Impaired autonomic vascular control: a non linear dynamic analysis

The specific role of autonomic vascular control in determining non-linear behaviour of RR intervals is not clear. In 10 T₁₂-L₄ paraplegic subjects (light vascular autonomic impairment), 12 T₅-T₁₁ paraplegic subjects (moderate vascular autonomic impairment), and 24 controls RR time series were recorded (10 min): 1) in resting supine position; 2) sitting on the wheelchair and 3) during a light (5 W) arm exercise. Fractal dimension (FD), approximate entropy (ApEn) and the α scaling exponent (α-DFA, detrended fluctuation analysis) were calculated. The lesional level significantly affected ApEn (p = 0.004), FD (p = 0.007) and α-DFA (p = 0.002). Autonomic activation did not influence FD and α-DFA, but significantly affected ApEn (p = 0.035). It seems that FD and α-DFA are influenced by the changes in non-linear RR dynamics due to vascular autonomic impairment but not to autonomic activation, whereas ApEn may be equally responsive to either condition.