Characteristics of a reversed circadian blood pressure rhythm in pregnant women with hypertension.

The objective of the study was to describe the 24h blood pressure (BP) pattern in pregnant women with a reversed circadian BP rhythm. The 24h BP monitorings (24BPM) were performed in 73 pregnant women hospitalised for hypertension. Daytime (6.00 am to 10.00 pm) and night-time (10.00 pm to 6.00 am) BP variables were calculated. A reversed circadian BP rhythm was defined as a day/night mean BP ratio < 1.0. Fourteen women had a reversed circadian BP rhythm. Their diurnal mean BP was equal to women with a normal rhythm, but their nocturnal mean BP was significantly higher and their BP oscillation amplitudes tended to be lower. The day/night mean SBP and DBP ratios correlated significantly, with the DBP ratios slightly higher than corresponding SBP ratios. At repeated 24BPM (n = 14), the day/night ratio did not change but a reversed rhythm occurred during anti-hypertensive medication in one case, and a reversed rhythm switched spontaneously to normal in one case. The diurnal BP pattern did not differ between women with a reversed and a normal circadian BP rhythm. Women with a reversed rhythm had a higher nocturnal BP, but this was part of the definition. The BP variations were generally smaller in the group with a reversed rhythm, although the variations were still large. The definition with a day/night ratio cut-off at 1.0 was rather a convenient mathematical choice than a biologically-determined limit. The day/night BP ratio remained unchanged at repeated measurements, but a reversed rhythm was not a constant phenomenon in occasional cases. Women with a reversed circadian BP rhythm were therefore not a well-defined group and, with exception for a tendency to smaller BP fluctuations, no specific behavioural BP pattern could be described. Until the normal circadian BP rhythm in normal pregnancy has been described, there is no possibility to identify women with an abnormal circadian BP rhythm. Ideally, any definition of an abnormal rhythm should be related to the clinical relevance.