Blood Flow as a Technology in Percutaneous Absorption: The Assessment of the Cutaneous Microcirculation by Laser Doppler and Photoplethysmographic Techniques

Optical techniques for blood flow measurement were first introduced almost 70 years ago with the innovation of photoplethysmography (1), substantiated and expanded by Hertzman (2). Laser Doppler techniques came forth 40 years later (3), followed by the manufacture of commercial devices (4,5), which are used more frequently than photoplethysmography. These optical methodologies enable tracing of the movement of red blood cells in the skin. This is useful in following percutaneous penetration, when the penetrant has an effect on blood vessels or on blood flow. In addition, physiology and anatomy of the skin can be studied, as well as pathology. Moreover, laser Doppler flowmetry (LDF) measurements are applicable in the evaluation of internal diseases and conditions that affect the skin microvasculature.