Analysis of cardiovascular instability by a mathematical model of baroreflex control

A mathematical model of the short-term arterial pressure control is used to investigate the possible origin of blood pressure waves (Mayer waves) and of heart rate variability signals. The model includes a pulsating heart, the pulmonary and systemic circulation, and various feedback regulatory mechanisms. Feedback mechanisms are activated by changes in systemic arterial pressure (arterial baroreflex) and in right atrial pressure (cardiopulmonary baroreflex) and work on systemic resistance, systemic venous unstressed volume, heart contractility and heart period. The latter involves a balance between sympathetic and vagal activities (sympato-vagal balance). A sensitivity analysis on the parameters of feedback mechanisms revealed that a significant increase in the gains and time delays (up to 9 s) of all the arterial baroreflex sympathetic mechanisms is required to induce instability. In this condition, systemic arterial pressure exhibits spontaneous oscillations with a period of about 20 s, similar to Mayer waves. Moreover, an increase in the gain and time delay (up to 3.5 s) of the arterial baroreflex vagal mechanism causes the appearance of unpredictable fluctuations in heart period, with spectral components in the range 0.08-0.12 Hz. The cardiopulmonary baroreflex plays a less important role in the genesis of the aforementioned instability phenomena.