Preoptic hypothalamic warming suppresses laryngeal dilator activity during sleep.

Upper airway dilator activity during sleep appears to be diminished under conditions of enhanced sleep propensity, such as after sleep deprivation, leading to worsening of obstructive sleep apnea (OSA). Non-rapid eye movement (NREM) sleep propensity originates in sleep-active neurons of the preoptic area (POA) of the hypothalamus and is facilitated by activation of POA warm-sensitive neurons (WSNs). We hypothesized that activation of WSNs by local POA warming would inhibit activity of the posterior cricoarytenoid (PCA) muscle, an airway dilator, during NREM sleep. In chronically prepared unrestrained cats, the PCA exhibited inspiratory bursts in approximate synchrony with inspiratory diaphragmatic activity during waking, NREM, and REM. Integrated inspiratory PCA activity (IA), peak activity (PA), and the lead time (LT) of the onset of inspiratory activity in PCA relative to diaphragm were significantly reduced in NREM sleep and further reduced during REM sleep compared with waking. Mild bilateral local POA warming (0.5-1.2 degrees C) significantly reduced IA, PA, and LT during NREM sleep compared with a prewarming NREM baseline. In some animals, effects of POA warming on PCA activity were found during waking or REM. Because POA WSN activity is increased during spontaneous NREM sleep and regulates sleep propensity, we hypothesize that this activation contributes to reduction of airway dilator activity in patients with OSA.

Diaphragm plasticity following intrinsic laryngeal muscle denervation in rats.

PURPOSE: During inspiration, recruitment of the intrinsic laryngeal muscles (ILM) reduces the inspiratory load on the ventilatory pump muscles. The purpose of our study was to determine 1) whether the diaphragm adapts to denervation of the ILM, and 2) whether the additional stimulus of exercise training affects the degree to which the diaphragm adapts to ILM denervation. METHODS: Thirty-six male Sprague-Dawley rats (2 months) were randomly divided into sedentary control (SC), sedentary-denervated (SD), and exercise-denervated (ED) groups. Control animals underwent sham operations, whereas ILM-denervated animals underwent bilateral transection of the recurrent laryngeal nerves. Three weeks after surgery, animals in the ED group performed a treadmill training protocol for a period of 6 wk. RESULTS: Denervation (SD and ED animals) of the ILM significantly increased diaphragm citrate synthase activity (20%), in vitro endurance, and time to peak twitch tension (15%), and reduced (13%) peak tetanic tension (Po, N x cm(-2)). No independent training effect over and above the effects attributed to denervation of ILM were noted in ED animals. CONCLUSION: The results highlight the role of vocal cord dilator function during both eupnea and exercise-induced hyperpnea.