Biomedical subjects
Publications and source records attributed to G Rau.
Two identical LVADs were equipped with different types of heart valve prostheses (Björk-Shiley disk and PU-valves) and tested in two simultaneous calf experiments for 28 days each. Noise levels, accelerations of the pump housing and thrombus formation were higher for the mechanical valve pump.
The ability of body surface potential mapping to localize coronary arterial narrowings during exercise stress testing was investigated. An array of 48 chest wall electrodes, simultaneously recorded, was used. Digital filtering and signal processing, data reduction techniques and discriminant analysis were applied to process the information. Forty patients whose coronary angiograms showed a single significant narrowing of either the left anterior descending or right coronary artery were selected for further study. On the basis of body surface potential mapping, the site of coronary arterial narrowing was correctly classified in 88% of the patients.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
We have developed an anesthesia information system (AIS) that supports the anesthesiologist in monitoring and recording during a surgical operation. In development of the system, emphasis was placed on providing an anesthesiologist-computer interface that can be adapted to typical situations during anesthesia and to individual user behavior. One main feature of this interface is the integration of the input and output of information. The only device for interaction between the anesthesiologist and the AIS is a touch-sensitive, high-resolution color display screen. The anesthesiologist enters information by touching virtual function keys displayed on the screen. A data window displays all data generated over time, such as automatically recorded vital signs, including blood pressure, heart rate, and rectal and esophageal temperatures, and manually entered variables, such as administered drugs, and ventilator settings. The information gathered by the AIS is presented on the cathode ray tube in several pages. A main distributor page gives an overall view of the content of every work page. A one-page record of the anesthesia is automatically plotted on a multicolor digital plotter during the operation. An example of the use of the AIS is presented from a field test of the system during which it was evaluated in the operating room without interfering with the ongoing operation. Medical staff who used the AIS imitated the anesthesiologist's recording and information search behavior but did not have responsibility for the conduct of the anesthetic.
A diffusion chamber similar to that proposed by J.J. McGrath (J. Microsc., in press) was constructed which allows microscopic observation of osmotically induced volume changes of individual cells in small (microliter) sample volumes. The cells are kept fixed in position in the upper compartment of the chamber by means of a highly permeable membrane and exposed to a step-like change in concentration generated in the lower compartment. An electrical conductivity probe in the upper compartment was used to monitor the temporal change of salt concentration as experienced by the cells. The rise from isotonic to hypertonic can be approximated by an exponential function. Its time constant of tau = 2.08 sec seems to be mainly determined by the change in flushing solution as tau = 1.48 sec was measured with no membrane installed. With human lymphocytes, no loss of cell volume was detected before 5 sec, i.e., when 95% of the final concentration was reached extracellularly. A step change can hence be assumed when modeling exosmosis for determining the lymphocyte membrane permeability. The equations for coupled transport of water and salt were solved numerically and fitted to the experimental data. The results were also compared to various other transport models described in the literature. Human lymphocytes are almost ideally semipermeable with a hydraulic reference permeability of Lp = 4.23 X 10(-4) cm/sec (3.13 X 10(-3) micron X atm-1 X sec-1) at T = 23 degrees C. The temperature and concentration dependence are described by an activation energy Ea = 14.3 kJ/mol and a concentration coefficient alpha 2 = 0.261 osmol/kg. An osmotically inactive volume fraction of 36.9% was determined from the final cell volumes reached asymptotically after shrinkage.
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.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Changes in QRS complexes and ST-T segments were measured in 70 patients after acute anterior-wall myocardial infarction. Intracoronary streptokinase infusion was undertaken in the acute phase in 58 patients, 12 other patients treated conventionally without infusion serving as controls. Precordial ECG mapping employed 48 unipolar precordial leads. If recanalization of an occluded coronary artery was achieved, there was a significant rise in R amplitude (sum of R-wave amplitudes in the 48 leads) from 12.4 +/- 10.9 to 16.2 +/- 11.2 mV, within a period of up to four months after the acute stage. If thrombolysis failed or only conventional treatment had been practised, there was no rise in R-wave amplitude. Renewed occlusion of a vessel previously re-opened by streptokinase infusion produced a reduction in R-wave amplitude from 14.0 +/- 13.0 to 9.8 +/- 11.0 mV. The S-T segment elevation regressed immediately after recanalization of the coronary artery. The S-T segments were iso-electric after four months. Re-occlusion caused renewed S-T segment elevation up to monophasic form. Precordial ECG mapping is thus well suited for serial controls after various re-perfusion measures.
