Ultradian but not circadian blood pressure rhythms correlate with renal dysfunction in children with chronic renal failure

Whereas the diurnal fall of BP (dipping) is an important prognostic marker in patients with chronic renal failure (CRF), the integrity of physiologic ultradian (i.e., shorter than 24 h) cardiovascular rhythms in patients with CRF is unknown. Also, the relationship between conventional dipping analysis and Fourier spectral rhythm analysis has not been examined in renal hypertension. The prevalence and dimensions of the circadian and three ultradian (12, 8, and 6 h) cardiovascular rhythms were studied by ambulatory BP monitoring in 214 children (aged 3 to 18 yr) with CRF (stage 2 to 4 chronic kidney disease) and no antihypertensive treatment compared with 938 healthy control subjects, and the relationship of rhythm characteristics to conventional dipping parameters, renal function, proteinuria, and serum electrolytes was assessed. The CRF cohort exhibited significantly reduced amplitudes of the circadian and all ultradian cardiovascular rhythms studied (all P < 0.01). Moreover, all BP and most heart rate rhythms showed significantly delayed acrophases (time of peak; P < 0.01). Whereas conventional BP dipping parameters (day/night difference, day/night ratio) and the 24-h BP amplitude were independent of renal function, the 8-h BP amplitude was positively correlated with GFR (r = 0.3, P = 0.01) and inversely correlated with the urinary protein/creatinine ratio (r = -0.27, P < 0.05), and the 6-h BP amplitude was inversely correlated with proteinuria (r = -0.3, P < 0.02). Children who displayed 24- or 12-h cardiovascular rhythms had significantly lower serum calcium levels than children without these rhythms. In summary, children with CRF display not only blunted circadian but also blunted ultradian cardiovascular rhythms. Ultradian but not circadian rhythms or conventional dipping parameters are quantitatively associated with renal function and proteinuria.