Detrended fluctuation analysis of compound action potentials re-corded in the cutaneous nerves of diabetic rats

The electrophysiological alterations in nerves due to diabetes are classically studied in relationto their instantaneous frequency, conduction velocity and amplitude. However, analysisof amplitude variability may reflect the occurrence of feedback loop mechanisms thatadjust the output as a function of its previous activity could indicate fractal dynamics.We assume that a peripheral neuropathy, such as that evoked by diabetes, the inabilityto maintain a steady flow of sensory information is reflected as a breakdown of the longrange power-law correlation of CAP area fluctuation from cutaneous nerves. To test this, wefirst explored in normal rats whether fluctuations in the trial-to-trial CAP area showed aself-similar behavior or fractal structure by means of detrended fluctuations analysis (DFA),and Poincare plots. In addition, we determine whether such CAP fluctuations varied by diabetesinduction. Results showed that CAP area fluctuation of SU nerves evoked in normalrats present a long term correlation and self-similar organization (fractal behavior) fromtrial to trial stimulation as evidenced by DFA of CAP areas. However, CAPs recorded in diabeticnerves exhibited significant reductions in area, larger duration and increased areavariability and different Poincare plots than control nerves. The Hurst exponent value determinedwith the DFA method from a series of 2000 CAPs evoked in diabetic SU nerveswas smaller than in control nerves. It is proposed that in cutaneous nerves of normal ratsvariability of the CAP area present a long term correlation and self-similar organization(fractal behavior), and reflect the ability to maintain a steady flow of sensory informationthrough cutaneous nerves. Nevertheless, this is not the case for sural nerves of diabeticrats which is reflected as a breakdown of the long range power-law correlation of CAParea fluctuation. Nonlinear time series analysis of CAP area fluctuations is a valuable new insight tool that can be used for the study of alterations in transmission of sensoryinfor-mation in humans suffering diabetes or under other demyelination diseases.