(P004) CHARACTERIZING DYSPNEA IN RELATION TO INVASIVE EXERCISE HEMODYNAMICS IN PATIENTS WITH DYSPNEA OF UNKNOWN ORIGIN: A RETROSPECTIVE ANALYSIS

Background: Dyspnea is a subjective experience of breathing discomfort consisting of qualitatively distinct sensations varying in intensity. Dyspnea of unknown origin (DUO) presents with elusive etiology despite thorough diagnostic evaluation. Exercise right heart catheterization (RHC) is increasingly employed to identify central hemodynamic contributions, not evident at rest, that may explain DUO. This investigation provides an opportunity to improve our understanding of the relationship between clinical tools assessing dyspnea and hemodynamic responses to exercise.

METHODS AND RESULTS: A retrospective analysis was conducted in patients who underwent RHC with exercise between August 2022 to February 2024 while consenting to participate in a hemodynamic registry. Patients were defined as having DUO based on persistent dyspnea alongside a left ventricular ejection fraction >50%, peak tricuspid regurgitation velocity < 2.8 m/s, low probability of pulmonary hypertension, and negative findings of cardiopulmonary and hematological pathologies. On the day of the RHC, patients completed the Medical Research Council Dyspnea questionnaire. At rest and during submaximal exercise, patients completed The Multidimensional Dyspnea Profile (MDP) and ratings of perceived exertion (RPE; Borg 0-10). RHC was performed at supine rest and during at least one 6-min stage of semi-upright submaximal cycling between 15-70 W. Patients were classified as abnormal when the change from rest to submaximal exercise for the mean pulmonary artery pressure (mPAP) to cardiac output (CO) slope (ΔmPAP/ΔCO) was ≥3mmHg/L/min and/or the pulmonary artery wedge pressure (PAWP) to CO slope (ΔPAWP/ΔCO) was ≥2mmHg/L/min. Among 19 patients, 9 had abnormal (ABN; 62±12 years, 44% Female) and 10 normal (NOR; 59±17 years, 90% Female) exercise hemodynamics with non-significantly more females in the ABN group (p=0.057). The prevalence of comorbidities, the resting supine and semi-upright hemodynamics did not differ between the two groups (all p>0.05) apart from a greater pulmonary vascular resistance (PVR) in ABN compared to NOR (2.0±0.6 vs 1.5±0.6 WU, p=0.038) at semi-upright rest. Individual MDP items, the immediate perception and emotional response domains, and RPE scores did not differ between groups at rest or during submaximal exercise (all p>0.05).

Conclusion: Dyspnea is complex and the present results suggest that while cardiopulmonary hemodynamic abnormalities may contribute to the subjective experience of breathing discomfort in a portion of referred patients (47%), a considerable proportion present with normal hemodynamics. As such, the degree of dyspnea does not appear predictive of hemodynamic abnormalities.