Altered sucking dynamics in a breastfed infant with down syndrome: a case report
A term neonate is born with the ability to suck; this neuronal network is already formed and functional by 28 weeks gestational age and continues to evolve into adulthood. Because of the necessity of acquiring nutrition, the complexity of the neuronal network needed to suck, and neuroplasticity in infancy, the skill of sucking has the unique ability to give insight into areas of the brain that may be damaged either during or before birth.
Interpretation of the behaviors during sucking shows promise in guiding therapies and how to potentially repair the damage early in life, when neuroplasticity is high. Sucking requires coordinated suck-swallow-breathe actions and is classified into two basic types, nutritive and non-nutritive.
Each type of suck has particular characteristics that can be measured and used to learn about the infant's neuronal circuitry. Basic sucking and swallowing are present in embryos and further develop to incorporate breathing ex utero.
Due to the rhythmic nature of the suck-swallow-breathe process, these motor functions are controlled by central pattern generators.
Abnormal nutritive sucking as an indicator of neonatal brain injury
The coordination of swallowing, breathing, and sucking is an enormously complex sensorimotor process. Because of this complexity, brain injury before birth can have an effect on these sucking patterns.
Clinical assessments allow evaluators to score the oral-motor pattern, however, they remain ultimately subjective. Thus, clinicians are in need of objective measures to identify the specific area of deficit in the sucking pattern of each infant to tailor therapies to their specific needs. These therapies are performed to train the infant to suck appropriately using these subjective assessments along with the experience of the therapist usually a speech therapistbut newer, more objective measures are coming along.
Recent studies have correlated pathological sucking patterns with neuroimaging data to get a map of the affected brain regions to better inform therapies. The purpose of this review is to provide a broad scope synopsis of the research field of infant nutritive and non-nutritive feeding, their underlying neurophysiology, and relationship of abnormal activity with brain injury in preterm and term infants. As early as the 's researchers began examining the sucking behavior of infants.
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Sucking patterns of infants were differentiated based on the frequency and intensity of the sucking, which was found to correlate with whether or not fluid breastmilk or formula is present. These patterns became known as nutritive and non-nutritive sucking 13 — 5.
Based on this deconstruction, research in the 's focused on evaluating how an infant would modify these two skills to obtain nutrients using lab-made apparatus' that would control when nutrient was released based on the amount of suction or expression 6. These experiments demonstrated the incredible learning ability of an infant's brain to adapt to changing conditions in line with more recent ideas of brain neuroplasticity during the early years of life 9 — Nurses also began noticing the relationship between feeding as an infant and speaking ability later in life Concurrently, other groups began looking into the relationship between brain injury and sucking; they observed differences between non-nutritive sucking of normal, term infants, and those who experienced perinatal stress with or without neurological s 3.
The 's brought the confirmation that the anatomy and physiology of the infant, feeding on a pure liquid diet, is profoundly different than the adult This paved the way for the field of dysphagia in infants to be studied and treated differently than in adults. The following decade, dysphagia in infants and children became a focus of researchers and clinicians alike as medical care improved outcomes for preterm infants.
Also, neuroscientists and speech therapists began to investigate the correlation between sucking pattern in infancy and fine motor skills around 6 months, speech-language delays at 18 months, and developmental delay at 24 months In the 's the field broadened ificantly to include molecular, developmental, and genetic biology 15 The new millennia began with trials that confirmed developmental enhancement interventions and physical therapy performed on infants with brain injury were not working well 111718even though success had been seen with older children 19 — Another compounding factor was identification of infants with brain injury by MRI, which is unreliable as a sole predictor of clinical impairment or prognosis 22 — Clearly, interventions need to be tailored to the term and preterm infants with brain injury and the injury itself needs other modalities for identification During this time, the idea of neuroplasticity became the topic of numerous studies in cerebral palsy research which clearly demonstrates re-organization of the brain as a result of a prenatal or perinatal brain insult 26 — Additionally, brain injury repair is being elucidated in both human and animal studies 32 — These advancements have led to the current research field of identifying brain injury through evaluation of sucking as well as habilitation of sucking in infants to potentially repair brain injury.
Early in the investigations of infant's sucking it became clear that there are two distinct types, namely, nutritive and non-nutritive sucking.
Vacuum characteristics of the sucking cycle and relationships with milk removal from the breast in term infants
As an infant gains more experience, these sucking patterns mature in strength and efficiency. The variation within an individual is small, however there could be fairly ificant interindividual variations. NNS occurs at up to two sucks per second frequency in short, fast bursts 1314 The bursts can last anywhere from 2 to 12 s burst duration with a rest period pause between bursts of 3—13 s [ 338 ; Figure 1 ]. As the infant ages, the frequency and burst duration may increase to a NNS pattern considered more mature, closer to two sucks per second with a duration between 2—8 s and less inter-burst duration and inter-rest period variations, hence a smoother, more regular NNS 38 When breast-feeding, a newborn will begin with NNS until the milk ejection reflex occurs, then will switch to nutritive sucking If NNS is not encouraged, by breast-feeding or pacifier use, for example, it will disappear by 4—5 months of age, however, fascinatingly it can be found in some adults with degenerative cerebral diseases Figure 1.
