Modification of locomotion-respiration coupling in patients with obstructive sleep apnea syndrome

INTRODUCTION: Locomotion is a complex motor task integrating sensory-motor and cognitive inputs through central pattern generator control. Locomotion-respiration coupling (LRC), defined as the synchronization between gait and breathing events, has been described during running and walking. Patients with obstructive sleep apnea syndrome (OSAS) exhibit altered gait patterns during wakefulness, which appear to be partially independent of nocturnal symptomatic treatment. While intermittent hypoxia may induce long-term ("fixed") central nervous system alterations, OSAS patients also display "reversible" adaptive mechanisms during wakefulness aimed at preventing upper airway (UA) collapse, involving changes in respiratory control and posture. Whether these adaptive mechanisms affect LRC and contribute to gait alterations remains unknown. METHODS: Ten awake patients with controlled OSAS treated with a mandibular advancement device (MAD) and ten matched healthy controls performed a one-minute walking trial on an instrumented treadmill with motion capture. Ventilation was assessed via thoracic expansion, and spatiotemporal gait parameters were extracted from kinematic and force platform data. LRC was quantified using phase-locking values (PLV) between ventilatory events and sagittal-plane joint kinematics. OSAS patients were assessed both with and without their MAD. RESULTS: Compared with controls, OSAS patients exhibited a longer double-stance phase and a shorter swing phase. Expiratory events occurred preferentially during double stance in OSAS patients, whereas controls showed a higher occurrence during swing. PLV analysis revealed increased synchronization between inspiratory events and hip and knee motion, as well as between expiratory events and trunk and hip motion in OSAS patients. These significative differences were no longer observed when patients wore their MAD. Logistic regression demonstrated that PLV metrics of inspiratory-hip and expiratory-trunk coupling effectively discriminated OSAS patients from controls, but not when UA stabilization was applied. CONCLUSION: Awake patients with controlled OSAS exhibit altered gait patterns characterized by increased locomotion-respiration coupling. This heightened synchronization likely reflects adaptive, reversible strategies aimed at limiting UA collapsibility during wakefulness rather than fixed hypoxia-related impairments alone. LRC may represent a functional marker of daytime motor alterations in OSAS and a potential target for interventions addressing UA mechanics beyond nocturnal treatment.