Investigation of the relationship between the viscoelastic properties and muscle strength of accessory respiratory muscles in obstructive sleep apnea

Background: The link between respiratory muscle strength and viscoelastic properties of accessory muscles offers a perspective for individualized treatment in Obstructive Sleep Apnea Syndrome (OSAS). Purpose: This study investigated associations between respiratory muscle strength and viscoelastic properties of the sternocleidomastoid (SCM) and rectus abdominis (RA) in OSAS. Methods: Patients with moderate (n = 33) and severe OSAS (n = 45) diagnosed by polysomnography were included. Muscle viscoelasticity was assessed using Myoton (R) PRO, and respiratory strength (maximal inspiratory (MIP), maximal expiratory pressure (MEP)) was measured by spirometer at rest and during maximal efforts. Results: In moderate OSAS, MEP-best correlated negatively with left SCM elasticity at rest (r =-0.622, p < 0.001), elasticity during inspiration (r =-0.401, p = 0.021), and stiffness (r =-0.357, p = 0.041). In severe OSAS, MEP-best correlated negatively with left SCM stiffness (r =-0.380), right SCM elasticity at rest (r =-0.393) and inspiration (r =-0.495), and left SCM elasticity during expiration (r =-0.323). MIP-best correlated negatively with right SCM elasticity during inspiration (r =-0.301) and left SCM elasticity during expiration (r =-0.323). Age correlated positively with SCM and RA parameters, while AHI correlated negatively with SCM and RA stiffness/elasticity, especially left RA elasticity during expiration (r =-0.544, p < 0.001). Side-specific differences were noted. Conclusion: Both inspiratory (SCM) and expiratory (RA) muscles are important in OSAS. With greater severity, viscoelastic properties shift from active support to passive adaptation, with RA contributing alongside SCM to functional changes.