Discrimination and spectral resolution of ultradian and circadian periodicities for 24-hour blood pressure patterns on sodium manipulation in normotensive humans.

The effects of a severe (10-20 mEq/24-h) but short-term (7-days) restriction in dietary sodium on 24-h blood pressure (BP) patterns were investigated in 20 normotensive volunteers (10 men, 10 women; 20-25 years old) by means of non-invasive automatic sphygmomanometric monitoring (recordings at 1-h interval) at home, with subjects in bedrest. Statistical methods used include bivariate Gaussian distribution analysis for systolic and diastolic BP bivariate discriminant analysis, periodic regression analysis with a 24-h period (cosinor method) and spectral analysis of time series. Casual BP measurements were unable to detect the tensinogenic effects, while the bivariate Gaussian analysis documented a total rearrangement in the pattern distribution to show discriminated values of BP after sodium restriction. A significant decrease (p less than 0.01) in the 24-h mean level (mesor) for systolic BP was observed. An increase in the extent of fluctuation (amplitude) for the circadian components was documented by the spectral analysis, mainly in diastolic BP patterns. Such a phenomenon of 'amplitude magnification' was not accompanied by a change in the repartition of the ultradian and circadian harmonic components. The extensive changes in the time structure support the hypothesis of an interaction of sodium regimen with the centrally-located oscillators which physiologically organize the circadian rhythmicity of BP.