Arterial pressure control during non-hypo/hypertensive changes in central venous volume: assessment with multivariate autoregressive modeling

To evaluate how small decreases and increases of central volume influence heart rate and arterial pressure control multivariate autoregressive techniques were used to quantify the interactions between respiration, RR interval and arterial blood pressure during random interval breathing, at 3 low levels of lower body negative pressure and 3 low levels of increased central volume. In addition to the classic spectral parameters for each signal, the algorithms were used to derive the closed-loop feedforward and feedback gains for the baroreflex and the effects of respiration on RR interval. With reductions of central volume below control, baroreflex and respiratory sinus arrhythmia gains were generally reduced, while with increases of volume above control, they increased only for the first two levels, and decreased at the highest volume. These findings indicate that reflex heart rate control is maximum with mild hypervolemia, and are consistent with the presence of the Bainbridge reflex in healthy humans.