Laser Doppler Flowmetry and Imaging: Methodological Studies

Laser Doppler flowmetry (LDF) and laser Doppler imaging (LDI) are modern methods for non-invasive and continuous assessment of skin blood flow. The techniques are based on the phenomenon that monochromatic light transilluminating a perfused tissue is spectrally broadened owing to scattering by moving blood cells. In this study, methodological aspects of the two methods are presented. LDF was used in healthy subjects and in patients with peripheral arterial occlusive disease to determine the skin perfusion pressure by measuring the flow cessation external pressure (FCEP). With a normal ankle index, FCEP is lower than the ankle pressure and with a decreased ankle index, FCEP correlates with the ankle pressure. LDF and LDI were used in healthy subjects to investigate the mechanisms of skin blood flow regulation particularly related to the sympathetic nervous system, and to elucidate the interrelation between skin temperature and skin blood flow. We found that LDF and LDI can be used to monitor sympathetic vasoconstriction. The interrelation between skin temperature and skin blood flow as measured with the laser Doppler techniques is ambiguous. LDI was used to examine the pathophysiological background to cold intolerance experienced by patients with traumatic division of the ulnar artery. Although ligation of the ulnar artery causes reduced finger skin blood flow, cold intolerance cannot be attributed solely to alterations in blood flow. A clinical test based on LDI was developed for routine assessment of the sympathetic vasoconstrictor response (VAC). Healthy subjects as well as patients with sympathectomy due to hand hyperhidrosis underwent the test procedure. A VAC nomogram was constructed in relation to which the patients with sympathectomy showed a clearly attenuated response. Finally, LDI was combined with digital photography to facilitate the interpretation of blood flow profiles in relation to clinical signs, and the device proved to be of clinical value