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METHOD OF TIDAL EXPIRATORY FLOW VOLUME LOOP CONSTRUCTION DOES NOT ALTER EXPIRATORY FLOW LIMITATION MEASUREMENT

Abstract

Amy Rebecca Sheldon, Savannah J. Barbieri, William C. Norris, Marc A. Augenreich, Austin D. Gooch, Jonothan L. Stickford. Appalachian State University, Boone, NC.

Background: Various methods exist to construct flow-volume loops (FVL) during exercise, and the method selected could alter the quantification of the mechanical constraints to exercise ventilation. Therefore, the purpose of this study was to investigate different methods of FVL construction on ventilatory parameters related to breathing pattern, operational lung volumes, and exercise flow limitation. Methods: Twelve (N=12) participants completed an incremental exercise test on a cycle ergometer. Inspiratory capacity maneuvers were performed each minute of exercise in order to measure operational lung volumes and assess ventilatory dynamics. FVLs were constructed using two techniques: 1) a single representative breath (TYP) selected from breaths measured during exercise and 2) a polar mean loop (i.e., the mean point for every 1° rotation) using 8-12 breaths during exercise (POLAR). Data from these loops were compared with the mean of all breaths collected during the stage (MEAN). Data were compared using repeated-measures analysis of variance. Values reported are mean ± standard deviation. Results: The TYP loop presented higher minute ventilation (V̇E) compared with the POLAR loop (TYP: 54±3 L∙min-1, POLAR: 52±3 L∙min-1; P = 0.024) but neither was different form the MEAN minute ventilation (P > 0.05). The difference in V̇E between TYP and POLAR was attributed to differences in the breathing frequency (TYP: 29±1, MEAN: 28±1; p=0.002), and in particular, inspiratory time (P < 0.05) between the two methods. Operational lung volume, as assessed via inspiratory capacity, was different between TYP and POLAR (TYP: 3.55±0.22 L; POLAR:3.52±0.22 L ; P = 0.013) However, despite the statistically different operational lung volumes, the technique for construction of the FVL did not alter the quantification of expiratory flow limitation (P > 0.05). Conclusion: These findings indicate that the technique used to construct exercise FVL alters quantification of breathing patterns via changes to breathing frequency and also impacts operational lung volumes. However, though statistically different, the differences likely are not clinically meaningful, especially considering that the method does not impact clinical indicators used in the assessment of mechanical limitations to ventilation.

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