# The Effect of Mechanical Circulatory Support on Blood Flow in the Ascending Aorta: A Combined Experimental and Computational Study

^{*}

## Abstract

**:**

## 1. Introduction

^{TM}MCS device in a model of the aorta to demonstrate that the Impella CP support augmented the velocity, WSS, and pressure drop within the aorta. Wang et al. [32] used CFD analysis to describe the additional effect of MCS on the native pulsating aortic flow and the wall shear stress distribution for a patient-specific aorta model.

## 2. Methods and Materials

#### 2.1. Experimental Setup

^{®}frame grabber and Xcap

^{TM}software for real-time image acquisition. The frame rate was set at 192 Hz, and the PIV algorithm was configured with a 50% overlap. In addition to the minimal effect of image distortion (due to the curved walls of the model), the post-processing algorithm used a pre-defined calibrated image mask of the model, as described in a previous study [44], which used the same model and was well-calibrated for optical distortions.

#### 2.2. Cases Studied

#### 2.3. Post-Processing

#### 2.4. Numerical Model

**V**is the velocity vector, and $\rho $ and $\mu $ are the density and dynamic viscosity of the blood, respectively. The blood was assumed to be homogenous, incompressible ($\rho $ = 1 gr/mL), and Newtonian (with viscosity $\mu $ = 3.5 cP). The model’s geometry was similar to the experimental model. The numerical model was previously used and validated [50,51]. The numerical mesh (shown in Figure 5) consisted of 2,608,560 tetrahedral elements. The SST k-ω low-Reynolds numerical model was used [52].

## 3. Results

## 4. Discussion

- Swirling flow reduces the TKE of the pump’s jet inlet and improves the flow distribution near the aortic valve and the ascending aorta (and may reduce the risk of release of emboli from the aorta wall);
- Swirling flow increases the dominance of vortical flow near the valve and in the ascending aorta;
- In the case of the CW inlet case, the vortex was drawn toward the posterior wall of the aorta, while in the CCW inlet case, the vortex was drawn toward the anterior wall of the aorta;
- A high flow rate washed out the local turbulence near the pump inlet downstream toward the aortic arch, and thus, the local vortices formed near the outlet were more distributed in the ascending aorta;
- pLVAD with a CCW rotating impeller (such as in the Impella pump) induced non-physiological CCW helical flow in the descending aorta (which is the opposite of the natural helical flow);
- Clockwise swirl combined better with the natural helical flow.

- Examining the effect of CCW helical flow in the descending aorta on the flow to the branching arteries (e.g., coronaries, subclavian, carotid, and renal);
- Examining the effects of different rotational velocities on the flow;
- Examining the effects of a beating heart and the obtained combined flow (including the aortic valve’s dynamics);
- Examining the effects of the different flow features on each other.

## Supplementary Materials

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**A schematic description of the hydraulic experimental setup, including a glass model, two pumps, a reservoir, a regulating valve, and sealing rubber. Blue arrows indicate flow direction.

**Figure 3.**The PIV system: (

**A**) schematic description of the PIV setup, and (

**B**) photo of the experimental model.

**Figure 4.**(

**A**) The examined cross-sections, and (

**B**) an example orientation view of the blue vertical cross-sections. Arrows indicate flow direction.

**Figure 6.**Examples of velocity (vectors and magnitudes) comparison between the obtained PIV and CFD results in three representative cross-sections and cases (2.5 L/min): (

**A**) jet case, sagittal section, (

**B**) CW case, coronal section, and (

**C**) CCW case, distal section. Note that for the numerical results, velocities above 0.15 m/s are colored in red.

**Figure 7.**Velocity vectors and streamlines with two example flow rates (1 and 2.5 L/min) in the three flow configurations (jet, CW, and CCW), delineate three dominant phenomena in the flow field. Arrows indicate vortices’ directions.

**Figure 8.**Reverse flow of the incoming jet (phenomenon no. 1) in the sagittal section at 2.5 L/min for the jet inlet (left) and CW inlet (right): (

**A**) results of PIV vectors, (

**B**) velocities, and (

**C**) CFD velocity vectors. Black/white arrows indicate flow directions and blue arrows indicate the impeller’s rotation.

**Figure 9.**Helical flow in the descending aorta (phenomenon no. 3) from the CFD simulation for the three inlet cases (2.5 L/min): (

**A**) jet inlet, (

**B**) CW inlet, and (

**C**) CCW inlet. Arrows indicate the directions of the inlet flow.

**Figure 10.**PIV vorticity maps for the different cases and cross-sections along the aorta model at 2.5 L/min: (

**A**) jet inlet, (

**B**) CW inlet, (

**C**) CCW inlet. Blue arrows indicate flow direction, and black arrows indicate vorticities’ directions.

**Figure 11.**Locations of the vortices in the aorta—a combination of velocity (vectors and magnitudes) in the transverse cross-sections (PIV) and sagittal sections (CFD). (

**A**) CW inlet case, (

**B**) CCW inlet case. Note that for the numerical results, velocities above 0.15 m/s are colored in red.

**Figure 12.**Velocity vectors and vorticity magnitudes as a function of flow rate in the three sections: (

**A**) jet inlet, (

**B**) CW inlet, and (

**C**) CCW inlet. Positive values indicate CW rotational flow and negative values indicate CCW rotational flow.

**Figure 14.**Box plots of the TKE distribution values for the different cases along the distal (

**A**), middle (

**B**), and proximal (

**C**) cross-sections of the aorta with a flow rate of 2.5 L/min.

Experiment | Numerical Boundary Conditions | |||
---|---|---|---|---|

Flow Rate | Rotational Speed * | Jet Inlet | CW Inlet | CCW Inlet |

1 L/min | 9000 RPM | u = 0.21 m/s ω = 0 rad/s | u = 0.21 m/s ω = 900 rad/s CW | u = 0.21 m/s ω = 900 rad/s CCW |

1.5 L/min | 12,000 RPM | u = 0.32 m/s ω = 0 rad/s | u = 0.32 m/s ω = 1270 rad/s CW | u = 0.32 m/s ω = 1270 rad/s CCW |

2 L/min | 15,500 RPM | u = 0.42 m/s ω = 0 rad/s | u = 0.42 m/s ω = 1630 rad/s CW | u = 0.42 m/s ω = 1630 rad/s CCW |

2.5 L/min | 19,000 RPM | u = 0.53 m/s ω = 0 rad/s | u = 0.53 m/s ω = 2000 rad/s CW | u = 0.53 m/s ω = 2000 rad/s CCW |

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**MDPI and ACS Style**

Hazan Shenberger, S.; Avrahami, I.
The Effect of Mechanical Circulatory Support on Blood Flow in the Ascending Aorta: A Combined Experimental and Computational Study. *Bioengineering* **2024**, *11*, 238.
https://doi.org/10.3390/bioengineering11030238

**AMA Style**

Hazan Shenberger S, Avrahami I.
The Effect of Mechanical Circulatory Support on Blood Flow in the Ascending Aorta: A Combined Experimental and Computational Study. *Bioengineering*. 2024; 11(3):238.
https://doi.org/10.3390/bioengineering11030238

**Chicago/Turabian Style**

Hazan Shenberger, Sapir, and Idit Avrahami.
2024. "The Effect of Mechanical Circulatory Support on Blood Flow in the Ascending Aorta: A Combined Experimental and Computational Study" *Bioengineering* 11, no. 3: 238.
https://doi.org/10.3390/bioengineering11030238