Non-invasive measurement of tissue oxygenation using near infrared (NIR) spectroscopy

Non-invasive optical spectroscopy across many centimetres of living tissue is possible at wavelengths between 650 nm and 1100 nm. The short wavelength cut-off wavelength is caused by absorption of light by haemoglobin and the long wavelength cut-off by water absorption. Typical NIR attenuation coefficients are one optical density loss for each centimetre of tissue travelled. Haemoglobin is present in the circulation, and in its oxygenated (HbO/sub 2/) and deoxygenated (Hb) forms acts as an indicator of blood oxygenation while cytochrome c oxidase (Cyt) in its oxidised and reduced forms is present in the tissue and acts as an indicator of intracellular oxygenation. Problems of multiple scattering in tissue spectroscopy are examined and a method proposed for determining the differential pathlength. Possibilities of adapting the technique to bedside monitoring are also discussed.<
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