Does low frequency power of arterial blood pressure reflect sympathetic tone?

We tested whether power spectral analysis of arterial blood pressure (ABP) is a feasible tool to detect differences in peripheral sympathetic nerve activity in normotensive and hypertensive rats with differing basal sympathetic tones. Nine Wistar Kyoto rats (WKY), 10 Sprague-Dawley rats (SD), 10 spontaneously hypertensive rats (SHR) and 9 hypertensive transgenic rats harbouring the mouse Ren-2 gene (TGR) were chronically instrumented with femoral artery catheters and nerve electrodes around the sympathetic major splanchnic nerve. Two days after surgery ABP and splanchnic nerve activity (SpNA) were recorded in the conscious state during basal conditions as well as during alpha 1-adrenergic receptor blockade. Power spectra and squared coherence in the low (LF, 0.02-0.20 Hz), mid (MF, 0.20-0.80 Hz) and high (HF, respiration peak +/- 0.3 Hz) frequency bands were calculated for ABP and SpNA. Mean blood pressure in SHR (133 +/- 8 mmHg) and TGR (142 +/- 8 mmHg) was significantly higher (P < 0.05) than in WKY (115 +/- 3 mmHg) and SD (95 +/- 4 mmHg). SpNA in SHR was higher than in WKY (23.4 +/- 6.4 microV vs. 11.6 +/- 0.8 microV, P < 0.05) while SpNA in TGR was lower than in SD (20.1 +/- 3.9 microV vs. 28.8 +/- 4.2 microV, P < 0.05). LF and MF components of ABP variability were not significantly higher in those rats with high sympathetic tones. However, alpha 1-adrenergic receptor blockade reduced LF and MF components of ABP and SpNA in all strains except SHR. LF and MF coherence was not greater in rats with high sympathetic tones than in those with low sympathetic tones. The reduction of LF and MF components of ABP variability by alpha 1-adrenergic receptor blockade indicates an important contribution of peripheral sympathetic nerve activity to LF and MF blood pressure variability on an acute basis. However, the lack of higher LF and MF power in the ABP spectra of those rats with high SpNA together with the finding that LF and MF coherence was not higher in those rats with high SpNA led to the conclusion that LF and MF spectral components of ABP do not appear to be suitable markers for the prevailing sympathetic nerve activity.