Muscular Response in Sleep-Disordered Breathing Patients: New Methods of Assessment and Measurement

Background: Obstructive sleep apnea (OSA) is a heterogeneous disorder influenced by both anatomical collapsibility and non-anatomical factors, such as neuromuscular response. Identifying these traits through simplified clinical surrogates is crucial for personalized precision medicine. Methods: This exploratory retrospective study evaluated 207 home polygraphy recordings of Italian patients to assess sleep-stage-specific Apnea–Hypopnea Index (REM vs. NREM AHI) as a clinical surrogate indicator of the balance between anatomical collapsibility and neuromuscular compensation. Patients were stratified by severity into simple snorers (AHI < 5 events/h), mild OSA (AHI 5–15 events/h), and severe OSA (AHI > 30 events/h). REM and NREM AHI values were compared and correlated with Apnea Index (AI), Hypopnea Index (HI), body mass index (BMI), and cumulative nocturnal desaturation indices (CT < 90% and T < 90 min). Results: In non-severe patients (simple snorers and mild OSA), REM AHI was significantly higher than NREM AHI (REM/NREM ratio > 1), suggesting relative neuromuscular protection during NREM sleep. Conversely, in severe OSA patients, the REM/NREM ratio progressively decreased and approached unity, with NREM AHI prevailing. Furthermore, NREM predominance was significantly associated with a higher AI and a worse cumulative desaturation indicating a globally more severe disease. Conclusions: A predominance of REM AHI characterizes milder OSA presentations with effective NREM muscular compensation, whereas NREM predominance aligns with an anatomically dominant, severe phenotype. Decomposing AHI into REM and NREM components provides a practical, readily available clinical surrogate to estimate the anatomy–neuromuscular balance and guide PALM-oriented personalized treatments.