How might non nutritional sucking protect from sudden infant death syndrome
Introduction
SIDS is defined as “The sudden and unexpected death of an infant younger than 1 year and usually beyond the immediate perinatal period, which remains unexplained after a thorough case investigation, including performance of a complete autopsy and review of the circumstances of death and of the clinical history. Onset of the lethal episode was presumably during sleep”.[1] The leading cause of mortality for children between the age of one month and one year, SIDS remains a diagnosis of exclusion. The variables associated with SIDS can be grouped in two categories: epidemiological and post-mortem findings[1]. In the autopsy there are “soft” findings that are consistently reported, which will be discussed later. The epidemiological variables can be grouped in three categories: prenatal, postnatal, and genetic/ demographic[1], [2]. The “triple risk” model is the leading theory to explain SIDS pathophysiology. It does not promote a single cause, instead it proposes “sudden death in SIDS results from the intersection of three overlapping factors: (1) a vulnerable infant; (2) a critical developmental period in homeostatic control, and (3) an exogenous stressor(s).” [3] The abovementioned epidemiological variables all fall under the “vulnerable infant” category when discussed within the triple risk model.
Pacifier use is the strongest protective factor found in the epidemiological studies for SIDS. It is noteworthy that sleep position recommendations, avoiding prone positioning, is grouped under risk factors for SIDS. The pacifier association has been described in numerous studies across countries, continents, and time.[4], [5], [6], [7] However, a universally accepted mechanism that explains how a pacifier could help prevent deaths in SIDS is lacking. There are well known adverse effects related to pacifier use including issues with odontogenesis,[8] lactation,[5], [9] and infection.[5], [10] Lacking a plausible mechanism to explain the protective effect of pacifier use in SIDS has fostered the notion that the relationship is casual rather than causal. The aforementioned coupled with recognized adverse consequences to the practice has hampered adoption of pacifiers as a SIDS prevention strategy.
We propose suction assisted, velo-glossal adherence mediated, pharyngeal airway stabilization as the mechanism to help explain the pacifier-SIDS association. Our hypothesis is based on the prolonged apnea theory and the following well described phenomena: negative pressure induced by suction on the pacifier (or digit sucking) leads to approximation and adherence of the anterior surface of the soft palate and the posterior surface of the tongue. This adherence immobilizes the soft palate and tongue, stabilizing the pharyngeal airway, thereby promoting the preferred nasal breathing route of infants.
Section snippets
Pacifier protective effect
The pacifier hypothesis was first brought up by Cozzi in 1979[11]. His hypothesis was modeled within the prolonged apnea theory[12], [13] which at the time it was believed infants were obligate nose breathers,[14] this was later disproved[15]. Cozzi proposed the vacuum induced, glossoptosis mediated airway collapse. According to his hypothesis a pacifier could help prevent airway collapse: “Sleeping infants sucking dummies do not respond to nasal occlusion with signs of pharyngeal obstruction
SIDS and sleep disordered breathing
The prolonged apnea theory had an uncontested title for SIDS pathophysiology for about 20 years, when a tragic event shattered its prominence. Steinschneider’s paper[13] basically established the apnea paradigm in the early 1970′s, one of its most dramatic aspects was the later death of two of his research subjects (siblings) who had prior history of “near- miss SIDS”. His paper suggested that “near miss” cases are at increased risk for future SIDS, that it had a familial component, and that it
The soft palate as a pivotal structure in SIDS
The soft palate can adopt three critical positions to act as a valve that directs airflow through the nasal route, neutral, or the buccal route (Fig. 1, Fig. 2).[29] The superior muscle group (tensor levi palitini, and levator veli palitini) is responsible for elevating the soft palate and obstructing the nasopharynx, promoting buccal breathing route. The inferior muscle group (palatoglossal, palatopharyngeal) is responsible for the approximation of the soft palate to the posterior aspect of
Suction assisted velo-glossal adhesion
Velo-glossal approximation and adhesion in infants is not a new concept.[30], [31] Awareness and understanding of the phenomena is also central to understanding our hypothesis. In adults the close apposition of the velum and the tongue directs the breathing route through the nose.[29] In 1975, Tonkin mentioned “There is quite a strong adherence of the tongue to the palate and in the sleeping infant, this suction must be broken before the mouth can be opened. Perhaps the length of the soft
Reconciliation with SIDS epidemiologic associations
Pacifiers do not remain in place throughout the entire period of sleep and are often found dislodged from the buccal cavity at the end of the sleep period. [5], [40] How then might pacifiers protect against SIDS? Velo-glossal adhesion explains why pacifiers have a protective effect after removal from the mouth. Suction establishes the adhesive seal between the soft palate and the posterior aspect of the tongue. Evidence of seal maintenance after pacifier removal is provided by Tonkin whom
Reconciliation with SIDS autopsy findings
Although autopsy findings are “soft” and ultimately SIDS continues to be a diagnosis of exclusion, Beckwith noted “the impressive repetitiveness of a narrow spectrum of minor changes lends great weight to an unitarian concept of SIDS.”[45] Petechiae in intrathoracic organs is the most common autopsy finding. This finding along with pulmonary congestion and edema are purported secondary to high intrathoracic negative pressure generated when breathing against an occluded airway[45]. However, the
The unstable airway model
We hypothesize that during sleep the infant has a preferred airway arrangement, which we will call the “stable airway,” that has a low risk for collapse. Soft palate disengagement from the tongue, a random event, leads to an “unstable airway.” The unstable airway is inherently at risk for collapse. The infant has salvage mechanisms that allow it to restore the stable airway arrangement. Cycling between stable airway and unstable airway is probably a relatively frequent event. In SIDS failure of
Conclusion
A large subgroup of SIDS cases (averaged at 60% as calculated by a meta analysis of 7 large epidemiological studies [7], and up to 90% according to one study[18]), have pathophysiology that intersects with the potential protective mechanism provided by pacifiers. We propose suction assisted velo-glossal adherence mediated pharyngeal airway stabilization as a mechanism to explain the SIDS protective association with pacifiers.
Given the very definition of SIDS, obtaining unequivocal proof of our
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Akash P. Naidu: Diagnostic Radiology Department, Miller School of Medicine, University of Miami, Miami, Florida.
Afe Alexis: Internal Medicine Program, Miller School of Medicine, University of Miami, Miami, Florida.
Disclosure
The authors certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed
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