Abstract
The Ultrasound Velocity Profiling (UVP) technique allows real-time, non-invasive flow mapping of a fluid along a 1D-measuring line. This study explores the possibility of using the UVP technique and X-ray video-fluoroscopy (XVF) to elucidate the deglutition process with the focus on bolus rheology. By positioning the UVP probe so that the pulsed ultrasonic beam passes behind the air-filled trachea, the bolus flow in the pharynx can be measured. Healthy subjects in a clinical study swallowed fluids with different rheological properties: Newtonian (constant shear viscosity and non-elastic); Boger (constant shear viscosity and elastic); and shear thinning (shear rate-dependent shear viscosity and elastic). The results from both the UVP and XVF reveal higher velocities for the shear thinning fluid, followed by the Boger and the Newtonian fluids, demonstrating that the UVP method has equivalent sensitivities for detecting the velocities of fluids with different rheological properties. The velocity of the contraction wave that clears the pharynx was measured in the UVP and found to be independent of bolus rheology. The results show that UVP not only assesses accurately the fluid velocity in a bolus flow, but it can also monitor the structural changes that take place in response to a bolus flow, with the added advantage of being a completely non-invasive technique that does not require the introduction of contrast media.
Highlights
The rheological properties of the bolus profoundly influence the swallowing process in normal individuals and those suffering from dysphagia, i.e. abnormal swallowing [1, 2]
Fluid elasticity was expressed as the extensional viscosity determined by the Hyperbolic Contraction Flow (HCF) method (Fig. 3)
The commercial thickener Nutilis fluid used in the clinical study that showed thinning behaviour in shear deformation showed extension thinning behaviour, i.e. the extensional viscosity decreased with increasing extension rate, as found previously [6]
Summary
The rheological properties of the bolus profoundly influence the swallowing process in normal individuals and those suffering from dysphagia, i.e. abnormal swallowing [1, 2]. People with normal swallowing function adjust to the bolus rheology, which is a manifestation of the internal resistance to flow [3]. As low-viscosity fluids deform and flow with a higher velocity during swallowing, they may enter into the larynx if the laryngeal closure does not occur in a timely fashion [4, 5]. The rapid transport of the bolus during the pharyngeal phase of swallowing is challenging to handle for patients who are suffering from dysphagia [5]. Patients who are suffering from dysphagia are restricted to consuming thickened fluids, which is a well-established food-based strategy for the management of dysphagia [7]. The rationale for adding the thickeners is based on the concept of
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