Laryngeal function is vital to airway protection. While swallow is mediated by the brainstem, mechanisms underlying increased risk of dysphagia after cervical spinal cord injury (SCI) are unknown. We hypothesized that loss of descending phrenic drive affects swallow and breathing differently, and loss of ascending spinal afferent information alters swallow regulation. We recorded electromyograms from upper airway and chest wall muscles in freely breathing pentobarbital-anesthetized cats and rats. Inspiratory laryngeal activity increased ~two-fold following C2 lateral-hemisection. Ipsilateral to the injury, crural diaphragm EMG amplitude was reduced during breathing (62 ± 25% change post-injury), but no animal had complete termination of activity; 75% of animals increased contralateral diaphragm recruitment, but this did not reach significance. During swallow, laryngeal adductor and pharyngeal constrictor muscles increased activity, and diaphragm activity was bilaterally suppressed. This was unexpected because of the ipsilateral-specific response during breathing. Swallow-breathing coordination was also disrupted and more swallows occurred during early expiration. Finally, to determine if the chest wall is a major source of feedback for laryngeal regulation, we performed T1 total transections in rats. As in the C2 lateral-hemisection, inspiratory laryngeal recruitment was the first feature noted. In contrast to the C2 lateral-hemisection, diaphragmatic drive increased after T1 transection. Overall, we found that SCI alters laryngeal drive during swallow and breathing, and reduced swallow-related diaphragm activity. Our results show behavior-specific effects, suggesting SCI affects swallow more than breathing, and emphasizes the need for additional studies on the effects of ascending afferents from the spinal cord on laryngeal function.

Swallow is a complex behavior that consists of three coordinated phases: oral, pharyngeal, and esophageal. Esophageal distension (EDist) has been shown to elicit pharyngeal swallow, but the physiologic characteristics of EDist-induced pharyngeal swallow have not been specifically described. We examined the effect of rapid EDist on oropharyngeal swallow, with and without an oral water stimulus, in spontaneously breathing, sodium pentobarbital anesthetized cats (n = 5). Electromyograms (EMGs) of activity of 8 muscles were used to evaluate swallow: mylohyoid (MyHy), geniohyoid (GeHy), thyrohyoid (ThHy), thyropharyngeus (ThPh), thyroarytenoid (ThAr), cricopharyngeus (upper esophageal sphincter: UES), parasternal (PS), and costal diaphragm (Dia). Swallow was defined as quiescence of the UES with overlapping upper airway activity, and it was analyzed across three stimulus conditions: 1) oropharyngeal water infusion only, 2) rapid esophageal distension (EDist) only, and 3) combined stimuli. Results show a significant effect of stimulus condition on swallow EMG amplitude of the mylohyoid, geniohyoid, thyroarytenoid, diaphragm, and UES muscles. Collectively, we found that, compared to rapid cervical esophageal distension alone, the stimulus condition of rapid distension combined with water infusion is correlated with increased laryngeal adductor and diaphragm swallow-related EMG activity (schluckatmung), and post-swallow UES recruitment. We hypothesize that these effects of upper esophageal distension activate the brainstem swallow network, and function to protect the airway through initiation and/or modulation of a pharyngeal swallow response.

This study utilized a convenience sample (n = 510) to investigate misconceptions of traumatic brain injury (TBI) among first and second year graduate students in physical therapy (PT), occupational therapy (OT), and speech-language pathology (SLP) training programs. Eighty-six-point-seven percent of participants were female, and 87.70% were white. All participants completed a survey comprised of items relating to general information about TBI, coma and unconsciousness, memory loss, recovery, and concussion. Descriptive and summary statistics indicated the persistence of misconceptions regarding coma and unconsciousness, memory loss, recovery, and concussion among graduate students in PT, OT, and SLP training programs. Group comparisons were conducted to identify differences according to discipline (PT, OT, or SLP) and university designation (first or second year graduate student). Kruskall-Wallis vi analyses revealed no statistically significant difference in knowledge across disciplines regarding general information about TBI or recovery, however there was a statistically significant difference regarding knowledge of coma and unconsciousness, memory loss, and concussion. Mann-Whitney analyses revealed no significant difference in knowledge of general information about TBI, coma and unconsciousness, or recovery according to university designation, however there was a statistically significant difference in knowledge of memory loss and concussion. vii

Airway protection is maintained through a constellation of behaviors. The laryngeal adductor reflex (LAR) responds to mechanical or chemical stimulation of the laryngeal orifice with rapid adduction of the vocal folds. While there are abundant serotonin receptors on laryngeal motoneurons, the effects of serotonin agents on the LAR have not been investigated. To this end, a dose response protocol of 8‐OH‐DPAT (5HT1A receptor agonist) was performed on adult cats (n = 2). Animals were anesthetized using an intravenous dose of sodium pentobarbital and then tracheostomized. Electromyogram (EMG) activity of laryngeal muscles was recorded and LARs were induced by infusing water into the larynx during both normocapnia (0% CO2) and hypercapnia (10% CO2) conditions. A series of six cumulative doses (1 – 300 μg/kg) were delivered intra‐venously. 8‐OH‐DPAT is thought to activate the serotonergic raphe neuron autoreceptors at lower doses and the post‐synaptic receptors on target neurons at higher doses. LAR occurred as a response to water stimulus in 50±23% of control trials. LAR occurrence was modulated by 8‐OH‐DPAT in a dose‐dependent manner: LAR frequency at lower doses may have decreased but this was variable, and LAR frequency appeared to be increased at higher doses (LAR occurred in 13±18%, 17±23%, 50±70%, 57±9%, 84±7%, and 60±4% of stimulus trials at 1, 3, 10, 30, 100, and 300 μg/kg doses, respectively). LAR can be used as a strong clinical predictor of swallow impairment; while other airway protective behaviors require activity across multiple cranial nerves, the LAR is regulated by only laryngeal branches of the vagus nerve. Thus, the LAR is a promising biomarker for testing novel therapeutic agents. These results suggest that pharmacological interventions may be capable of facilitating laryngeal function in patients suffering from dysphagia.