Abstract Rationale Expiratory flow limitation (EFL) is an exercise limitation and contributor to dyspnea that can be directly observed during cardiopulmonary exercise testing (CPET). An explanation for this is airway disease leads to air trapping resulting in dynamic hyperinflation (DH). With exercise, exertional needs aren’t met by enlarging tidal volume or increasing inspiratory flow resulting in dyspnea via reduced mechanical ventilatory capacity. This happens at rest, early, and peak exercise. While this is common in patients with obstructive lung disease, it can also be found in obesity who, during normal tidal breathing, breathe near residual volume. This results in reduced expiratory reserve volume, intrinsically reducing expiratory flow rates, and increases risk of airway closure during tidal breathing. In this study, we assess for relationship between obesity class and timing of EFL during CPET. We propose higher classes of obesity are correlated with early or even at rest EFL. Methods This is a retrospective observational study based on data retrieved from August 2022 to March 2025 at the University of Rochester Medical Center. Subjects referred for CPET, age 18 or older with BMI 25 or greater who exhibited EFL during testing were included. Subjects who were pregnant, incarcerated, or had known underlying obstructive lung disease or FEV1/FVC ratio 0.7 on the day of testing were excluded. 43 subjects met inclusion criteria and were grouped by BMI class. Variables of interest were age, sex, BMI, FEV1/FVC as well as CPET measurements including DH and EFL. Timing of EFL was determined by first occurrence of 40% overlap of tidal exercise, expiratory, as well as maximum expiratory flow loops. Work-watts at this time was also recorded. Results Baseline demographics did not vary significantly between groups except for BMI. Resting EFL and DH was similar between groups. Post hoc comparison indicated overweight subjects had significantly longer mean time to EFL of 439 seconds but not obesity class II-III subjects. Furthermore, overweight subjects had significantly greater mean respiratory exchange ratios (RER) than obesity groups. Conclusions Time to EFL varied by BMI class, however this association did not hold when indexed to watts at EFL, suggesting similarity in effort dependent occurrence of EFL. Resting EFL and DH was also similar between BMI classes, questioning the impact of obesity on this phenomenon. RER decreased with obesity class; previous studies have suggested metabolic inflexibility due to glucose intolerance can result in decreased RER due to differences in carbohydrate utilization. This abstract is funded by: None
Sepiol et al. (Fri,) studied this question.