Feasibility study of intelligent LVAD control for optimal heart failure therapy.

Background: Left ventricular assist devices (LVAD) are operated at constant speeds (rpm), consequently, pump flow is passively determined by the pressure difference between the LV and aorta. Since the diastolic pressure gradient (~70 mmHg) is much larger than the systolic gradient (~10 mmHg), the majority of pump flow occurs during systole. This limitation results in sub-optimal LV volume unloading, LV washing, and diminished vascular pulsatility that may be associated with increased risk for clinically-significant adverse events, including stroke, bleeding, arteriovenous malformations, and aortic insufficiency. To address these clinical adverse events, an intelligent control strategy using pump speed modulation was developed to provide dynamic LV unloading during the cardiac cycle to produce near-physiologic pulsatile flow delivery similar to that of the native heart. Materials and Methods: The objective of this study was to integrate a novel algorithm to dynamically control Medtronic HVAD pump speed and demonstrate proofof-concept by characterizing hemodynamic performance in a mock flow loop primed with a blood analog solution (glycerol-saline, 3 cP) and tuned to simulate class IV heart failure (HF). The intelligent LVAD control was operated a varying pump speeds (Dspeed = 0, 1000, 1500, 2000, 2500 rpm) and systolic durations (30%, 35%, and 40%); systolic duration correlates to the time spent at either the high or low pump speed setting. The intelligent LVAD control strategy modulates pump speed within a cardiac cycle triggered from an R-wave of an EKG waveform set to 80 BPM. This pump speed modulation control strategy allows for pulsatile operation of a continuous flow LVAD within a single cardiac cycle. Hemodynamic waveforms (LV pressure-volume, aortic pressure-flow, and pump flow) and intrinsic pump parameters (speed and current) were recorded and analyzed for each test condition. We hypothesize that pump speed modulation may be configured for optimal volume unloading (rest), vascular pulsatility (reloading), and/or washing. Results and Discussion: The intelligent LVAD control system successfully demonstrated the ability to rapidly increase and decrease HVAD pump speed within a single cardiac cycle to provide asynchronous, synchronous co-pulsation, and synchronous counter-pulsation profiles for all systolic durations (30, 35, 40%) and Drpm tested (D1000, D1500, D2000, D2500). Asynchronous support was achieved when pump speed increase (or decrease) was independent of the cardiac cycle, co-pulsation support was achieved when increase in pump speed was timed with beginning of systole corresponding with ventricular contraction (systole), and counter-pulsation support was when increase in pump speed was timed with the end of systole corresponding with ventricular filling (diastole). Ideally, the intelligent control would increase (or decrease) the HVAD pump speed instantaneously upon R-wave detection; however, two distinct time delays were observed: (1) a time delay from detection of the R-wave trigger and increase (or decrease) of pump speed for systolic durations of 35% and 40% (being 45 ± 3.0 ms and 82 ± 3.0 ms respectively and (2) a delay in LVAD flow when pump speed was increased which is hypothesized to be from the blood analog solution’s fluid inertia. Left ventricular stroke volume decreased for all LVAD pump speed modulation operating conditions compared to baseline (HF with LVAD off) indicating that the intelligent control strategy was able to reduce LV volume with increasing HVAD support. The highest flow was achieved with the HVAD operated at a fixed speed of 4000 rpm; however, co-pulsation pump speed modulation at the largest pump speed differential (low = 1500, high = 4000, Drpm = 2500, and systolic duration 30%) resulted in a mean pump speed 3,300 ± 1,200 rpm. By comparison, the forward flow at fixed pump speed of 4,000 rpm was 4.8 L/min compared to a mean co-pulsation rpm was 4.5 L/min. Additionally, all operating settings for the intelligent control during pulsatile function produced an average forward flow through the aortic valve, while in contrast at higher fixed speeds (3,500 and 4,000 rpm) the mean aortic flow was negative. Pulse pressure (DP) decreased with increasing mean pump speed (rpm) for all operating modes (fixed, asynchronous, co-pulsation, counter-pulsation). When operating at the same mean pump speed (rpm) copulsation has increased hemodynamic benefit for pulsatility when compared to counterpulsation and fixed speed at the same mean pump (rpm). Conclusion: The results of this study show the ability of the intelligent HVAD control strategy to increase and decrease pump speed within a single cardiac cycle. This study showed that asynchronous modulation with phases of co-pulsation can generate near physiologic pulse pressure and vascular pulsatility when compared to counterpulsation support, while counter-pulsation can generate greater ventricular volume unloading and diastolic augmentation when compared to co-pulsation. Furthermore, the clinical impact of this study is that through speed modulation adverse events of continuous flow LVADs may be reduced such as incidences of bleeding associated with decreased pulsatility and a decrease in the risk of thrombus formation from poor washing around the aortic valve

Investigation of vacuum polarization in t-channel radiative Bhabha scattering

We discuss the possibility of a precision measurement of vacuum polarization in t-channel radiative Bhabha scattering at a high luminosity collider. For illustration, the achievable precision is estimated for the BaBar experiment at PEP-II and for the OPAL experiment at LEP

