Circadian profile of low-frequency oscillations in blood pressure and heart rate in hypertension.

Electrocardiogram and intraarterial blood pressure (BP) were recorded in 35 normotensive (NT), 29 borderline hypertensive (BHT), and 30 mildly hypertensive (HT) men (aged 35 to 45 years) by the Oxford method over a 24-h period. Consecutive data segments of 5 min were extracted from the recordings for frequency domain analysis. Heart rate (HR) and BP variability was calculated for oscillations between 0.05 and 0.12 Hz, usually referred to as Mayer waves. Power and median frequency of the oscillations were determined. Some 10% of the segments were excluded from the analysis because of artifacts and transients. The results were averaged for 5-h periods in the evening, at night, and during the day. In the BHT subjects, the median frequency of the Mayer waves was shifted to lower frequencies as compared with the NT subjects. This was seen at night and during the day. The phenomenon presumably reflects an increased latency in the sympathetic vasomotor control of the baroreceptor reflex. No between-group differences were found in the normalized spectral power values. Five years later, 24 NT, 22 BHT, and 19 HT subjects were reassessed using casual BP and noninvasive ambulatory 24-h monitoring. In the initial phase, the median frequencies for the 5-h periods showed no evident linear relationship with the corresponding BP levels. However, the median frequencies showed high inverse correlations with the follow-up ambulatory BP levels. In the evening and during the day, the median frequency showed a significant inverse correlation also with the increment in BP. No clear relationship was found between power estimates and BP levels or future increments in BP. In conclusion, the frequency shift of Mayer waves to lower frequencies is associated with an increased risk of developing established hypertension.