Circadian blood pressure variability is associated with autonomic and baroreflex-mediated modulation of the sinoatrial node

The day-night variability of blood pressure (BP) is of interest in the analysis of ambulatory blood pressure monitoring (ABPM). The aim of this study was to investigate whether the nocturnal BP reduction was associated with the autonomic and baroreflex-mediated modulation of the sinoatrial node in normotensive and hypertensive subjects.

63 consecutive untreated male subjects (40 hypertensive and 23 normotensive) were studied. Spectral parameters of RR interval variability and the alphaLF index (a measure of baroreflex gain) were calculated at rest. Then all the subjects performed a 24-h ABPM.

As regards the relationships involving 24-h BP and resting heart rate (HR) and HR variability parameters, a significant correlation was found between mean RR and both systolic and diastolic nocturnal BP falls (r = 0.40, p < 0.001, r = 0.32, p < 0.01, respectively); moreover, a significant correlation was found between the nocturnal fall of systolic BP and both the LF/HF ratio and absolute power of HF (r = -0.25, p < 0.05 and r = 0.29, p < 0.05, respectively). The alphaLF index was significantly associated with the nocturnal diastolic BP fall (r = 0.26, p < 0.05) whereas the association with the systolic fall did not reach statistical significance (r = 0.23, p = 0.07).

The relationship found between the nocturnal reduction of BP and both the LF/HF ratio and HF power of RR variability suggests that factors influencing the sympatho-vagal modulation to the heart are associated with the day-night variability of blood pressure. Moreover, the relationship between BP fall and the spontaneous baroreflex sensitivity index alphaLF, may indicate a role of the baroreflex-mediated arc function in the BP adjustments occurring during the night.