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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 1 (1972), S. 31-43 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Thein vitro surface characteristics of articular cartilage were assessed by light and scanning electron microscopy and by profile measurement of their replicated contours. Both wet and dehydrated articular surfaces contained arrays of 20–40 μm diameter depressions which were similar in shape, magnitude and frequency to the underlying cell lacunae. While there were limitations attached to the replication and profile-measurement techniques, the results indicated that wet articular surfaces contained depressions which were 0.2–5.0 μm deep and were superimposed on undulations of approximately 600 μm pitch and 3–4 μm amplitude. As yet, no quantitative work has been conductedin vivo to determine the articular contours of the living joint. Since there is some uncertainty as to whether thein vivo articular contours contain arrays of depressions or similarly shaped humps, we do not yet have any reliable data on the degree of irregularity of thein vivo articular surface topography.
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  • 2
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The dynamic response of adrenocortical secretion of cortisol to intravenous infusion of ACTH was studied in 11 dogs 2 hr after hypophysectomy. This response was then compared to the response of the isolated adrenal perfusedin situ with ACTH, studied by Urquhartet al. (1968a,b). The comparison was facilitated by analysis in the frequency domain, effected by Fast Fourier Transform. The mode time for rise to 80% of steady-state secretion rate was 3 min faster for the infused preparation, despite the fact that in this preparation ACTH was distributed in blood and metabolized in part prior to presentation to the adrenal. Power spectral analysis revealed 1.6 times as high frequency power in the response of the infused preparation as in that of the perfused preparation. Complex division of the frequency-domain representations of the two responses led to identification of a transfer function to preface a previously reported model of adrenal response. This transfer function was a negative time delay of 2.6 min. The results indicate that the intact adrenal is dynamically more responsive than is thein situ perfused adrenal. The dynamic description obtained herein can be used for inference of proximal dynamic elements of the adrenocortical control system by a procedure of deconvolution similar to that defined in this paper.
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  • 3
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A field-theory model of blood-pulse measurement by four-electrode impedance plethysmography was developed and tested empirically. The model relates current distribution in the upper arm to the configuration of the drive electrodes. It predicts observed impedance change as a function of sense-electrode configuration and the increase in segmental volume associated with each blood pulse. The model was simulated on a digital computer for a number of critical cases. Corresponding measurements were taken on human subjects with an improved instrumentation system, which virtually eliminated the artifact caused by the skin-electrode interface. These measurements substantiated the major predictions of the model. It was concluded that precise impedance measurements were closely related to changes in segmental volume, and that any change in conductivity caused by the incoming arterial blood probably played a minor role. Insight was gained into the optimum placement of drive and sense electrodes at this measurement location.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 1 (1972), S. 115-133 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The introduction of computer-directed secondary testing techniques into a Multiphasic Health Testing System will bring about a need for on-line classification of patients. This paper discusses one method for classifying patients by means of their responses to a medical history questionnaire. The questionnaire data are processed through a trainable pattern classifer which uses a linear discriminant function. The algorithm selected for training purposes is based upon a fixed-increment error correction scheme and is a function of a predetermined maximum likelihood ratio value. The accuracy of the pattern classifier was tested by means of published questionnaire data relating to two different disease categories. Preliminary results indicate that the pattern classifier can be trained to a high degree of accuracy (〉90%) and that the savings in computer storage space for this classification approach is significant.
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  • 5
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Radio-frequency rediation properties of the implanted transmitter were studied. Two models using spheres representing the biological body were studied theoretically; one is for current loop without insulation, and the other, a loop housed in a small spherical insulation embedded in the lossy sphere. The observed anomalous phenomenon, that received rf field is increased after transmitter is embedded in a biological body, has been explained theoretically. Increase of rf field occurs when effective wavelength approaches diameter of sphere and loss tangent of medium is less than or near 1. When loop is at center of spherical body, the radiation pattern is closely the same as that of loop in free space. When loss tangent is less than 1, maximum field strength occurs if effective wavelength is equal to diameter of sphere. When loop is off-centered, orientation of the loop is found to be important in determining field strength and radiation pattern. If the magnetic dipole moment direction of loop is perpendicular to radial axis of the sphere, rf field is 5≈10 times stronger than when the dipole direction is parallel. These results will be useful in the design of implant telemetry systems.
