0866 Decoding Expiratory Flow Patterns in Primary Snoring, Pediatric Obstructive Sleep Apnea and Leigh Syndrome: Novel Biomarker of Brainstem Dysfunction

Abstract Introduction Breath-to-breath analytics have advanced characterization of obstructive sleep apnea (OSA), yet pediatric applications and expiratory dynamics remain understudied. Expiration may carry physiologic signatures of brainstem control, and Leigh syndrome (LS), a disorder with central respiratory dysfunction, provides a model to evaluate such abnormalities. We compared expiratory morphologies in children with LS, OSA, and primary snoring (PS). Methods With IRB approval, we conducted a retrospective study of baseline diagnostic polysomnography from seventeen PS controls, six LS patients, and eighteen AHI-sex-age-matched OSA patients. A breath-to-breath algorithm was created to quantify three expiratory morphologies (normal, ramp, pause) after removal of all scored apneas. Algorithm was written in C programming language and statistics were computed using Python. Results Age and sex distribution were similar across groups, and AHI did not differ between LS and OSA (13.3±5.3 vs 12.3±4.3, p=0.72). PS had the lowest AHI by design (1.82± 0.69). Despite similar total expiration duration, LS had the shortest cycle period (CP), PS intermediate, and OSA the longest. Expiration-to-CP ratio was lowest in OSA(0.548±0.053s) versus LS(0.599±0.029s, p=0.036) and PS(0.602±0.019s, p< 0.002), while the inspiration-to-CP ratio was highest in OSA, indicating an inspiratory-heavy pattern that did not by itself separate LS from PS. Expiratory morphology revealed clearer disease-specific signatures. Expiratory pause duration was shortest in PS(0.68±0.12s) compared with OSA(1.03±0.36s, p< 0.001) and LS(0.94±0.41s, p=0.043) and pause-to-CP ratio was higher in LS and OSA than PS. Paused breaths were infrequent in OSA but common in LS and PS, whereas ramp breaths predominated in PS(76.9%±14.4%), were reduced in LS(46.6%±30.2%) and OSA(40.4%±21.8%), p=0.0082 and 1.5x10-6 respectively. LS showed increased ramp-to-CP ratios (0.321±0.058s) versus OSA (0.268±0.052s) and PS (0.259±0.041s, both p< 0.05). Findings persisted even when including hypopneas and when restricting comparisons to mild OSA. Conclusion This is the first pediatric study examining novel expiratory dynamics across disease groups. Our results suggest that expiratory morphologies characterized by pauses and ramps may distinguish between PS, LS and OSA patients and are affected by both central and obstructive disease states. Expiratory mechanisms may therefore provide biomarkers of respiratory control integrity and reveal new exciting mechanistic pathways. Support (if any) JMR: P01 HL144454, R01 HL144801, R01 HL151389, R01 HL126523 MLC: HRSA2T2MC0007 WTP: K08HL179396, SRS, PBF.