Fractal dimension analysis of the muscle sympathetic nerve activity

In order to analyze sympathetic nerve discharges as an entity, not as the decomposed parts, a non-linear mathematical analyzing technique including chaos and fractal theory was utilized in healthy normal subjects. Muscle sympathetic nerve activity (MSNA) was recorded using the microneurography technique during supine position and tilt up position. MSNA was integrated by the integrator and analyzed in the computer system using the non-linear mathematical analyzing technique. Time series data of the sympathetic nerve discharges were quantified in R-R interval time series data and analyzed with the Lorenz plot. Fractal dimension analysis of the MSNA was performed by the changing coarse graining level (box-counting method). Both during supine position and tilt up, MSNA showed the characteristics of fractals. After the tilt up of the bed, MSNA tone was increased and the fractal dimensions of both R-R interval and MSNA were increased. Our results suggest that MSNA tone contributed to the increases of the fractal dimension.