Elsevier

Medical Engineering & Physics

Volume 30, Issue 9, November 2008, Pages 1149-1158
Medical Engineering & Physics

Pressure pulsation in roller pumps: A validated lumped parameter model

https://doi.org/10.1016/j.medengphy.2008.02.007Get rights and content

Abstract

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 20 mmHg and 33 mmHg 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.

Introduction

During open-heart surgery, cardiopulmonary bypass (CPB) is used to relieve heart and lungs of their normal life sustaining functions. Roller pumps are used to undertake the functions of blood circulation in approximately 50% of CPB [1], [2].

For decades, roller pumps were the most accepted pumps for CPB [3], due to their numerous key features: low cost; predictable mean flow obtained by controlling the arm speed or choosing different tubes’ inner diameter sizes, a quicker response to servo-control; simpler design and thus fewer moving parts which would be subject to malfunction.

Nevertheless, they suffer from several limitations: they normally deliver uncontrolled pulsatile inlet and outlet pressure, which generates high frequency harmonics in pressure signals [4]; a phenomenon known as spallation [5], [6] exists, which consists of micro-particles detaching from the tubing inner walls due to cyclic compression by the rollers; blood trauma and microemboli delivered to the patient appears to be more than that encountered with centrifugal pumps [7], [8].

In the last years, computational studies and models of CPB hemodynamics have been reported. In particular, they were aimed at simulating patient hemodynamics during artificial perfusion [9], [10], developing automated perfusion strategies [11], [12], [13], and optimizing the design of CPB circuits [14], but none of them was focused on the pumping element, usually modelled as a pure flow generator. A two-dimensional CFD model of a roller pump is reported in [15]. This study gave useful information about roller pump fluid dynamics; however the model did not focus on the uncontrolled pulsatility dynamics.

The aim of the present study is to provide a lumped parameter model which clarifies the uncontrolled pressure pulsatility generation mechanisms in roller pumps, thus allowing considerations on achievable performance improvements of roller-type peristaltic pumps.

Section snippets

Experimental setup

A twin roller pump (Sarns™ 7000, Terumo CVS, Ann Arbor, MI, USA) connected to an open air reservoir by means of two hydraulic lines, made up of 3/8 in. × 1/16 in. PVC pipes, formed the experimental setup (Fig. 1). At the pump inlet and outlet lines, screw clamps allowed the increase of the pump hydraulic load.

Pressures at the pump inlet and outlet sections were measured by using two pressure transducers (MicroSwitch 143PC05D, Honeywell International Inc., Morristown, NJ, USA), connected to the

Results

Measured and simulated inlet and outlet pressures are shown in Fig. 5. Panels from a to f correspond to the experiments as specified in Table 2. For each numerical simulation, parameters were further manually adjusted by matching the modelled inlet and outlet pressure oscillations with the mean values, resonant frequency and damping of those measured.

Absolute and Normalized Average Euclidean Errors between measured and simulated pressures at the inlet and outlet pump sections are reported in

Discussion

The main part of the presented lumped parameter model is represented by the roller subsystem, which comprises two flow generators – one representing the forward flow (Q_roll) caused by the roller feeding into the pump housing, and the other the flow due to the engaging/disengaging mechanisms (Q_ed) – and a variable resistance (Rr), which represents the backflow resistance across the lumen between the roller and the pump stator. This relatively simple lumped model was able to reproduce several

Conclusions

A simple and effective dynamical model of a roller pump was presented. It has been elucidated that the roller subsystem (Fig. 4) was responsible for the unwanted pressure pulsation generation. The tube compression/release mechanism (actuated by the rollers during their engaging and disengaging phases) caused the pressure at the pump inlet/outlet to abruptly increase/decrease thus triggering pressure oscillations.

This model thus revealed the generation mechanism of the uncontrolled pressure

Conflict of interest

The authors do not have any financial and personal relationships with other people or organisations that could inappropriately influence (bias) the work entitled “Pressure pulsation in roller pumps: A validated lumped parameter model”.

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