A diffuse reflectance spectroscopic study of UV-induced erythematous reaction across well-defined borders in human skin.

INTRODUCTION: The colour of tissue is often of clinical use in the diagnosis of tissue homeostasis and physiological responses to various stimuli. Determining tissue colour changes and borders, however, often poses an intricate problem and visual examination, constituting clinical praxis, does not allow them to be objectively characterized or quantified. Demands for increased inter- and intra-observer reproducibility have been incentives for the introduction of objective methods and techniques for tissue colour (e.g. erythema) evaluation. The aim of the present paper was to study the border zone of a UVB-provoked erythematous response of human skin in terms of blood volume and oxygenation measured by means of diffuse reflectance spectroscopy using a commercial probe. MATERIAL AND METHODS: A provocation model, based on partial masking of irradiated skin areas, defines two erythema edges at every skin site responding to the UV irradiation. In every subject, five test sites were exposed with a constant UV light irradiance (14 mW/cm(2)), but with different exposure times (0, 3, 6, 9 and 12 s). An analysis of the spectral data measured across the two edges was performed for every scan line. The oxygenized and deoxygenized haemoglobin contents were estimated in every measurement point, using a modified Beer-Lambert model. RESULTS: The fit of the experimental data to the model derived by the modified Beer-Lambert law was excellent (R(2)>0.95). Analysing data for the chromophore content showed that the erythematous response in the provoked areas is dominated by the increase in oxyhaemoglobin. The widths for the left and right border zone were estimated to be 1.81+/-0.93 and 1.90+/-0.88 mm, respectively (mean+/-SD). The unprovoked area between the two edges was estimated to be 0.77+/-0.68 mm. CONCLUSION: While the chosen data analysis performed satisfactorily, the ability of the probe design to differentiate the spatial aspects of a reaction with abrupt borders was found to be suboptimal resulting in a probable overestimation of the erythematous edge slope. Probe modification or imaging techniques are possible solutions.

Phototesting with a divergent UVB beam in the investigation of anti-inflammatory effects of topically applied substances.

BACKGROUND: Phototesting based on a single exposure to a divergent ultraviolet B (UVB) beam with radially decreasing UVB doses can be used to determine an individual's minimal erythema dose (MED). Laser Doppler perfusion imaging (LDPI) data can be combined with dosimetry data to produce objective dose-response plots in addition to the MED. The aim of this study was to investigate whether the divergent beam protocol could be used to demonstrate and quantify the anti-inflammatory effects of clobetasol diproprionate (Dermovate), pharmaceutical-grade acetone and a gel vehicle, applied after skin provocation by UVB. METHOD: Sixteen Caucasian subjects were illuminated with the divergent beam on three areas close together on the left side of their upper backs. Two of the provoked areas on each subject were treated with acetone, gel vehicle or Dermovate, and one area was left untreated as a control. Skin blood perfusion was assessed 6 and 24 h after UVB illumination using LDPI. The reaction diameter, the mean perfusion, and the average dose-response plots for each group and treatment were extracted from the LDPI data. RESULTS: Application of the topical steroid clobetasol diproprionate after UVB provocation markedly decreased the inflammatory response. Acetone and the gel vehicle also showed mild anti-inflammmatory effects in two of the parameters but not for the mean perfusion response. The mean diameter differences between controls and treated reactions had predominantly positive 99% confidence intervals. Analysis of the dose-response data at doses higher than the MED showed a linear relationship (0.89