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Noninvasive ambulatory twenty-four-hour blood pressure (BP) monitoring was carried out in 30 normotensive subjects (16 women, 14 men), aged twenty-five to sixty years (mean thirty-eight) and in 29 mild essential hypertensive patients without target organ damage (14 women, 15 men), aged twenty-three to sixty-one years (mean thirty-nine). Hypertensive patients were not treated, and they discontinued any antihypertensive treatment at least four weeks before the study. During the daytime period (6 AM-10 PM) BP was monitored every fifteen minutes, and during the night (10 PM-6 AM), every thirty minutes. Obviously, mean twenty-four-hour systolic blood pressure (SBP) and diastolic blood pressure (DBP) were higher in hypertensive patients (P < 0.001). There was a persistent correlation in the group of mild hypertensives between successive BP hourly mean readings (r ranged from 0.61 to 0.93 for SBP and from 0.45 to 0.82 for DBP). In normotensive subjects these correlations failed in particular periods: 8 AM-9 AM, r = 0.30 for SBP and 0.45 for DBP; 1 PM-3 PM, r = 0.17-0.49 for SBP and 0.28-0.37 for DBP; 9 PM to midnight, r = 0.21-0.57 for SBP and 0.23-0.38 for DBP.

The influence of advancing age on cardiovascular function has been the subject of many studies in the last few years. The increase of average life span and proportion of old people in the general population stimulated a number of studies in order to obtain a deeper knowledge of the normal physiology of aged individuals. Cross-sectional and longitudinal studies are used to examine the effects of aging. Both type of studies have some drawbacks. The cross-sectional study is planned to analyze at one time a group of individuals of different ages. In such study, it is difficult to eliminate genetic or environmental differences among groups. Furthermore, the older groups may represent a selected long-lived subset of the younger population. A longitudinal study examines the same individuals as their age advances and, therefore, a very prolonged time is required for studying humans. In such a study among many other obvious obstacles, an important one is the possible changes in methodology, not always easy to differentiate from age changes. In any case, the extent to which these studies may analyze the normal aging process is determined by the level of certainty regarding the absence of disease. This requirement can be difficult to be met, owing to the prevalence of atherosclerosis or occult coronary disease in the old age [1].

Hypotension with lightheadedness and near syncope occurred in three patients during effective ventricular pacing. Hemodynamic studies demonstrated a decrease in cardiac output ranging from almost no decrease to 15 percent, presumably related to the loss of effective atrial contraction. The decrease in output was too small to explain by itself the reduced blood pressure, which resulted from paradoxic reduction of total peripheral resistance in one patient and from failure of resistance to increase in two. Baroceptor reflexes (Valsalva response) were normal in all three patients; hence it is suggested that the failure of compensatory increases in total peripheral resistance may be due to a reflex from the sudden atrial distension that occurs during atrioventricular (A-V) dissociation. The fluctuations in arterial pressure during ventricular pacing were synchronous with the appearance of cannon waves in the right atrial pressure tracing. Arterial pressure during A-V dissociation thus appears to be balanced by two opposite reflexes: the baroceptor reflex, which attempts to compensate for reduction in output, and atrial distension, which reduces peripheral resistance.