Vagal regulation during bottle feeding in low-birthweight neonates: Support for the gustatory-vagal hypothesis

Respiratory sinus arrhythmia (RSA), vagal tone and biobehavioral integration: Beyond parasympathetic function

Linchpin to the entire area of psychophysiological research and discussion of the vagus is the respiratory and cardiovascular phenomenon known as respiratory sinus arrhythmia (RSA; often synonymous with high-frequency heart-rate variability when it is specifically linked to respiratory frequency), i.e. rhythmic fluctuations in heart rate synchronized to inspiration and expiration. This article aims 1) to clarify concepts, terms and measures commonly employed during the last half century in the scientific literature, which relate vagal function to psychological processes and general aspects of health; and 2) to expand upon an earlier theoretical model, emphasizing the importance of RSA well beyond the current focus upon parasympathetic mechanisms. A close examination of RSA and its relations to the vagus may 1) dispel certain commonly held beliefs about associations between psychological functioning, RSA and the parasympathetic nervous system (for which the vagus nerve plays a major role), and 2) offer fresh perspectives about the likely functions and adaptive significance of RSA, as well as RSA's relationship to vagal control. RSA is neither an invariably reliable index of cardiac vagal tone nor of central vagal outflow to the heart. The model here presented posits that RSA represents an evolutionarily entrenched, cardiovascular and respiratory phenomenon that significantly contributes to meeting continuously changing metabolic, energy and behavioral demands.

The vagal paradox: A polyvagal solution

Although there is a consistent literature documenting that vagal cardioinhibitory pathways support homeostatic functions, another less frequently cited literature implicates vagal cardioinhibitory pathways in compromises to survival in humans and other mammals. The latter is usually associated with threat reactions, chronic stress, and potentially lethal clinical conditions such as hypoxia. Solving this 'vagal paradox' in studies conducted in the neonatal intensive care unit served as the motivator for the Polyvagal Theory (PVT). The paradox is resolved when the different functions of vagal cardioinhibitory fibers originating in two anatomically distinguishable brainstem areas are recognized. One pathway originates in a dorsal area known as the dorsal motor nucleus of the vagus and the other in a ventral area of the brainstem known as nucleus ambiguus. Unlike mammals, in all ancestral vertebrates from which mammals evolved, cardioinhibitory vagal fibers primarily originate in the dorsal motor nucleus of the vagus. Thus, in mammals the vagus nerve is 'poly' vagal because it contains two distinct efferent pathways. Developmental and evolutionary biology identify a ventral migration of vagal cardioinhibitory fibers that culminate in an integrated circuit that has been labeled the ventral vagal complex. This complex consists of the interneuronal communication of the ventral vagus with the source nuclei involved in regulating the striated muscles of the head and face via special visceral efferent pathways. This integrated system enables the coordination of vagal regulation of the heart with sucking, swallowing, breathing, and vocalizing and forms the basis of a social engagement system that allows sociality to be a potent neuromodulator resulting in calm states that promote homeostatic function. These biobehavioral features, dependent on the maturation of the ventral vagal complex, can be compromised in preterm infants. Developmental biology informs us that in the immature mammal (e.g., fetus, preterm infant) the ventral vagus is not fully functional and myelinization is not complete; this neuroanatomical profile may potentiate the impact of vagal cardioinhibitory pathways originating in the dorsal motor nucleus of the vagus. This vulnerability is confirmed clinically in the life-threatening reactions of apnea and bradycardia in human preterm newborns, which are hypothetically mediated through chronotropic dorsal vagal pathways. Neuroanatomical research documents that the distribution of cardioinhibitory neurons representing these two distinct vagal source nuclei varies among mammals and changes during early development. By explaining the solution of the 'vagal paradox' in the preterm human, the paper highlights the functional cardioinhibitory functions of the two vagal source nuclei and provides the scientific foundation for the testing of hypotheses generated by PVT.

