Pathogenesis of laryngeal narrowing in patients with multiple system atrophy.

1. We do not fully understand the pathogenesis of nocturnal laryngeal stridor in patients with multiple system atrophy (MSA). Recent studies suggest that inspiratory thyroarytenoid (TA) muscle activation has a role in the development of the stridor. 2. The breathing pattern and firing timing of TA muscle activation were determined in ten MSA patients, anaesthetized with propofol and breathing through the laryngeal mask airway, while the behaviour of the laryngeal aperture was being observed endoscopically. 3. Two distinct breathing patterns, i.e. no inspiratory flow limitation (no-IFL) and IFL, were identified during the measurements. During IFL, significant laryngeal narrowing was observed leading to an increase in laryngeal resistance and end-tidal carbon dioxide concentration. Development of IFL was significantly associated with the presence of phasic inspiratory activation of TA muscle. Application of continuous positive airway pressure suppressed the TA muscle activation. 4. The results indicate that contraction of laryngeal adductors during inspiration narrows the larynx leading to development of inspiratory flow limitation accompanied by stridor in patients with MSA under general anaesthesia.