Role of fluid cohesiveness in safe swallowing

Abstract

In patients with dysphagia, it has been a practice to thicken fluid food to prevent aspiration-the transport of a bolus into the trachea instead of the oesophagus. In these patients, aspiration is a risk behaviour and is closely related to pneumonia (caused by the aspiration of oral bacteria into the lungs). Since excessive thickening of fluids can cause adverse effects, such as lowering the palatability of food, subsequent reduction of liquid intake, dehydration and malnutrition, identifying the optimum thickening level is vital. Thickening might not only increase fluid viscosity, but could also modify its cohesiveness, which is another key factor affecting aspiration. Even though cohesiveness is more of a concept than a well-defined measurable parameter, this property describes the degree of coherency provided by the internal structure of a material against its fractional breakup. In fluids, this concept is less explored than in solids, powders and granules, and during the last decade few scientists have tackled this topic. Although the role of cohesiveness in the swallowing of heterogeneous solid foods is briefly overviewed, the aim of the present paper is to introduce the concept of cohesiveness for a relatively homogeneous fluid bolus and its effect on swallowing. Cohesiveness is highly correlated with the extensibility and yield stress of the fluid, suggesting that a high cohesiveness could have an important role in preventing aspiration.

Keywords: Biophysics; Quality of life; Risk factors.

Fig. 1

a Extensional deformation of 0.5% locust bean gum solution. b Extensional deformation of 0.5% guar gum solution. c Extensional deformation of 0.5% xanthan solution. All the measurements were performed at 25 °C. Solutions are extended from the initial length L₀ (=3 mm) with the initial diameter D₀ (=6 mm) to the final length L_f (=11 mm) at 0.16 mm/ms. Each set of images presents the filament at rest (−50 ms), at the initial moment of the extensional experiment (0 ms), and at 6 time frames preceding the filament rupture time, t_b (breakup time). d Extensional deformation of water (Turcanu and unpublished)

Fig. 2

Effect of 10:1 water or α-amylase solution addition on the capillary breakup time and shear viscosity at 50/s of a starch-based and a gum-based dysphagia product (replotted from ref. ). The viscosity range is classified into four stages: Thin, Level 1, Level 2 and Level 3 according to the National Dysphagia Diet (NDD)

Fig. 3

Elastic stress (storage modulus × strain) of xanthan gum and locust bean gum solutions at 20 °C and angular frequency = 6.28 rad/s.plotted as a function of strain. Concentrations of polysaccharide: 0.3, 0.45, 0.6, 0.75 and 0.9% for xanthan gum (a) and 0.5, 0.6, 0.7, 0.75, and 0.8% for locust bean gum (b), represented by open circles, closed triangles, open triangles, crosses, and closed circles in increasing order for each polysaccharide. The yield stress and strain were estimated from the maximum point in the curve

Fig. 4

a Representative profile of the swallowing sound in the case of 15 mL water (20 °C). t₁, the closure of the epiglottis; t₂, the bolus flow; t₃, the opening of the epiglottis in order of occurrence. t_1-2, time interval between the termination of the epiglottis closure and the initiation of the flow of bolus; t_2-3, time interval between the termination of the flow of bolus and the initiation of the epiglottis opening. b Duration t₂ in swallowing polysaccharide solutions as a function of steady shear viscosity at 10/s. closed circle: xanthan gum; open circle: LBG. Serving volume of polysaccharide solutions was 15 mL. Each datum was standardized with that for control (water). Data with asterisk are significantly different between xanthan gum and LBG at p < 0.05

Fig. 5

Correlation between the duration t₂ and the score of each sensory attribute in swallowing polysaccharide solutions. Serving volume of polysaccharide solutions was 15 mL. a Sensory cohesiveness (bolus formation); b Sensory swallowing ease. The t₂ was standardized with the corresponding data for water. Sensory evaluation was represented by a visual analogue scale (VAS)

Fig. 6

Shear rate dependence of the viscosity of xanthan X2 and guar (G1 and G2) solutions containing iopamidol. The measurement temperature: 36.5 °C. The shear rate was changed stepwise up to 1000/s for 10 min

Fig. 7

Videofluorography of a patient who showed aspiration for two sample solutions G1 and G2, and without aspiration for X2. The videofluorographic observation described in the present paper was approved by Ethic Committee of Musashino Red Cross Hospital in accordance with the Declaration of Helsinki