Polyvagal Theory: A biobehavioral journey to sociality

A polyvagal perspective clarifies the neurobiological and biobehavioral shifts that occurred during evolutionary transition from asocial reptiles to social mammals. This transition enabled mammals, unlike their reptilian ancestors, to derive a biological benefit from social interactions. This innovation enabled social behavior to function as a neuromodulator that could efficiently regulate and optimize autonomic function to support homeostatic processes. This journey is highlighted by the phylogenetic transition during which the autonomic nervous system was repurposed to suppress defensive strategies to support and express sociality. The product of this transition was an autonomic nervous system with capacities to self-calm, to spontaneous socially engage others, and to mitigate threat reactions in ourselves and others through social cues. Thus, social behavior became embedded with specific neurobiological processes that had capabilities to support homeostatic functions leading to optimized health, growth, and restoration. Polyvagal Theory emphasizes sociality as the core process in mitigating threat reactions and supporting mental and physical health.

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Sociality in mammals co-evolved with a repurposed autonomic nervous system.

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Evolution repurposed the mammalian ventral vagal complex in the brainstem to support sociality.

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Social behavior functions as a neuromodulator optimizing behavioral, autonomic, and emotional state regulation.

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Neuroception reflexively detects risk or safety without awareness and shifts autonomic state to support adaptive behaviors.

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Unlike their reptilian ancestors, mammals have a neuroception to safety that fosters sociality by calming autonomic state.

Transcutaneous Auricular Vagus Nerve Stimulation-Paired Rehabilitation for Oromotor Feeding Problems in Newborns: An Open-Label Pilot Study

Neonates born premature or who suffer brain injury at birth often have oral feeding dysfunction and do not meet oral intake requirements needed for discharge. Low oral intake volumes result in extended stays in the hospital (>2 months) and can lead to surgical implant and explant of a gastrostomy tube (G-tube). Prior work suggests pairing vagus nerve stimulation (VNS) with motor activity accelerates functional improvements after stroke, and transcutaneous auricular VNS (taVNS) has emerged as promising noninvasive form of VNS. Pairing taVNS with bottle-feeding rehabilitation may improve oromotor coordination and lead to improved oral intake volumes, ultimately avoiding the need for G-tube placement. We investigated whether taVNS paired with oromotor rehabilitation is tolerable and safe and facilitates motor learning in infants who have failed oral feeding. We enrolled 14 infants [11 premature and 3 hypoxic-ischemic encephalopathy (HIE)] who were slated for G-tube placement in a prospective, open-label study of taVNS-paired rehabilitation to increase feeding volumes. Once-daily taVNS was delivered to the left tragus during bottle feeding for 2 weeks, with optional extension. The primary outcome was attainment of oral feeding volumes and weight gain adequate for discharge without G-tube while also monitoring discomfort and heart rate (HR) as safety outcomes. We observed no adverse events related to stimulation, and stimulation-induced HR reductions were transient and safe and likely confirmed vagal engagement. Eight of 14 participants (57%) achieved adequate feeding volumes for discharge without G-tube (mean treatment length: 16 ± 6 days). We observed significant increases in feeding volume trajectories in responders compared with pre-stimulation (p < 0.05). taVNS-paired feeding rehabilitation appears safe and may improve oral feeding in infants with oromotor dyscoordination, increasing the rate of discharge without G-tube, warranting larger controlled trials.

Heart Rate Variability as a Feeding Intervention Outcome Measure in the Preterm Infant

BACKGROUND

Feeding interventions for preterm infants aim to reduce the physiologic stress of feeding to promote growth. Heart rate variability (HRV) is a potential noninvasive measure of physiologic stress that may be useful for evaluating efficacy of feeding interventions.

PURPOSE

To evaluate whether HRV is a sensitive measure of physiologic stress compared with standard physiologic outcomes in the context of a feeding intervention study.

METHODS

This was a secondary analysis of a within-subjects, cross-over design study comparing usual care feeding with a gentle, coregulated (CoReg) feeding approach in 14 infants born less than 35 weeks' postmenstrual age. HRV indices were calculated from electrocardiogram data and compared with standard physiologic outcomes, including oxygen saturation (Spo2), respiratory rate (RR), apnea, heart rate (HR), and bradycardia. Data were analyzed using linear mixed modeling.

RESULTS

Infants fed using the CoReg approach had fewer apneic events and higher RR, suggesting they were able to breathe more during feeding. No statistically significant differences were found in SpO2, HR, bradycardia, or high frequency power (the most commonly reported measure of HRV). Infants fed using the usual care approach had significantly higher SD12, a measure of HRV indicating randomness in the HR, which is a potential indicator of elevated stress.

