Nonspecific vasodilatation during transdermal iontophoresis-the effect of voltage over the skin.

We used laser Doppler perfusion imaging (LDPI) to study nonspecific vasodilatation during iontophoresis. In iontophoresis studies, nonspecific vasodilatation occurs as a result either of galvanic currents or of the applied voltage over the skin. We made dose-response measurements to study the effect of ionic strength of the vehicle on the nonspecific vasodilatation during iontophoresis of sodium chloride and deionized water, while we monitored the voltage over the skin. We found that anodal and cathodal ionotophoresis induced a voltage over the skin that was dependent on the ionic strength of the test solution. The nonspecific vasodilatation during anodal iontophoresis was less pronounced than during cathodal iontophoresis, and was independent of the voltage over the skin. The nonspecific vasodilatation in cathodal iontophoresis was related to the voltage over the skin, and was possibly mediated by depolarization of local sensory nerves. In experiments using cathodal iontophoresis, therefore, the ionic strengths of the vehicle and the drug are important when vasoactive drugs are examined, as the nonspecific vasodilatation needs to be controlled for. As the vasodilatation that we observed was heterogeneously distributed within the area of iontophoresis, LDPI may provide more accurate measurements than conventional laser Doppler perfusion monitoring.

Measurement of depth of burns by laser Doppler perfusion imaging.

Laser Doppler perfusion imaging (LDPI), is a further development in laser Doppler flowmetry (LDF). Its advantage is that it enables assessment of microvascular blood flow in a predefined skin area rather than, as for LDF, in one place. In many ways this method seems to be more promising than LDF in the assessment of burn wounds. However, several methodological issues that are inherent in the LDPI technique, and are relevant for the assessment of burn depth, must be clarified. These include the effect of scanning distance, curvature of the tissue, thickness of topical wound dressings, and pathophysiological effects of skin colour, blisters, and wound fluids. Furthermore, we soon realised that to examine the perfusion image generated by LDPI adequately the process of analysis was appreciably improved by the simultaneous use of digital photography. In the present investigation we used both in vitro and in vivo models and also examined burned patients, and found that the listed factors all significantly affected the LDPI output signal. However, if these factors are known to the examiner, most of them can be adjusted for. If the technique is further improved by minimizing such effects and by reducing the practical difficulties of applying it to a burned patient in the burns unit, the technique may find uses in everyday clinical decision-making.