The effect of saliva on the viscosity of thickened drinks.

Powdered thickeners are used to modify drink consistency in the clinical management of dysphagia. These thickeners are composed of primarily modified maize starch; some varieties also incorporate powdered gums. Amylase is a digestive enzyme found in saliva that initiates the breakdown of starch. To determine the significance of this process in dysphagia management, we measured the effects of human saliva on the viscosity of thickened drinks. Two thickeners were studied: one comprising modified maize starch alone and one that included additional gums. These were added to drinks with neutral and acidic pH: water and orange juice. Two clinical scenarios were simulated: (1) the effect of saliva on fluid as it is swallowed and (2) the effect when saliva enters a cup and contaminates a drink. Saliva was found to reduce the viscosity of water thickened with maize starch in both scenarios: (1) 90% reduction after 10 s and (2) almost 100% reduction in viscosity after 20 min. The thickener composed of gums and maize starch showed a significant reduction but retained a level of thickening. In contrast, thickened orange juice (pH 3.8) was not observed to undergo any measurable reduction in viscosity under the action of saliva.

A portable self-sensing rheometer for investigation and therapy of swallowing disorders.

Dysphagia is a medical condition in which the safety or efficiency of eating and drinking is compromised. Thin, watery fluids flow too quickly through the oral anatomy during an abnormal swallow, pre-empting airway protective mechanisms, and potentially resulting in fluid entry into the lung. Dysphagia therapy consists of reducing flow speed during swallowing by increasing fluid viscosity using thickeners. Bolus viscosity must be specified and presented to the patient within a well-defined range for effective therapy. Thickeners produce non-Newtonian fluids, rendering current subjective methods for fluid assessment unreliable. Widespread quantification of fluid viscosity is presently impractical as rheometers are costly and complicated to use. Alternative techniques also have disadvantages such as operation at shear rates inappropriate to fluid use. A simple and inexpensive rheometer has been constructed to remedy this situation using a self-sensing electromagnetic actuator. This avoids the need for separate force and displacement sensors, with benefits for simplicity and robustness. The actuator and fluid interface were designed for viscosities consistent with those used for dysphagia therapy. The self-sensing rheometer was found to be able to resolve the different dynamic viscosities obtained from three commonly used therapeutic fluid consistency levels in close agreement with results from a reference laboratory rheometer. Widespread use of the rheometer could remove the subjectivity of fluid assessment, increasing accuracy of fluid specification and therapy across all consistencies and fluid types.