Blood pressure and heart rate rhythmicity: Differential effects of late pregnancy

Arterial blood pressure (BP) and heart rate (HR) of 31 hospitalized pregnan t women at low risk of hypertension were automatically monitored for 48 h a t 15-min intervals. Each of the recorded 56 data series for systolic arteri al pressure (SAP), diastolic arterial pressure (DAP), and HR was chronobiol ogically assessed by linear-nonlinear rhythmometry. The rhythm-adjusted mea n (MESOR), circadian amplitude, circadian acrophase, and best-fitting perio d were grouped by pregnancy trimester and further subjected to analysis of variance. BP MESOR remained unaltered, whereas HR MESOR increased significa ntly in middle and late pregnancy. Ultradian rhythms, with an amplitude hig her than that of the circadian rhythm, were found in 25% of the SAP records in the second and third trimester. Such ultradian rhythms were not detecte d in the simultaneously recorded HR. Finally, the group BP and HR circadian acrophases coincided in the first trimester, but were significantly apart in mid and late pregnancy. These observations support the notion that the c oordination of BP and HR rhythmicity involves different physiological mecha nisms. Analysis of the individual variability in the chronobiological end p oints (based on the records of nine women monitored in each pregnancy trime ster)revealed that only the BP MESOR was well reproducible in the course of pregnancy and may be useful in early diagnosis of gestational hypertension . (C) 1999 Elsevier Science Inc.