IMPLICATIONS FOR PRACTICE

SD12 was more sensitive to stress than SpO2, HR, and bradycardia. The utility of HRV as a measure of feeding outcomes in clinical practice needs further exploration.

IMPLICATIONS FOR RESEARCH

Further exploration of HRV as an intervention outcome measure is needed, particularly evaluating nonlinear indices, such as SD12.

Autonomic nervous system function in infants with transposition of the great arteries

The ability to maintain and respond to challenges to homeostasis is primarily a function of the autonomic nervous system (ANS). In infants with complex congenital heart defects this ability may be impaired. This study described change in ANS function before and after surgical correction in infants with transposition of the great arteries (TGA) and in healthy infants. A total of 15 newborn infants with TGA were matched with 16 healthy infants on age, gender, and feeding type. The ANS function was measured using heart rate variability (HRV). Data were collected preoperatively in the 1st week of life and postoperatively before, during, and after feeding at 2 weeks and 2 months of age. Infants with TGA demonstrated significantly lower high-frequency and low-frequency HRV preoperatively (p < .001) when compared with healthy infants. At 2 weeks, infants with TGA were less likely than healthy infants to demonstrate adaptive changes in high-frequency HRV during feeding (Wald Z = 2.002, p = .045), and at 2 months, 40% of TGA infants exhibited delayed postfeeding recovery. Further research is needed to more thoroughly describe mechanisms of a physiologically adaptive response to feeding and to develop nursing interventions supportive of these high-risk infants.

Evidence-based intervention for young children born premature: preliminary evidence for associated changes in physiological regulation

The current study examined whether changes in maternal behaviors following an evidence-based treatment-Parent-Child Interaction Therapy (PCIT)-was associated with improvements in cardiac vagal regulation in young children born premature. Participants included 28 young children (mean age = 37.79 months) that were born premature and presented with elevated externalizing behavior problems. To assess cardiac vagal regulation, resting measures of respiratory sinus arrhythmia (RSA) and RSA change (withdrawal or suppression) to a clean-up task were derived pre and post-treatment. Results indicated that an increase in behaviors mothers are taught to use during treatment (i.e., do skills-praise, reflection, and behavioral descriptions) was associated with an improvement in children's post-treatment RSA suppression levels. The current study illustrates the important role of caregiver behavior in promoting physiological regulation in children born premature.

Warmth is analgesic in healthy newborns

This study identifies a behavioral and nonpharmacologic means of preventing and reducing newborn pain. Our objective was to determine whether warmth is analgesic in newborn infants undergoing vaccination-a routine painful hospital procedure. We used a prospective randomized controlled trial of 47 healthy full-term newborn infants. Infants were randomized into 1 of 3 conditions prior to vaccination: warmth exposure, pacifier suckling, or sucrose taste. Crying, grimacing, and heart rate differences were analyzed between groups before, during, and after vaccination as outcome measures. Warmer infants cried significantly less than sucrose taste or pacifier suckling after vaccination. Heart rate patterns reflected this analgesia. Core temperature did not differ between study groups. Providing natural warmth to newborn infants during a painful procedure decreases the crying and grimacing on par with the "gold" standard treatments of sucrose or pacifier.

The Early Development of the Autonomic Nervous System Provides a Neural Platform for Social Behavior: A Polyvagal Perspective

We present a biobehavioral model that explains the neurobiological mechanisms through which measures of vagal regulation of the heart (e.g., respiratory sinus arrhythmia) are related to infant self-regulatory and social engagement skills. The model describes the sequential development of the neural structures that provide a newborn infant with the ability to regulate physiological state in response to a dynamically changing postpartum environment. Initially, the newborn uses primitive brainstem-visceral circuits via ingestive behaviors as the primary mechanism to regulate physiological state. However, as cortical regulation of the brainstem improves during the first year of life, reciprocal social behavior displaces feeding as the primary regulator of physiological state. The model emphasizes two sequential phases in neurophysiological development as the fetus transitions to postpartum biological and social challenges: 1) the development of the myelinated vagal system during the last trimester, and 2) the development of cortical regulation of the brainstem areas regulating the vagus during the first year postpartum.

Cardiorespiratory measures before and after feeding challenge in term infants are related to birth weight

AIM

This study tested the hypothesis that, within a few hours of delivery, cardiorespiratory measure taken during feeding provides markers of group differences related to birth weight. A secondary hypothesis was that high-frequency heart period variability would be related to underlying differences in autonomic control associated with birth weight.

