Effects of baroreflex activities on IABP hemodynamics in a closed loop hybrid cardiovascular model

Objectives: Aim of this work is the integration of the autonomic mechanism of pressure regulation during temporary IABP assistance in a hybrid circulatory model. Methods: The hybrid model is based on merging computational and hydraulic models. The lumped parameter computational model includes the upper thoracic aorta, circulatory districts (upper body, kidneys, splanchnic, lower body, pulmonary, coronary circulation) and left/right hearts. The hydraulic model provides a representation of the lower thoracic aorta by a silicon rubber tube containing a 40cc IAB. An additional numerical module provides a representation of the baroreflex mechanism in terms of afferent and efferent sympathetic nerve activity (ANA, ENA). Baroreflex model acts as a feedback control loop that regulates the blood pressure by changing heart rate (HR), peripheral resistance and venous tone of each circulatory district. Experiments were conducted applying IABP assistance to a pathological circulatory condition. Results: The increment of diastolic pressure due to IABP provides an increment of ANA (+7%) and a decrement of ENA(-9%). Operating the IABP induced a reduction in HR by -6% (90 vs. 95 bpm), in kidney and upper body resistances by -5% (5.43 vs. 5.72 and 5.17 vs. 5.44 mmHg·s/mL, respectively). IABP also induced an increment in kidney flow by +7% (0.63 vs. 0.59 L/min) and upper body flow by +6.8% (0.50 vs. 0.46 L/min). By switching the IABP assistance frequency from 1:1 to 1:2 or 1:3 the mentioned effects reduce progressively. Results indicate that the short term effects of IAB are small, even in the presence of a model including baroreflex control. Conclusions: The model provides an instrument for the assessment of IABP effects on baroreflex mechanism due to the increase of mean diastolic blood pressure. This contributes to predict and study the global evolution of hemodynamic condition after IABP activation and the resultant change in organ flows.