Aortic and right atrial systolic pressures during cardiopulmonary resuscitation: A potential indicator of the mechanism of blood flow

The absolute difference between aortic and right atrial systolic pressure (systolic pressure gradient) and the difference between the aortic diastollic and right atrial diastolic pressure (coronary perfusion pressure) were evaluated in a series of 63 adult mongrel dogs undergoing five different methods of cardiopulmonary resuscitation (CPR). Fluid-filled pressure monitoring catheters were placed in the ascending aorta and right atrium in each of the animals after induction of anesthesia with morphine sulfate and 1% halothane and oxygen. The animals were then fibrillated with a transvenous electrode catheter that had been introduced into a ventricle. After a "down time" of 3 minutes during which no CPR was performed, the animal's lungs were ventilated, and one of five methods of CPR was initiated. The systolic pressure gradient and coronary perfusion pressure were measured in all animals 1 minute after CPR was begun, and in all but the group undergoing open-chest cardiac massage after 7 minutes and 17 minutes of CPR. The systollic pressure gradient and coronary perfusion pressure were greatest during open-chest cardiac massage (true cardiac compression), intermediate in external mechanical CPR (Thumper) and standard CPR (greater in small dogs than large dogs), and lowest in CPR performed with a combined thoracic and abdominal vest apparatus (predominantly thoracic pump). The observation that the systolic pressure gradient between intrathoracic chambers is largest in open-chest cardiac massage and smallest in vest CPR suggests that similar measurements recorded during the performance of human cardiac resuscitation may be useful in determining the mechanism of blood flow.