METHODS AND SUBJECTS

One hundred four term infants in the lowest, middle, and highest birth weight quintiles were enrolled. Exclusion criteria were evidence of drug abuse, congenital anomalies, Apgar scores less than 7 or admission to the neonatal intensive care unit. Within 96 h of delivery, heart and respiratory rates, blood pressures and heart period variability were measured before, during and after feeding.

RESULTS

Term babies in the lowest quintile of birth weights have lower heart rates prior to feeding but greater increases in heart rate during the early postprandial period. Assessments of high-frequency heart period variability suggest that small term infants have greater parasympathetic tone before feeding and more sustained parasympathetic withdrawal following feeding.

CONCLUSION

Measurements of cardiorespiratory functions before and after feeding are related to birth weight and may provide markers that can help identify the most vulnerable of infants with small size at birth.

Effects of nutritive and non-nutritive sucking on infant heart rate variability during the first 6 months of life

The effects of eating on heart rate variability (HRV) differ between adults and newborns. This may reflect the impact of suckling on the overall psychophysiological and autonomic nervous system maturation. The purpose of the present study was to explore whether the reactions of HRV during feeding change towards the adult pattern during the first 6 months of life. In addition, the effects of non-nutritive and nutritive sucking on heart rate (HR) and HRV were compared. The participants were 23 infants on whom recordings were performed as newborns and at 6, 12 and 24 weeks old. Nutritive sucking caused an increase in HR and a decline in HRV. The results were consistent with previous reports of a decrease in high frequency components of HRV during feeding in newborns, reflecting a decrease in parasympathetic activity. This response was apparent in all four ages studied, and remained similar throughout the 6-month period. However, age as an independent factor seemed to influence both HR and HRV. Pacifier sucking had no significant effects on HRV at any age. The results demonstrate the physical strain that sucking imposes on the baby, with a specific autonomic nervous system response involved. We consider this response an essential part of the overall psychophysiological maturation of infants.

Heart rate variability in premature infants during feeding

Early mother-infant interaction, a potentially major contributor to the development of a premature infant's behavioral and physiologic regulation, has received very little research attention. This study examined the development of physiologic regulation in relation to maternal-infant feeding interaction for 43 premature infants, from the time caregiving responsibility was transferred to the mother through each infant's 4th postterm month. Infants and mothers were seen in a special care nursery just before discharge and in home at 1 and 4 months postterm age. General linear mixed models were used to examine the changes in infant heart rate variability (HRV) and Positive Affective Involvement and Sensitivity/Responsiveness scores over time and infant HRV over feeding conditions (prefeeding, feeding, and postfeeding). Significant differences were found for high-frequency and low-frequency HRV over time (p < .001 and p = .014, respectively). However, maternal feeding behavior did not show a significant effect of time (p = .24). The feeding condition effect on high-frequency HRV was significant (p < .001), with HRV lower during feeding compared to both prefeeding and postfeeding. Maternal feeding behavior was not associated with infant HRV. Discovering the ways in which maternal feeding behavior contributes to infant physiologic regulation may require study of the relationship of HRV to infant feeding behavior.

Temperament and vagal tone in boys with fragile X syndrome

Physiological hyperarousal, an elevated state of physiological arousal and poor modulation, has been postulated to be a significant source of behavior problems in children with fragile X syndrome (FXS). Temperament has been associated with behavior problems and may also reflect biological reactivity. Young boys with FXS display poorly modulated and low levels of vagal tone (Roberts, Dev Psychobiol 2001;39:107-123) and high activity, poor attention, low adaptability, poor persistence, and low intensity when compared with a reference sample of typically developing (Hatton, Dev Med Child Neurol 1991;41:625-632). In this study, we integrated physiological indices of vagal tone with temperament ratings and compared a sample of 29 young boys with FXS to 31 typically developing boys matched on chronological age and ethnicity. Boys with FXS were more active, less adaptable, and less persistent than the comparison group. Boys with FXS also showed lower baseline levels and less suppression of vagal tone in response to changing task demands. A relationship between baseline vagal tone and persistence was shown across both groups. However, group differences in temperament dimensions did not appear to be mediated or moderated by vagal tone.

