Session P36.2

Autonomic Response Evaluation during Gradual Body Weight Support: Comparison between Spectral and Symbolic Analysis

V Magagnin*, EG Caiani, L Fusini, M Turiel,
S Cerutti, A Porta

Politecnico di Milano
Milano, Italy

Recently developed robot-driven walking therapies include body weight support (BWS) during assisted locomotion. However, the effect of BWS itself on the autonomic nervous system is unknown. Our aim was to evaluate the autonomic nervous system response during BWS in normal subjects, by both autoregressive power spectral analysis (AR) and symbolic analysis (SA) of heart rate variability (HRV).
Methods: In 10 normal subjects (23±2.3 years) in standing position, ECG (sampling rate 2048 Hz) was collected during 5 phases of 5 min each with different % of BWS applied: 0%, 25%, 50%, 75%; and 100%. The %BWS were applied in random order and followed each by 5 min sitting. After HRV series extraction, AR was computed by Levinson-Durbin recursion (Akaike figure of merit). The existing oscillations were classified as very low frequency (<.04 Hz), low-frequency (LF, 04-.14 Hz) and high-frequency (HF, .15-.4 Hz). The LF and HF powers were expressed in both normalized (LFnu, HFnu) and absolute (LFRR, HFRR) units. For SA, HRV series were uniformly quantized over 6 bins, thus becoming a series of symbols (from 0 to 5). These values were grouped into words of length 3, which were classified into 4 families according to the type of variation of symbols in each word: i) no variation (0V); ii) one variation (1V); iii) two like variations (2LV); iv) two unlike variations (2UV). Then, the rate of occurrence of each family (0V%, 1V%, 2LV%, 2UV%) was assessed.
Results: Increase in BWS induced a progressive reduction in mean RR, significant at 75% and 100% vs 0% (Friedman test). Moreover, a reduction in HFRR at 100% vs 0% was noted, while LFnu and HFnu showed respectively an increasing and decreasing trend with increase in BWS. SA showed an increasing trend during 75% and 100% in 2UV%, and a corresponding decrease in 0V%.
Conclusions: Results from both AR and SA indicated a gradual sympathetic activation and parasympathetic inhibition with increasing %BWS. Since changes were not remarkable, our findings suggest that increase in BWS generates a light sympathetic stimulation. Our results could help to tailor robot-driven walking therapies preventing discomfort and improving rehabilitation.

(Abstract Control Number: 72)