Waveform analysis of laser Doppler signals from normal and diabetic feet

Cutaneous perfusion of the feet of normal volunteers and diabetic patients were measured by laser Doppler fluxmetry. A test paradigm was followed in which the feet were studied at room temperature, during cooling, and during rewarming after cooling. The data files were analyzed using sequential Fourier techniques on serial 20 second segments. Contour plots were generated from the resulting 120 Fourier spectra and compared between the diabetic patients and the normal volunteers. The use of contour plots was found to be helpful in differentiating the diabetic from normal foot plots during this type of stress testing. Significant portions of the power spectra were found in the low frequencies (0.1-0.2 Hz) but there was also a strong component corresponding to the cardiac cycle with at least one harmonic of that cycle observed at two times the heart rate. Diabetic patients exhibited reductions in cutaneous perfusion with cooling in both the low frequency and heart rate frequencies. Sequential spectral analyses arranged in contour plots provide significant information about cutaneous perfusion using laser Doppler fluxmetry and prove useful in evaluating other pathologies characterized by cutaneous perfusion abnormalities