Cutaneous Blood Perfusion Laser Doppler Flowmetry

The laser Doppler flowmetry (LDF) is an excellent noninvasive technique for monitoring cutaneous blood perfusion. As an early indicator of inflammation and changes in the microcirculation, LDF has been applied in many fields of clinical medicine and dermatology in healthy skin as well as in inflammatory diseases (17), and also for research purposes in the vulvar skin (5,8,18,19). Monochromatic, coherent light is emitted onto the skin and reflected at different wavelengths by the tissue and by the moving red blood cells in small vessels. The reflected light is detected photoelectrically and a dimensionless output signal is generated, which is proportional to the red blood cell flow. The signal is then processed in a personal computer, and the perfusion level can be displayed and calculated in a color-coded manner on the screen. Areas of interest can be defined and analyzed separately. By using a Laser Doppler Perfusion Imager (LDPI), the disadvantage of placing the probe directly on the skin can be avoided. Furthermore, larger areas of up to 12 cm2 can be mapped (18). However, in the genital area, scanning larger areas is difficult, as the vulvar skin is not flat and, therefore, not parallel to the probe, which can lead to artifacts (18). The laser Doppler technique has been used to quantify the irritant response of the vulva to sodium lauryl sulfate (SLS) in an experimental setting. By using measuring intervals of 45 seconds with a sampling rate set at one measurement per second, a higher baseline but a lower blood flow increase of the vulvar skin was detected as compared to the forearm skin after exposure to SLS. The sensitivity for detecting changes of the relative blood flow was higher compared to visual scoring (7,8). In lichen sclerosus lesions, the perfusion was found to be elevated and even increased after mechanical alteration, due to scratching, mast cell degranulation, histamine release, and reactive vasodilatation (20). In epithelial tumors, such as the vulvar squamous cell carcinoma, increased cutaneous perfusion was detected using LDPI, which was attributed to neoangio-genesis with a lack of autonomic control (21). This method is relatively time consuming and easily influenced by environmental as well as individual-related factors (22). Constant measurement conditions, such as room temperature and relative humidity, must be maintained, as well as rest periods for the subjects (at least 20 minutes) prior to the measurements.

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