Does sympathetic activity contribute to growth of preterm infants?

BACKGROUND

Emerging evidence on faster growth in preterm infants with higher heart rate as opposed to the classical approach calls for further research.

AIMS

to test whether (1) high or low heart rate and (2) heart rate during the first days of life predict greater weight gain in preterm infants.

METHODS

A retrospective study analyzing two daily measures of heart rate obtained during restful sleep, total daily calorie intake and daily weight gain measured always in the morning before meal were collected from the medical files.

RESULTS

Analysis of 90 healthy preterm infants born at 32-36 weeks of gestation revealed that increased mean heart rate during hospitalization predicted greater weight gain even when controlling for calorie intake, birth weight, gestational age, appropriateness of birth weight for gestational age, and length of hospitalization. Mean heart rate during the first three days of life yielded the same pattern of results. Post-hoc analysis of variance between infants with mean daily heart rate </=139 bpm vs. >/=140 bpm showed that infants with higher heart rate achieved a significantly higher weight gain.

CONCLUSIONS

It is suggested that, contrary to adults, in neonates an anabolic activity is represented by increased sympathetic functioning within the normal range. The implications of a slower growth rate for additional developmental care and individual considerations of appropriate stimulation in preterm infants are discussed.

Physiological regulation and infantile anorexia: a pilot study

OBJECTIVE

To examine whether infantile anorexia is associated with physiological dysregulation.

METHOD

This study included eight toddlers with infantile anorexia and eight healthy eaters matched for age, race, socioeconomic status, and gender. Physiological measures of heart period and respiratory sinus arrhythmia were assessed across three different situations: mother-toddler interaction, toddler-stranger interaction, and toddler left alone with a toy while mother and stranger talked to each other at the other side of the room.

RESULTS

Across all three situations, toddlers with infantile anorexia showed significantly shorter heart periods (i.e., faster heart rates) than controls (p <.05). In addition, as social demand decreased from episode 2 to episode 3, control toddlers exhibited an increase in respiratory sinus arrhythmia, whereas toddlers with infantile anorexia showed a decrease in respiratory sinus arrhythmia (p <.001).

CONCLUSIONS

Toddlers with infantile anorexia showed consistently shorter heart periods and were less adaptive in their physiological regulation than controls. Such physiological dysregulation may constitute a tendency for less optimal internal homeostatic regulation of feeding in toddlers with infantile anorexia.

Effects of sponge bathing on vagal tone and behavioural responses in premature infants

The purpose of this study was to evaluate the effects of sponge bathing on physiological (vagal tone, heart rate, heart period, oxygen saturation) and behavioural responses in newly born premature infants in the intensive care unit of a university hospital in South Korea. A convenience sample was taken of 40 infants who were between 27 and 36 weeks gestational age at birth and free of congenital defects. The infants' physiological parameters were recorded 10 min before, during and after bathing. To determine behavioural status, tools were modified from the instruments used in a previous study by Scafidi et al. (1990). Analysis of the results showed that the premature infants reacted to sponge bathing with decreases in vagal tone and heart period and increases in heart rate. Oxygen saturation did not demonstrate any remarkable alteration during bathing. Also, there were no significant differences in behavioural signs, motor activity and behavioural distress. Results of this study indicated that nurses in a neonatal intensive care unit should decide according to a premature infant's physiological state whether or not to give a sponge bath.

Heart rate variability of preterm neonates quantified by energy entropy

Identifying variables predictive of neurobehavioural sequelae is a key objective in the study of high-risk neonates. Examination of heart rate variability (HRV) characteristics may be a finer discriminator of the neonate's response to physiologic stressors than the mean heart rate. The energy entropy of the heart beat tachogram, computed in four different domains, was used to quantify the HRV in 13 preterm neonates. The entropies of energies were computed from 1024 interbeat time intervals obtained once per week from 26 to 35 weeks postconceptional age (PCA). The energy entropy computed in three of the domains, like the standard deviation of intervals, distinguished between the 10 neonates that were measured at 35 weeks PCA with 100% specificity and 67% sensitivity, but did not distinguish between healthy and unhealthy neonates at earlier ages. The findings suggest that energy entropy may be a discerning measure of physiologic stress in the preterm infant, although future research is needed to refine the test and determine statistical significance.