Intra-aortic balloon shape change: effects on volume displacement during inflation and deflation.

It has been observed that operating the intra-aortic balloon at an angle to the horizontal resulted in a reduction of the volume displaced toward the coronary arteries and compromised afterload reduction. Therefore, the aim of this work is to examine whether changing the current balloon shape, which has not been altered for 40 years, could compensate for the negative hemodynamic effects due to angulation. We tested two tapered balloons, increasing diameter (TID) and decreasing diameter (TDD), and compared the results with those obtained from a standard cylindrical balloon. The balloons were tested in vitro at 60 beats/min and a static pressure of 90 mm Hg. The balloons were operated at four angles (0°, 20°, 30°, 45°), and the pressure at three locations along the balloon (base, middle, and tip) was also measured. Flow rate upstream of the tip of the balloon was also measured to indicate the flow displaced toward the coronary circulation. The relative volume displaced toward (VUTVi) and suctioned away from (VUTVd) the simulated ascending aorta, during inflation and deflation, respectively, is reduced when a standard cylindrical balloon is operated at an angle to the horizontal. The TDD provided the greatest VUTVi and also produced the largest pulse pressure during deflation. Although the TID provided less VUTVi and VUTVd at smaller angles, it was not markedly affected by the change of angle. According to these results, different balloon shapes analyzed, with comparable volume to that of a cylindrical balloon, produced greater inflation and deflation benefits, at the horizontal and at a range of angles to the horizontal. Further investigations are required to optimize the shape of the tapered balloons to fit into the available physiological space.

Effects of intra-aortic balloon pump timing on baroreflex activities in a closed-loop cardiovascular hybrid model.

Despite 50 years of research to assess the intra-aortic balloon pump (IABP) effects on patients' hemodynamics, some issues related to the effects of this therapy are still not fully understood. One of these issues is the effect of IABP, its inflation timing and duration on peripheral circulation autonomic controls. This work provides a systematic analysis of IABP effects on baroreflex using a cardiovascular hybrid model, which consists of computational and hydraulic submodels. The work also included a baroreflex computational model that was connected to a hydraulic model with a 40-cm(3) balloon. The IABP was operated at different inflation trigger timings (-0.14 to 0.31 s) and inflation durations (0.05-0.45 s), with time of the dicrotic notch being taken as t = 0. Baroreflex-dependent parameters-afferent and efferent pathway activity, heart rate, peripheral resistance, and venous tone-were evaluated at each of the inflation trigger times and durations considered. Balloon early inflation (0.09 s before the dicrotic notch) with inflation duration of 0.25 s generated a maximum net increment of afferent pathway activity of 10%, thus leading to a decrement of efferent sympathetic activity by 15.3% compared with baseline values. These times also resulted in a reduction in peripheral resistance and heart rate by 4 and 4.3% compared with baseline value. We conclude that optimum IABP triggering time results in positive effects on peripheral circulation autonomic controls. Conversely, if the balloon is not properly timed, peripheral resistance and heart rate may even increase, which could lead to detrimental outcomes.

Impact of varying diastolic pressure fitting technique for the reservoir-wave model on wave intensity analysis.

The reservoir-wave model assumes that the measured arterial pressure is made of two components: reservoir and excess. The effect of the reservoir volume should be excluded to quantify the effects of forward and backward traveling waves on blood pressure. Whilst the validity of the reservoir-wave concept is still debated, there is no consensus on the best fitting method for the calculation of the reservoir pressure waveform. Therefore, the aim of this parametric study is to examine the effects of varying the fitting technique on the calculation of reservoir and excess components of pressure and velocity waveforms. Common carotid pressure and flow velocity were measured using applanation tonometry and doppler ultrasound, respectively, in 1037 healthy humans collected randomly from the Asklepios population, aged 35 to 55 years old. Different fitting techniques to the diastolic decay of the measured arterial pressure were used to determine the asymptotic pressure decay, which in turn was used to determine the reservoir pressure waveform. The corresponding wave speed was determined using the PU-loop method, and wave intensity parameters were calculated and compared. Different fitting methods resulted in significant changes in the shape of the reservoir pressure waveform; however, its peak and time integral remained constant in this study. Although peak and integral of excess pressure, velocity components and wave intensity changed significantly with changing the diastolic decay fitting method, wave speed was not substantially modified. We conclude that wave speed, peak reservoir pressure and its time integral are independent of the diastolic pressure decay fitting techniques examined in this study. Therefore, these parameters are considered more reliable diagnostic indicators than excess pressure and velocity which are more sensitive to fitting techniques.

Hemodynamics of a pulsatile left ventricular assist device driven by a counterpulsation pump in a mock circulation.

The BCM (CardialCare, Minneapolis, MN, U.S.A.) is a pusher-plate pulsatile left ventricular assist device (LVAD) that is operated by counterpulsation pumps. The purpose of this work was to assess the fluid dynamics associated with operating the BCM in a mock circulation, and also to examine the similarities between hemodynamic parameters produced by this device in vitro and those produced by the left ventricle (LV) in vivo. The BCM was connected to a true size silicon rubber aorta and operated by an intra-aortic balloon pump. We examined the performance of the device at two system pressures (6.5 and 8 kPa); at three heart rates (60, 80, and 100 bpm); and at three pumping frequencies (1:1, 1:2, 1:3). Pressure and flow were measured in the upper descending aorta, and wave intensity analysis was used to calculate the peak intensity and energy of the compression and expansion waves. Pressure and flow waveforms produced by the BCM LVAD in vitro under different loading conditions were similar to those observed in vivo under similar loadings. Pusher-plate-type LVADs can produce compression and expansion waves similar to those generated by healthy LV in vivo.