Femoral artery doppler signal analysis in lower limb ischaemia.

The functional significance of the iliac artery stenosis was assessed non invasively using femoral artery Doppler signals and a new method of blood velocity waveform quantification. This mathematical analysis provided an index, the Laplace Transform Damping (LTD), which was compared with Pulsatility Index (PI) of 263 limbs, in patients with iliac occlusive atherosclerosis was demonstrated by arteriogram and in normal volunteers. Normal LTD results ranged from 0.26 to 0.43 with detection of minor iliac stenosis (less than 50%) at 0.51 (0.38 to 0.63) and major stenosis (greater than 50%) at 0.83 (0.55 to 0.99). LTD was not affected by raised distal impedance associated with superficial femoral artery (SFA) occlusion. PI however was poor at predicting the severity of iliac lesions in the presence of SFA occlusion. LTD and PI specificities and sensitivities were examined using receiver operator curves. At a value of 0.6 LTD was more sensitive than PI in separating major from minor iliac stenoses and at 0.4 LTD separated normals from the early disease group with a sensitivity of 81% and specificity of 88%. This preliminary experience with Laplace Transform Damping analysis suggests that it will improve the assessment of iliac stenosis especially in the presence of femoro-popliteal disease.