Laser doppler flux reappearance time (FRT) in patients with lower limb atherosclerosis and healthy controls

Laser doppler flowmetry was used to examine the skin circulation in the lower limb during postischaemic reactive hyperaemia. Flux reappearance time (FRT), the time from tourniquet deflation to the start of the hyperaemic response, was detremined from the recorded curves, and the aim of the study was to investigate whether FRT is dependent on total limb vascular resistance or to the resistance in a segment of the limb. FRT was first compared with the clinical situation of the examined subjects, and with the resting ankle blood pressure index (API). Controls had an immediate hyperaemic response (FRT ⩽3 s), while patients with critical ischaemia had prolonged FRT (> 48 s). Among the claudicators there was no significant correlation between API or ankle blood pressure and FRT. When FRT was compared with angiography, all claudicators who only had significant atherosclerosis proximal to the tourniquet, had FRT values within the control range. Patients who only had distal atherosclerosis had prolonged values (> 15 s), indicating that FRT is independent of proximal atherosclerosis and reflects the vascular resistance in the arteries in the segment between the tourniquet and the measuring probe. This interpretation was supported by the reduction of pathologically prolonged FRT when the distance between the tourniquet and the measuring site was reduced. We conclude that FRT as measured by this technique seems to reflect the vascular resistance in the run off arteries distal to the tourniquet.