Low-flow Pump Research Articles

Automated low flow pump system for the treatment of refractory ascites: a single-center experience.

Ascites is a common complication of liver cirrhosis and represents the main cause of hospitalization among patients with cirrhosis. First-line therapy for those patients is the use of diuretics and dietary sodium restriction. However, 10 % of patients per year become therapy refractory to diuretic treatment with the need of repeated high-volume paracentesis or transjugular intrahepatic portosystemic shunt (TIPS). For these patients, an automated pump system (Alfapump/Sequana Medical) was developed. Here, we describe our single-center experience of ten consecutively implanted pump systems. Between 08/13 and 11/14, ten Alfapump systems were implanted in patients with refractory ascites all suffering from liver cirrhosis. Those patients were treated as a bridge to transplant (4/10) or as an end-stage therapy (6/10). Median follow-up was 165 days (23-379 days). Postimplant, the need of paracentesis could be markedly reduced to a mean of 0.45 (0-4/month) per month. In eight patients, paracentesis was not needed after implantation of the pump system. The median daily output volume was 1000 ml/day (450-2000 ml/day). Prerenal insufficiency was a recurrent complication in the postoperative period. The Alfapump system is a useful system in the treatment of patients suffering from therapy refractory ascites. However, due to the high level of comorbidities, careful patient selection and postoperative monitoring are required.

PWE-141 Alfa pump for the treatment of refractory ascites: a “real world” experience from the uk

<h3>Introduction</h3> Up to 10% of cirrhotic patients with ascites become refractory to diuretic therapy requiring either large volume paracenteses (LVP), transcutaneous intrahepatic portosystemic shunt (TIPSS) or liver transplantation (LT). In patients where TIPSS or LT is contraindicated, repeated LVP is the only option. LVP is an uncomfortable procedure requiring hospital visits and has risk of complications. The ALFA pump is a surgically implanted automated low flow pump system that transports fluid from the peritoneal cavity to the bladder and is an alternative treatment option for patients with refractory ascites. Our aim was to evaluate the early “real world” experience of the ALFA pump for the treatment of refractory ascites from centres in the UK. <h3>Method</h3> Retrospective case note review of the outcomes of patients who had an ALFA pump implanted for refractory ascites outside trials at 4 NHS hospitals since Sept 2013. <h3>Results</h3> ALFA pumps were implanted in 9 patients (6 male, 3 female; median age 74, range 41–81) at four centres (4 NCL, 2 UCL, 2 CAM, 1 QEHB). 7 patients had ascites related to cirrhosis (4 Child-Pugh B, 3 Child-Pugh C), 1 due to congestive cardiac failure and 1 with portal hypertension due to arterio-venous malformation. Prior to insertion of the ALFA pump the median frequency of paracenteses was every 10 days (range 7 – 20) and the median volume of ascites drained was 9 litres (range 8 to 12). ALFA pumps were successfully implanted in all patients. Requirement for paracenteses was substantially reduced post ALFA pump implantation with 7 patients no longer requiring any paracenteses. In one patient the pump blocked after 3 weeks and required reimplantation with a second pump that also blocked and the patient has returned to LVP. In another patient the pump blocked after 8 months and a second ALFA pump was successfully implanted. All 9 patients had ALFA pump related complications including 4 post-operative seromas, 3 bladder catheter migrations/occlusions, 5 site related infections, 6 acute kidney injury/electrolyte disturbance and 1 urinary incontinence. 5 of the 9 patients were alive with a functioning pump 6 months after implantation. <h3>Conclusion</h3> The ALFA pump offers an alternative option for patients who have refractory ascites in whom TIPSS and LT are contraindicated. ALFA pump implantation substantially reduces the need for paracenteses in a cohort of patients who had previously required a significant number of LVP. ALFA pump related complications were frequent suggesting the need for careful patient selection in this high risk group. Outcomes of a randomised controlled trial are eagerly awaited. <h3>Disclosure of interest</h3> None Declared.

