when speech pathologists thicken liquids , one of the properties they are changing is viscosity . liquids may be described by several properties , including viscosity , density , and elastic parameters , among others . as described herein , standardized solutions for evaluating dysphagia are characterized using viscosity , as measured with a viscometer , as a key parameter . in simple terms , the torque required to rotate a spindle immersed in the solution is measured . as discussed in detail by li et al ( 1992 ) dysphagia 7 : 17 - 30 , viscous liquids are classified as either newtonian or non - newtonian . a newtonian liquid flows at a rate which is directly proportional to the applied shear force while a liquid not obeying this proportionality is deemed to be non - newtonian . the complexity and cost of viscometers makes them impractical for dietitians and speech pathologists to utilize in most clinical settings . therefore , clinicians often resort to simpler means of generating a rough estimate of viscosity , such as the line spread test ( lst ) as a practical alternative to characterizing the viscosity of thickened liquids . the lst was originally developed in the 1940 &# 39 ; s as a simple tool to measure food “ consistency .” see 8 . grawemeyer & amp ; pfund ( 1943 ) food research 8 : 105 - 108 , and adams & amp ; birdsall ( 1946 ) food industries 78 - 80 . the lst measures the “ flow ” of a food / liquid by placing a standard amount of food / liquid in a cylinder , lifting the cylinder and allowing the food / liquid to flow on a horizontal surface for 1 minute and then measuring the distance it has spread . the simplicity of this tool is extremely appealing in clinical practice to measure objectively the general consistency of thickened liquids . as described in the examples , the lst can roughly distinguish between the viscosity of pre - thickened liquids , and may be a first step toward establishing the utility of this tool in clinical practice . however , the lst is not overly discriminating as a tool to measure viscosity . thus , the principal object of the invention is to provide a set or kit of solutions of known and standardized viscosity . the solutions in the kit come pre - made , as ready - to - use liquids , or in pre - measured dry powders or gels that can then be diluted with an appropriate liquid vehicle to yield solutions of the required viscosity . the first embodiment of the invention is a pair of viscosity - standardized solutions for evaluating dysphagia in human subjects . specifically , at least two edible solutions are required , the two solutions being selected from among : a first solution having a viscosity of between about 1 and 60 cp , a second solution having a viscosity of between about 300 and 2000 cp , and a third solution having a viscosity great than about 3 , 000 cp . viscosity of the compositions is measured at room temperature , generally about 23 ° c ., and can be determined using any number of conventional and commercially available spindle - type viscometers , such as those manufactured by brookfield engineering laboratories , middleboro , mass . brookfield &# 39 ; s instruments use a rotating spindle immersed in the fluid to measure viscosity . brookfield &# 39 ; s instruments are of the cone - and - plate rheometer - type design and are ideal for measuring the viscosity of non - newtonian fluids at low shear rates . the preferred instrument from among brookfield &# 39 ; s offerings is model lvdv1 +, an 18 - speed model with digital readout . viscometers and their operation are widely known and will not be described in great detail herein . for detailed information regarding brookfield &# 39 ; s model lvdv1 + viscometer , see brookfield &# 39 ; s manual no . m / 92 - 021 - m0101 , available from the manufacturer and also on - line at www . brookfieldengineering . com . for detailed information regarding measuring viscosity , see li et al , supra , and brookfield &# 39 ; s technical manual entitled “ more solutions to sticky problems ” ( also available at www . brookfieldengineering . com ). for radiographic imaging of the mouth and throat , it is preferred that compositions having the above - noted viscosities are formulated using a liquid base vehicle having an identifiable food flavor , such as a juice flavor or honey , chocolate , vanilla , etc . apple juice is particularly preferred a base vehicle . apple juice is very advantageous for this purpose because it is widely available , relatively inexpensive , and pulp - free . it is quite palatable and familiar to virtually everyone , and can be stored and transported as a concentrate . the liquid base can be naturally or artificially flavored , and can also contain additional components such as colorants , preservatives , and the like . to the liquid vehicle is added a thickening agent and / or a radio - opaque imaging agent . because a suspension of radio - opaque material will , by itself , increase the viscosity of a thin liquid to within the above - noted viscosities , depending upon the nature of the suspension used , a thickening agent may not be required to arrive at solutions having the desired viscosity . any other type of non - pulpy juice , liquid , or water may be used as the vehicle . a fruit juice is much preferred as the vehicle , however , because of its familiar taste and aroma . an ultimate goal of the invention being an accurate evaluation of the patient &# 39 ; s true swallowing dynamics , presenting an imaging composition which is as closely simulative as possible to a food the patient would normally ingest and enjoy is highly desirable . the preferred thickening agent for use in the present invention is a commercially available preparation marketed by novartis ( basel , switzerland ) under the registered trademark “ thickenup .” while the “ thickenup ” formulation is preferred , any suitable food thickener ( e . g ., “ thick it ”- brand thickener ( milanti co .) starch , sugars , glycols , etc ., may be used ). the preferred radio - opaque imaging agent is a suspension of barium sulfate . suitable barium sulfate and barium sulfate suspensions are available commercially from numerous sources . preferred commercially available barium sulfate and edible suspensions thereof can be obtained from the e - z - em corporation , westbury , n . y . specifically preferred are the products bearing e - z - em catalog nos . l147 , l164 , l168 , and l178 ( liquid barium sulfate suspensions ), catalog no . 764 ( high density barium sulfate suspension ), and catalog no . 745 ( bulk barium sulfate for suspension ). particularly preferred for use in both the first and second solutions is “ enteroh ” brand barium suspension ( catalog no . l147 ), from e - z - em . it is critical when formulating the compositions to include the proper amount of imaging agent and / or thickener because both components will contribute to the ultimate viscosity of the composition and there must also be the proper amount of imaging agent present in the composition to generate useful radiographic images ( when an imaging agent is used ). if there is too little imaging agent , the composition will be invisible to x - rays , if there is too much imaging agent , the composition will be too opaque . commercially purchased apple juice at room temperature , ( single - strength , about 6 . 5 to 7 . 0 brix , at about 23 ° c . ), 140 ml , is admixed with 90 ml of “ entero h ” brand barium sulfate suspension , available commercially from e - z - em . the mixture is thoroughly agitated until uniform . to ensure consistency of application , it is much preferred that the composition be made no more than 2 . 5 hours before use . the formulation should be administered at room temperature . this formulation yields a low - viscosity composition of about 25 cp . commercially purchased apple juice at room temperature , ( single - strength , about 6 . 5 to 7 . 0 brix , at about 23 ° c . ), 30 ml , is admixed with from about 170 to about 400 ml of “ liquid polibar ” brand barium sulfate suspension , available commercially from e - z - em corporation . the mixture is thoroughly agitated until uniform . to ensure consistency of application , it is much preferred that the composition be made no more than 2 . 5 hours before use . the formulation should be administered at room temperature . this yields a solution having a viscosity of from about 300 to about 2000 cp . commercially purchased apple juice at room temperature , ( single - strength , about 6 . 5 to 7 . 0 brix , at about 23 ° c . ), 120 ml , is admixed with about 50 ml ( 3 tablespoons ) of “ thickenup ” brand thickener . ( as sold commercially , the “ thickenup ” thickener includes a sliding measuring spoon .) the juice and thickener mixture is agitated thoroughly and allowed to sit undisturbed for no less than 10 minutes . to this mixture is added about 92 ml of “ liquid polibar ” brand barium sulfate suspension , available commercially from e - z - em corporation . the mixture is again thoroughly agitated until uniform . to ensure consistency of application , it is much preferred that the composition be made no more than 2 . 