Researchers design device to assess children’s lungs

Technology under development at Oxford University could allow doctors to monitor lung diseases in young children by measuring the gases they breathe out.

A team of researchers led by Dr Andrew Farmery are creating a non-invasive device that uses a computer model to determine the condition of a patient’s lungs based on sensor readings of how much oxygen or other gases they exhale.

‘[Children] are very difficult to study because they don’t co-operate with you in the same way that adults might,’ Farmery told The Engineer.

‘You can ask an adult to breathe out or hold their breath, but with children and babies, especially if they’re on a ventilator, you don’t have the opportunity for that. So we wanted a non-invasive system that requires no patient co-operation.’

The device will use a mouthpiece to inject gas at varying concentrations into the lungs of children with conditions such as asthma and cystic fibrosis.

Sensors will detect the proportion of gas exhaled and software will use this information to calculate several lung characteristics that will allow doctors to assess a patient’s condition.

These include the total lung volume at rest, the proportion of breath that never reaches the lung’s gas exchangers (known as dead space) and how unevenly distributed the ventilation and diffusion of gas is in an unhealthy lung.

To successfully monitor the very small quantities of gas exhaled from young children’s lungs will require very rapid sensors, said Farmery.

The technology will also need a very accurate system for injecting the gas at the required and changing concentrations into the patient’s lungs.

This will have to be able to adapt fast enough to changing breathing patterns, so that the amount of gas entering the lungs is consistent whether the patient is taking a large or small breath.

Farmery and his team have been researching this process for almost 10 years and have tested the principle on adult patients.

They now plan to use a £469,000 EPSRC grant to miniaturise the sensing technology and create a proof-of-concept device for children that by 2014 can be taken to medical manufacturers for prototyping.

The system will work by regularly increasing and decreasing the concentration of a specific gas (such as oxygen or nitrous oxide) the patient is breathing in, effectively creating a signal that can be plotted as a repeating ‘sinusoidal’ wave.

The concentration of gas that is exhaled will vary in a similar way and produce a corresponding signal. In a healthy lung, changing the frequency of the inhale signal (the speed at which the gas concentration is varied) will produce a predictable change in the exhale signal.

But in an unhealthy lung, where gas ventilation and diffusion varies throughout the lung depending on the patient’s condition, the returned signal becomes more difficult to predict.

‘By looking at how the lung responds to changes in frequency, we can model the degree of heterogeneity in the ventilation and diffusion of the lung,’ said Farmery.