Effects of Spinal Section and of Positive-Feedback Excitatory Reflex on Sympathetic and Heart Rate Variability (original) (raw)
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The spinally mediated 10-Hz rhythm in the sympathetic nerve activity of cats
Journal of the autonomic nervous system, 1995
To examine the origin of the so-called '10-Hz rhythm' in the sympathetic nerves, the mass discharges of the white ramus of the third thoracic segment (T3WR) and the inferior cardiac nerve (ICN) and the activities of single postganglionic neurons in the stellate ganglion were recorded in spinal cats. During the chemical or electrical stimulation of the spinal cord, the time of peak of discharges in the sympathetic nerves was analyzed. Both intrathecal administration of N-methyl-D-aspartic acid (NMDA; 3-10 mM) and continuous high frequency (80-200 Hz) electrical stimulation of the dorsolateral funiculus at the second cervical level increased activity of the sympathetic nerves in a similar fashion. In these conditions, modes of the inter-peak interval histograms (IPIH) were about 100 ms (range; 90-130 ms), the inverse of about 10 Hz, but no correlation was observed in autocorrelograms of these peaks of discharges. Therefore, this 100-ms interval activity might have some signifi...
Estimation of self-similarity is a promising tool for quantifying alterations in cardiovascular dynamics. To evaluate the as yet unexplored influence of sympathetic vascular regulation on the scaling exponent, namely on the parameter characterizing self-similarity, we studied patients with a spinal cord injury as a model of progressively impaired vascular control. We considered 24 able-bodied subjects (AB) and 23 paraplegics with increasing lesion levels: between T 12 and L 4 (ns7); T 5 and T 11 (ns9); and C 6 and T 4 (ns7). We recorded the heart rate in three conditions characterized by increasing sympathetic activation: supine (SUP), sitting (SIT) and exercise (EXE). We calculated the scaling exponent by detrended fluctuation analysis (H DFA). Sympathetic activation had different effects on H DFA , depending on the lesion level. H DFA tended to decrease in AB from SUP (0.85q0.02; mean-qSEM) and SIT (0.84q0.02) to EXE (0.79q0.02). It remained constant in the T 12 –L 4 group (0.92q0.04, 0.94q0.05 and 0.94q0.04, respectively), while it increased significantly in the T 5 –T 11 group (0.88q0.07, 0.94q0.05, 1.00q0.08) and increased even more in the C 6 –T 4 group (0.83q0.07, 0.91q0.05, 1.06q0.06). Results suggest that heart-rate self-similarity depends on vascular sympathetic control, because it is altered by spinal-cord lesions, even when cardiac neural control is intact.