Mathematical evaluation of 24-hour blood-pressure variability in young, middle-aged and elderly hypertensive patients.

The characteristics of 24-hour blood pressure variation in hypertensive patients were assessed using new indices of variability. Blood pressure of 43 inpatients with essential hypertension was measured using a portable device without disturbing daily behaviors. Variances in systolic and diastolic pressure values obtained for a day (SDd2), and short-term (SDh2) and long-term (SD24(2) variances were calculated; their relationship was expressed as SDd2 = SDh2 + SD24(2). SDh and SD24 were expedient in assessing the relatively fast and slow blood-pressure variations, respectively. The results showed that the ratio SDh2/SDd2 (percentile of the short-term variance in a whole-day variance) increased and therefore SD24(2)/SDd2 decreased as age increased for both systolic and diastolic pressures. It was found, moreover, that systolic SDh was significantly related to age and baroreflex sensitivity, and systolic SD24 to the heart rate during waking hours. The physiological and clinical significance of SDh and SD24 is discussed, briefly, including arterial wall stiffness.