Touching outlawed by hands-free monitor – Photon02

A Loughborough University research team, led by Professor Peter Smith and Vincent Crabtree, has developed a way of monitoring the blood flowing in human body tissue without actually touching the skin. This hands-free technique could one day be used to assess patients during surgery and monitor the healing of wounds or burns. Other applications include a remote heart rate monitor.

Speaking at the Photon02 Conference in Cardiff on Monday 2 September Mr Crabtree will explain how the team adapted an existing optoelectronic monitoring technique by removing the need for skin contact.

The conventional technique, called photoplethysmography (PPG), involves illuminating a section of the body, which is in contact with the detector, and working out how much of the light is absorbed. This is done by detecting a cardiovascular pulse wave, which consists of a large static component relating to the blood in the veins and a smaller dynamic component relating to the blood in the arteries. The size and shape of the pulse wave depends on the properties of the blood flowing through the tissue, this is worked out from how much light the tissue sample absorbs.

Professor Smith`s team realised that the skin contact probes used in previous PPG monitoring systems were often hard to attach to difficult-to-reach parts of the body. When a patient moves the probes also interfere with the signal. Building a non-contact PPG system increased these interference problems, as the longer distances between the body and the detector meant that interference due to movement and the presence of natural light was increased.

The team combatted these problems by first filtering out interference from natural light by taking a measurement when the body was not illuminated. This reading was then deducted from the pulse signal when the system was switched on.

Patient movement was much harder to deal with. By conducted a series of experiments the relationship between movement and the received signal was found. Using these results the team built a computer programme that predicts how the pulse signal is affected by movements and automatically corrects it.

Mr Crabtree said: “By addressing the issues of signal corruption, a remote PPG system has been demonstrated for the first time. Future applications for this technology could be extensive. However, the remote PPG signal quality has only been investigated over a range of several centimetres so far.”