Stressing the System: Biomechanics of Sequential Swallowing in Healthy Adults.

PURPOSE: Sequential drinking of multiple liquid swallows requires sustained airway protection. Volume swallowed and speed of delivery may be altered by instruction and delivery method, for example, open cup versus straw drinking. Our clinical purpose was to explore the optimal method for "stressing the system" in a swallow assessment to provide the most useful information possible. This study investigated how task affected sequential drinking biomechanics. METHOD: Videofluoroscopic swallow studies of 318 healthy adults (20-99 years) were analyzed: 179 adults drank barium liquid from a 90-ml open cup with the instruction "drink this as you normally would" and 139 drank 100 ml of barium liquid via a straw with the instruction "finish the cup as quickly as possible." Timing and displacement measures were taken. Hyolaryngeal complex (HLC) behavior was classified into four types: HLC-I, reopening of laryngeal vestibule between swallows while HLC still elevated; HLC-II, sustained complete laryngeal vestibule closure; HLC-III mixed sequential (mix of HLC-I and II); or HLC-IV discrete swallows wherein HLC returns to resting position between swallows. RESULTS: All HLC patterns were observed across participants: HLC-I (cup: 23%; straw 22%), HLC-II (cup: 23%; straw 31%), HLC-III (cup: 3%; straw 23%), or HLC-IV (cup: 51%; straw 24%). Straw drinking was significantly more likely to elicit sequential swallows compared to cup drinking, which resulted in greater sustained airway closure. Age was not significantly associated with HLC pattern. There were significant differences in timing and displacement measures between cup- and straw-drinking tasks and across HLC patterns. CONCLUSIONS: Straw drinking with the instruction "finish the cup as quickly as possible" elicited sequential swallows more often than cup drinking with greater sustained airway closure. It also provided greater opportunity to view pharyngeal capability and airway protection ability and may represent a more challenging airway swallow pattern.