Technology targeting for sustainable intensification of crop production in the Delta region of Bangladesh

Abstract. Remote sensing data are nowadays being acquired within short intervals and made available at a low cost or for free. This opens up opportunities for new remote sensing applications, such as the characterization of entire regions to identify most suitable areas for technology targeting. Increasing population growth and changing dietary habits in South Asia call for higher cereal production to ensure future food security. In the Delta area of Bangladesh, surface water is considered to be available in quantities large enough to support intensification by adding an irrigated dry season crop. Fuel-efficient, low lift axial flow pumps have shown to be suitable to carry water to fields that are within a buffer of four hundred meters of the rivers. However, information on how and where to target surface water irrigation efforts is currently lacking. We describe the opportunities and constraints encountered in developing a procedure to identify cropland for which axial flow pumps could be successfully deployed upon in a 43’000 km2 area. First, we isolated cropland and waterways using Landsat 5 and 7 scenes using image segmentation followed by classification with the random forest algorithm. Based on Landsat 7 and 8 scenes, we extracted maximum dry season enhanced vegetation index (EVI) values, which we classified into fallow, low-, and high-intensity cropland for the last three years. Last, we investigated the potential for surface water irrigation on fallow and low-intensity land by applying a cropping risk matrix to address the twin threats of soil and water salinity. Our analysis indicates that there are at least 20,000 ha of fallow land under the low-risk category, while more than 100,000 ha of low-intensity cropland can be brought into intensified production. This information will aid in technology targeting for the efficient deployment of surface water irrigation as a tool for intensification.

Automated low flow pump system for the treatment of refractory ascites: A multi-center safety and efficacy study

Refractory ascites (RA) affects 10% of patients with advanced cirrhosis and ascites. Usual therapy includes large volume paracentesis, and in selected patients, a transjugular portosystemic shunt (TIPS). These therapies may be associated with increased morbidity: paracentesis may induce circulatory dysfunction and impair quality of life and TIPS may induce encephalopathy and is associated with increased mortality in patients with severe liver dysfunction. We present the results of a multicenter, non-randomized trial to assess the safety and efficacy of a new automated pump system for treatment of RA. Forty patients at 9 centers (February 2010-June 2011) received an implanted pump for the automated removal of ascites from the peritoneal cavity into the bladder, from where it was eliminated through normal urination. Patients were followed-up for 6months. The primary study outcome was safety. Secondary outcomes included recurrence of tense ascites and pump performance. Surgical complications occurred early in the study and became less frequent. The pump system removed 90% of the ascites and significantly reduced the median number of large volume paracentesis per month [3.4 (range 1-6) vs. 0.2 (range 0-4); p <0.01]. Cirrhosis-related adverse events decreased along follow-up. The automated pump seems an efficacious tool to move out ascites from the peritoneal cavity to the bladder. Its safety is still moderate, but a broad use in different countries will improve the surgical technique as well as the medical surveillance. A prospective randomized clinical trial vs. large volume paracentesis is underway to confirm these preliminary results.

Development and numerical analysis of low specific speed mixed-flow pump

With the development of the city, the market of the mixed flow pump with large flux and high head is prospect. The KSB Shanghai Pump Co., LTD decided to develop low speed specific speed mixed flow pump to meet the market requirements. Based on the centrifugal pump and axial flow pump model, aiming at the characteristics of large flux and high head, a new type of guide vane mixed flow pump was designed. The computational fluid dynamics method was adopted to analyze the internal flow of the new type model and predict its performances. The time-averaged Navier-Stokes equations were closed by SST k-ω turbulent model to adapt internal flow of guide vane with larger curvatures. The multi-reference frame(MRF) method was used to deal with the coupling of rotating impeller and static guide vane, and the SIMPLEC method was adopted to achieve the coupling solution of velocity and pressure. The computational results shows that there is great flow impact on the head of vanes at different working conditions, and there is great flow separation at the tailing of the guide vanes at different working conditions, and all will affect the performance of pump. Based on the computational results, optimizations were carried out to decrease the impact on the head of vanes and flow separation at the tailing of the guide vanes. The optimized model was simulated and its performance was predicted. The computational results show that the impact on the head of vanes and the separation at the tailing of the guide vanes disappeared. The high efficiency of the optimized pump is wide, and it fit the original design destination. The newly designed mixed flow pump is now in modeling and its experimental performance will be getting soon.

