Noninvasive Detection of Bilirubin in Discrete Vessels

Bilirubin, at the levels encountered in hyperbilirubinaemia, makes a similar contribution to blue light absorption as reduced haemoglobin makes to red light absorption of blood. Whilst this supports the possibility of extending pulse oximetry into the blue part of the spectrum for the noninvasive monitoring of bilirubin, the modulating effects of discrete blood vessels tend to disrupt the relationship between blood absorption coefficients and pulsations in light transmission through tissue at these wavelengths. The relationship between the pulsatile attenuation of blue and green light and serum bilirubin concentration was investigated with a Beer-Lambert pulse oximetry model, a discrete blood vessel model, and in vivo. Whilst the Beer-Lambert model indicated a positive relationship between the blue/green light pulsatile attenuation ratio and serum bilirubin, both in vivo testing and the discrete blood vessel model demonstrated negative correlations. The variability in results from in vivo tests indicated that these correlations could not be used for reliable bilirubin estimation.