Theoretical advantages of abdominal counterpulsation in CPR as demonstrated in a simple electrical model of the circulation

Abstract

Animal studies and preliminary clinical observations suggest that the addition of interposed abdominal compressions (IAC) to ventilation and chest compression of standard cardiopulmonary resuscitation (CPR) augments blood flow, blood pressures, and immediate survival. To investigate the physical basis for enhanced circulation during IAC-CPR, we developed an electrical model of the circulation. Heart and blood vessels were modeled as resistive-capacitive networks, pressures as voltages, blood flow as electric current, blood inertia as inductance, and the cardiac and venous valves as diodes. External pressurization of the heart and great vessels, as would occur in CPR, was simulated by application by half-sinusoidal voltage pulses between vascular capacitances and ground. Closed-chest CPR was simulated by pressurization of all intrathoracic capacitances. IAC was simulated by similar pressurization of the inferior vena cava and abdominal aorta, 180 degrees out of phase with chest compression. During simulation of CPR, IAC improved cranial and myocardial perfusion at all levels of chest compression pressure by amounts linearly related to peak abdominal pressure, suggesting that the abdomen can function as a second, independent blood pump during CPR. Brain and heart flow were improved further during simulated vasoconstriction in kidneys, abdominal viscera, and extremities. Based on the fundamental properties of the cardiovascular system represented in the model, abdominal counterpulsation provides a rational basis for flow augmentation during CPR.

Cardiac, thoracic, and abdominal pump mechanisms in cardiopulmonary resuscitation: Studies in an electrical model of the circulation

“…Although the dynamic compliance of arteries and veins is known to decrease measurably as the vessels become more distended, the model included constant compliances during any one stimulation. (Reduced venous compliance with volume loading has been stimulated separately by changing the venous capacitance and zero-flow pressure and repeating the simulation [13].) Instead, this simple model was limited to the "plumbing aspects" of the circulation--the movement of blood through resistive elements connected by elastic conduits in a closed circuit similar to the circulatory system--in order to determine how these primary physical elements can be compressed to produce an artificial circulation.…”

“…As a working approach to the modeling problem, therefore, we have begun with the presumed normal values indicated in Table 2, and then performed simulations with other values to answer specific questions concerning variations in venous capacitance, arterial capacitance, and peripheral vascular resistance [13].…”

“…In a previous article [13] we described the influence of compression force and peripheral vascular resistance when abdominal counterpulsation is combined with thoracic pump CPR in such a model. This subsequent research was conducted with the following objectives:…”

Interposed abdominal compression CPR: a comprehensive evidence based review

“…A number of investigators with a biomedical engineering bent have investigated IAC-CPR by building mechanical, electrical, or computer models [6][7][8][9][10][11] . A good example of this genre is provided by the electrical model of Ralston and Babbs 8 , who appreciated the analogy between the flow of current around an electrical circuit and the circulation of blood through systemic and pulmonary vessels.…”

“…A good example of this genre is provided by the electrical model of Ralston and Babbs 8 , who appreciated the analogy between the flow of current around an electrical circuit and the circulation of blood through systemic and pulmonary vessels. In their simulations electrical resistance mimicked physiological resistance of vascular beds.…”