Sensitivity And Specificity Of Geometric Techniques To Identify Expiratory Flow Limitation During Exercise

Expiratory flow limitation (EFL) contributes to exercise intolerance and is thought to be requisite for dynamic hyperinflation (DH) during exercise. However, EFL identification is challenging. While encroachment of the spontaneous expiratory flow-volume (SEFV) curve on the maximal expiratory flow-volume curve has been used to identify EFL, this approach has well-known limitations, including the need to perform pre-exercise forced maneuvers and lung volume alignment. Another technique to identify EFL, the rectangular area ratio (RAR), quantifies the degree of convexity or concavity of the SEFV curve; it has the advantage of requiring no additional measurements. PURPOSE: To evaluate the sensitivity and specificity of encroachment and RAR to identify EFL during exercise in healthy lean and obese males, by assuming that EFL is requisite for DH. METHODS: Twelve lean [mean(SD): 30(6) yr; BMI 23.6(2.5) kg/m2; V̇O2peak 2.67(0.75) L/min] and 12 obese [30(6) yr; BMI 37.6(3.8) kg/m2; V̇O2peak 2.88(0.55) L/min] males, enrolled in the National Center for Male Reproductive Epigenomics study (NCT04175678), underwent spirometry and cycling ramp incremental exercise testing to intolerance. Inspiratory capacity maneuvers every 2-min were used to establish DH, defined as a > 100 mL increase in end-expiratory lung volume during exercise. We tested sensitivity and specificity of encroachment and RAR to identify EFL. For RAR, a falling RAR during any phase of exercise or presence of RAR <0.5 was used to identify EFL. RESULTS: DH occurred in 2 lean and 8 obese participants. In the lean group, EFL was identified by encroachment in 9 participants (none showing DH) and by RAR in 3 (none showing DH). In the obese group, EFL was identified by encroachment in 10 participants (6 with DH), and by RAR in 6 (3 with DH). Thus, encroachment had 60% sensitivity and 7% specificity for EFL detection, while RAR had 40% sensitivity and 64% specificity. CONCLUSION: We found that the RAR approach was more specific than encroachment to identify DH, and therefore may be a better marker of EFL occurrence. While sensitive, encroachment yielded a high rate of false positives. Further research is warranted to validate the efficacy of RAR as a marker of EFL and explore its potential applications in clinical settings. This study is supported by NIH/NICHD: P50HD098593. Michele Girardi is supported by the Johnny Carson Foundation