A high-altitude snow chemistry record from Amundsenisen, Dronning Maud Land, Antarctica

In this paper a detailed record of major ions from a 20 m deep firn core from Amundsenisen, western Dronning Maud Land, Antarctica, is presented. The core was drilled at 75° S, 2° E (2900 m a.s.l.) during austral summer 1991/92. The following ions were measured at 3 cm resolution: Na+, Mg2+, Ca2+, Cl−, NO3−, S04 2− and CH3SO3H (MSA). The core was dated back to 1865 using a combination of chemical records and volcanic reference horizons. The volcanic eruptions identified in this core are Mount Ngauruhoe, New Zealand (1974–75), Mount Agung, Indonesia (1963), Azul, Argentina (1932), and a broad peak that corresponds in time toTarawera, New Zealand (1886), Falcon Island, South Shetlands, Southern Ocean (1885), and Krakatau, Indonesia (1883). There are no trends in any of the ion records, but the annual to decadal changes are large. The mean concentrations of the measured ions are in agreement with those from other high-altitude cores from the Antarctic plateau. At this core site there may be a correspondence between peaks in the MSA record and major El Niño–Southern Oscillation events

Balancing Corn Yield Goals and N Fertilization Rates

Establishing realistic yield goals is essential for environmentally and economically sustainable crop production. It is also important because many of the variable inputs, including fertilizer N rates, are often based upon those goals. If yield goals are beyond what uncontrollable factors such as rainfall can support, many controllable inputs such as N fertilizer will probably be used at rates in excess of crop needs. This scenario will result in reduced nutrient recovery, decreased profitability or return on fertilizer investment, and an increased potential for N loss to groundwater resources. If yield goals are set too low, crop nutrient needs may be underestimated leading to loss of yield, quality, and profit

Spatial variability of snow chemistry in western Dronning Maud Land, Antarctica

During the austral summer of 1993-94 a number of 1-2 m deep snow pits were sampled in connection with firn-coring in western Dronning Maud Land, Antarctica. The traverse went from 800 to about 3000 m a.s.l. upon the high-altitude plateau. Profiles of cations (Na+, K+, Mg2+, Ca2+), anions (Cl−, NO3-, SO4 2- , CH3SO3 −) and stable oxygen isotopes (δ18O) from 11 snow pils are presented here. Close to the coast 2 m of snow accumulates in about 2-3 years, whilst at sites on the high-altitude plateau 2 m of snow accumulates in 10—14 years. The spatial variation in ion concentrations shows that the ions can be divided into two groups, one with sea-salt elements and methane sulfonate and the other with nitrate and sulfate. For the sca-salt elements and methane sulfonate the concentrations decrease with increasing altitude and increasing distance from the coast, as well as with decreasing temperature and decreasing accumulation rate. For nitrate and sulfate the concentrations are constant or increase with respect to these parameters. This pattern suggests that the sources for sca-salt elements and methane sulfonate are local, whereas the sources for nitrate and sulfate are a mixture of local and long-range transport

Soil quality, yield stability and economic attributes of alternative crop rotations

Three long-term rotational crop studies in Iowa and one in Wisconsin were examined for conclusive evidence of rotational effects on soil quality. Long-term yield data also were evaluated to determine if there was a quantifiable relationship between soil quality and yield or yield stability

Crop Residue Harvest Economics: An Iowa and North Dakota Case Study

Rigorous economic analyses are crucial for the successful launch of lignocellulosic bioenergy facilities in 2014 and beyond. Our objectives are to (1) introduce readers to a query tool developed to use data downloaded from the Agricultural Research Service (ARS) REAPnet for constructing enterprise budgets and (2) demonstrate the use of the query tool with REAPnet data from two field research sites (Ames, IA, and Mandan, ND) for evaluating short-term economic performance of various biofuel feedstock production strategies. Our results for both sites showed that short-term (\u3c3 years) impacts on grain profitability were lower at lower average annual crop residue removal rates. However, it will be important to monitor longer term changes to see if grain profitability declines over time and if biomass harvest degrades soil resources. Analyses for Iowa showed short-term breakeven field-edge biomass prices of $26–$42Mg−1 among the most efficient strategies, while results for North Dakota showed breakeven prices of $54–$73 Mg−1. We suggest that development of the data query tool is important because it helps illustrate several different soil and crop management strategies that could be used to provide sustainable feedstock supplies

Crop Rotation Effects on N03-N Leaching and Corn Yields Under Manure Management Practices

Nonpoint source nutrient pollution is recognized as an important environmental and social issue for several reasons. First, manure from swine production facilities can have serious impacts on the quality of surface and ground water resources. Second, several states are in the process of creating laws to reduce nitrogen and phosphorus loadings from manure to soil and water resources. Third, pollution of water resources from nutrients supplied by manure to croplands will set parameters for developing public policies on the management of manure