Swallow Safety in Infant Pigs With and Without Recurrent Laryngeal Nerve Lesion

Exploring the interaction of viscosity and nipple design on feeding performance in an infant pig model

Infant feeding behaviors are modulated via sensorimotor feedback, such that sensory perturbations can significantly impact performance. Properties of the nipple and milk (e.g., nipple hole size and viscosity) are critical sources of sensory information. However, the direct effects of varying milk and nipple properties on infant motor output and the subsequent changes in feeding performance are poorly understood. In this study, we use an infant pig model to explore the interaction between nipple hole size and milk viscosity. Using high-speed videofluoroscopy and electromyography, we measured key performance metrics including sucks per swallow and suck duration, then synchronized these data with the onset and offset of activity of jaw opening and closing muscles. The combination of a small nipple hole and thick milk resulted in negative effects on both suck and swallow performance, with reduced feeding efficiency compared to the other treatments. It also appears that this combination of viscosity and hole size disrupts the coordination between correlates of tongue and jaw movements. We did not see a difference in feeding efficiency between viscosities when infants fed on the large-hole nipple, which may be the result of non-Newtonian fluid mechanics. Our results emphasize the importance of considering both fluid and nipple properties when considering alterations to an infant's feeding system.

The Pathway from Anatomy and Physiology to Diagnosis: A Developmental Perspective on Swallowing and Dysphagia

Dysphagia results from diverse and distinct etiologies. The pathway from anatomy and physiology to clinical diagnosis is complex and hierarchical. Our approach in this paper is to show the linkages from the underlying anatomy and physiology to the clinical presentation. In particular, the terms performance, function, behavior, and physiology are often used interchangeably, which we argue is an obstacle to clear discussion of mechanism of pathophysiology. We use examples from pediatric populations to highlight the importance of understanding anatomy and physiology to inform clinical practice. We first discuss the importance of understanding anatomy in the context of physiology and performance. We then use preterm infants and swallow-breathe coordination as examples to explicate the hierarchical nature of physiology and its impact on performance. We also highlight where the holes in our knowledge lie, with the ultimate endpoint of providing a framework that could enhance our ability to design interventions to help patients. Clarifying these terms, and the roles they play in the biology of dysphagia will help both the researchers studying the problems as well as the clinicians applying the results of those studies.

Pharyngeal biorhythms during oral milk challenge in high-risk infants: Do they predict chronic tube feeding?

BACKGROUND

Eating difficulties are common in high-risk neonatal intensive care unit (NICU) infants; mechanisms remain unclear. Crib-side pharyngo-esophageal motility testing is utilized to assess contiguous swallowing physiology, and cross-system interplay with cardio-respiratory rhythms. Aims were to: (1) identify whether distinct pharyngeal rhythms exist during oral milk challenge (OMC), and (2) develop a chronic tube feeding risk prediction model in high-risk infants.

METHODS

Symptomatic NICU infants (N = 56, 29.7 ± 3.7 weeks birth gestation) underwent pharyngo-esophageal manometry with OMC at 40.9 ± 2.5 weeks postmenstrual age (PMA). Exploratory cluster data analysis (partitioning around k-medoids) was performed to identify patient groups using pharyngeal contractile rhythm data (solitary swallows and swallows within bursts). Subsequently, (a) pharyngeal-esophageal, cardio-respiratory, and eating method characteristics were compared among patient groups using linear mixed models, and (b) chronic tube feeding prediction model was created using linear regression.

RESULTS

Three distinct patient groups were identified with validity score of 0.6, and termed sparse (high frequency of solitary swallows), intermediate, or robust (high swallow rate within bursts). Robust group infants had: lesser pharyngeal and esophageal variability, greater deglutition apnea, pharyngeal activity, and esophageal activity (all p < 0.05), but less frequent heart rate decreases (p < 0.05) with improved clinical outcomes (milk transfer rate, p < 0.001, and independent oral feeding at discharge, p < 0.03). Chronic tube feeding risk = -11.37 + (0.22 × PMA) + (-0.73 × bronchopulmonary dysplasia) + (1.46 × intermediate group) + (2.57 × sparse group).

CONCLUSIONS

Robust pharyngeal rhythm may be an ideal neurosensorimotor biomarker of independent oral feeding. Differential maturation of cranial nerve-mediated excitatory and inhibitory components involving foregut, airway, and cardiac rhythms distinguishes the physiologic and pathophysiologic basis of swallowing and cardio-respiratory adaptation.

