Laser Doppler Perfusion Monitoring and Imaging especially as regards testing for sympathetic nerve function

Abstract: The operating principle of all laser Doppler methods is based on the fact that incident photons shift in wavelength when interacting with moving blood cells passing through the microvascular network. After photodetection and further signal processing, the recorded parameter can be considered an arbitrary measure of tissue blood flow, and this is referred to as ?perfusion?. Laser Doppler perfusion monitoring with a probe (LDPM) gives a real-time recording from a small area, whereas imaging by use of a scanner (LDPI) creates an instant view of the spatial distribution over a wider area. Measurements are influenced by a variety of instrumental factors such as probe configuration and light wavelength. This thesis presents findings regarding changes of skin microcirculation when assessed by various technologies, and special attention was paid to those changes induced by sympathetically mediated vasoconstriction. Finger skin blood flow was investigated both in healthy subjects, and in patients with diabetes mellitus. Measurements with LDPM were performed with different probe configurations related to distance between emitting and detecting fibres. Measurements with LDPI were performed with different light wavelengths. In three experimental series, contra-lateral hand cooling induced vasoconstriction. In one series, the effects of local heating were explored. Besides the perfusion parameter, details regarding the concentration of moving blood cells and their average velocity were displayed and analysed. Our clinical findings are coherent with technical and theoretical assumptions. Hence, the wider fibre separation in LDPM the deeper the measurement and an increment in wavelength seem to have a similar effect. However, superficial capillary blood flow and deeper shunt blood flow cannot reliably be distinguished from one another by means of these different instrumental standards. Neither can the separation of the perfusion parameter into velocity and concentration with safety be used for this purpose. However, velocity and concentration may be used for clarifying various microcirculatory events from the physiological point of view. We found for instance that the two components act merely parallel at low and moderate perfusion rates, whereas a high perfusion rate primarily is associated with an increase in concentration. By applying frequency analysis, it was furthermore shown that the movement of the column of blood periodically reaches the peripheral vascular bed concurrently with the cardiac cycle whereas concentration remains the same. As microvascular blood flow cannot be measured quantitatively and due to varying instrumental design, the need for widely accepted and standardised test procedures and protocols is apparent. The cold pressor test used in this thesis is just one example. Under such given circumstances, the test parameter may be practically independent of the laser Doppler device used, as shown by the vasoconstriction index in the present studies. Diabetic patients showed an attenuated vasoconstriction response, and the index can reliably be used to monitoring peripheral sympathetic nerve function in these patients.