Non-invasive monitoring of blood glucose

Non-invasive methods for blood component analysis are attractive by their evident advantages such as real time monitoring, immunity to infection, possibility to control the concentrations of blood components, and providing painless measurement as often as necessary. A simple algorithm that uses the logarithmic ratio of two signals was successfully applied in the case of noninvasive bilirubin measurement. In contrast with bilirubin, glucose absorption takes place in the near infrared range where absorption by other components such as water, proteins, hemoglobin is significant. Therefore, a proper algorithm should use signal wavelengths, which are relatively free from the overlapping with the absorption bands of other major components. At the same time, the influence of other blood components whose concentrations may induce optically interfering signals should be minimized. The authors present here a simple, but efficient algorithm, which can be described on the base of analysis of the light propagation in blood. The algorithm may use any number of discrete wavelengths. A pulsed polychromatic light source is used. The light source emits a light pulse with a time duration of 500 /spl mu/s in wide bandwidth which includes light in the near infrared spectrum (energy of the pulse in near infrared range is 900 mW). Light source and detector unit was carefully designed so that reflected light from the skin surface was not measured. Prisms, fiber bundles, dispersing elements, etc. were used for propagating, directing and collecting oflight. The distance between the beam and detector, which could be adjusted between 2 and 10 mm, was set to be sufficient to avoid surface reflection and to minimize the effects of tissue scattering. Four interference filters as spectral selective elements around wavelengths 1625 nm, 1364 nm, 1300 nm and 1200 nm were used. Two different light sources, flash lamp and LED array were tried for the experiment.