Classification of Unsteady Flow Patterns in a Rotodynamic Blood Pump: Introduction of Non-Dimensional Regime Map

Abstract

Rotodynamic blood pumps (also known as rotary or continuous flow blood pumps) are commonly evaluated in vitro under steady flow conditions. However, when these devices are used clinically as ventricular assist devices (VADs), the flow is pulsatile due to the contribution of the native heart. This study investigated the influence of this unsteady flow upon the internal hemodynamics of a centrifugal blood pump. The flow field within the median axial plane of the flow path was visualized with particle image velocimetry (PIV) using a transparent replica of the Levacor VAD. The replica was inserted in a dynamic cardiovascular simulator that synchronized the image acquisition to the cardiac cycle. As compared to steady flow, pulsatile conditions produced periodic, transient recirculation regions within the impeller and separation in the outlet diffuser. Dimensional analysis revealed that the flow characteristics could be uniquely described by the non-dimensional flow coefficient (Φ) and its time derivative ([Formula: see text]), thereby eliminating impeller speed from the experimental matrix. Four regimes within the Φ-[Formula: see text] plane were found to classify the flow patterns, well-attached or disturbed. These results and methods can be generalized to provide insights for both design and operation of rotodynamic blood pumps for safety and efficacy.

Debate

“…Second, a peak flow equivalent to the natural aortic peak flow cannot be achieved by the existing pumps -the length and cross area of the outflow graft conduit of a continuous LVAD cause a considerably higher resistance compared with the natural aorta or a former pulsatile assist device. Third, an exaggerated pulsatility would most probably increase shear-induced blood trauma, although detailed studies of pulsatile blood trauma have not been achieved, because of the complexity of both numerical and in-vitro experiments [13,14 & ,15 && ]. For all these reasons, artificial pulsatility has been limited to lower pulsatility levels and/or lower beat rate than in the natural system (in-vitro results indicating a normal physiological level of pulsatility have been flawed by missing Windkessels [16]).…”

“…A counterpulsing mode would lead even to lower arterial pulsatility! An asynchronous mode may be advantageous, because it allows lower cycle-numbers and concomitant higher pulsatility [13]. Together with the multiple questions on myocardial training and recovery, a lot of uncertainties remain.…”

Numerical analysis of different cardiac functions and support modes on blood damage potential in an axial pump

“…The pulsatile amplitude of left ventricular pressure P LV and aortic pressure P AO may rise temporarily or permanently during exercise or recovery, causing flow range variations in LVADs. 2,4 Unfavorable inner flow fields will occur when pump work at very low flow rates. 5…”

Semi-supervised learning of local structured output predictors

“…The forms of output are various, usually including binary class label and continues response. The problem of predicting binary class label is called classification [13,14,15,16,17,18,19,20,21], while the problem of predicting continues response is called regression [22,23,24,25]. Both of these two problems have many applications, such as computer vision, natural language processing, bioinformatics, and finance.…”