Christina Kolyva

How much of the intraaortic balloon volume is displaced toward the coronary circulation

Objective During intraaortic balloon inflation, blood volume is displaced toward the heart (Vtip), traveling retrograde in the descending aorta, passing by the arch vessels, reaching the aortic root (Vroot), and eventually perfusing the coronary circulation (Vcor). Vcor leads to coronary flow augmentation, one of the main benefits of the intraaortic balloon pump. The aim of this study was to assess Vroot and Vcor in vivo and in vitro, respectively. Methods During intraaortic balloon inflation, Vroot was obtained by integrating over time the aortic root flow signals measured in 10 patients with intraaortic balloon assistance frequencies of 1:1 and 1:2. In a mock circulation system, flow measurements were recorded simultaneously upstream of the intraaortic balloon tip and at each of the arch and coronary branches of a silicone aorta during 1:1 and 1:2 intraaortic balloon support. Integration over time of the flow signals during inflation yielded Vcor and the distribution of Vtip. Results In patients, Vroot was 6.4% ± 4.8% of the intraaortic balloon volume during 1:1 assistance and 10.0% ± 5.0% during 1:2 assistance. In vitro and with an artificial heart simulating the native heart, Vcor was smaller, 3.7% and 3.8%, respectively. The distribution of Vtip in vitro varied, with less volume displaced toward the arch and coronary branches and more volume stored in the compliant aortic wall when the artificial heart was not operating. Conclusion The blood volume displaced toward the coronary circulation as the result of intraaortic balloon inflation is a small percentage of the nominal intraaortic balloon volume. Although small, this percentage is still a significant fraction of baseline coronary flow.

Discerning aortic waves during intra-aortic balloon pumping and their relation to benefits of counterpulsation in humans

An explanation of the mechanisms leading to the beneficial hemodynamic effects of the intra-aortic balloon pump (IABP) is lacking. We hypothesized that inflation and deflation of the balloon would generate a compression (BCW) and an expansion (BEW) wave, respectively, which, when analyzed with wave intensity analysis, could be used to explain the hemodynamic benefits of IABP support. Simultaneous ascending aortic pressure (Pao) and flow rate (Qao) were recorded in 25 patients during control conditions and with IABP support of 1:1 and 1:2. Diastolic aortic pressure augmentation (Paug) and end-diastolic aortic pressure (ED Pao) reduction were calculated from Pao. Energies of the BCW and BEW were obtained by integrating the wave intensity contour over time. Paug was 19.1 mmHg (SD 13.6) during 1:2 support. During 1:1 support significantly higher Paug of 21.1 mmHg (SD 13.4) was achieved (P < 0.001). ED Pao decreased from 50.9 mmHg (SD 15.1) to 43.9 mmHg (SD 15.7) (P < 0.0001) during 1:1 assistance and the decrease was not statistically different with 1:2. During 1:1 support the energy of BCW was correlated positively to Paug (r = 0.83, P < 0.0001) and energy of the BEW correlated negatively to ED Pao (r = 0.78, P < 0.005); these relationships were not statistically different during 1:2. In conclusion, the energies of the BCW and BEW are directly related to Paug and ED Pao, which are the conventional hemodynamic parameters indicating IABP benefits. These findings imply a cause and effect mechanism between the energies of BCW and BEW, and IABP hemodynamic effects.

A Mock Circulatory System With Physiological Distribution of Terminal Resistance and Compliance: Application for Testing the Intra-Aortic Balloon Pump

A mock circulatory system (MCS) was designed to replicate a physiological environment for in vitro testing and was assessed with the intra-aortic balloon pump (IABP). The MCS was comprised of an artificial left ventricle (LV), connected to a 14-branch polyurethane-compound aortic model. Physiological distribution of terminal resistance and compliance according to published data was implemented with capillary tubes of different sizes and syringes of varying air volume, respectively, fitted at the outlets of the branches. The ends of the aortic branches were connected to a common tube representing the venous system and an overhead reservoir provided atrial pressure. An IABP operating a 40-cc balloon was set to counterpulsate with the LV. Total arterial compliance of the system was 0.94 mL/mm Hg and total arterial resistance was 20.3 ± 3.3 mm Hg/L/min. At control, physiological flow distribution was achieved and both mean and phasic aortic pressure and flow were physiological. With the IABP, aortic pressure exhibited the major features of counterpulsation: diastolic augmentation during inflation, inflection point at onset of deflation, and end-diastolic reduction at the end of deflation. The contribution of balloon inflation and deflation was also evident on the aortic flow pattern. This MCS was verified to be suitable for IABP testing and with further adaptations it could be used for studying other hemodynamic problems and ventricular assist devices.

