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Non-invasive Continuous Measuring the Oxygen Saturation by Listening To the Sound of Light

Patients that suffer from stroke, shock and other brain diseases can benefit in the near future from POSTs (Photoacoustic Oxygen SaTuration sensor) – a new invention by Nanyang Technological University scientists which could help doctors to diagnose these brain disorders in their early stage for better treatment outcomes.

Researchers at Nanyang Technological University’s School of Electrical and Electronic Engineering (EEE) have created an iPhone-sized sensor to help doctors to detect shock in the early stage non-invasively. Their breakthrough could lead to a more effective diagnosis that will lead to better treatments of shock and other brain related diseases.

In hospital ERs, OTs and ICUs, it is a matter of life to rapidly and accurately detect the patient who is suffering from shock, and to rapidly institute treatment to save their lives. Shock is a state where there is a reduced delivery of blood and oxygen to the tissues to meet metabolic needs. There are typical clinical features of shock, such as fast heart rates, low blood pressures, altered mental status and reduced urine output, but many patients may not exhibit these features. There are also biochemical measures of shock, but they are only begin to be raised later in the disease process.

Haemoglobin oxygen saturation of blood in the central veins (SvO2), however, begins to fall early in shock even when blood pressures appear normal. In patients with shock, the SvO2 becomes lower than normal (<65%), reflecting a poor delivery of blood to oxygen-starved tissues. On the other hand, abnormally high levels of SvO2 reflects a reduced ability of the tissues to metabolise oxygen. Thus, SvO2 is an invaluable parameter for shock diagnosing.

Conventionally, SvO2 can only be measured invasively using catheters in the right superior vena cava or in the jugular vein. The insertions of such catheters are by themselves risky, and only performed in select patients. Thus measurements of these values cannot be performed as a screening tool to identify patients who may be missed.

A group from EEE of Nanyang Technological University had designed a novel portable sensor --POSTs, that can detect SvO2 accurately in a non-invasive manner. The sensor works by shining light of different colours on patients' neck and then "listening to" the resultant sound generated by the blood in the central vein to infer the SvO2. The result is very accurate (~ 2%) since oxygenated and de-oxygenated haemoglobin show distinct signatures in absorbing different colours of light and the generated sound waves could be accurately localised (<1 mm) with high signal to noise ratio. The measurement process is real time and the device is iPhone sized, making it suitable for continuous monitoring.

Professor Zheng Yuanjin from EEE said: “The results demonstrate that POSTs has great potential in non-invasive SvO2 measurement and could be used in the ICUs in the near future for early detection of shock, which reduces the onus of doctor and the pain of patients.”

 

Photoacoustic Oxygen SaTuration Sensor (NTU EEE Prof. Zheng Yuanjin’s Lab)

 

 
 

By Professor Zheng Yuanjin, School of EEE

 
 
 
 
Published on: 31-Oct-2016