Swallowing is an essential motor act that coordinates the movement of food or saliva from the mouth through the pharynx and into the esophagus while protecting the upper airways from aspiration of those materials. Disordered swallowing, or dysphagia, results when bolus movement from the oropharyngeal phase into the esophageal phase is uncoordinated. Dysphagia directly causes or increases the risk of aspiration during swallowing in many clinical pathologies including Parkinson’s disease, Alzheimer’s disease, cerebrovascular incidents (stroke) in addition to being prevalent among the elderly population. The coordination between breathing and swallowing is mediated through the interaction of the swallow and respiratory Central Pattern Generators (CPGs) located in the brainstem. In the pharyngeal phase of swallow respiratory airflow is temporarily interrupted, and then reset, when the bolus moves through the pharyngeal space. The lungs retain enough air during the swallow apnea to protect the lower airways from accidental aspiration of residual bolus material, modulate the latency to initiate the swallow, while providing sensory feedback for processing within the brainstem network. The timing of the pharyngeal phase of swallow with respiration occurs across a continuum of lung volumes. Following swallow, the latency to initiate inspiration of the subsequent respiratory cycle increases. The swallow-mediated increase in cycle duration on respiration may depend upon the central processing of pulmonary afferents that may also affect reconfiguration of the respiratory CPG to express the swallow CPG. The peripheral and central mechanisms of swallow-breathing coordination remain poorly understood. Here, the relationship between central inspiratory output and the resultant mechanical inflation of the lungs was manipulated and dissociated to test the hypothesis that a centrally- and peripherally-mediated “swallow gate” coordinates swallow initiation with central respiratory activity and vagally-mediated pulmonary feedback. We obtained data from decerebrate adult cats of either sex that fully recovered from isoflurane anesthesia prior to the decerebration procedure. Fictive swallows were elicited using electrical stimulation of the superior laryngeal nerves (SLN) or injection of water (Water) into the pharyngeal cavity. Both stimuli were presented at random during the central respiratory cycle and/or the mechanical ventilation cycle. Mechanical ventilation was either triggered in-phase with phrenic discharge activity or it was set independent of phrenic discharge activity. These two modes of mechanical ventilation facilitated our ability to analyze the collective and individual effect of lower airway feedback on swallow-breathing coordination. The efferent discharge activities were recorded from the right hypoglossal (XII), left phrenic (Phr), left lumbar iliohypogastric (Lum) and right vagus (X) or the right recurrent laryngeal (RLN) nerves using silver bipolar hooked electrodes. All nerve activity was full-wave rectified, amplified, RC integrated (τ=200-500 ms) and low-pass filtered prior to analysis for effects on swallow-breathing coordination across stimulation-ventilation conditions. We observed post-inspiratory type (Post-I) and expiratory type (Exp) swallows that produced discrete effects on central respiratory rhythm across all conditions. The Post-I type swallows disturbed the duration and amplitude of preceding central inspiratory activity, without affecting the duration of central expiratory activity. The Exp type swallows prolonged central expiration but produced no effect on central inspiratory activity. We observed that lung inflation negatively modulated swallow initiation during fixed mechanical ventilation in the absence of central respiratory output, i.e., during central apnea. Most swallow elicited during central apnea initiated during periods of low lower airway afferent feedback. Collectively, these findings extend the role for lower airway feedback beyond its role as a provider of lung afferent surveillance and identifies lower airway feedback as a modulator of swallow-breathing coordination.

Résumé : L’ictère néonatal, lié à l’hyperbilirubinémie, touche 90% des nouveau-nés prématurés. L’hyperbilirubinémie provoque des troubles neurologiques aigus (somnolence, dystonie, difficultés alimentaires, atteinte de l’audition) et a été reliée à des anomalies du contrôle respiratoire. Ces résultats suggèrent une neurotoxicité de la bilirubine sur le tronc cérébral, qui pourrait aussi affecter les centres déglutiteurs. Le but de cette étude est de tester notre hypothèse selon laquelle l’hyperbilirubinémie altère la déglutition nutritive et la coordination déglutition-respiration chez l’agneau prématuré. 11 agneaux prématurés (nés 14 jours avant terme) ont été randomisés dans un groupe contrôle (n = 6) et un groupe bilirubine (n = 5). À 5 jours de vie, une hyperbilirubinémie modérée (150-250 μmol/L) était induite pendant 17h chez les agneaux du groupe bilirubine. La déglutition était étudiée par l’enregistrement de la pression pharyngée, et la respiration était évaluée par pléthysmographie d’inductance respiratoire et oxymétrie de pouls. L’effet de l’hyperbilirubinémie sur la déglutition nutritive (DN) était évalué pendant une alimentation au biberon standardisée, avec du lait de brebis. Un second enregistrement était réalisé 48h plus tard, après normalisation de la bilirubine. L’alimentation était moins performante (mL/min) dans le groupe bilirubine (p = 0,002) avec des DN moins fréquentes (p = 0,003) et de plus petit volume (p = 0,01). Ces différences n’étaient pas retrouvées à distance de