Frequency response characteristic of sympathetic mediated low-frequency blood pressure fluctuations in conscious rats

A quantitative relationship between power densities of blood pressure (PBP) and sympathetic nerve activity (PSNA) in a low-frequency range (LF, 0.016-0.85 Hz), expressed as PSNA=PBPxax10bx(frequency) was proposed in pentobarbital-anesthetized rats. For evaluating the general applicability of this equation, the quantitative relationship of power density ratio Hf=PBP/PSNA across frequency was tested in a conscious state. Wistar rats were chronically instrumented with a femoral artery catheter and recording electrode around the renal sympathetic nerve. The blood pressure and renal sympathetic nerve activity were monitored both under pentobarbital anesthesia and in a conscious state. Linear regression analysis of the relationship between the frequency and logarithmic magnitude of the power density ratio in the LF range revealed excellent fit in both conditions (r=-0.96+/-0.01 and -0.93+/-0.01 for anesthetized and conscious rats, respectively). Comparing the regression lines, rats under pentobarbital anesthesia had significantly larger values for the y-intercept and slope compared to rats in a conscious state (y-intercepts: 0.80+/-0.09>0.53+/-0.08; slopes: -2.86+/-0.26>-1.62+/-0.21). Our results demonstrate that it is also feasible to use the weighted PBP in LF as a quantitative index of sympathetic variability in conscious rats, but the evaluation of possible complications controlling the regression parameters is called for.