The mechanism of blood pressure variability: Study in patients with fixed ventricular pacemaker rhythm

Background: Several studies have shown that heart rate variabilityplays an anti-oscillatory role in the regulation of blood pressurevariability in humans. We tested whether systolic blood pressurevariability in patients with a fixed ventricular pacemaker rhythmdiffers from that in patients with sinus rhythm. Methods and Results: In 18 patients with a fixed ventricularpacemaker rhythm and in ten age-matched patients with sinusrhythm the systolic blood pressure oscillation and the low andhigh-frequency spectral components of systolic blood pressurewere studied in the resting supine position during spontaneousbreathing and during forced deep ventilation of 6 cycles. min^–1.Patients with a pacemaker had a higher amplitude of systolicblood pressure oscillation than control subjects during spontaneousbreathing (13.5 ± 2.0 mmHg vs 6.4 ± 1.6 mmHg,P=0.035), and a slight but not significant difference also persistedduring forced deep ventilation (19.0 ± 2.3 mmHg vs 15.0± 2.3 mmHg, P=0.18). The increment in systolic bloodpressure fluctuation from spontaneous breathing to forced deepventilation was less marked in the pacemaker group than in thecontrol subjects (40% vs 130%, P=0.43). Although all the systolicblood pressure spectral components of the pacemaker patientswere higher during both spontaneous breathing and forced deepventilation, the differences between the two groups did notreach statistical significance. Conclusions: Our observations in patients with a fixed ventricularpacemaker rhythm suggest that the mechanical effects on theintrathoracic vessels and the consecutive stroke volume changesare responsible for respiration-related systolic blood pressureoscillation and reflex systolic blood pressure changes.