An extended model of blood pressure variability: incorporating the respiratory modulation of vascular resistance.

Short-term blood pressure variability is generally attributed to the baroreflex feedback control on heart rate and systemic vascular resistance (SVR), and the mechanical effect of respiration on stroke volume. Although it is known that respiration affects sympathetic outflow and deep breaths can lead to peripheral vasoconstriction, the respiratory modulation of SVR has been little studied. In the present study, we investigated the dynamics resulting from the respiratory modulation of SVR and its effect on blood pressure variability by employing structured and minimal modeling approaches. Using peripheral arterial tonometry as a noninvasive measure of SVR, we were able to estimate the respiratory-vascular conductance coupling mechanism. We found that the dynamics of the sigh-vasoconstriction reflex could be reproduced only when the respiratory modulation of SVR was incorporated into the closed-loop model. Lastly, we demonstrated that taking this respiratory modulation effect into account is essential for accurately estimating the dynamics of the SVR baroreflex.