THE MECHANISM OF BLOOD-PRESSURE VARIABILITY - STUDY IN PATIENTS WITH FIXED VENTRICULAR PACEMAKER RHYTHM

Background: Several studies have shown that heart rare variability pla ys an anti-oscillatory role in the regulation of blood pressure variab ility in humans. We tested whether systolic blood pressure variability in patients with a fixed ventricular pacemaker rhythm differs from th at in patients with sinus rhythm. Methods and Results: In Ig patients with a fixed ventricular pacemaker rhythm and in ten age-matched patie nts with sinus rhythm the systolic blood pressure oscillation and the low and high-frequency spectral components of systolic blood pressure were studied in the resting supine position during spontaneous breathi ng and during forced deep ventilation of 6 cycles . min(-1). Patients with a pacemaker had a higher amplitude of systolic blood pressure osc illation than control subjects during spontaneous breathing (13.5 +/- 2.0 mmHg vs 6.4 +/- 1.6 mmHg, P=0.035), and a slight but not significa nt difference also persisted during forced deep ventilation (19.0 +/- 2.3 mmHg vs 15.0 +/- 2.3 mmHg, P=0.18). The increment in systolic bloo d pressure fluctuation from spontaneous breathing to forced deep venti lation was less marked in the pacemaker group than in the control subj ects (40% vs 130%, P=0.43). Although all the systolic blood pressure s pectral components of the pacemaker patients were higher during both s pontaneous breathing and forced deep ventilation, the differences betw een the two groups did not reach statistical significance. Conclusions : Our observations in patients with a fixed ventricular pacemaker rhyt hm suggest that the mechanical effects on the intrathoracic vessels an d the consecutive stroke volume changes are responsible for respiratio n-related systolic blood pressure oscillation and reflex systolic bloo d pressure changes.