In a consecutive series of 56 patients with acute myocardial infarction, ST segment depression and elevation in the electrocardiographic limb leads I, II, and III were summated for each patient before and immediately after intracoronary streptokinase infusion and the results compared with the angiographic findings. Forty three patients had angiographically confirmed reperfusion of an initially occluded vessel and showed a significant decrease in summated ST shift. The ST segment changes in the limb leads virtually returned to normal in all 43 patients, and in most, inverted T waves developed. Thrombolysis was unsuccessful in 10 patients, and the infarct related coronary artery was already patent in three. When these two groups are combined, all 13 patients without reperfusion showed no significant change in summated ST segment shift. During percutaneous transluminal angioplasty inflation of the balloon in the vessel that was previously occluded simulated reocclusion and was followed by new ST elevation if the artery supplied viable myocardium. In a further consecutive study of 54 patients with anterior myocardial infarction, the precordial R waves and Q waves were studied over the four to six months following infarction using a standardised 48 electrode mapping system. All patients underwent a repeat angiogram after four to six months. In 36 patients the infarct related vessel was patent. They showed a significant mean increase in summated precordial R wave amplitude and a reduction in the mean number of precordial leads without R waves. In 18 patients with unsuccessful thrombolysis or reocclusion there was a further reduction in mean summated R wave amplitude and an increased number of precordial leads not showing R waves. Precordial R wave mapping seems to be a valuable non-invasive method of assessing the salvage of myocardium after reperfusion and the damage caused by reocclusion. Loss of R waves in the acute phase of myocardial infarction does not necessarily mean an irreversibly damaged myocardium.
In a pilot study, a computerized precordial mapping system monitored ischaemia on-line in 50 patients (40 with acute myocardial infarction and 10 with unstable angina, class IV (Canadian Cardiovascular Society). All had ST-segment depression or elevation greater than or equal to 0.2 mV in one or more precordial leads when they were admitted to our coronary care unit. After preliminary precordial mapping with 48 electrodes to localize the area of ischemia, 5 to 8 electrodes were placed in and around the centre of the ST-segment changes. The patients were monitored between 24 and 48 h (mean 35.5 h). To minimize problems caused by artifacts, ECG signal quality was improved by the averaging technique. Thereafter, the ECG was evaluated with respect to Q and R wave amplitudes and ST-segment changes. At 3 min intervals, Q and R wave amplitudes and ST segment elevations or depressions, summed for all leads were plotted as a histogram. ECG signal quality was excellent and there were no problems with the attachment of the electrodes. All patients were treated with nitroglycerine intravenously and high doses of heparin and, in several cases, nifedipine as well. Some patients received thrombolytic therapy with streptokinase. Despite therapy, 21 ischaemic attacks were documented in five patients. Seventeen attacks were seen in patients with acute infarction but who were not treated with streptokinase. All attacks were accompanied by chest pain. The duration of ischaemia ranged from 18 to 87 min. Several attacks were stopped immediately by therapy.(ABSTRACT TRUNCATED AT 250 WORDS)
Exercise electrocardiograms were registered in 50 patients with significant coronary artery stenosis (lumen narrowing greater than or equal to 70%) and in 20 controls without cardiac disease using automated registration (mapping). All patients had a normal ECG at rest and typical angina. ST-segment depression of more than 0.1 mV 60 ms after the J-point in three adjoining leads and in three consecutive registrations could be shown in 46 of the 50 patients (sensitivity 92%) with coronary artery disease, however in no proband of the control group. The sum of the R-amplitudes in the precardiac leads (sigma R) was calculated before and during maximal exercise and six minutes after. Diminution of R-wave amplitudes during exercise was seen in both groups. Six minutes after exercise initial values had been nearly regained. Differentiation of both groups using R-wave amplitudes after exercise thus was impossible. Even using only leads with ST-segment lowering during exercise, a slight increase of R-amplitudes could be measured in only one case. In all other patients R-wave amplitudes diminished also in the ischaemic area with increasing ST-segment depression. RS-inversion was shifted towards the cardiac apex. Thus an increase of R-wave amplitudes indicating coronary arterial disease does not occur in unipolar chest leads in patients with significant coronary artery stenosis and ST-segment lowering during exercise.
Explore the source record for details and available documents.
Technical systems in medical applications reach a complexity level where man-system-interface design on the basis of ergonomic principles and guidelines becomes mandatory. Personnel, equipment, environmental, and system ergonomics can be identified as the main areas of ergonomic research. Ergonomics in medicine considers the physician-patient-machine relationship in a specific task environment. The interaction between physician (or patient) and technical system deserves special design attention in order to ensure user acceptance and overall man-machine-system efficiency. We discuss the examples of an automated diagnosis system and an intraoperative patient monitoring system. We conclude that a task-oriented approach in systems design, including the designated users and considering ergonomic design principles, can create improved man-machine interfaces in the medical field.
Explore the source record for details and available documents.