Measurements of Intra-Aortic Balloon Wall Movement During Inflation and Deflation: Effects of Angulation

Abstract

The intra-aortic balloon pump (IABP) is a ventricular assist device that is used with a broad range of pre-, intra-, and postoperative patients undergoing cardiac surgery. Although the clinical efficacy of the IABP is well documented, the question of reduced efficacy when patients are nursed in the semi-recumbent position remains outstanding. The aim of the present work is therefore to investigate the underlying mechanics responsible for the loss of IABP performance when operated at an angle to the horizontal. Simultaneous recordings of balloon wall movement, providing an estimate of its diameter (D), and fluid pressure were taken at three sites along the intra-aortic balloon (IAB) at 0 and 45°. Flow rate, used for the calculation of displaced volume, was also recorded distal to the tip of the balloon. An in vitro experimental setup was used, featuring physiological impedances on either side of the IAB ends. IAB inflation at an angle of 45° showed that D increases at the tip of the IAB first, presenting a resistance to the flow displaced away from the tip of the balloon. The duration of inflation decreased by 15.5%, the inflation pressure pulse decreased by 9.6%, and volume decreased by 2.5%. Similarly, changing the position of the balloon from 0 to 45°, the balloon deflation became slower by 35%, deflation pressure pulse decreased by 14.7%, and volume suctioned was decreased by 15.2%. IAB wall movement showed that operating at 45° results in slower deflation compared with 0°. Slow wall movement, and changes in inflation and deflation onsets, result in a decreased volume displacement and pressure pulse generation. Operating the balloon at an angle to the horizontal, which is the preferred nursing position in intensive care units, results in reduced IAB inflation and deflation performance, possibly compromising its clinical benefits.

Keywords: Balloon diameter; Counterpulsation; Deflation; Flow; Inflation; Intra-aortic balloon pump; Operating angle; Pressure; Visualization.

Figure 1

Schematic of the experimental setup. The reservoir was connected to the artificial aorta (AO) via two polyurethane tubes; two capillary tubes and two air‐filled syringes constitute the up‐ and downstream physiological impedance in terms of resistances and compliances (see Khir et al. [6]). The balloon is placed in the middle of the artificial AO. A pressure catheter is placed along the balloon to measure pressure at the IAB tip, center, and base. The thick arrow indicates the direction upstream of the balloon where a flow probe is snug‐fitted to the artificial AO for measuring the volume displaced and suctioned due to inflation and deflation. When the button is pressed, it triggers the IABP, high‐speed camera, and data acquisition for simultaneous measurements of the pressure, flow, and balloon filming. The dashed lines indicate the field of view of the camera. The lateral distance between the water level in the reservoir and the center line of the IAB was kept at 1.2 m for both the horizontal angled (0°, 45°) positions by raising the reservoir appropriately to maintain the same static mean pressure at the center of the balloon (90 mm Hg).

Figure 2

Flow waveform (solid line) and balloon catheter helium pressure (dotted line) are plotted against time. The area integrated under the solid line between points A and B indicates the volume displaced away from the tip of the balloon (upstream) during inflation. The area integrated above the solid line between points B and C indicates the volume suctioned from the tip of the balloon during deflation. The flow scale indicates negative value at the onset of inflation due to the deflation of the previous cycle.

Figure 3

Diameter at the horizontal (solid line) and at 45° (dashed line) at the tip (A), center (B), and base (C) of the balloon. The diameter waveforms of the base and center of the IAB are similar in shape at 0 and 45°, while the tip shows different dynamics of both inflation and deflation. Diameter at 45° is always larger during deflation at all parts of the balloon. Thick arrow in (A) indicates an earlier and larger peak tip diameter at 45 than 0°.

Figure 4

Pressure difference between tip and base of the balloon (solid line) at a horizontal position (A) and at 45° (B), with the IABP uncalibrated helium pressure (dotted line). A clear peak is visible and indicated by the downwards pointing arrow immediately after deflation onset at 45° but missing at 0°. This peak indicates that at 45°, immediately after deflation onset as indicated by the upward pointing arrows, the pressure decreases more steeply at the base than at the tip.

Figure 5

Diameter, D, at the horizontal (A) and angled (B) positions for tip (dotted line), center (dashed line), and base (solid line) of the balloon. While at a horizontal position (A), the inflation peak appears first at the base followed by center and tip; at an angle (B), inflation is less linear and shows a first smaller inflation peak at the tip of the IAB.

Figure 6

Diameter (D, black line) and pressure (P, gray line) waveforms at the tip of the balloon at 0° (solid line) and 45° (dotted line). Dashed and solid vertical arrows indicate the reduced deflation pulse at the angled and horizontal positions, respectively, while the horizontal arrow indicates the potential cause related to this loss, a delayed deflation of IAB tip.