Increased diastolic time fraction as beneficial adjunct of α1-adrenergic receptor blockade after percutaneous coronary intervention

The effect of alpha1-receptor blockade with urapidil on coronary blood flow and left ventricular function has been attributed to relief of diffuse coronary vasoconstriction following percutaneous coronary intervention (PCI). We hypothesized that an increase in diastolic time fraction (DTF) contributes to the beneficial action of urapidil. In eleven patients with a 63% (SD 13) diameter stenosis, ECG, aortic pressure (Pa) and distal intracoronary pressure (Pd), and blood flow velocity were recorded at baseline and throughout adenosine-induced hyperemia. Measurements were obtained before and after PCI and after subsequent alpha1-receptor blockade with urapidil (10 mg ic). DTF was determined from the ECG and the Pa waveform. Functional parameters such as coronary flow velocity reserve, fractional flow reserve, and an index of hyperemic microvascular resistance (HMR) were assessed. Urapidil administration after PCI induced an upward shift in the DTF-heart rate relationship, resulting in a 3.1% (SD 2.7) increase in hyperemic DTF at a constant heart rate (P < 0.005) due to a shorter duration of systole. Hyperemic Pa and Pd decreased, respectively, by 6.1% (SD 6.6; P < 0.05) and 5.7% (SD 5.8; P < 0.01) after alpha1-blockade. Although epicardially measured functional parameters were on average not altered by alpha1-blockade due to concurrent changes in pressure and heart rate, HMR decreased by urapidil in those patients where coronary pressure remained constant. In conclusion, alpha1-receptor blockade after PCI produced a modest but significant prolongation of DTF at a given heart rate, thereby providing an adjunctive beneficial mechanism for improving subendocardial perfusion, which critically depends on DTF.

Pressure-wave energy relationship during IABP counterpulsation in a mock circulation: changes with angle and assisting frequency.

Purpose Despite decades of successful clinical use of the Intra-Aortic Balloon Pump (IABP), certain aspects of its operation are not yet fully understood. This work aims to investigate in vitro the mechanism underlying balloon inflation and deflation with varying assisting frequency and operating angle with respect to the horizontal, by studying the corresponding pressure and wave energy changes. Methods A mock circulatory system (MCS), with physiological distribution of peripheral resistance and compliance, presented a controllable test bed. We used Wave Intensity Analysis (WIA) to identify balloon-generated waves and quantify their energy. Conventional hemodynamic parameters were also calculated. Tests were repeated at varying operating angles (0°-45°), resembling the semi-recumbent position in the ICU, and at different assisting frequencies (1:1, 1:2, 1:3). Two balloons (25 cc and 40 cc in volume) were tested. Results The main waves associated with counterpulsation were identified as a backward compression wave associated with balloon inflation and a backward expansion wave associated with balloon deflation. Results showed that the IABP inflation and deflation benefits are reduced with increasing angle, in terms of the size of the inflation and deflation waves as well as in terms of diastolic pressure augmentation and end-diastolic pressure reduction. Both WIA findings and pressure parameters indicated 1:1 as the most effective mode of pumping. Conclusions This study shows that, in vitro, a greater benefit of counterpulsation can be achieved in the horizontal position at 1:1 assisting frequency, with a good correlation between wave and pressure results.

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.

Newly shaped intra-aortic balloons improve the performance of counterpulsation at the semirecumbent position: an In Vitro study

Abstract The major hemodynamic benefits of intra‐aortic balloon pump (IABP) counterpulsation are augmentation in diastolic aortic pressure (P aug) during inflation, and decrease in end‐diastolic aortic pressure (ΔedP) during deflation. When the patient is nursed in the semirecumbent position these benefits are diminished. Attempts to change the shape of the IAB in order to limit or prevent this deterioration have been scarce. The aim of the present study was to investigate the hemodynamic performance of six new IAB shapes, and compare it to that of a traditional cylindrical IAB. A mock circulation system, featuring an artificial left ventricle and an aortic model with 11 branches and physiological resistance and compliance, was used to test one cylindrical and six newly shaped IABs at angles 0, 10, 20, 30, and 40°. Pressure was measured continuously at the aortic root during 1:1 and 1:4 IABP support. Shape 2 was found to consistently achieve, in terms of absolute magnitude, larger ΔedP at angles than the cylindrical IAB. Although ΔedP was gradually diminished with angle, it did so to a lesser degree than the cylindrical IAB; this diminishment was only 53% (with frequency 1:1) and 40% (with frequency 1:4) of that of the cylindrical IAB, when angle increased from 0 to 40°. During inflation Shape 1 displayed a more stable behavior with increasing angle compared to the cylindrical IAB; with an increase in angle from 0 to 40°, diastolic aortic pressure augmentation dropped only by 45% (with frequency 1:1) and by 33% (with frequency 1:4) of the drop reached with the cylindrical IAB. After compensating for differences in nominal IAB volume, Shape 1 generally achieved higher P aug over most angles. Newly shaped IABs could allow for IABP therapy to become more efficient for patients nursed at the semirecumbent position. The findings promote the idea of personalized rather than generalized patient therapy for the achievement of higher IABP therapeutic efficiency, with a choice of IAB shape that prioritizes the recovery of those hemodynamic indices that are more in need of support in the unassisted circulation.

