Rhythmic oscillations of blood pressure and R-R interval in patients with chronic renal failure.

Rhythmic blood pressure (BP) and R-R interval (R-R) oscillations at low-, mid- and high-frequency bands (LF: 0.02-0.06 Hz; MF: 0.07-0.14 Hz; HF: 0.15-0.40 Hz) were compared between uraemic patients maintained on haemodialysis and control subjects. The LF and MF power spectra of BP were attenuated more in patients than in controls. With subjects standing, the MF power spectrum of BP increased significantly in both groups. With subjects supine, the plasma norepinephrine concentration was higher, and its increment upon standing was greater in patients than in controls. Each R-R frequency power spectrum decreased more in patients than in control subjects. The HF power spectrum of R-R, i.e. a vagal tone index, systematically decreased upon standing in the control subjects but not in the patients. The linear coupling between BP and R-R oscillations was strongest in the HF band, decreasing in the MF and LF bands. Transfer function analysis indicated that, in uraemic patients, linear BP/R-R relationships were altered in the HF band but remained normal in the LF and MF bands. The present results suggest that, first, the decreased amplitude of Mayer waves, i.e. the MF power spectrum of BP, observed in uraemic patients can be attributed to low sensitivity of the vasculature to sympathetic stimuli, and, secondly, autonomic modulation of linear BP/R-R relationships is frequency-dependent.