Advances in Swallowing Neurophysiology across Pediatric Development: Current Evidence and Insights

Purpose of Review

This review article analyzes current evidence on the neurophysiology of swallowing during development and offers expert opinion on clinical implications and future research directions.

Recent Findings

In the past five years, basic and clinical research has offered advances in our understanding of pediatric swallowing neurophysiology. Animal models have elucidated the role of brainstem circuits and the peripheral and central nervous system in neonatal swallowing. Recent human studies have further showcased that fetal and infant swallowing require cerebral inputs in order to develop functionally. Finally, neurophysiological and neuroimaging studies are starting to better define these cerebral inputs, as well as neuroplastic adaptations that may be needed for optimal feeding development.

Summary

The neural development of swallowing is a complex and dynamic process. Continued research is needed to better understand influences on swallowing neural development, which can be essential for improving prevention, diagnosis, and interventions for pediatric dysphagia.

Nasal respiratory support and tachypnea and oral feeding in full-term newborn lambs

Newborn infants with respiratory difficulties frequently require nasal respiratory support such as nasal continuous positive airway pressure (nCPAP) or high-flow nasal cannulae (HFNC). Oral feeding of these infants under nasal respiratory support remains controversial out of fear of aspiration and cardiorespiratory events. The main objective of this study was to evaluate the safety of oral feeding under different types of nasal respiratory support in newborn lambs without or with tachypnea. Eight lambs aged 4-5 days were instrumented to record sucking, swallowing, respiration, ECG, oxygen saturation, and arterial blood gases. Each lamb was given two bottles of 30 mL of milk with a pause of 30 s under videofluoroscopy in four conditions [no respiratory support, nCPAP 6 cmH₂O, HFNC 7 L/min, HFNC_CPAP (= HFNC 7 L/min + CPAP 6 cmH₂O)] administered in random order. The study was conducted in random order over 2 days, with or without standardized tachypnea induced by thoracic compression with a blood pressure cuff. Generalized linear mixed models were used to compare the four nasal respiratory supports in terms of safety (cardiorespiratory events and aspiration), sucking-swallowing-breathing coordination, and efficacy of oral feeding. Results reveal that no nasal respiratory support impaired the safety of oral feeding. Most of the few laryngeal penetrations we observed occurred with HFNC_CPAP. Nasal CPAP modified sucking-swallowing-breathing coordination, whereas the efficiency of oral feeding decreased under HFNC_CPAP. Results were similar with or without tachypnea. In conclusion, oral feeding under nasal respiratory support is generally safe in a term lamb, even with tachypnea.NEW & NOTEWORTHY The practice of orally feeding newborns suffering from respiratory problems while on nCPAP or HFNC remains controversial for fear of triggering cardiorespiratory events or aspiration pneumonia, or aggravating chronic lung disease. The present results show that bottle-feeding is generally safe in full-term lambs under nasal respiratory support, both without and with tachypnea.

Increased viscosity of milk during infant feeding improves swallow safety through modifying sucking in an animal model

Infants experiencing frequent aspiration, the entry of milk into the airway, are often prescribed thickened fluids to improve swallow safety. However, research on the outcomes of thickened milk on infant feeding have been limited to documenting rates of aspiration and the rheologic properties of milk following thickening. As a result, we have little insight into the physiologic and behavioral mechanisms driving differences in performance during feeding on high viscosity milk. Understanding the physiologic and behavioral mechanisms driving variation in performance at different viscosities is especially critical, because the structures involved in feeding respond differently to sensory stimulation. We used infant pigs, a validated animal model for infant feeding, to test how the tongue, soft palate, and hyoid respond to changes in viscosity during sucking and swallowing, in addition to measuring swallow safety and bolus size. We found that the tongue exhibited substantive changes in its movements associated with thickened fluids during sucking and swallowing, but that pharyngeal transit time as well as hyoid and soft palate movements during swallowing were unaffected. This work demonstrates the integrated nature of infant feeding and that behaviors associated with sucking are more sensitive to sensorimotor feedback associated with changes in milk viscosity than those associated with the pharyngeal swallow, likely due to its reflexive nature.

