Abstract 17415: Oxygen Uptake Kinetics at the Onset of Incremental Ramp Exercise During Cardiopulmonary Exercise Testing in Patients Undergoing Evaluation of Dyspnea on Exertion

Abstract

Background: A high metabolic cost of initiating exercise, defined by workload equivalents of unloaded cycle ergometry exercise, has been described in obese patients with HFpEF. Implications of high BMI and exaggerated metabolic cost of exercise initiation on responses to incremental ramp exercise have not been defined. We hypothesized that exaggerated metabolic cost of exercise initiation would result in delayed metabolic response to incremental ramp exercise. Methods: Patients underwent invasive cardiopulmonary exercise testing (CPET) on a cycle ergometer, including rest, unloaded exercise, and maximum incremental ramp exercise. Mean response time (MRT) was defined as 67% of the time to reach steady state VO 2 during unloaded exercise. On-ramp VO 2 kinetics were defined by the amount of time that it took for VO 2 to permanently increase by 5% (t 5% ), 10% (t 10% ), and 15% (t 15% ) above steady state after initiation of incremental ramp exercise. These values were adjusted for ramp and related to demographic and CPET measures by multivariate linear regression. Results: 200 patients referred for evaluation of exertional dyspnea and suspected HFpEF (age 55 ± 16 years, 45% female, BMI of 30 ± 6 kg/m 2 , 52% HTN, 17% DM) demonstrated variability in their on-ramp VO 2 uptake kinetics after reaching steady state during unloaded exercise. Delayed VO 2 kinetic responsiveness to incremental ramp exercise, as measured by t 5% , t 10% , and t 15%, was not related to age but was directly related to BMI, internal work, and prolonged MRT for VO 2 upon exercise initiation. Conclusion: In this initial description of VO 2 uptake kinetic patterns during the transition from unloaded to incremental ramp exercise, increased BMI, slow exercise onset VO 2 kinetics, and heightened metabolic cost of exercise initiation are all related to delayed VO 2 on-ramp kinetics. Delayed on-ramp O 2 kinetics merit further evaluation in relation to functional limitations in dyspneic patients referred for suspicion of HFpEF.