A method to detect insulin resistance, diabetes and/or cardiovascular or autonomic neuropathy complications, the method comprising performing a spectral analysis using Fast Fourier Transformation (FFT) of the first derivative of total records of an oximeter wave form (plethysmograph), to obtain 3 frequencies high (PTGHF), low (PTGLF) and very low (PTGVLF) frequencies wherein the sum of the 3 frequencies is the total power of the spectral analysis in ms2 (PTG TP) and wherein the sum of the amplitude of the 3 frequencies is the PTG Index of the Spectral Analysis (PTGi).