The contractile patterns, anatomy and physiology of the hyoid musculature change longitudinally through infancy

All mammalian infants suckle, a fundamentally different process than drinking in adults. Infant mammal oropharyngeal anatomy is also anteroposteriorly compressed and becomes more elongate postnatally. While suckling and drinking require different patterns of muscle use and kinematics, little insight exists into how the neuromotor and anatomical systems change through the time that infants suckle. We measured the orientation, activity and contractile patterns of five muscles active during infant feeding from early infancy until weaning using a pig model. Muscles not aligned with the long axis of the body became less mediolaterally orientated with age. However, the timing of activation and the contractile patterns of those muscles exhibited little change, although variation was larger in younger infants than older infants. At both ages, there were differences in contractile patterns within muscles active during both sucking and swallowing, as well as variation among muscles during swallowing. The changes in anatomy, coupled with less variation closer to weaning and little change in muscle firing and shortening patterns suggest that the neuromotor system may be optimized to transition to solid foods. The lesser consequences of aspiration during feeding on an all-liquid diet may not necessitate the evolution of variation in neuromotor function through infancy.

Pathophysiology of aspiration in a unilateral SLN lesion model using quantitative analysis of VFSS

OBJECTIVE

The purpose of this study was to elucidate the pathophysiology of aspiration in previously studied female infant piglets after a unilateral superior laryngeal nerve (uSLN) lesion.

METHODS

Videofluoroscopic swallow studies (VFSS) were acquired from 15 female piglets ages 2-3 weeks (9 with uSLN lesion and 6 controls). VFSS were analyzed at 30 frames/second sampling rate. Quantitative measures were conducted and compared between groups using published methodologies for VFSS assessment in adult and infant humans. Measures included the: 1) number of lingual-palatal contacts (LPC) (i.e. pre-swallow), 2) total pharyngeal transit time (TPT), 3) offset of swallow (offP), as well as onset of: 4) pharyngeal stage (onP), 5) pharyngoesophageal segment opening (oPES), 6) maximum PES opening (maxPES), 7) airway closure onset (oAC), and 8) maximum airway closure (maxAC). Measures 5-7 were determined relative to onP. Bolus residue was rated by severity (0 (none) to 3 (severe)). A gamma regression was used to compare continuous measures between lesioned and control groups.

RESULTS

The number of LPC (p = .006), TPT (p = .023) and timing of maxAC (p = .041) were significantly greater in the uSLN lesion than the control group.

CONCLUSIONS

Outcomes of this study replicated prior published findings and elucidated that piglets with right uSLN lesions exhibited delayed maxAC. Noteworthy was the use of clinically relevant quantitative videofluoroscopic measures in piglets for comparison to future studies in human pediatric populations.

Muscle activity and kinematics show different responses to recurrent laryngeal nerve lesion in mammal swallowing

Understanding the interactions between neural and musculoskeletal systems is key to identifying mechanisms of functional failure. Mammalian swallowing is a complex, poorly understood motor process. Lesion of the recurrent laryngeal nerve, a sensory and motor nerve of the upper airway, results in airway protection failure (liquid entry into the airway) during swallowing through an unknown mechanism. We examined how muscle and kinematic changes after recurrent laryngeal nerve lesion relate to airway protection in eight infant pigs. We tested two hypotheses: 1) kinematics and muscle function will both change in response to lesion in swallows with and without airway protection failure, and 2) differences in both kinematics and muscle function will predict whether airway protection failure occurs in lesion and intact pigs. We recorded swallowing with high-speed videofluoroscopy and simultaneous electromyography of oropharyngeal muscles pre- and postrecurrent laryngeal nerve lesion. Lesion changed the relationship between airway protection and timing of tongue and hyoid movements. Changes in onset and duration of hyolaryngeal muscles postlesion were less associated with airway protection outcomes. The tongue and hyoid kinematics all predicted airway protection outcomes differently pre- and postlesion. Onset and duration of activity in only one infrahyoid and one suprahyoid muscle showed a change in predictive relationship pre- and postlesion. Kinematics of the tongue and hyoid more directly reflect changes in airway protections pre- and postlesion than muscle activation patterns. Identifying mechanisms of airway protection failure requires specific functional hypotheses that link neural motor outputs to muscle activation to specific movements.NEW & NOTEWORTHY Kinematic and muscle activity patterns of oropharyngeal structures used in swallowing show different patterns of response to lesion of the recurrent laryngeal nerve. Understanding how muscles act on structures to produce behavior is necessary to understand neural control.