Hamdy. Differential changes in human pharyngoesophageal motor excitability induced by swallowing, pharyngeal stimulation, and anesthesia. Am J Physiol Gastrointest Liver Physiol 285: G137-G144, 2003. First published February 26, 2003 10.1152/ajpgi.00399.2002We investigated the effects of water swallowing, pharyngeal stimulation, and oropharyngeal anesthesia on corticobulbar and craniobulbar projections to human swallowing musculature. Changes in pathway excitability were measured via electromyography from swallowed intraluminal pharyngeal and esophageal electrodes to motor cerebral and trigeminal nerve magnetic stimulation. After both water swallowing and pharyngeal stimulation, pharyngoesophageal corticobulbar excitability increased (swallowing: pharynx ϭ 59 Ϯ 12%, P Ͻ 0.001; esophagus ϭ 45 Ϯ 20%, P Ͻ 0.05; pharyngeal stimulation: pharynx ϭ 76 Ϯ 19%, P Ͻ 0.001; esophagus ϭ 45 Ϯ 23%, P ϭ 0.05), being early with swallowing but late with stimulation. By comparison, craniobulbar excitability increased early after swallowing but remained unaffected by pharyngeal stimulation. After anesthesia, both corticobulbar (pharynx ϭ Ϫ24 Ϯ 10%, P Ͻ 0.05; esophagus ϭ Ϫ28 Ϯ 7%, P Ͻ 0.01) and craniobulbar excitability showed a late decrease. Thus swallowing induces transient early facilitation of corticobulbar and craniobulbar projections, whereas electrical stimulation promotes delayed facilitation mainly in cortex. With removal of input, both corticobulbar and craniobulbar projections show delayed inhibition, implying a reduction in motoneuron and/or cortical activity.
Faucial pillar (FP) stimulation is commonly used in swallowing rehabilitation, yet its physiological basis remains uncertain. We investigated the effects of intraoral FP stimulation on human corticobulbar excitability and swallowing behavior, to explore the possibility of a central mechanism for functional change. In 10 healthy subjects, corticobulbar projections to pharynx were investigated with transcranial magnetic stimulation, via intraluminal electrodes, before and up to 1 h after 10 min of electrical FP stimulation with three frequencies (0.2, 1, and 5 Hz) or sham and peripheral (median nerve) stimulation. In a second study, swallowing behavior was assessed with videofluoroscopy before and after FP stimulation. FP stimulation at 5 Hz inhibited the corticobulbar projection (-14 +/- 6%, P < 0.02) and lengthened swallow response time (+114 +/- 24%, P = 0.02). By comparison, FP stimulation at 0.2 Hz facilitated this projection (+60 +/- 28%, P < 0.04), without enhancing swallowing behavior. Neither 1-Hz, sham, nor median nerve stimulation altered excitability. Thus changes in corticobulbar excitability to FP stimulation are frequency dependent with implications for the treatment for neurogenic swallowing dysfunction.
Deglutitive aspiration is common after stroke and can have devastating consequences. While the application of oral sensory stimulation as a treatment for dysphagia remains controversial, data from our laboratory have suggested that it may increase corticobulbar excitability, which in previous work was correlated with swallowing recovery after stroke. Our study assessed the effects of oral stimulation at the faucial pillar on measures of swallowing and aspiration in patients with dysphagic stroke. Swallowing was assessed before and 60 min after 0.2-Hz electrical or sham stimulation in 16 stroke patients (12 male, mean age = 73 +/- 12 years). Swallowing measures included laryngeal closure (initiation and duration) and pharyngeal transit time, taken from digitally acquired videofluoroscopy. Aspiration severity was assessed using a validated penetration-aspiration scale. Preintervention, the initiation of laryngeal closure, was delayed in both groups, occurring 0.66 +/- 0.17 s after the bolus arrived at the hypopharynx. The larynx was closed for 0.79 +/- 0.07 s and pharyngeal transit time was 0.94 +/- 0.06 s. Baseline swallowing measures and aspiration severity were similar between groups (stimulation: 24.9 +/- 3.01; sham: 24.9 +/- 3.3, p = 0.2). Compared with baseline, no change was observed in the speed of laryngeal elevation, pharyngeal transit time, or aspiration severity within subjects or between groups for either active or sham stimulation. Our study found no evidence for functional change in swallow physiology after faucial pillar stimulation in dysphagic stroke. Therefore, with the parameters used in this study, oral stimulation does not offer an effective treatment for poststroke patients.
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