Evaluation of the quantum yield for E-->Z isomerization of bilirubin bound to human serum albumin. Evidence of internal conversion processes competing with configurational photoisomerization

Light-emitting diodes: a novel light source for phototherapy

High intensity light-emitting diodes (LEDs) are being studied as possible light sources for the phototherapy of hyperbilirubinemic neonates. These power-efficient, low heat-producing light sources have the potential to deliver high intensity light of narrow wavelength band in the blue-green portion of the visible light spectrum, which overlaps the absorption spectrum of bilirubin (BR). We compared the efficacy between single LEDs of different color and then constructed a prototype phototherapy device using 300 blue LEDs. The efficacy of this device was compared with that of conventional phototherapy devices by measuring the in vitro photodegradation of BR in human serum albumin. When blue, blue-green, green, and white LEDs were compared, the blue light was the most effective in degrading BR by 28% of dark control, followed by blue-green (18% of control), and then white light (14% of control). Green light was the least effective (11% of control). The prototype device with three focused arrays, each with 100 blue LEDs, generated greater irradiance (> 200 microW.cm-2.nm-1) than any of the conventional devices tested. It also supported the greatest rate of BR photodegradation. We conclude that light from LEDs should be considered a more effective treatment for hyperbilirubinemia than light from presently used phototherapy devices. Furthermore, the unique characteristics of this light source may make it especially suitable for use in safe and lightweight home phototherapy devices.

Fibreoptic phototherapy in the management of jaundice in low birthweight neonates

A fibreoptic phototherapy device has been compared with conventional white and special blue fluorescent phototherapy lamps to evaluate its efficacy in lowering serum bilirubin levels in low-birthweight neonates. Fibreoptic phototherapy was found to be as effective as white light and less effective than blue light, as assessed by (i) the bilirubin concentration after 24 h of phototherapy and at the end of phototherapy, (ii) the duration of phototherapy, (iii) the percentage daily decline rate and (iv) the overall percentage decline rate (p < 0.05). There were no failures of phototherapy and the need for re-exposure was low (4.7% of the total sample), with no difference between groups. The fibreoptic approach represents a promising way to aggregate synergically the most recent optical technologies and develop a modern, efficient and caring phototherapy system for low-birthweight infants.

Quantum yield and skin filtering effects on the formation rate of lumirubin

Photocyclization of bilirubin to lumirubin in the skin of jaundiced infants exposed to blue-green light irradiation is considered to be the most important process for bilirubin elimination from the organism. The quantum yield phi LR of the bilirubin-->lumirubin photoreaction has been recently measured and found to vary with the excitation wavelength, with a peak at about 520 nm. The quantum yield phi ZE for the strongly competing reversible configurational photoisomerization of bilirubin has also been recently shown to be wavelength dependent and to decrease significantly in the long-wavelength part of the absorption band of bilirubin. These new data are taken into account to model the bilirubin photochemistry in vivo by using a simplified skin optical model based on the Kubelka-Munk theory. The rate kappa LR of formation of lumirubin has been evaluated for the case of a four-layer skin and for monochromatic and narrow-band coloured fluorescent lamps. The effects of long-wavelength increase in phi LR, decrease in phi ZE and skin optical losses all combine to shift significantly the optimal rate of formation of lumirubin towards the green. These results suggest that a significant improvement in phototherapy might be obtained with the introduction of new lamps emitting in the blue-green spectral region between 490 and 510 nm.