ALTERED DYNAMICS OF THE CIRCADIAN RELATIONSHIP BETWEEN SYSTEMIC ARTERIAL-PRESSURE AND CARDIAC SYMPATHETIC DRIVE EARLY ON IN MILD HYPERTENSION

This study was designed to test the hypothesis that simultaneous non-i nvasive assessment of the circadian variations in both intermittent ar terial pressure and the continuous 24 h changes of spectral markers of cardiac neural control could provide new information on cardiovascula r regulatory mechanisms, in hypertensive patients and normotensive sub jects. To test this hypothesis we studied 18 subjects with mild hypert ension and II normotensive subjects in whom we recorded simultaneously non-invasive intermittent arterial pressure and Holter electrocardiog ram for 24 h. We also studied the same subjects during resting and sta nding conditions in the clinical laboratory. 2. The normalized power o f the low-frequency (similar to 0.1 Hz) spectral component of R-R inte rval variability, considered mainly a marker of sympathetic drive to t he sino-atrial node, was, at rest, significantly higher in the hyperte nsive than in the normotensive subjects, as already reported. Moreover , the values of the low-frequency component at rest recorded in the cl inical laboratory were significantly correlated with those obtained fr om ambulatory recording during night rest. The decrease in the values of arterial pressure during the night-time was accompanied by a reduct ion in the power of the low-frequency component only in the case of no rmotensive subjects. Accordingly, the slope of the regression of the l ow-frequency component as a function of systolic arterial pressure dur ing ambulatory recordings was steep in normotensive subjects and fiat in hypertensive subjects. 3. The computer analysis of Holter recording s combined with ambulatory arterial pressure monitoring seems to provi de a new method with which to quantify the early changes in cardiovasc ular regulatory mechanisms that could help to identify individuals at higher risk.