Cutaneous vasomotor reactions in response to controlled heat applied on various body regions of healthy humans: evaluation of time course and application parameters.

Skin permeability and local blood perfusion are important factors for transdermal drug delivery. Application of heat is expected to enhance microcirculation and local perfusion and/or blood vessel permeability, thus facilitating drug transfer to the systemic circulation. In addition, heating prior to or during topical application of a drug may facilitate skin penetration, increase kinetic energy, and facilitate drug absorption. The aim of the present study was to investigate skin vasomotor responses to mild heat generated by a controlled heat device on several body regions of healthy male and female subjects. Skin vasomotor responses in different body regions were recorded following different heat application paradigms (38, 41 and 43 °C, each for 15, 30, 60 sec). Test regions were forehead, forearm, dorsal hand, dorsal foot, and abdomen. Prior to and following the application of heat, local blood perfusion and skin temperature were measured by means of laser Doppler imaging (LDI) and thermography, respectively. It was found that a short-lasting heat application (43 °C for 60 sec) causes significant cutaneous hyperaemia (up to 2 folds increase in skin perfusion, and 5 °C increase in skin temperature) existing for up to 15 minutes. The site of application and sex did not influence the responses. The method was well tolerated without causing any pain or discomfort. These data suggest that controlled heat application is a simple, non-invasive method to significantly enhance local perfusion which may improve transcutaneous drug delivery.