The effects of head movements and fluids with increasing viscosity on swallowing sounds

Cervical auscultation (CA) is an affordable, non-invasive technique for diagnosis of dysphagia (swallowing difficulties). CA involves swallowing characterization either via accelerometers or microphones. Though characteristics of the swallowing sound are well known, there is also need for a complete understanding of the baseline characteristics of the device, as well as any in influence of the head motion, age and gender. Also, the effects of fluid viscosity on swallowing accelerometry signals is well understood, there are still open questions about these effects on swallowing sounds. In order to examine these parameters, data was collected from 56 healthy participants. At first, they performed six different tasks with absence of swallowing, than they would complete five water swallows, five swallows of nectar-thick apple juice, and five swallows of honey-thick apple juice. These swallows were completed in neutral head and chin-tuck head positions. After pre-processing of collected signals, a number of features in time, frequency and time-frequency domains were extracted. Statistical test for baseline characteristic of swallowing sound showed that only the skewness and peak frequency did not possess statistical difference for all tasks. This results of the peak frequency indicates that head movement does not significantly affect the swallowing sound, and there is no need for removing those components. However, there is no observed gender, but age dependence was found in the swallowing sound. Nevertheless, participant's age should be considered in the future studies about swallowing sound. The same test was used for investigating influence dependence, and it demonstrated that significant influence of viscosity was found in most of the features. In general, features extracted from swallows in the neutral head position were affected more than swallows from the chin-tuck position. Furthermore, most of differences were found between water and fluids with higher viscosity. Almost no significant difference were found between swallows involving nectar-thick and honey-thick apple juices. Our results also showed that thicker fluids had higher regularity and predictability as demonstrated by the information theoretic features, and a lower frequency content as demonstrated by features in the frequency domain. Therefore, viscosity of fluids should be considered in future investigations involving swallowing sounds