Does the Expiratory Disproportion Index Remain Predictive of Airway Stenosis in Obese Patients?

The expiratory disproportion index (EDI) is the ratio of forced expiratory volume in 1 second divided by peak expiratory flow rate multiplied by 100. An elevated EDI (>50) can help differentiate upper airway stenosis from other dyspnea etiologies, but this has not been verified when considering body habitus. We hypothesize that the predictive value of elevated EDI in diagnosing airway stenosis will be lower in obese patients as compared to nonobese patients.

Retrospective cohort study.

Patients >18 years old with recorded pulmonary function test values, body mass index (BMI), and airway imaging were reviewed retrospectively from January 2011 to October 2018. EDI was recorded for four cohorts: nonobese and nonstenotic, obese and nonstenotic, nonobese and stenotic, and obese and stenotic, to determine the mean EDI and the sensitivity and specificity of an elevated EDI.

Mean EDI values were 66.53 ± 17.66 and 49.55 ± 2.04 in the nonobese stenotic and nonstenotic groups, respectively (P < .01). They were 58.00 ± 10.79 and 45.02 ± 1.42 in the obese stenotic and nonstenotic groups, respectively (P < .01). At a threshold of >50, EDI had a sensitivity of 83.3% and specificity of 56.2% in differentiating between stenotic and nonstenotic cases in the nonobese cohort and 50.0% and 71.9% in the obese cohort.

As previously established, mean EDI values were significantly different in stenotic and nonstenotic patients in both BMI cohorts. However, at the established threshold of >50, EDI was not as sensitive at identifying stenotic cases in obese patients as in nonobese patients. This suggests that the EDI remains useful in obese patients when elevated but should not be relied upon to rule out stenosis.

4 Laryngoscope, 131:606-609, 2021.