Aortic function in patients during intra-aortic balloon pumping determined by the pressure-diameter relation.

OBJECTIVE

The physiologic basis for the hemodynamic and clinical improvement achieved by the use of intra-aortic balloon pumping in patients with cardiogenic shock has not been clarified in all its aspects. This study evaluated the possible contribution of pump-induced alterations of aortic mechanics to the overall benefit gained by the implementation of this therapeutic modality in patients with acute heart failure of ischemic origin.

METHODS

The aortic pressure-diameter relation was obtained by use of an intravascular catheter for aortic diameter measurements developed in our institution and previously validated, simultaneously with a catheter-tip micromanometer for aortic pressure measurements at the same aortic level. Aortic function indices were compared before and during intra-aortic balloon pumping in 12 patients with cardiogenic shock.

RESULTS

Intra-aortic balloon pumping increased cardiac index and aortic distensibility by 24% and 30%, respectively, and reduced myocardial oxygen demand by 31% (P <.001 for all alterations). Energy loss caused by aortic wall viscosity increased by 207% (P <. 001). The aortic diameter augmentation index increased by 68% (P <. 001); the aortic pressure augmentation index decreased by 117% (P <. 001). Linear regression analysis showed that cardiac index and myocardial oxygen demand were related with the aortic stiffness constant both before and during intra-aortic balloon pumping.

CONCLUSIONS

During intra-aortic balloon pumping, aortic distensibility was improved, and wave reflection from the arterial periphery was reduced. The relationship between cardiac index and myocardial oxygen demand and aortic stiffness suggests that improvement of the elastic properties of the aorta was an important mechanism by which intra-aortic balloon pumping improved circulatory function.