INTRATHORACIC PRESSURE FLUCTUATIONS MOVE BLOOD DURING CPR: COMPARISON OF HEMODYNAMIC DATA WITH PREDICTIONS FROM A MATHEMATICAL MODEL

Whether blood f low during cardiopulmonary esuscitation (CPR) results from intrathoracic pressure fluctuations or direct cardiac compression remains controver-sial We developed a mathematical model that predicts that blood f low due to intrathoracic pressure fluctuations should be insensitive to compression rate over a wide range but dependent on the applied force and compression duration. I f direct compression of the heart plays a major role, however, the model predicts that f low should be dependent on compression rate and force, but above a threshold, insensi-tive to compression duration. These differences in hemodynamics produced by changes in rate and duration form a basis for determining whether blood flow dur-ing CPR results from in trathoracic pressure fluctuations or from direct cardiac com-pression. The model was validated for direct cardiac compression by studying the hemodynamics of cyc#c ardiac deformation following thoracotomy infour anesthe-tized, 21-32-kg dogs. As predicted by the model, there was no change in myocardial or cerebral perfusion pressures when the duration of compression was increased from 15 ~ to 45 % of the cycle at a constant rate of 60/min. There was, however, a si