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

Abstract

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 approximately 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 approximately 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 approximately 2 s (i.e., approximately 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 approximately 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 approximately 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.

Spectral Analyses of Cardiovascular Control in Rodents with Spinal Cord Injury

“…This is consistent with previous studies in humans (Claydon and Krassioukov, 2007;Houtman et al, 2000;Inoue et al, 1991;Munakata et al, 2001), and likely reflects injury to descending sympathetic pathways (Randall et al, 2005), and consequent loss of tonic sympathetic drive to the key resistance and capacitance vessels in the splanchnic vascular bed in those with high-level SCI (Claydon and Krassioukov, 2007;Inoue et al, 1991). Accordingly, hypotension was apparent in animals with T3 SCI, but not in those with T10 SCI.…”

“…We, and others, have observed this resting hypotension in rodents with chronic high-level SCI (Laird et al, 2006), and in people with SCI (Claydon and Krassioukov, 2007;Claydon et al, 2006;Mathias, 2006). One other study examined LF SAP in rodents after acute (up to 1 week) high-level SCI and found a similar reduction in LF SAP (Randall et al, 2005). It is interesting that the LF oscillations in SAP were markedly reduced, but not abolished, in the T3 SCI animals.…”

Extended longitudinal analysis of arterial pressure and heart rate control in unanesthetized rats with type 1 diabetes

“…Interestingly, the 0.4 Hz rhythm conforms to the same self-similar behavior characteristic of lower frequencies after interruption of sympathetic outflow via spinal cord transection between T 4 and T 5 (Randall, et al, 2005). From this we concluded “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” (Randall, et al, 2005). If so, it appears that sympathetic control of the circulation was functionally intact through 6 months of diabetes in this animal model, even during the behavioral changes attendant to transitioning from light to dark and vice versa .…”

Autonomic assessment of animals with spinal cord injury: tools, techniques and translation

“…Spectral analysis has been applied to examine blood pressure variation in rats with acute SCI. 70 At 1 and 6 days after complete transection at T4-T5, rats exhibited reduced power in the low-frequency range, indicative of reduced sympathetic tone (or increased parasympathetic tone 85 ) that affects blood pressure control. There are currently no data applying spectral analysis to more chronic experimental SCI.…”