The effect of ultrafiltration transmembrane permeation on the flow field in a surrogate system of an artificial kidney

Renal Replacement Therapies generally associated to the Artificial Kidney (AK) are membrane-based treatments that assure the separation functions of the failing kidney in extracorporeal blood circulation. Their progress from conventional hemodialysis towards high-flux hemodialysis (HFHD) through the introduction of ultrafiltration membranes characterized by high convective permeation fluxes intensified the need of elucidating the effect of the membrane fluid removal rates on the increase of the potentially blood-traumatizing shear stresses developed adjacently to the membrane. The AK surrogate consisting of two-compartments separated by an ultrafiltration membrane is set to have water circulation in the upper chamber mimicking the blood flow rates and the membrane fluid removal rates typical of HFHD. Pressure drop mirrors the shear stresses quantification and the modification of the velocities profiles. The increase on pressure drop when comparing flows in slits with a permeable membrane and an impermeable wall is ca. 512% and 576% for $ \mathrm{CA}22/5\%{\mathrm{SiO}}_2 $ and $ \mathrm{CA}30/5\%{\mathrm{SiO}}_2 $ membranes, respectively.

Biological age and its role in stratification of cardiac risk

Risk stratification in elderly patients is very important, as none of the applied models for the prediction of mortality in cardiac surgery does not take into account the whole complex of physiological features of the aging organism.Theobjectivewas to analyze the effectiveness of the method of qualitative assessment of biological age.Material and methods.Our study included 127 patients (87 male and 40 female) aged 65 to 84 years (mean age – 72.2±4.7 years) who underwent elective cardiac surgery. Perioperative factors were analyzed. The primary endpoint of the study was a 30-day mortality rate.Results.The total 30-day mortality rate was 13.4 % (17 patients). Perioperative predictors of 30-day mortality rate were the calculated values of the CAF scale (p=0.006), the surgery volume (p=0.044), the use of extracorporeal blood circulation (p=0.048).Conclusion.The use of qualitative assessment of biological age allows to more accurate predict the mortality in cardiac elderly patients.

Mock loop for bubble generation in a centrifugal blood pump for fault simulation

In extracorporeal blood circulation intensive care treatments, the occurrence of gas within the circulation is one known major hazard. This gas volume can cause severe harm to the patient like infarctions. Consequently, within risk assessment for these treatments gas bubbles are usually addressed by either constructive or signal based approaches. All signal-based approaches do have in common that they need a sufficient amount of data to be parameterized. These data can only be acquired in animal trials or laboratory experiments, as they could result in harm to patients. Hence, we designed a mock loop, which is automatically able to create annotated data of gas bubbles injected into an extracorporeal circulation. We were able to run this setup with a periodicity of 15 seconds, which results in 240 annotated measurements per hour. For the evaluation, we created 1095 bubbles of varying sizes (0.3 to 0.5 ml). The elaborated setup enables us to produce a great amount of annotated data, which is shown to be comparable to manually generated data in a convenient and fully automated manner.

Decentralized safety concept for closed-loop controlled intensive care

This paper presents a decentralized safety concept for networked intensive care setups, for which a decentralized network of sensors and actuators is realized by embedded microcontroller nodes. It is evaluated for up to eleven medical devices in a setup for automated acute respiratory distress syndrome (ARDS) therapy. In this contribution we highlight a blood pump supervision as exemplary safety measure, which allows a reliable bubble detection in an extracorporeal blood circulation. The approach is validated with data of animal experiments including 35 bubbles with a size between 0.05 and 0.3 ml. All 18 bubbles with a size down to 0.15 ml are successfully detected. By using hidden Markov models (HMMs) as statistical method the number of necessary sensors can be reduced by two pressure sensors.

PVC-plasticizer DEHP in medical products: do thin coatings really reduce DEHP leaching into blood?

The hemocompatibility of artificial surfaces in extracorporeal blood circulation systems can be improved by coatings. According to the literature, heparin coatings should avoid the leaching of the plasticizer di(2-ethylhexyl) phthalate (DEHP) into the blood from components made from plasticized polyvinyl chloride (PVC). DEHP and its metabolites are known to impair the fertility of male rodents; effects on human fertility are assumed. Three different surface coatings with and without heparin were examined in a Chandler Loop model at 37°C using fresh human blood to evaluate their hemocompatibility and barrier property to plasticizer. The levels of toxic oxidation products of DEHP generated in the blood, particularly, were found as high as in the uncoated tubing. The coatings improved the hemocompatibility, but are not safe protection against the hazardous metabolites of DEHP. For pregnant women, neonates and children, we would recommend using the available surface-coated plasticized PVC tubing sets, but free of DEHP.

Paradoxical attenuation of leukocyte rolling in response to ischemia- reperfusion and extracorporeal blood circulation in inflamed tissue

In contrast to acute preparations such as the exteriorized mesentery or the cremaster muscle, chronically instrumented chamber models allow one to study the microcirculation under “physiological” conditions, i.e., in the absence of trauma-induced leukocyte rolling along the venular endothelium. To underscore the importance of studying the naive microcirculation, we implanted titanium dorsal skinfold chambers in hamsters and used intravital fluorescence microscopy to study venular leukocyte rolling in response to ischemia-reperfusion injury or extracorporeal blood circulation. The experiments were performed in chambers that fulfilled all well-established criteria for a physiological microcirculation as well as in chambers that showed various extents of leukocyte rolling due to trauma, hemorrhage, or inflammation. In ideal chambers with a physiological microcirculation (<30 rolling leukocytes/mm vessel circumference in 30 s), ischemia-reperfusion injury and extracorporeal blood circulation significantly stimulated leukocyte rolling along the venular endothelium and, subsequently, firm leukocyte adhesion. In contrast, both stimuli failed to elicit leukocyte rolling in borderline chambers (30–100 leukocytes/mm), and in blatantly inflamed chambers with yet higher numbers of rolling leukocytes at baseline (>100 leukocytes/mm), we observed a paradoxical reduction of leukocyte rolling after ischemia-reperfusion injury or extracorporeal blood circulation. A similar effect was observed when we superfused leukotriene B4 (LTB4) onto the chamber tissue. The initial increase in leukocyte rolling in response to an LTB4 challenge was reversed by a second superfusion 90 min later. These observations underscore 1) the benefit of studying leukocyte-endothelial cell interaction in chronically instrumented chamber models and 2) the necessity to strictly adhere to well-established criteria of a physiological microcirculation.

Protease Removal by Means of Antiproteases Immobilized on Supports as a Potential Tool for Hemodialysis or Extracorporeal Blood Circulation

This work studies protease concentration decrease in aqueous solutions in contact with a modified polyethersulphone graft membrane onto which antiproteases were immobilized. As a model of protease/antiprotease interaction, elastase and α1-antitrypsin were used. Experiments were carried out either under fixed amounts of immobilized antiproteases and variable protease concentration or under fixed protease concentration and variable amounts of immobilized antiproteases. In both cases, active protease concentrations decreased with increase in contact time with the membrane. Experimental conditions under which active elastase concentration becomes zero were also found. Occurrence of the same phenomenology has also been ascertained with protease solutions obtained from human blood neutrophils. The membrane activated with α1-antitrypsin showed differential inhibitory power on elastase and cathepsin G. This technology could open new perspectives in manufacturing new membranes to be used in hemodialysis and extracorporeal circulation when elastase is released.