Evaluation of the use of lower body perfusion at 28 C in aortic arch surgery

Although hypothermic circulatory arrest (HCA) and selective cerebral perfusion (SCP) are widely used for cerebral protection during aortic arch surgery, these strategies offer no protection for mesenteric ischaemia during prolonged circulatory arrest. This study explored mesenteric haemodynamics, metabolism, oxidative stress and inflammatory response levels during isolated SCP and combined cerebral and lower body perfusion (CLBP) in pigs. Fourteen pigs (35-45 kg) were cooled on CPB to 28°C. After 10 min of HCA, they were randomized to 60 min of isolated SCP (n = 7) and CLBP (n = 7) at low-flow pump rates: 10 ml/kg/min (SCP) and 20 ml/kg/min (LBP). Microspheres were injected at baseline, 5 and 60 min of SCP/CLBP and 5 and 60 min off CPB, to calculate mesenteric regional blood flow (RBF). Lactate levels and Oxy-DNA expression [fluorescence activated cell sorting (FACS)] in the portal venous blood were determined at the same time points. Semi-quantitative assessment of inflammatory cytokines was performed using real-time polymerase chain reaction (PCR) and immunhistochemical analyses. At baseline mesenteric, RBF was 61 ± 31 ml/min/100 g in the jejunum and 78 ± 43 ml/min/100 g in the colon. Whereas SCP provided a residual mesenteric RBF of 5%, CLBP offered 47% of the baseline jejunal (34 ± 10 ml/min/100 g) and 68% of the colonic RBF (52 ± 34 ml/min/100 g; P = 0.001). Lactate levels were significantly higher in then SCP group (15 ± 2 vs. 11 ± 3 mmol/l; P = 0.01). Oxy-DNA increased, reaching 137% of baseline (SCP) and 129% (CLBP) at 60 min SCP/CLBP, but recovered promptly during reperfusion. Real-time PCR revealed a massive increase in early cytokine expression vs. baseline, showing significant higher interleukin (IL) -6 (29 vs.2; P = 0.027) and COX-relative expression (7 vs. 3, P = 0.016) in the SCP group. Immunhistochemical analysis confirmed a higher immunological activity in the SCP group, showing more intensive signal for tumour necrosis factor-α, IL-6 and p38 when compared with the CLBP group. Low-flow CLBP provides a diminished but considerable mesenteric RBF, leading to lower lactate and oxidative stress levels and a diminished local inflammatory response reaction than isolated SCP.

Static Stress and Modal Analysis of the Impeller of the High-Pressure Low-Flow Pump

Based on the design conditions,the structure strength and modal analysis are carried on the impeller by One-way Fluid-structure Interaction technique in ANSYS Workbench platform. The results show that under the water stress, the maximum deformation occurs on the brink of the blade, the maximum equivalent stress occurs at the liner near the blade pressure surface, the deformation of the blade has a great influence on the vibration of the pump.

Effects of Pollutant Diesel Fuels on Neurobehavioral Performance among Workers in Locomotive Depot

Problem statement: Diesel fuel contains various combinations of hydro carbons such as cyclohexane, n-hexane, benzene and toluene which can cause health problems in major exposure of that pollutant in locomotive depots. Studies were c onducted to evaluate the exposure towards diesel fuel pollutant and the effect on neurobehavioral pe rformances among workers in locomotive depots. Approach: Method used was questionnaire form and neurobehavioral performances were measured by WHO NCTB test among 17 exposure workers and 17 control workers. Air pollutant measurement was carried out by GilAir Sampler Low flow pump and analyzed using NMAM method 1500 and 1501. Measured diesel fuel pollutant are Total Volatile O rganic Compound (TVOC), cyclohexane, n-hexane, benzene and toluene in three sampling point which a re Power Generator Car (PGC), Locomotive (LOCO), producer and receiver of diesel fuel (PPD). Impact assessment NCTB neurobehavioral was carried out. Results: Measured result showed that overall mean of concentration for Total Volatile Organic Compound (TVOC) was respectively 1.93+0.70 ppm, 1.05+0.19 ppm and 1.01+0.17 ppm in PGC, Loco and PPD. Average concentration of cyclohexane, n-hexane, benzene and toluene at PGC, Loco, PPD was respectively 0.11+0.02, 0.01+0.01, 0.15+0.07, 0.02+0.00, 0.01+0.00, 0.01+0.00, 0.05+0.01, 0.03+0.00, 0.06+0.03, 0.10+0.08, 0.06+0.03, 0.10+0.06. All the pollutants measured did not exceed the permissible level based on USECHH 2000. Test for neurobehavioral performance between exposed workers and control showed there are significant difference for SA test non preferred hand (p = 0.03, p< 0.05) and test PAT1 (p = 0.01, p < 0.05). There are significant relationship between NCTB test such as BVR, SA1, SA2 and PAT1 compared to the factor of age, service period and educational level. Conclusion: This study showed that there are significant corre lation between cyclohexane concentration with SA 3 (both sides of hand) with value r = -0.53, p<0.05 and benzene with DS test, SA 1 (dominant hand), SA 3(both sides of hand) and respectively with value r = -0.57,- 0.54, -0.64, p<0.05. It can be concluded that expos ed workers towards diesel pollutant in locomotive industry affect the neurobehavioral performances wh ich correlate the hand-eye coordination of cognitive function, speed stimulation of motor nerv e, visual and memory.

