Doctors are working on drugs to treat cystic fibrosis

Chris Clark from Bristol came up with the idea for the inflatable device after caring for her son Cellen, 8, who has the condition.

Children with cystic fibrosis (CF) need physiotherapy two or three times a day for around 20 minutes at a time to clear the thick, sticky lung secretions from blocking the air tubes.

They have to be positioned at an angle for the therapy.

Small children can lie across their parent's knee.

But as children grow older, they have to rest on so-called tipping wedges to have their treatment.

These are usually solid 'cheese wedge' shapes, usually made of plastic.

'Bulky'

Ms Clark, who lives with Cellen and her other son Jamie, 14, in Bristol, says while these are fine to use at home, they cannot be transported - and holidays can be difficult.

She told BBC News Online: "I have to make a lot of trips to see my parents who live in Essex.

"You can't fold the traditional wedges and put then into a boot, or take them on a plane.

"Even the bean-bags which you can use are too bulky to transport."

My aim is to help other mothers who want to travel about and give their children a better quality of life Chris Clark

"I realised the need for a portable device after a frustrating holiday to France. I decided I would have to do something."

With the help of her father, Chris started designing a portable, inflatable wedge, using computer design.

She then approached local manufacturers in a search for a suitable material.

"It had to be something that would not harbour bacteria and something that could be inflated and deflated easily."

Some prototypes were made, but none were suitable.

Production aim

Chris then teamed up with Innovate Design in London who helped her find a Chinese company who could create a version.

They made a wedge from flocked PVC - the same material that airbeds are made of.

The wedge is blown up using an air pump.

Now Chris is looking for a manufacturer to help her take the wedge into production.

"I would hope it could sell at around �50. But first, I've got to find someone to make it."

She adds: "My aim is to help other mothers who want to travel about and give their children a better quality of life."

A spokeswoman for the Cystic Fibrosis Trust said: "Any new device needs to be checked out. There are various types of wedges already available.

"This could be something that could be useful for other families."