Skin temperature changes and changes in skin blood flow monitored with laser Doppler flowmetry and imaging: A methodological study in normal humans

The aim of the present study was to elucidate the interrelation between changes in skin temperature and changes in skin blood flow, as measured by laser Doppler techniques. Therefore, 17 healthy volunteers were studied upon immersion of both feet in water of 15 degrees C for 10 min followed by body warming for 30 min. Measurements using laser Doppler flowmetry (LDF) were performed from the nailfold of the big toe, while measurements using laser Doppler imaging (LDI) were performed from the dorsum of the foot. Temperatures were recorded simultaneously from the toe tip and the dorsal foot skin. Temperatures at the toe tip were significantly lower than at the dorsal foot skin. Cooling caused decreased values in all parameters, with restitution during indirect heating. There was an exponential interrelation between LDF and temperature readings from the toe owing to very high LDF values at the end of indirect heating. On the dorsum of the foot, relative changes in LDI and temperature showed a linear relationship (r(s)=0.65), although LDI values were consistently higher than temperatures. It is concluded that temperature readings constitute an ambiguous measure of skin blood flow. On the toe tip, blood flow through opened arteriovenous shunts during indirect heating does not correlate with temperature. Cooling of the foot decreases skin temperature, mainly by heat conduction, whereas skin blood flow is only slightly reduced.