Toxic effect of naphta exposure on respiratory system among workers in the tyre industry

A cross-sectional study was carried out on workers in a tyre manufacturing industry in Malaysia to determine the effects of naphtha exposure on lung functions and respiratory symptoms. Sixty male workers exposed to naphtha and 42 unexposed workers were selected for this study. Personal air monitoring carried out using solid sorbent tubes and low flow pumps (Model: PAS-500 Personal Air Sampler). Personal air monitoring showed that the mean air naphtha concentration was 28.50 mg/m3, the median was 28.47 mg/m3 and the inter quartile range of 1.27 mg/m3. The range was from 0.19 to 200.51 mg/m3 (PEL is 400 mg/m3). The lung function tests showed in 2 groups for all the 3 parameters (FVC%, FEV1% and FEV1/FVC) were in exposed group 96.16, 85.23 and 0.791 respectively and in Unexposed group was 113.23, 116.28 and 0.903 respectively.The lung function tests showed that there were significant difference in the 2 groups for FVC% (p < 0.001), FEV1% (p < 0.001) and FEV1/FVC% (p = 0.002). Multiple linear regression test showed that monthly household income significantly influence the FVC% predicted (b = 0.003, p < 0.001) and FEV1% predicted (b = 0.006, p < 0.001). In conclusion there was an inverse relationship between air naphtha concentrations and lung functions ability. Early impairment of the respiratory system is detected on the workers who are exposed to naphtha which made up of several chemicals. Key words: Lung function, naphtha concentrations, tyre manufacturing process.

A combined surgical and percutaneous approach through the axillary artery to introduce the Impella LP5.0 for short-term circulatory support

We describe a novel axillary approach for insertion and usage of the Impella LP5.0, a low cost micro-axial flow pump, in five patients requiring circulatory support after acute ST-segment elevation myocardial infarction (STEMI). This alternative approach for implantation of the Impella LP5.0 has been proven simple, safe and feasible, and less invasive in severely compromised patients. Our hybrid, percutaneous and surgical, approach offered acute short-term circulatory support in STEMI patients with acute heart failure, allowing myocardial recovery or selection for long-term mechanical support.

Unstable head-flow characteristic generation mechanism of a low specific speed mixed flow pump

This paper treats the flow instabilities in a mixed flow pump with a vaned diffuser. Test pump has a positive slope of a head-flow performance curve at 65% flow rate of BEP (Best Efficiency Point) because of a rotating stall. Dynamic Particle Image Velocimetry (PIV) and pressure fluctuation measurements are used for investigating the propagation mechanism of a rotating stall. It was found that unstable performance was caused by periodical large scale abrupt backflow generated from the vaned diffuser to the outlet of impeller. Further, the relation between the static pressure at the inlet of diffuser vane and the internal flow condition was clarified. From these experimental results, in order to improve the positive slope of a head-flow performance curve, to suppress the growth of strong vortex toward the inlet of diffuser vane was proved to be a key point.

An open oscillatory heat pipe water pump

The use of an open oscillatory heat pipe (or open pulsating heat pipe) for pumping water is considered, as the need to pump water in rural areas remains a primary requirement in developing rural areas. A possible design for the pump is given and has been constructed and tested and the pumping results are reported. A mathematical model whereby the pump may be theoretically simulated and its performance calculated is also given. The theoretical model is shown to reflect the complex non-linear behaviour of such a pump and a sensitivity analysis is conducted. Experimental flow rates of typically 0.2 mg/s at a pumping height of 100 mm were obtained. The simulation model calculated mechanical and theoretical efficiencies of 3% and 0.03% respectively. An experimentally determined thermal efficiency in the order of 0.00003% was obtained. It is concluded that unless the low pumping flow rates and pumping height limitations can be overcome that it is unlikely that an open oscillatory heat pipe water pump will be suitable for pumping the relatively large quantities of water required for agricultural purposes.

