Negative Pressure, Cavitation Effect and Swallowing

Objectives: The aim of this study was to determine the role of cavitation pressure & salivary viscosity on the generation of negative pressures during swallowing. Our hypothesis is that a brief drop in negative pressures will be seen due to cavitation, but not to the magnitude of that seen in a swallow. Methods: An intraoral pressure measurement appliance was adapted and artificial tongues made of silicone were used to test the generation of negative pressure during swallowing. The different viscosity liquids used were nectar, water and saliva. A typical swallow cycle, consisting of a cascade of positive, neutral and negative pressure was generated for each liquid. Results: Overall, it was found that negative pressures (~5 – 10 kPa) were generated as the tongue lifted off the appliance, regardless of tongue surface texture or viscosity of the liquid. These reductions were sharp and brief. Conclusion: Our findings support the hypothesis that negative pressures seen with our appliance were due to a cavitation-like mechanism. A film of liquid between the tongue and palate acted like an adhesive that required a force to pull apart. This force was relatively constant, irrespective of viscosity. Hence we conclude that observed negative pressures (~25 kPa) during previous swallowing are real and not the result of cavitation pressure (~5 - 10 kPa).