[Nervous mechanisms of spontaneous oscillations of systolic blood pressure and heart rate].

The phenomenon of rhythmic fluctuations in cardiovascular variables such as heart rate (HR) or arterial blood pressure (BP) has attracted the attention of workers in both pure and applied research. In recent years, the possibility of quantifying these oscillations by using power spectral analysis has aroused a growing interest. We investigated the fluctuations which underly the spontaneous variability of BP and HR in conscious rats. Intrafemoral pulsatile BP was computed to generate evenly spaced signals (systolic, diastolic, mean BP, HR) at 200 ms intervals. This equidistant sampling allowed a direct spectral analysis using a Fast Fourier Transform algorithm. Systolic Blood Pressure (SBP) and HR exhibited low frequency oscillations (Mayer waves, 20-605 mHz) and a high frequency oscillation related to respiration (1,855 mHz). The respiratory fluctuations in HR were almost abolished by vagal blockade (atropine). HR fluctuations in the low frequency regime were diminished by vagal blockade or cardiac sympathetic blockade (atenolol). The respiratory frequency fluctuations in SBP were markedly increased by alpha sympathetic blockade (prazosin). On the contrary the low frequency oscillations in SBP were reduced by alpha sympathetic blockade. These data indicate that in conscious rats: 1) the HR oscillation with respiration is vagally mediated, 2) the HR fluctuation in the low frequency regime is jointly mediated by beta sympathetic and parasympathetic activities, 3) the respiratory oscillation in SBP depends on fluctuations in cardiac output and is normally counteracted by the sympathetic tone, 4) the low frequency oscillations in SBP reflect the sympathetic activity to the resistance vessels.