5 hours before use . the formulation should be administered at room temperature . this yields a solution having a viscosity of about 3000 cp . for radiographic imaging purposes , the patient is positioned laterally before a suitable fluoroscopic device and asked to swallow one or more of the three compositions . a video fluoroscope and suitable recording equipment are then used to visualize and record the passage of the composition through the mouth and throat during and after swallowing . if desired , the study can be performed using any combination or both of the two edible solutions . the following example is included herein solely to provide a more complete and consistent understanding of the invention disclosed and claimed herein . the example does not limit the scope of the invention in any fashion . the example explores whether pre - thickened liquids ( from novartis nutrition , minneapolis , minn . ), whose viscosity has first been measured with a viscometer , can reliably be separated into “ nectar ” and “ honey ” categories using the line spread test . according to novartis &# 39 ; manufacturing standards , nine ( 9 ) of the samples tested were designated as “ nectar ” and then ( 10 ) of the samples tested were designated as “ honey ” ( 19 samples total ). the 19 samples were first examined using a brookfield viscometer , and then evaluated using the line spread test ( lst ). each sample was tested using either a brookfield hvt or lvt rotational viscometer ( brookfield engineering , stoughton , mass .). the sample to be measured was contained in either the small sample chamber provided by brookfield or a 600 ml griffin low - form beaker , depending on the spindle / chamber arrangement appropriate for each sample ( for details on equipment for viscosity measurement using these two brookfield instruments , see “ more solutions to sticky problems ,” available from brookfield engineering ). the shear rate and apparent viscosity of the non - newtonian liquids were estimated using the method described by li et al . ( 1992 ) dysphagia 7 : 17 - 30 . ( note that while newtonian liquid viscosity is a constant , regardless of liquid flow rate , non - newtonian liquid viscosity is not . the “ apparent viscosity ” describes the instantaneous viscosity at a given rate of flow ). for uniformity between different fluids , the apparent viscosity for each fluid was computed at a shear rate of approximately 15 sect − 1 . for the remainder of this example , the term “ viscosity ” refers to “ apparent viscosity at a shear rate of 15 sec − 1 ,” unless otherwise noted . the standard lst , mann & amp ; wong ( 1996 ) j am . diet . assoc . 96 : 585 - 588 , was carried out on a counter top using a piece of plexiglas with a template of pre - measured concentric circles spaced 0 . 25 inches ( 0 . 64 cm ) apart placed beneath it . the counter top was confirmed to be level with a carpenter s level . a pvc pipe , with an internal diameter of 2 inches ( 5 . 08 cm ) was positioned in the middle of the template and filled with 50 ml of the sample to be tested . the tube was lifted and the sample was allowed to spread for 1 minute . measurements of the diameter of the spreading sample were taken at 90 - degree increments and averaged . to give the line spread reading . this test was carried out three times to get an average line spread reading . for the example , the lst was also carried out using a 100 ml sample size to explore how volume might affect the line spread results . for both lst and viscosity values , group means were computed for nectar and honey consistencies and differences between the two categories tested using student &# 39 ; s t - test . to study the separation between nectar and honey consistencies further , a linear - discriminant analysis was performed . this analysis generates a classification rule to categorize each liquid into the nectar or honey group based on its lst value . the rule is generated by maximizing the difference between the two groups in a least squares sense . each value in the data set is then tested using the rule and the number of errors in classification was determined . statistical analyses were computed automatically using the sas statistical program ( the sas institute , cary , n . c .). group values for the lst and viscosity are presented in table 1 ( mean + sd ). there was a highly significant difference in line spread test results ( both 50 and 100 ml ) and viscosity values between nectar and honey consistencies ( p & lt ; 0 . 0001 by student &# 39 ; s t - test ). [ 0053 ] fig1 and 2 show line spread distance plotted as a function of viscosity for line spread volumes of 50 ml ( fig1 ) and 100 ml ( fig2 ). the first observation is that the lst discriminates very well between different classes of liquids . that is , the lst clearly differentiates between the nectar versus honey consistencies in the present study . as is clearly shown in both fig1 and 2 , these pre - thickened nectar and honey liquids fall into distinct categories , in terms of both line spread values and viscosity , in both the 50 ml and 100 ml test volumes . the classification rules computed from the discriminant analysis may be expressed as the line spread value that separates nectar and honey categories for each volume of sample tested . these separating line spread values are : 10 . 7 ( 50 ml sample , fig1 — horizontal dashed line ) and 17 . 