Waveform pattern of NNS. Graph represents the extent of the movement of the lever inside the bottle nipple, measuring the expression component of sucking with 1.
NNS occurs at up to two sucks per second in short, fast bursts lasting anywhere from 2 to 12 s with a pause between bursts of 3—13 s. There are several factors which may affect the different features of a NNS. For example, pacifier characteristics may impact the way an infant will suck on it.
The thickness of the silicone of a pacifier, therefore, its stiffness, will affect the NNS pattern of infants.
Stiffer pacifiers will elicit fewer sucks per burst, up to half as many, and also the strength, or amplitude, of each suck is decreased. The shape of the pacifier or any texture will also profoundly affect the NNS pattern 41 — Nutritive sucking NS occurs at a slower pace, about one suck per second 13and as the feed continues a burst—pause pattern emerges.
The first minutes of NS are steady with none or very few short pauses, as the feed continues, bursts appear with a pause between bursts that gets longer toward the end of the feeding [ 1444 ; Figure 2 ]. The rooting reflex, which is the movement of an infant's head toward a touch on their cheek accompanied by mouth gapping, is present at birth for neurologically normal infants born at 32 weeks gestational age GA and older, and sometimes even very preterm infants will root before 32 weeks PMA This reflex assists the infant in locating a food source and will disappear around 6 months old 1.
Figure 2. Waveform pattern of NS. A mature NS pattern demonstrates regular, smooth movement about one suck per second.
Nutritive sucking is a highly coordinated activity between sucking, swallowing, and respiration 3746 Sucking and swallowing skills develop in utero as the fetus regulates amniotic fluid levels 14164849 and must be further developed ex utero to incorporate breathing. Expression develops first and is the compression or stripping of the tongue against the hard palate to eject liquid Figure 3.
Suction is intraoral negative pressure that draws liquid into the mouth.
Suction also requires lowering the jaw to increase the volume of the mouth, closure of the nasal passage by the soft palate, and a tight seal by the lips to prevent air inflow. Figure 3. Skills required for sucking in infants.
A Infant at rest with the nipple inside the mouth. B Suction applied to the nipple to draw further into the mouth to form a teat and the tip of the tongue beginning to compress it. C Expression of the teat by the tongue movement against the hard palate. Figure 4.
Stages of NS. Early stages 1 — 3 are seen in preterm infants, while more mature stages 4 and 5 are seen in term infants as well as preterms after enough experience and maturation. Reprinted with permission from Lau This pause in breathing to swallow is termed swallowing apnea, or deglutition apnea. Infants, however, vary considerably in their swallow-respiration patterns for inter-infant comparisons as well as inter- and intra-feeding comparisons. As discussed in the next section, the anatomy and physiology of the infant is profoundly different than in the adult and allows feeding to be done simultaneously with breathing, which explains how an infant can have such variable patterns and not aspirate during feeding.
The evolution from suckle to mastication as the infant matures into childhood develops and changes in anatomy, physiology, and neural networks 151648 Unlike adults, an infant's epiglottis moves upward to the soft palate, which allows the trachea to remain open to the nasopharynx to permit constant breathing during sucking. This has been described as the liquid being made to go around each side of the epiglottis and flow into the pharynx and esophagus while still allowing laminar flow of air through the nasopharynx into the trachea [ 15525558 ; Figure 5 ].
The brief pause — ms in breathing by a sucking infant, deglutition apnea, has been attributed to neuronal control rather than an airway protection mechanism, perhaps in preparation for the more mature swallowing of an adult that requires aspiration prevention 15 Figure 5. Anatomy and physiology of the infant during feeding. Unlike the adult, the epiglottis moves upward toward the soft palate during feeding. The white indicates the fluid meal and demonstrates how it is made to go around the epiglottis and into the esophagus.
The dotted blue arrow indicates the air coming from the nasal passage during the feeding and demonstrates its laminar flow into the trachea. The coordination of swallowing, breathing and sucking is an enormously complex sensorimotor process, requiring five cranial nerves, at least 26 pairs of muscles, the cervical and thoracic spinal cord as well as at least 10 discrete brain areas 485253 Due to the rhythmic nature of the suck-swallow-breathe process, these motor functions are controlled by central pattern generators CPGs 1415374853 The interneurons of these CPGs are found in the brainstem, specifically the upper medullary and pontine areas, and have been shown to be capable of generating a basic swallow without other input 1448 ,