In Vitro Pulsatility Analysis of Axial-Flow and Centrifugal-Flow Left Ventricular Assist Devices
Journal of Biomechanical Engineering (Impact Factor: 1.78). 03/2013; 135(3):34505. DOI: 10.1115/1.4023525
Recently, continuous-flow ventricular assist devices (CF-VADs) have supplanted older, pulsatile-flow pumps, for treating patients with advanced heart failure. Despite the excellent results of the newer generation devices, the effects of long-term loss of pulsatility remain unknown. The aim of this study is to compare the ability of both axial and centrifugal continuous-flow pumps to intrinsically modify pulsatility when placed under physiologically diverse conditions. Four VADs, two axial- and two centrifugal-flow, were evaluated on a mock circulatory flow system. Each VAD was operated at a constant impeller speed over three hypothetical cardiac conditions: normo-tensive, hypertensive, and hypotensive. Pulsatility index (PI) was compared for each device under each condition. Centrifugal-flow devices had a higher PI than that of axial-flow pumps. Under normo-tension, flow PI was 0.98 ± 0.03 and 1.50 ± 0.02 for the axial and centrifugal groups, respectively (p < 0.01). Under hypertension, flow PI was 1.90 ± 0.16 and 4.21 ± 0.29 for the axial and centrifugal pumps, respectively (p = 0.01). Under hypotension, PI was 0.73 ± 0.02 and 0.78 ± 0.02 for the axial and centrifugal groups, respectively (p = 0.13). All tested CF-VADs were capable of maintaining some pulsatile-flow when connected in parallel with our mock ventricle. We conclude that centrifugal-flow devices outperform the axial pumps from the basis of PI under tested conditions.
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ABSTRACT: The Jarvik 2000 adult ventricular assist device (VAD) is a second-generation blood pump with mechanical contact bearings. The original configuration of the pump employed a pin bearing and a more recent configuration uses a cone bearing. We compare the hydrodynamic performance of the two designs under steady-state and pulsatile flow conditions in vitro. Furthermore, we employ the Intermittent Low Speed (ILS) Flowmaker Controller to demonstrate the effect on pulsatility index (PI) performance of both device configurations. We use an open-loop flow system in both steady-state and pulsatile arrangements, complete with pressure transducers and flow probes. Working fluid was a 3.6 cP blood-analog, glycerin-water solution. Steady-state flow tests were carried out to determine pressure-flow (H-Q) performance curves. Pulsatile tests under normotensive, hypertensive, and hypotensive conditions were executed with controller speed 3 (10 710 ± 250 rpm) at 100 beats per minute. Steady-state tests show greater capacity for pressure and flow with the cone bearing, compared with pin bearing, with best efficiency point (BEP) 68% greater for cone bearing. Pulsatile tests show the cone bearing design to yield a 20% increase in Qavg , a 17% decrease in pulsatility index (PIQ ), and a qualitative increase in pressure responsivity. The ILS mode (for both bearing designs) decreases Qavg by 68% and likewise increases PIQ by 360% and pulsatility ratio (Rpul ) by 200%. The ILS controller regularly reduces the flow, increasing pulsatility index during device operation. The Jarvik 2000 continuous-flow VAD can sustain pulsatile flow under pulsating pressure conditions. The new cone bearing design yields increased flow rates over the earlier pin bearing design.
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ABSTRACT: Continuous-flow left ventricular assist devices (LVADs) subject elements of the blood to significant stress, resulting in clinically significant and subclinical hemolysis. We sought to prospectively determine if baseline red cell osmotic fragility of an advanced heart failure patient - influences the hemolytic response to LVAD support. Osmotic fragility assesses the degree of red blood cell hemolysis under varying degrees of osmotic stress. Assays were prospectively obtained on 50 consecutive patients prior to placement of continuous flow LVADs: HeartMate II (n=34), Jarvik 2000 (n=5), HeartWare (n=6). The mean age was 60.2 years, 87% were male, and 47% were nonischemic. The overall median post-LVAD LDH was 583 (427-965) and there was no difference among devices. Mean hemolysis was 15.68 ± 12.96% at 0.45%NaCL (the inflection point of the osmotic fragility hemolysis curve). A scatter plot did not reveal any relationship between pre-op osmotic fragility and post-op LDH. Linear regression confirmed no predictive relationship (p=0.71). In conclusion, preoperative variations in osmotic fragility do not appear to account for differences in hemolysis following VAD placement. Mechanical forces generated by existing LVADs result in similar levels of biochemical hemolysis, as assessed by LDH, despite baseline differences in a patient's osmotic red cell fragility.
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