Effects of different viscous liquids and solid foods on swallowing speeds and sounds among healthy adults
Authors: Feng Chun , Volkman Kathleen , Wagoner Cheryl , Siu Ka‐Chun 
Published: October 2021

AbstractBackgroundDigital cervical auscultation (CA) has been proposed since the 1950s for screening aspiration among patients with dysphagia. Researchers have investigated the ‘external’ effects such as bolus viscosity, volume, and head and neck positions. However, the influences of standardized liquid viscosity and food texture on swallowing sounds have not been fully understood due to lacking uniform standardization of bolus preparation. Furthermore, a paucity of the literature recommends proper viscous liquids and foods to start swallowing training or monitor the swallowing progress during the continuum of disease based on acoustic signals.AimsTo investigate the effects of eight‐level liquids and foods on swallowing sound features based on the International Dysphagia Diet Standardisation Initiative (IDDSI).Methods & ProceduresWe collected swallowing sounds from 30 healthy participants ranging in age from 19 to 60 years and who were self‐reporting no history of swallowing disorders. Each participant swallowed liquids and foods regarding different consistency or texture with their head–trunk in a neutral position.Outcomes & ResultsFeatures of swallowing acoustic signals and the IDDSI flow test as well as food test confirmed the level 3 moderately thick (MO3) was more suitable to categorize into liquids and the level 4 extremely thick (EX4) was more corresponded to the properties of food bolus. We found significant differences in duration of acoustic signals across different liquids and foods except between swallowing level 0 thin liquid and level 1 slightly thick liquid, as well as EX4 and level 5 minced and moist. Our results also demonstrated liquid viscosity significantly impacted the peak intensity of swallowing sounds.Conclusions & ImplicationsAs an initial exploration of digital CA across eight levels of different liquids and foods according to the IDDSI, we established the baseline findings for future comparisons with other study populations or other various consistent liquids/foods. Although both MO3 and EX4 can be considered as liquid or food boluses with high thickness, MO3 might be suitable as the ‘start liquid’ for patients with dysphagia; however, the decision still needs to be confirmed by the healthcare provider based on patients’ safety and the area of deficit. We also concluded there are influences of varied fluid consistency and food texture on swallowing sounds. Furthermore, future investigations should explore whether changing viscosity levels could either continuously or discretely disturb the swallowing acoustic signals.What this paper addsWhat is already known on the subject
Previous studies have found that the ‘external’ effects such as bolus viscosity, volume, and head and neck positions. Due to lacking uniform standardization of bolus preparation, there is limited information about the influences of standardized liquid viscosity and food texture on swallowing sounds.What this paper adds to the existing knowledge
As an initial exploration, we utilized digital CA with a large sample of viscous liquids and different textures of foods based on the IDDSI to investigate the swallowing sounds.What are the potential or actual clinical implications of this work?
This study confirms that the effects of various fluid consistency and food texture on swallowing acoustic signals. However, the findings of this study support the need for further research relating to changing viscosity could either continuously or discretely disturb the swallowing acoustic signals.