The effects of ageing on nocturnal blood pressure (BP) and the circadian rhythm of BP were studied. Ambulatory BP and heart rate (HR) were monitored at 30-minute intervals for 24 hours, in 326 normotensive volunteers aged 15-83. The following groups were monitored: young: < 40 yrs, n = 177; middle: 40 yrs < or = - < 60 years, n = 100; old: 60 yrs < or =, n = 49 Firstly, the ratio of nocturnal fall (RONF) of BP (or HR) was calculated as follows: [(average day time BP (or HR)-average night time BR (or HR)]/averaged whole day BP (or HR) x 100. Then we calculated 2 measurements: 1. The dipper (RONF of BP (or HR) > or = 10% 2. The non-dipper. (RONF of BP (or HR) < 10%. A cosine fitting technique using the least-squares method was employed to find the circadian rhythm of BP and HR. The results of the study showed that the incidence of the non-dipper on systolic BP (SBP) was higher for old subjects than for young subjects. In addition, the nocturnal BP and HR were higher for old subjects than for young subjects. The circadian amplitude of HR was lower in old subjects. The circadian midline estimating statistic of rhythm (MESOR) or SBP increased with age. The circadian acrophase of BP and HR increased with age.non-dippers of BP and HR were observed in any age groups. The frequency of BP and HR non-dipper was greater for old subjects than young subjects. This result may suggest the clinical significance of nocturnal BP and HR for the evaluation of hypertensive subjects.
This paper reports on software developed to compute least-squares spectra over a specified interval. This approach facilitates the viewing of a changing time structure in non-stationary time series, smaller than the observation span. The programme is illustrated by a case of solar activity, gauged by yearly Wolf numbers, for the 1700-1999 span that shows the presence of a very unstable component with a period of around-100 years and an about-11-year solar cycle. This method, although demostrated here on a geophysical example, has a broad scope of applications in biology and medicine.
Data from two independent studies are reanalyzed to determine how the MESOR and the circadian amplitude (A) of blood pressure (BP) as well as the 24-hour standard deviation (SD) of heart rate (HR) relate to vascular disease risk. In one prospective study, risk is quantified by the actual number of events that occurred within 6 years. In the other retrospective study, the left ventricular mass index (LVMI) was used as a surrogate outcome measure available for all subjects. The BP MESOR is found to be linearly related to risk. By contrast, the circadian BP-A and the 24-hour SD of HR show a nonlinear relation with risk, which is elevated only after a threshold value for BP-A or HR-SD is exceeded. For the diagnosis of a deviation in BP and HR, the recommendation to monitor for 7 days at the outset seems as reliable an assessment as practical, but it may not be sufficient, and the patient must be advised that further monitoring may be needed.
