Bolus Consistency A nd Swallowing I n Children A nd Adults

Research has shown that swallowing in adults is affected by bolus consistency. Little is known, however, regarding the effect of bolus consistency on swallowing in children. Electromyographic (EMG) data from typically developing fiveand eight-year-old-children and adults were obtained from the following muscles as they swallowed boluses of different consistencies: (1) right upper lip, (2) right lower lip, (3) submental, and (4) laryngeal strap. Signal analyses included calculating EMG onset and offset and average EMG amplitude of muscle activity during swallowing. Findings revealed that by five years of age, children employ adult-like control strategies during swallowing: significant differences in duration and magnitude of muscle activity resulted as a function of bolus consistency. General observations revealed, however, that swallowing in children is characterized by muscle activity that is shorter in duration. Similarities and differences in the biomechanics of swallowing between children and adults are important to consider during clinical evaluations and treatment of children with dysphagia. Jacki L. Ruark, Gary H. McCullough, Rebecca L. Peters, and Christopher A. Moore (2002) "Bolus Consistency And Swallowing In Children And Adults" Dysphagia #17 pp.24-33 Version of Record available @ www.springer. com (DOI: 10.1007/s00455-001-0098-0) The clinical evaluation of a child with suspected dysphagia includes presenting various liquid and food items to determine the effect of bolus consistency on swallowing [1]. Identifying consistencies that are safe for swallowing allows clinicians not only to determine the need for diet modification (e.g., eliminating problem consistencies from the child's diet), but also to monitor swallowing skills and establish pertinent treatment goals [2]. One compensatory strategy frequently employed to enhance swallowing in children with dysphagia is to alter the physical characteristics of food substances within a child's diet (e.g., thickening of liquids to improve bolus formation) [3]. It is generally assumed that some consistencies are easier to swallow than others, and swallowing coordination in children is affected by bolus consistency [4]. Although positive clinical outcomes are frequently reported subsequent to consistency modification in children with dysphagia [2], quantitative evidence regarding the effect of bolus consistency on swallowing in children is lacking. In adults, several studies have focused on the effect of bolus consistency on the coordinative variables of swallowing [5-7]. For example, Dantas and Dodds [5], using concurrent recordings of submental and infrahyoid EMG activity and videofluoroscopy of adults during swallowing, found that boluses of barium paste yield greater duration and amplitude of submental and infrahyoid muscle activity than liquid barium. Additionally, the onset of infrahyoid EMG activity occurs later in the swallow for barium paste (i.e., onset of infrahyoid EMG activity occurs 0.25 s after initiation of submental EMG activity for barium paste, 0.18 s after initiation of submental EMG activity for liquid barium). In a study that used common liquid and food items to determine the effect of bolus consistency on swallowing in adults, Reimers-Neils et al. [7] found that the total duration of muscle activity of adults during swallowing (as measured by the duration of time from the initiation to cessation of submental and Introduction infrahyoid EMG activity during swallowing) significantly increased from liquid (e.g., water) to thin paste (e.g., pudding) and from thin paste to thick paste consistencies (e.g., cheese spread). Reimers-Neils and colleagues also found that the magnitude of submental EMG activity significantly increased when the adults swallowed thick versus thin pastes and thin or thick pastes versus liquids. Significant differences were not found, however, when comparing liquids to thin paste. The magnitude of infrahyoid EMG activity was similarly affected by bolus consistency, although the average EMG amplitude of the infrahyoid muscles did not differ significantly when adults swallowed thin versus thick pastes. The outcome of this investigation demonstrated that, although submental and laryngeal EMG activity of adults is affected by bolus consistency, the effect of bolus consistency on muscle activity during swallowing may not follow conventional clinical concepts (e.g., that a liquid bolus requires less magnitude of muscle activity during swallowing than pudding). In conclusion, these investigators recommended that further documentation be obtained regarding the effects of bolus consistency on swallowing in typical individuals. In addition, the authors suggested that liquid and food items used during swallowing evaluations and treatment be standardized. Empirical investigations regarding the maturation of the swallow have focused primarily on describing the coordination of swallowing with sucking and breathing in infants [e.g., 8,9]. Consequently, there is little understanding of the effects of bolus consistency on swallowing in typically developing children. The notion that a mature swallow is established during early development, e.g., by 15 months of age [10], suggests that swallowing in children and adults is similarly affected by bolus consistency. This assumption also implies that swallowing in children is characterized by similar relationships between submental and infrahyoid EMG activity and movements of various oropharyngeal structures as adults (e.g., infrahyoid EMG activity parallels the arrival of the bolus at the faucial pillars [5]). However, as dramatic alterations in neuromuscular and musculoskeletal systems transpire until at least 11 years of age [11,12], it is difficult to infer from adult studies the effect of bolus consistency on swallowing in children. In fact, there is little quantitative information regarding the ontogeny of swallowing in humans [13]. A better understanding of swallowing in children is necessary to determine when children should develop a more mature swallowing pattern and when the absence of mature patterns should become a concern. The goal of the present investigation was to obtain comprehensive EMG data from children and adults and determine whether children employ adultlike control strategies as they swallow boluses that differ in consistency. The following anatomcal and physiological factors led to the hypothesis that the average magnitude and duration of muscle activity during swallowing in children differs from adults: (1) the swallowing tract of children is shorter and is composed of muscle fibers that differ in size and histology [14,15] and (2) the central and peripheral nervous systems, including motor neurons, sensory receptors, and their connections, continue to develop into late childhood [11].