Does conventional intra-aortic balloon pump trigger timing produce optimal hemodynamic effects in vivo?

Purpose The intra-aortic balloon pump (IABP) provides circulatory support through counterpulsation. The hemodynamic effects of the IABP may vary with assisting frequency and depend on IAB inflation/deflation timing. We aimed to assess in vivo the IABP benefits on coronary, aortic, and left ventricular hemodynamics at different assistance frequencies and trigger timings. Methods Six healthy, anesthetized, open-chest sheep received IABP support at 5 timing modes (EC, LC, CC, CE, CL, corresponding to early/late/conventional/conventional/conventional inflation and conventional/conventional/conventional/early/late deflation, respectively) with frequency 1:3 and 1:1. Aortic (Qao) and coronary (Qcor) flow, and aortic (Pao) and left ventricular (PLV) pressure were recorded simultaneously, with and without IABP support. Integrating systolic Qao yielded stroke volume (SV). Results EC at 1:1 produced the lowest end-diastolic Pao (59.5 ± 7.8 mmHg [EC], 63.4 ± 11.1 mmHg [CC]), CC at 1:1 the lowest systolic PLV (69.1 ± 6.5 mmHg [CC], 76.4 ± 6.5 mmHg [control]), CC at 1:1 the highest SV (88.5 ± 34.4 ml [CC], 76.6 ± 31.9 ml [control]) and CC at 1:3 the highest diastolic Qcor (187.2 ± 25.0 ml/min [CC], 149.9 ± 16.6 ml/min [control]). Diastolic Pao augmentation was enhanced by both assistance frequencies alike, and optimal timings were EC for 1:3 (10.4 ± 2.8 mmHg [EC], 6.7 ± 3.8 mmHg [CC]) and CC for 1:1 (10.8 ± 6.7 mmHg [CC], −3.0 ± 3.8 mmHg [control]). Conclusions In our experiments, neither a single frequency nor a single inflation/deflation timing, including conventional IAB timing, has shown superiority by uniformly benefiting all studied hemodynamic parameters. A choice of optimal frequency and IAB timing might need to be made based on individual patient hemodynamic needs rather than as a generalized protocol.

Non-invasive assessment of the common carotid artery hemodynamics with Increasing exercise workrate using wave intensity analysis

Noninvasively determined local wave speed (c) and wave intensity (WI) parameters provide insights into arterial stiffness and cardiac-vascular interactions in response to physiological perturbations. However, the effects of incremental exercise and subsequent recovery on c and WI have not been fully established. We examined the changes in c and WI parameters in the common carotid artery (CCA) during exercise and recovery in eight young, healthy male athletes. Ultrasound measurements of CCA diameter and blood flow velocity were acquired at rest, during five stages of incremental exercise (up to 70% maximum work rate), and throughout 1 h of recovery, and noninvasive WI analysis [diameter-velocity (DU) approach] was performed. During exercise, c increased (+136%), showing increased stiffness with work rate. All peak and area of forward compression, backward compression, and forward expansion waves increased during exercise (+452%, +700%, and +900%, respectively). However, WI reflection indexes and CCA resistance did not significantly change from rest to exercise. Furthermore, wave speed and the magnitude of all waves returned to baseline within 5 min of recovery, suggesting that the effects of exercise in the investigated parameters of young, healthy individuals were transient. In conclusion, incremental exercise was associated with an increase in local CCA stiffness and increases in all wave parameters, indicative of enhanced ventricular contractility and improved late-systolic blood flow deceleration. NEW & NOTEWORTHY We examined hemodynamics of the common carotid artery using noninvasive application of wave intensity analysis during exercise and recovery. The hemodynamic adjustments to exercise were associated with increases in local common carotid artery stiffness and all waves’ parameters, with the latter indicating enhanced ventricular contractility and improved late systolic blood flow deceleration.