Efficacy of Tissue Plasminogen Activator for Thrombolysis in Central Venous Dialysis Catheters

Low blood flow is a frequent complication of central-vein (CV) dialysis catheters. Since thrombotic occlusion accounts for many cases of reduced blood flow, it is common practice to administer empiric thrombolytic therapy in an attempt to restore catheter patency and improve function. We prepared tissue plasminogen activator (tPA) from 50 mg lyophilized powder, which was diluted (1 mg/mL) in sterile water for injection. A volume of 1 mL was frozen in 3 cc polystyrene syringes at -20 degrees C and thawed at room temperature when needed. tPA was then administered into the arterial and venous ports of the central venous catheter in a volume equal to the manufacturer's stated luminal volume and was allowed to dwell for 30 minutes. tPA was administered 62 times in 25 patients with 30 catheters (11 Tesio, 17 PermCath, 2 Shiley) for treatment of low blood flow (pump speed < 250 mL/min). Complete restoration of patency was achieved in 23 episodes (mean blood flow pre-tPA 130 mL/min; post-tPA 320 mL/min); partial restoration of patency was achieved in 20 episodes (mean blood flow pre-tPA 69 mL/min; post-tPA 233 mL/min). tPA was just as likely to be effective in patients with complete catheter occlusion (i.e., no blood flow) as it was when some initial blood flow was present. Nineteen episodes failed to respond to tPA. These episodes occurred in 13 catheters, 12 of which ultimately underwent radiologic evaluation; an extraluminal cause for low blood flow was found in all 12 catheters (6 malpositioned, 6 fibrin sheaths). tPA at a dose of 1 mg/mL is effective for restoring patency in CV dialysis catheters. Failure to respond to tPA strongly suggests an extraluminal cause of catheter malfunction.

A new device for dynamic sampling of radon in air

A new system is proposed for the active sampling of radon in air, based on the well-known property of activated charcoal to retain radon. Two identical carbon-activated cartridges arranged in series remove the radon from the air being sampled. The air passes first through a desiccant cell and then the carbon cartridges for short sampling times using a low-flow pump. The alpha activity for each cartridge is determined by a liquid scintillation counting system. The cartridge is placed in a holder into a vial that also contains the appropriate amount of scintillation cocktail, in a way that avoids direct contact between cocktail and charcoal. Once dynamic equilibrium between the phases has been reached, the vials can be counted. Optimum sampling conditions concerning flow rates and sampling times are determined. Using those conditions, the method was applied to environmental samples, straightforwardly providing good results for very different levels of activity.

An Analysis of Low‐Flow Ground Water Sampling Methodology

AbstractLow‐flow ground water sampling methodology can minimize well disturbance and aggravated colloid transport into samples obtained from monitoring wells. However, in low hydraulic conductivity formations, low‐flow sampling methodology can cause excessive drawdown that can result in screen desaturation and high ground water velocities in the vicinity of the well, causing unwanted colloid and soil transport into ground water samples taken from the well. Ground water velocities may increase several fold above that of the natural setting. To examine the drawdown behavior of a monitoring well, mathematical relationships can be developed that allow prediction of the steady‐state drawdown for constant low‐flow pumping rates based on well geometry and aquifer properties. The equations also estimate the time necessary to reach drawdown equilibrium. These same equations can be used to estimate the relative contribution of water entering a sampling device from either the well standpipe or the aquifer. Such equations can be useful in planning a low‐flow sampling program and may suggest when to collect a water sample. In low hydraulic conductivity formations, the equations suggest that drawdown may not stabilize for well depths, violating the minimal drawdown requirement of the low‐flow technique. In such cases, it may be more appropriate to collect a slug or passive sample from the well screen, under the assumption that the water in the well screen is in equilibrium with the surrounding aquifer.

Controlled Laboratory Investigations of Wellbore Concentration Response to Pumping

The relationship between the ground water sample and the surrounding ground water environment is controlled by wellborn flow and mixing that carry ground water to the sampling device. Controlled laboratory conditions and uniform inflow and inflowing concentration allowed detailed investigations of wellbore concentration responses to pump-induced flow and mixing independent of external complicating influences. During pumping from the top of the screen, the results agreed with wellbore flow theory except for high-frequency, high-amplitude concentration fluctuations and mixing with the blank casing due to slight density contrasts (∼0.005%). Concentration fluctuations indicated partial mixing of ground water with well water and declining concentrations in the blank casing indicated that convection due to the slight density contrast overcame pump-induced velocities. During pumping from the bottom of the well, opposing forces of buoyancy and pumping produced small-scale cumulative mixing as the ground water from different portions of the screen approached the pump. Even during low-flow pumping (i.e., 220 mL/min), 5% of the water was prepurge well water after five well volumes were pumped. In the field the density contrasts that resulted in these mixing processes might be caused by a slight cooling of the wellhead or a slight increase in temperature with depth (>0.2°C/m). If the temperature gradient was more pronounced, the convective mixing of screen water with the potentially altered casing water would be more thorough and sampling without mixing would not be possible. If the temperature gradient is stable or if the water in the blank casing is not significantly altered, casing water mixing will not present a problem.

