Electrical-Impedance Biofeedback Instrumentfor Swallowing Rehabilitation
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
Biofeedback is an important tool in the rehabilitation of several dysphagic conditions. This thesis presents an investigation into using bio-impedance as a technique for providing biofeedback of the swallowing sequence, specifically sequencing in the pharynx. The motivation behind this project was to find an alternative rehabilitation tool for detecting pharyngeal sequencing, as the current tool of pharyngeal manometry is invasive and non-portable. This investigation included the design and creation of a bio-impedance measuring device named the Guided Utility for Latency in Pharyngeal Sequencing (GULPS). This system was continued from a previous unpublished investigation at the University of Canterbury, where an initial prototype was designed and created. It was found that this pre-existing system had numerous faults in both its hardware and software, limiting the use of the device.
Electrical impedance across the throat can be determined by applying a known constant amplitude current signal across the throat and recording the corresponding voltage. This impedance has been shown to change during a swallowing sequence due to a change in the structure of the throat. The principle used in this project was to investigate if two positions of impedance measurement could be used to determine the sequencing of the pharynx during a swallow. The design of the GULPS device was influenced by the pre-existing system and several prototypes were built to obtain a system capable of providing two channels of impedance measurement. Software was adapted from the pre-existing system to interface with this hardware to provide a system that could be attached to an external computer.
Various electrode positions for the final device were trialled aimed at measuring two similar, but temporally separated, impedance waveforms. It was found that positioning the electrodes close to the approximate position of the pharynx with a 40 mm gap between channels allowed for two temporally separated channels to be produced with three distinct features: two peaks and one trough in each of the GULPS waveforms. The GULPS device with these electrode positions was trialled on three `healthy' subjects and one dysphagic subject. The three features could be identified in both impedance waveforms in all four subjects.
To determine if the identified features related to the sequencing of the pharynx, the GULPS device was trialled alongside the current conventional method for detecting pharyngeal sequencing, pharyngeal manometry. The results from these trials revealed a potential relationship between the temporal separation of the second peaks found in the GULPS waveforms and the temporal separation of the pressure peaks from pharyngeal manometry. The GULPS device was trialled alongside pharyngeal manometry on one `healthy' and one dysphagic subject. A linear regression between peak-to-peak latencies between the two methods had an R squared value of 0.347 for the `healthy' subject and 0.241 for the dysphagic subject. However, these peaks were often difficult to detect, and could only be detected in 64% of swallows in the `healthy' subjects using the GULPS device in a standalone fashion and in 23% of swallows when used concurrently with manometry.
As the current GULPS device is unable to produce the desired results in a consistent manner, no definitive conclusions can be drawn on the ability of using bio-impedance to measure the pharyngeal sequence. Notwithstanding, substantial progress has been made towards a device for reliable measurement of pharyngeal sequencing and, together with the clinical benefits to be gained, more than justify further research and development into GULPS for dysphagia rehabilitation.