Variations in aortic pressure affect the mechanics of the intra-aortic balloon: an in vitro investigation.

This study aims to investigate the mechanics of the intra-aortic balloon (IAB) under different aortic pressure (P(ao)) and inclination (0-75 degrees). Pressure and flow were measured in an artificial aorta during IAB pumping with a frequency of 1:3. Volume displaced toward the "coronary arteries" during inflation (V(prox)) and "intra-aortic" pressure reduction during deflation (P(r)) were derived. IAB duration of inflation and deflation was determined with a high-speed camera visualization. When the aorta was horizontal, P(ao) raised from 45 mm Hg to 115 mm Hg, V(prox) reduced by 18% (25.0 +/- 1.0 mL vs. 30.4 +/- 1.9 mL) and P(r) increased by 117% (106.4 +/- 0.3 mm Hg vs. 48.9 +/- 0.6 mm Hg). When the aorta was inclined, at low P(ao) of 45 mm Hg, V(prox) was reduced by 30% from 0 degrees to 45 degrees (19.8 +/- 2.3 mL vs. 28.3 +/- 1.7 mL) and P(r) was reduced by 66% (16.5 +/- 0.1 mm Hg vs. 48.9 +/- 0.6 mm Hg). However, at high P(ao) of 115 mm Hg, V(prox) remained unchanged with increasing angle (20.0 +/- 1.0 mL) and P(r) was reduced by 24% (80.6 +/- 0.8 mm Hg vs. 106.4 +/- 0.3 mm Hg). Increasing P(ao) increased duration of inflation. At low P(ao), increasing angle resulted in increasing duration of inflation, but at high P(ao), increasing angle had the opposite effect. Duration of deflation generally decreased with P(ao) and increased with increasing angle. The IAB pump is affected by both P(ao) and angle, indicating that non-normotensive patients or patients in the semi-recumbent position might not receive the full benefits of IAB counterpulsation.