway obstruction, so there were 475 eligible flow-volume loops (48.6% of the 979 loops considered). Thirty-six (7.5%) of the 475 workups that included an accepted standard test reported a cause of upper-airway obstruction. The aggregate sensitivity for detecting upper-airway obstruction was 69.4%. Receiver-operating-curve analysis found that the individual criteria had poor diagnostic performance (area under the curve < 0.522) but that a newly proposed aggregate criterion performed better (area under the curve 0.605).
CONCLUSIONS: The prevalence of reported upper-airway obstruction was 7.5%. The quantitative criteria showed low sensitivity for detecting upper-airway obstruction but exceeded that of visual criteria. The aggregate criterion increased the sensitivity to 69.4%, which suggests the need for additional criteria to help predict upper-airway obstruction.