Unexplained dyspnea on exertion: cardiopulmonary exercise testing as a diagnostic tool

Background: Unexplained dyspnea on exertion (DOE) is a common complaint among adolescents, preventing them from exercising. Our study aimed to use a novel hybrid cardiopulmonary exercise test (CPET) combined with spirometry to elucidate potential causes of DOE in adolescents. Furthermore, we created a novel measurement using a ratio of the average change in respiratory rate (RR) to average change in tidal volume (VT) to assess abnormal ventilatory responses. We hypothesized that there would be significant differences in cardiopulmonary endpoints between diagnostic groups. Methods: We retrospectively reviewed the charts from a cohort of patients ages 9-20 with unexplained DOE who underwent Hybrid-CPET. The Hybrid-CPET consisted of ramped exercise to maximal exertion on a treadmill with continuous cardiopulmonary measurements and spirometry pre/post exercise. Patients were classified as exercise-induced laryngeal obstruction (EILO), deconditioning, or physiologic limitation (PL) based on accepted criteria. Breathing pattern disorder (BPD) was classified using the novel measurement of RR:VT. Cardiopulmonary and spirometry endpoints were compared between groups. Results: 65 patients met our criteria with an average age of 14.8 (9-20). EILO, BPD, and PL were the three most prevalent conditions. BPD had a greater maximum respiratory rate (60.7 ± 1.7 bpm) than PL (54.4 ± 1.2 bpm; p= 0.008) and EILO (54.4 ± 1.5 bpm; p=0.013) groups, but there was no difference between PL and EILO. The maximum tidal volume was significantly less in the BPD group (1.4 ± 0.05 L) than the PL (2.1 ± 0.11 L; p<0.001) and EILO (2.0 ± 0.09 L; p<0.001) groups, but there was no difference between PL and EILO. The maximum minute ventilation (VE) for the BPD group (85 ± 4 L/min) was less than the PL (114 ± 6 L/min; p<0.001) and EILO groups (107 ± 5 L/min; p=0.018), but there was no difference between EILO and PL. The RR:VT ratio for BPD (43.0 ± 1.2) was significantly greater than PL (21.7 ± 1.1; p<0.001) and EILO (22.6 ± 1.8; p<0.001). Conclusion: In the majority of pediatric patients with unexplained DOE, their perceived shortness of breath did not correlate to a functional limitation on exercise. EILO, BPD, and PL were the three most prevalent conditions. Using the ratio of RR:VT slopes proved to be a promising criterion for quantifying a BPD. The significant decrease in the VE for the BPD group suggests that the lack of balance between RR and VT may cause their perceived feelings of dyspnea. SMURRF Fellowship: Cincinnati Children's Hospital Medical Center This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.