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The hemolysis of human red blood cells (RBCs) after freeze-drying and resuspension depends on the vacuum-drying temperature. In an experimental study, RBCs were first solidified based on a modified high-yield cryopreservation protocol in the presence of hydroxyethyl starch and maltose. Afterward, they were vacuum-dried in a special low-temperature freeze-drying device at selected shelf temperatures between -5 and -65 degrees C. Subsequently, the dried samples were resuspended in an isotonic, phosphate-buffered saline solution. The hemolysis was determined according to a modified saline stability test. It decreases with a decreasing shelf temperature until a minimum is reached at -35 degrees C. A further decrease of the shelf temperature has no beneficial effect; the hemolysis even increases. To interpret these results, we assume that the hemolysis depends on two contrary damaging effects: (1) the higher the shelf temperature, the higher the probability of structural damages occurring during drying; (2) the lower the shelf temperature, the lower the driving force for water transport; this may lead to an incomplete intracellular dehydration which means that the cells are not in a glassy state at ambient temperature.

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The aim of this study was to measure in vivo the forces and moments acting therapeutically on the individual tooth in connection with the multiband technique. Securing and evaluating the planned in vivo measurements involves analysing the measuring accuracy of the system as a whole by means of corresponding in vitro investigations. Errors in determining the therapeutically effective force system may result from the electrical measurement of the mechanical quantities by the sensor system and from the fixing of the archwire in therapeutic position. The precision of this fixing is influenced by displacements induced by elasticities and mechanical tensions in the measuring system. Calibration test series have shown the sensor system to have a margin of error of less than 2%. The displacements influencing precision fixing of the archwire were determined by means of a laser position measuring system. For a maximum orthodontic force of 1.5 N, they are 0.06 mm in the least favourable case. The resulting measuring accuracy was determined analytically or graphically, depending on the key parameters. Successful in vivo studies of the therapeutically applied force systems are to be expected on the basis of these results.

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Centrifugal blood pumps are considered to be generally superior to the traditionally used roller pumps in cardiopulmonary bypass. In our institute a new lightweight centrifugal sealless blood pump with a unique spherical thrust bearing and with a magnetic coupling was developed, the HiFlow. The small design makes the pump suitable for applications in complex devices or close to a patient. Hemolysis tests were carried out in which the BioMedicus pump BP-80 and a roller pump were used as reference. The centrifugal pump HiFlow showed the least blood trauma within the group of investigated pumps. In summary, the HiFlow pump concept with its low priming volume and limited contact surfaces shows great potential for clinical applications in cardiopulmonary bypass. Also, the possibility of using the pump as a short-term assist device with an option of a pulsatile driving mode was demonstrated.

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A "QT"-interval driven rate responsive pacemaker can also be implanted on the occasion of pacemaker replacement. To evaluate the electrophysiological properties and limitations of chronic leads, in 30 patients the evoked intracardiac electrogram was recorded via the chronic lead during pacemaker replacement (14 different types, mean interval after implantation 111 (25-171 months). T-wave detectability was evaluated with different pulse amplitudes (2.5 and 5.0 V) and two pacemaker systems (TX 915, Rhythmyx) with different "fast recharge" mechanisms. In particular, the T-wave signal was influenced by capacitor discharge effects. At 2.5 V output T-wave amplitude was greater than or equal to 1.5 mV in all (19) patients, who could be paced at this voltage. However, at 5 V in 9/30 patients T-wave was less than 1 mV and detection was not possible in 6/30 cases. During pacing with the newly developed "QT"-interval driven, rate-responsive pacemaker (Rhythmyx) with two fast recharge pulses, in nine investigated patients the T-wave was markedly better discriminable compared to the TX 915 pacemaker. Accordingly, in 37 patients with implanted "QT"-controlled pacemakers (TX 911): n = 13; TX 915: n = 21; Rhythmyx: n = 3. Indication for pacemaker therapy: high degree AV block: n = 24, sick-sinus syndrome: n = 13) reliable T-wave sensing was possible at 2.5 V/0.2 ms output, whereas at 5 V/2 ms no T-wave sensing could be achieved in 8/37 cases. On the occasion of pacemaker replacement the "QT"-controlled pacemaker can be implanted without intraoperative measurements, whenever a pulse amplitude less than 2.5 V is sufficient for stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

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The freezing of biological cell suspensions can be understood in terms of ice formation in the external suspension medium and the cellular reactions to the changing environment. Cryomicroscopy allows a quantitative analysis of both categories of phenomena. Besides freezing stages of appropriate thermal design, the components used for that purpose include a microcomputer (PSI 80) based control system, an image analysis system (Intellect 100) and a spectrophotometer (MPV compact). The investigation of extracellular ice formation is focused on the following effects: The redistribution of solutes in the residual liquid and the resulting concentration profiles are determined photometrically or densitometrically. The transitions between various morphologies of the ice-liquid phase boundary (planar-cellular-dendritic) can be related to interface instability theories. With respect to solute segregation, the studies also involve the formation of bubbles from supersaturated gaseous solutes and freezing potentials resulting from the differential incorporation of cations and anions into the solid phase. The interaction between particles or cells and the advancing ice front is determined from critical interface velocities marking the transition between repulsion and entrapment. The effects of freezing on biological cells are studied mainly with blood cells, especially lymphocytes. The water efflux due to osmotical gradients across the membrane yields volume shrinkage curves which are recorded and analysed from video images for various cooling rates. Beyond a certain threshold cooling rate, intracellular ice starts to form, and different crystallization morphologies can be detected. The intracellular crystallization temperatures depend on cooling and warming rates as well as on the presence of penetrating cryoadditives. A fluorescence viability is used to determine the percentage of damaged cells immediately after thawing.

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