Cervical auscultation : bridging the gap in dysphagia assessment

Abstract

Cervical auscultation (CA) is an assessment of swallowing based on an analysis of the sounds of swallowing. It is an assessment that has researchers and clinicians alike, quietly pondering the meaning of the information it provides. To date, clinical dysphagia assessment has been dominated by the bed-side clinical examination and videofluoroscopy. The bed-side examination provides subjective information about swallowing status and is limited by its inability to accurately characterise the pharyngeal phase of the swallow. Videofluoroscopy is the industry accepted gold standard and provides unequivocal information about all facets of swallowing anatomy and physiology. It is also costly, time consuming and involves ionising radiation, limiting its use with dysphagie individuals. The chasm between these two techniques requires a bridge. It is hypothesised that CA can bridge this gap. This thesis provides an appraisal of the technique and the information it provides. CA can be either subjective or objective in nature. The subjective technique uses stethoscopes for perceptual appraisal of swallowing sound events. The objective technique uses acoustic detector units (eg. accelerometer or microphone) to detect the signal which can then be analysed using computer assisted acoustic software packages. The experiments in the current thesis are based on the latter technique. Optimal acoustic detection and placement is essential to adequately characterise the duration, intensity and frequency characteristics of the swallowing sound. Chapter 2 reviews the use of accelerometers and microphones in the detection of swallowing sounds. Contrary to previous findings, a high quality microphone was shown to provide excellent acoustic detection abilities. Site of placement of the acoustic detector unit was in general agreement with previous research, with the mid-point of the cricoid cartilage chosen for microphone placement. The air-borne noise rejecting characteristics of the microphone were found to be superior to the accelerometer, when the device was correctly applied and sealed to the skin surface. In objective CA, hardware is only part of the equation for accurate results. Acoustic analysis must also be correctly applied to gain the maximum information from the acoustic signal. Chapter 3 focuses on acoustic theory relevant to signal capturing, and analysis. Previous research methodology relating to sampling rates, and decomposition of the frequency component of the swallowing sound are controversial. A framework for signaturing of the swallowing sound is provided, based on sound acoustic theory and acoustic analysis of related biological sounds (eg. cardiac and respiratory sounds).