Computer studies of systemic and regional blood flow mechanisms during cardiopulmonary resuscitation.

Abstract

Based on the new concept that intrathoracic and abdominal pressure variations cause blood flow in most of the cardiopulmonary resuscitation (CPR) techniques, two mathematical models were developed to explore related mechanisms of blood flow. The models were based on a representation of the cardiovascular system by resistive, capacitive and inductive elements, and the existence of venous and cardiac unidirectional valves. Cyclic intrathoracic and abdominal pressure variations were simulated by modulating the pressure within the corresponding vessels. It was found that blood flow during CPR is highly dependent on venous valving and aortic valve competence. The systemic blood flow was calculated to be between 10 and 20 per cent of its normal value. The maximum flow under a cyclic pressure of 50 mmHg was 663 m/min−1, which was achieved with a pulse rate of 115 cycles per min and a duty cycle (ratio of artificial systole to cycle duration) of 58 per cent. The coronary blood flow was found to occur only during artificial diastole and was actually reversed during the compression phase. The systemic blood flow increased when pressure variations were delivered to the chest alone or when some phase lag was introduced between the thoracic and abdominal pressure waves. The mathematical model presented provided a tool to study the effect of thoracic and abdominal pressure waves on the circulation in CPR. The information derived from the model can be used to design better methods for CPR.