Application of autoregressive moving average spectral analysis for red blood cell sedimentation rate estimation by an ultrasonic interferometry method

The signal measured by the ultrasonic interferometry method (EchoCell) that allows one to estimate the sedimentation rate of red blood cells (RBCs), has been investigated until now in the time domain. So, in the present study, the authors propose as an alternate approach, the investigation of that signal in the frequency domain. Firstly an autoregressive moving average model (ARMA) was used to produce a waveform that approximates the original signal. The power spectrum density function based on the ARMA parameters was then calculated for non-aggregated and aggregated RBC suspensions at various hematocrits. The results shows that the calculated ARMA spectrum of the signal gives information on estimation of accumulation rate of RBCs, i.e., on their sedimentation rate.