5 ( 100 ml sample , fig2 — horizontal dashed line ). when the samples were re - tested based on this rule , there were no errors in classification , indicating that the line spread test does an excellent job of discriminating between these two broad categories of liquids . beyond the gross separation into nectar versus honey consistencies , however , there is no apparent predictive value of the line spread test for estimating apparent viscosity . in other words , it does not appear to be possible to assign a one - to - one relationship between apparent viscosity values and line spread test values . the goal of this example was to explore the utility of the line spread test ( lst ) as an objective measure of thickened liquid consistency . because increased viscosity is often associated with thickened liquids , line spread and viscosity values were compared to explore whether a relationship exists between the two tests . two results emerge from this example . on one hand , the lst was able to separate pre - thickened juices into nectar and honey categories unambiguously ( i . e ., with no errors ), a separation also provided by viscosity measurement . on the other hand , within this restricted group of liquids , there was no relationship between line spread and viscosity values . in other words , there was no predictive value in terms of viscosity using the lst , apart from the overall separation into nectar and honey categories . thus , the lst is not an accurate substitute for a viscosity - standardized solution ; a solution whose viscosity is accurately known prior to being administered to the subject . based on these results , there are two possibilities concerning the relationship between lst values and viscosity values . one is that decreased line spread test values are associated with increased viscosity , but that the lst simply is not sensitive enough to detect differences in viscosity within a given category of liquids ( i . e ., viscosity differences within the nectar or honey categories ). if this were true , however , it would be expected that an increase in the volume of test fluid from 50 to 100 ml would increase the sensitivity of the lst , and this was not found in the example ( compare fig1 and 2 ). a different possibility is that other fluid properties are altered along with viscosity , and that it is one or more of these other properties that are reflected in the lst values . indeed , one of the difficulties in interpreting lst values is that several fluid properties possibly affect the final value . density likely plays a role because the driving force for liquid spreading is provided by gravity ; viscosity plays a role through the retarding frictional forces at the liquid - solid interface . finally , elastic parameters , which relate to bolus “ cohesiveness ,” may also be important . the role of elastic properties in the dynamics of the lst is also supported by a survey of the civil engineering literature . a commonly used measure to field test the consistency of freshly mixed concrete is called the “ slump ” test . see , for example , schowalter & amp ; christianson ( 1998 ) j . rheol . 42 ( 4 ): 865 - 870 . this test is carried out in the same manner as the lst , except that the height of the fluid pool after spreading is measured rather than the radius to which the material spreads . ( conservation of fluid volume may be used to relate the slump height to the line spread difference . the calculation is very simple and emphasizes the intimate link between these two tests .) interestingly , this slump height has been shown to correlate with the “ normalized yield stress ” of the concrete mixture . yield stress is a measure of fluid elasticity and in these analyses is normalized by density , emphasizing the multi - factorial nature of the physical process of spreading . because concrete has a much higher yield stress than typical liquid foodstuffs , the slump test results are not directly applicable to the edible solutions described herein . however , the correspondence between the two tests suggests that yield stress and density are fluid properties which may affect the line spread distance . clearly the mechanical behavior of liquid foodstuffs is complex ; even more complex are their interactions with the swallowing system . however , the situation remains that : 1 ) dietary modifications are a common treatment technique ; and 2 ) there are no objective criteria for thickened liquid preparation for assessment and / or treatment . this has led to little inter - clinician agreement and reliability in terms of thickened liquid consistency . therefore , there is a great need for a pre - made solutions , or kits that yield solutions , of known and consistent viscosity , thereby removing one source of uncertainty in the diagnosis and evaluation of dysphagia .
disclosed are kits containing two or more viscosity - standardized , edible solutions for evaluating human subjects for dysphagia . also disclosed are corresponding methods of using the kits for diagnosing dysphagia and for radiographic imaging of the oropharynx .