Unidirectional blood flow can be naturally generated by changing intravascular pressure: an extracorporeal model for elucidating the blood flow mechanism in CPR

Objectives

There are two mechanisms for the generation of forward blood flow during extrathoracic cardiac compression for cardiac arrest; direct cardiac compression and thoracic pump. We postulate that the difference of vascular resistance from the arterial to peripheral capillary in tandem and the existence of competent venous valves make it possible for blood to flow forwardly by a simple change of intravascular pressure in a cardiac arrest model.

Methods

A mongrel dog was anesthetized with i.v. sodium pentobarbital. The dog was mechanically ventilated. The right femoral artery was cannulated. A double lumen catheter was introduced via the external jugular vein. The cardiac rhythm and heart rate were monitored. Midline thoracotomy was performed. After the infusion of heparin 300 U/kg, KCl 20 mEq was injected intravenously to induce cardiac arrest. A Y-shaped extracorporeal circuit was primed with heparinized normal saline beforehand. Each end of the two branches of the circuit has a 3/8-inch connector, respectively, and the other end was connected with a 50 cm³ syringe. A connector was introduced at the junction of the SVC and IVC via the right atrium. The aorta was transected above the aortic valve and another 3/8-inch connector was inserted directly into the ascending aorta. Indocyanine green dye was injected via the connector of the right atrium.

Results

At the beginning of syringe resuscitation, aortic and vena caval blood was drained slightly during the suction phase and the blood moved to in both directions during the push phase; however, the dye transferred gradually from the vena cavae to arterial side while showing a concomitant to-and-fro movement of its own with the repeated piston movement.

Conclusion

We observed that forward blood movement from the aorta to peripheral artery occurred without cardiac valves while changing the intravascular pressure using a syringe pump. This proves that an intravascular pressure change generated by direct cardiac compression or an intrathoracic pump during external cardiac compression can produce systemic blood flow probably both by the innate vascular resistance difference and by the intravenous valvular patency, irrespective of cardiac valve motion.