The Correlation of Mean Sympathetic Activity with Low-Frequency Blood Pressure and Sympathetic Variability

The low-frequency (0.2-0.8 Hz) component of blood pressure (BP) variability (LFBP) is used as an index of the low-frequency variability of sympathetic nerve activity (SNA) (LFSNA) in rats. It is unclear whether the LFBP can be used as an index of the mean SNA (mSNA). We investigated the correlation of the LFBP with different levels of the mSNA in this study to evaluate if it is a feasible tool for detecting differences in mSNA under physiological conditions. Correlation of the LFSNA with different mSNA levels was also investigated. The BP and renal SNA of rats were recorded in a nonanesthetized state. Values of the mSNA obtained from 531 recording epochs in six rats were graded into 30 levels with a bin resolution of 0.05 normalized units. A linear regression analysis showed that the correlation between the mSNA and LFSNA was higher than that between the mSNA and LFBP. The mSNA was well correlated with the LFSNA over a wider mSNA range, while it was correlated with the LFBP only in a restricted range. These results demonstrated a restricted condition under which measuring the LFBP can be a definitive index of the mSNA, and further suggest the possibility of using the weighted LFBP as an index of the mSNA via intermediation by the LFSNA for a wider mSNA range.