Search

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.

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.