The arterial baroreflex arc is implemented according to the feedback system illustrated in Figure 4. This system is aimed at tracking a setpoint () pressure through the following sequence of events. The baroreceptors sense and relay this pressure to the autonomic nervous system (ANS). The ANS compares the deviation between the sensed pressure and with zero and then responds by adjusting four parameters of the pulsatile heart and circulation in order to keep the ensuing near . The four adjustable parameters are , at end-systole ( ), , and . The ANS controls these parameters based on the history of specifically according to the following nonlinear, dynamical mapping:
The cardiopulmonary baroreflex arc is also implemented according to a feedback diagram analogous to Figure 4. However, the sensed pressure here is defined to be the effective right atrial transmural pressure ( ) of the pulsatile heart and circulation model.
The direct neural coupling mechanism between respiration and heart rate is characterized by a linear, time-invariant impulse response which maps fluctuations in instantaneous lung volume (; see Section 2.3) to fluctuations in . The impulse response is defined here by a linear combination of and , each of which are advanced in time by 1.5 s in order to account for the noncausality of this mechanism [6,9].