Blood pressure power within frequency range ~0.4 Hz in rat conforms to self-similar scaling following spinal cord transection

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 288; no. 3; pp. R737 - R741
• Main Authors: Randall, David C, Baldridge, Bobby R, Zimmerman, Ethan E, Carroll, Jonathan J, Speakman, Richard O, Brown, David R, Taylor, Robert F, Patwardhan, Abhijit, Burgess, Don E
• Format: Journal Article
• Language: English
• Published: 01.03.2005
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00544.2003

1 Department of Physiology, University of Kentucky College of Medicine, Lexington; 2 Departments of Biology, and Chemistry and Physics, Asbury College, Wilmore; 3 Center for Biomedical Engineering, Wenner-Gren Lab, University of Kentucky, Lexington; and 4 Cardinal Hill Rehabilitation Hospital, Lexington, Kentucky Submitted 22 September 2003 ; accepted in final form 19 October 2004 This study quantified the effect of interrupting the descending input to the sympathetic preganglionic neurons on the dynamic behavior of arterial blood pressure (BP) in the unanesthetized rat. BP was recorded for 4-h intervals in six rats in the neurally intact state and in the same animals after complete spinal cord transection (SCT) between T 4 and T 5 . In the intact state, power within the frequency range of 0.35–0.45 Hz was 1.53 ± 0.38 mmHg 2 /Hz (mean ± SD by fast Fourier transform). One week after SCT, power within this range decreased significantly ( P < 0.05) to 0.43 ± 0.62 mmHg 2 /Hz. To test for self-similarity before and after SCT, we analyzed data using a wavelet (i.e., functionally, a digital bandpass filter) tuned to be maximally sensitive to fluctuations with periods of 2, 4, 8, 16, 32, or 64 s. In the control state, all fluctuations with periods of 4 s conformed to a "self-similar" (i.e., fractal) distribution. In marked contrast, the oscillations with a period of 2 s (i.e., 0.4 Hz) were significantly set apart from those at lower frequencies. One day and seven days after the complete SCT, however, the BP fluctuations at 0.4 Hz now also conformed to the same self-similar behavior characteristic of the lower frequencies. We conclude that 1 ) an intact sympathetic nervous system endows that portion of the power spectrum centered around 0.4 Hz with properties (e.g., a periodicity) that differ significantly from the self-similar behavior that characterizes the lower frequencies and 2 ) even within the relatively high frequency range at 0.4 Hz self-similarity is the "default" condition after sympathetic influences have been eliminated. autonomic nervous system; sympathetic nervous system; spinal cord injury; fractal Address for reprint requests and other correspondence: D. C. Randall, Dept. Physiology, Univ. of Kentucky College of Medicine, Lexington, KY 40536-0298 (E-mail: randall{at}uky.edu )