Background: Cervical auscultation (CA) is an affordable, non-invasive technique used\r\nto observe sounds occurring during swallowing. CA involves swallowing\r\ncharacterization via stethoscopes or microphones, while accelerometers can detect\r\nother vibratory signals. While the effects of fluid viscosity on swallowing accelerometry\r\nsignals is well understood, there are still open questions about these effects on\r\nswallowing sounds. Therefore, this study investigated the influence of fluids with\r\nincreasing thickness on swallowing sound characteristics.\r\nMethod: We collected swallowing sounds and swallowing accelerometry signals from\r\n56 healthy participants. Each participant completed five water swallows, five swallows\r\nof nectar-thick apple juice, and five swallows of honey-thick apple juice. These\r\nswallows were completed in neutral head and chin-tuck head positions. After\r\npre-processing of collected signals, a number of features in time, frequency and\r\ntime-frequency domains were extracted.\r\nResults: Our numerical analysis demonstrated that significant influence of viscosity\r\nwas found in most of the features. In general, features extracted from swallows in the\r\nneutral head position were affected more than swallows from the chin-tuck position.\r\nFurthermore, most of the differences were found between water and fluids with higher\r\nviscosity. Almost no significant differences were found between swallows involving\r\nnectar-thick and honey-thick apple juices. Our results also showed that thicker fluids\r\nhad higher acoustic regularity and predictability as demonstrated by the\r\ninformation-theoretic features, and a lower frequency content as demonstrated by\r\nfeatures in the frequency domain.\r\nConclusions: According to these results, we can conclude that viscosity of fluids\r\nshould be considered in future investigations involving swallowing sounds.
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