Harmonic analysis of perfusion pumps

Inflammatory monocyte response due to altered wall shear stress in an isolated femoral artery model

Arteriogenesis (collateral formation) is accompanied by a pro-inflammatory state that may be related to the wall shear stress (WSS) within the neo-collateral vessels. Examining the pro-inflammatory component in situ or in vivo is complex. In an ex vivo mouse femoral artery perfusion model, we examined the effect of wall shear stress on pro-arteriogenic inflammatory markers and monocyte adhesion. In a femoral artery model with defined pulsatile flow, WSS was controlled (at physiological stress, 1.4×, and 2× physiological stress) during a 24 h perfusion before gene expression levels and monocyte adhesion were assessed. Significant upregulation of expression was found for the cytokine TNFα, adhesion molecule ICAM-1, growth factor TGFβ, and the transcription factor Egr-1 at varying levels of increased WSS compared to physiological control. Further, trends toward upregulation were found for FGF-2, the cytokine MCP-1 and adhesion molecules VCAM-1 and P-selectin with increased WSS. Finally, monocytes adhesion increased in response to increased WSS. We have developed a murine femoral artery model for studying changes in WSS ex vivo and show that the artery responds by upregulating inflammatory cytokines, adhesion molecules and growth factors consistent with previous in vivo findings.

A Novel Pulse Damper for Endothelial Cell Flow Bioreactors

PURPOSE

Peristaltic pumps (PP) are favored in flow bioreactors for their non-contact sterile design. But they produce pulsatile flow, which is consequential for the cultured cells. A novel pulse damper (PD) is reported for pulsatility elimination.

METHODS

The PD design was implemented to target static pressure pulsatility and flow rate (velocity) pulsatility from a PP. Damping effectiveness was tested in a macro-scale, closed-loop recirculating bioreactor mimicking the aortic arch at flow rates up to (4 L/min). Time-resolved particle image velocimetry was used to characterize the velocity field. Endothelial cells (EC) were grown in the bioreactor, and subjected to continuous flow for 15 min with or without PD.

RESULTS

The PD was found to be nearly 90% effective at reducing pulsatility. The EC exposed to low PP flow without PD exhibited distress signaling in the form of increased ERK1/2 phosphorylation (2.5 folds) when compared to those exposed to the same flow with PD. At high pump flow without PD, the cells detached and did not survive, while they were perfectly healthy with PD.

CONCLUSIONS

Flow pulsatility from PP causes EC distress at low flow and cell detachment at high flow. Elevated temporal shear stress gradient combined with elevated shear stress magnitude at high flow are believed to be the cause of cell detachment and death. The proposed PD design was effective at minimizing the hemodynamic stressors in the pump's output, demonstrably reducing cell distress. Adoption of the proposed PD design in flow bioreactors should improve experimental protocols.

Shear stress, energy losses, and costs: a resolved dilemma of pulsatile cardiac assist devices

Cardiac assist devices (CAD) cause endothelial dysfunction with considerable morbidity. Employment of pulsatile CAD remains controversial due to inadequate perfusion curves and costs. Alternatively, we are proposing a new concept of pulsatile CAD based on a fundamental revision of the entire circulatory system in correspondence with the physiopathology and law of physics. It concerns a double lumen disposable tube device that could be adapted to conventional cardiopulmonary bypass (CPB) and/or CAD, for inducing a homogenous, downstream pulsatile perfusion mode with lower energy losses. In this study, the device's prototypes were tested in a simulated conventional pediatric CPB circuit for energy losses and as a left ventricular assist device (LVAD) in ischemic piglets model for endothelial shear stress (ESS) evaluations. In conclusion and according to the study results the pulsatile tube was successfully capable of transforming a conventional CPB and/or CAD steady flow into a pulsatile perfusion mode, with nearly physiologic pulse pressure and lower energy losses. This represents a cost-effective promising method with low mortality and morbidity, especially in fragile cardiac patients.

Pressure pulsation in roller pumps: a validated lumped parameter model

During open-heart surgery roller pumps are often used to keep the circulation of blood through the patient body. They present numerous key features, but they suffer from several limitations: (a) they normally deliver uncontrolled pulsatile inlet and outlet pressure; (b) blood damage appears to be more than that encountered with centrifugal pumps. A lumped parameter mathematical model of a roller pump (Sarns 7000, Terumo CVS, Ann Arbor, MI, USA) was developed to dynamically simulate pressures at the pump inlet and outlet in order to clarify the uncontrolled pulsation mechanism. Inlet and outlet pressures obtained by the mathematical model have been compared with those measured in various operating conditions: different rollers' rotating speed, different tube occlusion rates, and different clamping degree at the pump inlet and outlet. Model results agree with measured pressure waveforms, whose oscillations are generated by the tube compression/release mechanism during the rollers' engaging and disengaging phases. Average Euclidean Error (AEE) was 20mmHg and 33mmHg for inlet and outlet pressure estimates, respectively. The normalized AEE never exceeded 0.16. The developed model can be exploited for designing roller pumps with improved performances aimed at reducing the undesired pressure pulsation.