Foetal bypass: concepts and controversies

One of the most controversial and challenging surgical undertakings of the next century promises to be foetal cardiac surgery. Animal studies have been underway for several years to gain an understanding of the physiological mechanisms required to achieve this undertaking. Not since the days of crosscirculation has there been a maternal risk associated with open-heart surgery. The diagnosis of congenital heart defects with foetal ultrasound can now be made as early as 12 weeks gestation. Simple cardiac abnormalities, such as valvular stenosis or atresia, alter intracardiac flow patterns and affect normal cardiac chamber development. Without early intervention, these complex lesions often require major surgical reconstruction, beginning in the neonatal period. Foetal cardiac bypass techniques have evolved from the use of roller pumps and bubble oxygenators primed with maternal blood to the use of an axial flow pump incorporated in a right atrial to pulmonary artery or aortic shunt. Because the blood entering the right atrium is oxygenated by the placenta, an oxygenator in the bypass circuit is probably not needed. The low prime axial flow pump system avoids the dilution of the foetus with the maternal adult haemoglobin and improves the outcome. A major focus of research has concentrated on maintenance of placental blood flow with the use of vasodilators and cyclooxygenase inhibitors. Investigation with primates will be necessary to confirm the placental physiology before human operations can be performed. As the foetal bypass challenges are overcome, there is the potential for a reduction in the number of complex cardiac lesions requiring early surgical intervention in the twenty-first century.

Electrical conductivity capillary technique: a new method for bivariate drop-size—concentration distribution measurements

A new capillary technique, based on electrical conductivity, is developed for the rapid and accurate in situ determination of the bivariate drop-size—concentration distribution for reactive liquid—liquid dispersions. The basic principle of this method is to force drops through a precision bored glass capillary by means of a low-flow gear pump, after collecting them in its funnel-shaped entrance. The electrical device is designed to measure drop size and drop concentration by difference of conductivity between dispersed phase and continuous phase as drops transformed into cylindrical slugs pass between two detection points in the capillary. This new technique can give information about the in situ state of a reactive dispersion and can provide with on-line monitoring and control of the quality of liquid dispersion process.

Hypothermia: Its possible role in cardiac surgery

The current safety of operations on the heart requiring cardiopulmonary bypass occurred because of a series of step-by-step laboratory and clinical investigations that were compromises between the time needed for heart repair and the brain's requirement for oxygen. The first step, so clearly shown in a paper by Bigelow and associates in 1950, was the reduction of the brain's need for oxygen by surface cooling to 28 ° to 32 °C, limited to this level by cardiac and pulmonary failure at levels lower than this. The six to eight minutes of circulatory arrest permitted time for repair of simple defects. This method was rapidly adopted by many surgeons. As low-flow pump oxygenators became available, blood cooling to 10 ° to 20 °C was introduced. This increased the periods of circulatory arrest to 30 to 60 minutes, and also made still longer periods of bypass with the pump oxygenator possible. Hypothermia to reduce oxygen and metabolic requirements is still an important adjunct to bypass, even with the currently used efficient pump oxygenators. It remains the most important component of mycardial preservation, and has made possible the delay needed for transportation between the harvesting and the transplantation of organs.

Micro-HPLC 2: Producing Linear Gradients with the “Linear-Generator” Made from Connected Exponential-Diluters

Abstract A new approach is described for generating linear gradients in micro-HPLC. The “linear-generator” replaces a single-chamber exponential-diluter with several smaller exponential-diluters connected in series and having the same total volume. This linear-generator provides the advantages of the exponential-diluter: (a) Only one high-pressure, precision, low-flow pump is required, thus reducing costs (an inexpensive low pressure pump is used to flush the chamber between gradients). (b) Gradient formation is simple and reliable and nearly independent of flow. In addition, the linear-generator has several advantages over the exponential-diluter: (c) Nearly linear (vs. convex) gradients are formed, (d) The full 0–100% gradient range can be covered (vs. nearly linear segments over only part of the gradient. (e) Gradients have a gentle on-set that quickly attains the final 100% concentration (vs. an abrupt onset and a very slow aproach to the final composition with the exponential-diluter.)