Exploring the role of rheology in bolus flow using an in-vitro approach – PhD Thesis by Waqas Muhammad

Swallowing disorders, termed ‘dysphagia’, are more common in the elderly but can also affect younger persons. Approximately, 8% of the world’s population suffers from dysphagia. A Texture Modified Diet (TMD), which increases bolus viscosity to adjust for the sluggish bolus handling mechanism, is the most common intervention. Other rheological properties, such as bolus elasticity, shear rate, and yield stress, are often ignored. While clinical examination is the standard and most appropriate way to diagnose dysphagia, difficulties arise in relation to the use of contrast media, ethics, and patient discomfort. To overcome these difficulties and to reduce the frequency of clinical analysis, an in vitro approach was adopted and an in vitro swallowing model was developed that can be used to perform experimental bolus visualisation and manometry, mimicking the in vivo counterpart of video fluoroscopy and manometry. To study bolus transport, the Incipientus Flow Visualizer was used. The device can simulate abnormal swallowing conditions, such as delayed epiglottis and Upper Esophageal Sphincter (UES) closure. Simulations of abnormal UES conditions, i.e. reduced UES area, yielded different pressure values in the lower pharynx. Therefore, the device can be used as a pre-clinical study tool to elucidate the relationship between bolus rheology and deglutition.