Non-contact blood monitor developed

A method of monitoring blood flow in human body tissue without touching the skin has been developed by researchers at Loughborough University, in the English Midlands.

This hands-free technique could one day be used for remote heart monitoring, and for the assessment of patients, either during surgery or the healing of wounds or burns.

The team, led by Professor Peter Smith, 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 that 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 static tissue components, and a smaller dynamic component relating essentially 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 and this is worked out from how much light the tissue sample absorbs.

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

Tracking these signals of interest is rather like trying to find a needle in a moving haystack. Detecting very small light sources at large distances can be done but when the signal is present in a background light source that is varying over levels far in excess of the signal size, then some further intelligence is required.

The researchers pinpointed the relationship between movement and the received signal by conducting a series of experiments, the results of which enabled them to establish appropriate illumination sources, adaptive detection systems and a computer program that not only predicts how the pulse signal is affected by movements, but automatically corrects it.

This technology will benefit patients and healthcare professionals in providing more accurate and reliable perfusion measurements in circumstances where contact is undesirable or perhaps not possible; examples include the monitoring of wound healing and peripheral arterial disease.