Pressure pulsation in roller pumps: a validated lumped parameter model

The Disconnect Between Extracorporeal Circulation and the Microcirculation: A Review

Extracorporeal circulation (ECC) procedures, such as cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation (ECMO), take over the function of one or more organs, providing clinicians time to treat underlying pathophysiological conditions. ECMO and CPB carry significant mortality rates for patients, despite prior decades of research focused on the resulting failure of critical organs. Since the focus of these procedures is to support blood flow and provide oxygen-rich blood to tissues, a shift in research toward the effects of ECMO and CPB on the microcirculation is warranted. Along with provoking systemic responses, both procedures disrupt the integrity of red blood cells, causing release of hemoglobin (Hb) from excessive foreign surface contact and mechanical stresses. The effects of hemolysis are especially pronounced in the microcirculation, where plasma Hb leads to nitric oxide scavenging, oxidization, formation of reactive oxygen species, and inflammatory responses. A limited number of studies have investigated the implications of ECMO in the microcirculation, but more work is needed to minimize ECMO-induced reduction of microcirculatory perfusion and consequently oxygenation. The following review presents existing information on the implications of ECMO and CPB on microvascular function and proposes future studies to understand and leverage key mechanisms to improve patient outcomes.

Optimal Design in Roller Pump System Applications for Linear Infusion

In this study, an infusion roller pump comprising two separate innovative resilient tube designs is presented. The first incorporates the flexible tubing cross-section area in its relaxed state as a lenticular one for power reduction reasons. The second keeps the previous lenticular cross-section along its length, while it additionally incorporates an inflating portion, for creating a momentary flow positive pulse to balance the void generated by the roller disengagement. Fluid–Structure Interaction (FSI) simulations cannot provide quantitatively realistic results, due to the limitation of full compression of the tube, and are only used qualitatively to reveal by which way to set the inflated portion along the tube length in order to suppress backflow and achieve constant flow rate. Finally, indirect lumen volume measurements were performed numerically and an optimum design was found testing eight design approaches. These indirect fluid volume measurements assess the optimum inflated tube’s portion leading to backflow and pulsating elimination. The optimum design has an inflation portion of 75 degrees covering almost 42% of the curved part of the tube, while it has a constant zone with the maximum value of inflated lenticular cross-section, within the portion, of 55 degrees covering about 73% of the inflation portion.

Dynamic modeling of the outlet of a pulsatile pump incorporating a flow-dependent resistance

Outlet tube models incorporating a linearly flow-dependent resistance are widely used in pulsatile and rotary pump studies. The resistance is made up of a flow-proportional term and a constant term. Previous studies often focused on the steady state properties of the model. In this paper, a dynamic modeling procedure was presented. Model parameters were estimated by an unscented Kalman filter (UKF). The subspace model identification (SMI) algorithm was proposed to initialize the UKF. Model order and structure were also validated by SMI. A mock circulatory loop driven by a pneumatic pulsatile pump was developed to produce pulsatile pressure and flow. Hydraulic parameters of the outlet tube were adjusted manually by a clamp. Seven groups of steady state experiments were carried out to calibrate the flow-dependent resistance as reference values. Dynamic estimation results showed that the inertance estimates are insensitive to model structures. If the constant term was ignored, estimation errors for the flow-proportional term were limited within 16% of the reference values. Compared with the constant resistance, a time-varying one improves model accuracy in terms of root mean square error. The maximum improvement is up to 35%. However, including the constant term in the time-varying resistance will lead to serious estimation errors.

A multichannel dampened flow system for studies on shear stress-mediated mechanotransduction

Shear stresses are powerful regulators of cellular function and potent mediators of the development of vascular disease. We have designed and optimized a system allowing the application of flow to cultured cells in a multichannel format. By using a multichannel peristaltic pump, flow can be driven continuously in the system for long-term studies in multiple isolated flow loops. A key component of the system is a dual-chamber pulse dampener that removes the pulsatility of the flow without the need for having an open system or elevated reservoir. We optimized the design parameters of the pulse dampening chambers for the maximum reduction in flow pulsation while minimizing the fluid needed for each isolated flow channel. Human umbilical vein endothelial cells (HUVECs) were exposed to steady and pulsatile shear stress using the system. We found that cells under steady flow had a marked increased production of eNOS and formation of actin stress fibers in comparison to those under pulsatile flow conditions. Overall, the results confirm the utility of the device as a practical means to apply shear stress to cultured cells in the multichannel format and provide steady, long term flow to microfluidic devices.