l’hyperbilirubinémie. La coordination déglutition-respiration était également altérée chez les agneaux du groupe bilirubine, indiquée par une tendance à la diminution de la durée de l’inhibition respiratoire pendant les bouffées de DN (p < 0,1), ceci pendant et après l’hyperbilirubinémie. Simultanément, pendant l’alimentation, les agneaux du groupe bilirubine passaient plus de temps en désaturations sévère (< 80%) que ceux du groupe contrôle. Enfin, une diminution de la fréquence respiratoire associée à une augmentation des apnées étaient observées dans les minutes suivant l’alimentation dans le groupe bilirubine (p < 0,05). La déglutition et la coordination déglutition-respiration sont altérées par l’hyperbilirubinémie modérée, chez l’agneau prématuré. La diminution globale d’efficacité de l’alimentation au biberon est associée à une poursuite de la respiration durant les bouffées de DN, ce qui pourrait favoriser les aspirations pulmonaires de lait. / Abstract : Rationale: Jaundice, secondary to hyperbilirubinemia (HB), develops in 90% of preterm newborns. HB induces acute neurological disorders (somnolence, abnormal tone, feeding difficulties, auditory dysfunction) and has been linked to alterations in respiratory control. These findings suggest neurotoxicity in the brainstem that could also affect swallowing centers. This study aims to test our hypothesis that HB impairs nutritive swallowing and swallowing‐breathing coordination in the preterm lamb. Methods: Two groups of preterm lambs (born 14 days prior to term), control (C, n = 6) and hyperbilirubinemia (HB, n = 5) were studied. At day 5 of life, moderate HB (150‐250 μmol/L) was induced during 17 h in HB lambs. Swallowing was assessed via recording of pharyngeal pressure, and respiration was studied by respiratory inductance plethysmography and pulsed oximetry. HB effect on nutritive swallowing was assessed during standardized bottle‐feeding with ewe milk. A second recording was performed 48 hours later, after recovery from hyperbilirubinemia. Results: Swallows were less frequent (p = 0.003) and of smaller volume (p = 0.01) in HB lambs, with a consequent decrease in minute swallowing in HB lambs (p = 0,004). These differences were not found after bilirubinemia was returned to normal. Swallowing‐breathing coordination was also impaired in HB lambs, as indicated by a tendency towards a decrease in % time with respiratory inhibition during bursts of swallows, during and after hyperbilirubinemia. Simultaneously, severe desaturations (< 80%) were longer in HB lambs than in C lambs. Finally, a decreased respiratory rate was observed immediately after feeding (p < 0,05), along with increased apneas duration. Conclusions: Both swallowing and swallowing‐breathing coordination are altered by acute, moderate HB in preterm lambs. The overall decreased efficiency at bottle‐feeding is accompanied by continuation of breathing during bursts of swallows, which may promote lung aspiration.

Introduction and rationale: Clinical experience with infants presenting with feeding difficulties and increasing referrals of infants with colic led to this study. There is uncertainty whether the speechlanguage therapist should play a role in the management of this condition. Despite extensive clinical research into the multiple factors related to the condition, the etiology of infantile colic has not yet been established. Suck- swallow-breathing coordination (SSBC), which is key to successful feeding, has not yet been investigated as a factor in this condition. Goals: The goal of the study was to give a comprehensive description of the symptoms and the SSBC of a group of young infants with colic. Sub-goal 1 was to compile a list of symptoms based on a description by parents of infants with infantile colic, which could be used to compare symptoms of a group of infants with the condition to a group without the condition. Sub-goal 2 was to describe SSBC, in a group of infants with the condition, by conducting a clinical assessment. Sub-goal 3 was to compare SSBC in a group of infants with colic to a group without the condition of the same age. Method: A descriptive survey design and interview guide was used in Phase 1. The parents of 60 infants with colic participated in this study. A correlation research design (Phase 2) and the List of symptoms for Infantile Colic (compiled in Phase 1) as well as the Assessment Protocol for SSBC (compiled in Phase 2) were used. A new research group of 50 participants with infantile colic and a control group of 28 participants with the condition, whose ages correlated with those of the research group, was selected. An interview was conducted with the parents of all participants. SSBC was clinically assessed in all the participants. Results: Parental description of infantile colic resulted in a comprehensive list of 27 symptoms. Audible swallowing of air and a feeding duration of more than 20 minutes were described more by parents than found in the literature. Statistically significant differences were found when the postural control and SSBC of the research group were compared with the control group. The difficulties with SSBC differed across the age categories of the participants. Conclusion: The study indicated that infantile colic is related to a disturbance in postural control and components of SSBC, and infants with the condition have subtle feeding difficulties. The speech-language therapist therefore has a role to play in the clinical assessment of infantile colic and the development of treatment strategies. / Dissertation (MA)--University of Pretoria, 2014. / lk2014 / Speech-Language Pathology and Audiology / MA / Unrestricted