Help for dysphagia

A cheap, self-sensing device that accurately measures food consistency to help control the diet of elderly people who have difficulty swallowing is being developed by researchers at

(UCL).

People with dysphagia — disorders that affect a person's ability to swallow — as a result of a stroke or cancer of the head or neck, are prescribed fluid foods of a particular thickness so they can be swallowed safely.

At present, the required viscosity of food, which varies from person to person, is prescribed by speech and language therapists and interpreted by nurses using subjective terms such as 'honey thick'. The new device would enable consistencies to be defined exactly.

'A few years ago, I made a little gadget that was able to move and provide force, and at the same time it could sense how much force it was applying and how much it was moving without any force or displacement sensors,' said Dr Ben Hanson at UCL. 'It is basically a coil of wire and a magnet, and not much else.'

By using a mathematical model, the researchers can predict a certain relationship between the current and voltage in the device. Any changes to this relationship, for example caused by an increased force on it, produces an unexpected current-voltage relationship that is compared with the model and converted into a measurement of fluid viscosity.

The new battery-powered device will be based on one that Hanson first created at Leeds University to measure the consistency of bone cement used to glue in hip joints. Usually, after mixing up the cement as a paste (which sets after about 15 minutes), surgeons simply hold a small lump of it in their hands and use their judgement to determine the optimum point of viscosity for applying the cement.

'What they needed was a viscometer or a rheometer, but those things are really expensive and delicate and you need to be trained to use them,' said Hanson.

'With our device, you have a little pot of cement and you stick a little spindle into it and the device tries to spin the spindle back and forwards by about 10°. The stiffer the cement, the harder it is to turn and the device measures that and displays the results on a graph.'

People with dysphagia will have difficulty swallowing runny liquids such as water, because it either spills out of their mouth or runs to the back of their throat, so they inhale it into their lungs, where it can stay and become infected, possibly leading to death.

Runny liquids are therefore thickened to a certain level of viscosity with a powder, but this is not straightforward because the behaviour of different foods with the powder mixture is unpredictable. This means when the same volume of powder is mixed with orange juice, a different consistency would be obtained than if it were mixed with hot coffee, for example.

In the new application, Hanson will use the device to measure the viscosity of the food, and also to better understand the elastic qualities of the food fluids.

'When you mix up these powders and liquids, as well as being thick, they have got an elastic component to them — like a blancmange,' he said. 'If you have got some on a spoon, it will sit there and not run off, so in some senses it is very viscous. But if you wanted to swallow it, it is easy to do because it mushes up into a runny mixture in your mouth. The technical term for this is pseudo-plastic.'

Eventually, the UCL team aims to develop an indicator that can be used by everyone as a standard measurement of consistency corresponding to numbers on a scale. Industry partner Fresenius Kabi, a manufacturer of the food-thickening products, is also interested in the benefits of the device for training purposes.

Anh Nguyen