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  • 6
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The instantaneous left intraventricular pressure-volume ratio, e(t)= p(t)/[v(t)−v d], in which p(t), v(t) and v d are intraventricular pressure, volume and a correction factor, respectively, was shown by our experimental studies to be independent of mechanical loading conditions and yet vary markedly with changes in contractile state of the ventricle. The studies also indicated that the e(t) curve under a given contractile state could be described as e(t)=αe o(βt), in which e o(t) represents e(t) under arbitrarily defined control contractile state and heart rate, and α and β are magnitude and duration parameters of the given e(t) with respect to e 0(t). The present mathematical analysis of mechanical relationship between ventricular performance represented by e(t) and myocardial contraction shows that the α and β parameters related to myocardial force, F, and shortening velocity of contractile element, V ce, respectively. Using a two-element model of myocardium and a thick-wall sphere or cylinder model of the ventricle we found that F(t)=αHe 0(βt) and V ce(t)=βK j[de 0(βt)/d(βt)]/e 0(βt). Both H and K j are functions of ventricular volume and are specific to the geometric model used, whereas the mode of afterload affects K j only. The mathematically derived F−V ce curves and their shifts owing to variations of α, β, H and K j under isotonic, isobaric and isovolumetric contractions simulated the experimentally established F−V ce curves from papillary muscle and their characteristic shifts reported by other investigators. On these bases we conclude that e(t) explicitly expresses the dynamic characteristics of myocardial contractions, which further supports our experimental contention that e(t) can be used as a useful index of contractile state of the ventricular chamber.
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  • 7
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The oxygenation rate of blood flowing through permeable tubes can be increased by mixing or turbulence of the blood. Staging of the tubes has been suggested as one means of enhancing the oxygenation rate. A series of experiments has been performed to investigate the feasibility of staging and the results show a definite advantage in oxygen transfer compared with regular straight tubes.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 1 (1973), S. 285-315 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Decisions, which are responses to questions such as “What shall we do?” and scientific conclusions, which are responses to questions such as “What are the facts?” are sufficiently different to justify the development of a decision methodolgy different from the classical Scientific Method which guides scientific research. The environment in which health care decisions are embedded, i.e., the life cycle of a health program or project, imposes requirements for a capability to communicate, discuss, review, and track the factors on which decisions are based. The information elements needed for decision making (alternatives, states, outcomes, risk, values), as well as the process needed to generate these decision elements, are described and the additional requirements which they impose on a decision methodology (rationality and the early formulation of an evaluation model) are identified. Decision and utility theory provide a philosophical framework plus two essential ingredients for explicitly implementing the decision process: (1) a rational basis for explicitly measuring preferences (value judgments) on a “utility” scale and (2) a rational rule for making decisions when outcomes are uncertain, i.e., maximize expected utility. A general objective function which combines measures of value (utility) and estimates of risk (probability) into an expression representing the computation of expected utility is presented and discussed. The objective function and the relationships of its elements to the activities of the decision process are illustrated with a relatively simple example. Some implications of simplified special cases of the general objective function are pointed out.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 1 (1973), S. 324-332 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A two-electrode transthoracic impedance measuring system has been used to measure tidal volume and ventilation in infants. When the electrodes are positioned bilaterally immediately below the axillae, the impedance change is linear with lung volume change. It can be used to measure tidal volume within 1.5 ml (SD) when the system is calibrated by matching its output with that from a small spirometer or a reverse body plethysmograph for a few breaths. Unsatisfactory records are obtained if the electrodes are placed low on the chest (below the nipple line). Total ventilation can be measured which is automatically calibrated in ml/min when the tidal volume signal is accurately adjusted. A built-in system can be used to correct for the artifact related to cardiac activity, if it exists, thereby increasing the accuracy of the monitor for recording ventilation. Body movement, particularly of the arms, interferes with the impedance signal, but the lack of discomfort for the subject minimizes such movement artifacts. Satisfactory quantitative measurements of tidal volume and ventilation have been recorded for up to 6 hr without requiring recalibration. The instrument permits long-term monitoring of tidal volume and ventilation without restricting the airway or interfering with the medical management of the infant.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 1 (1973), S. 368-380 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A small digital computer (a Digital Equip. Corp. LINC-8) has been interfaced to voltage clamp control circuitry and a buffer memory in order for it to both control experiments and provide fast and flexible data acquisition. The experiments are designed and run from the computer graphic terminal in a conversational language, offering the experimenter programmed control over input voltage-time patterns and the rate of data sampling. Because many records are usually required and biological preparations tend to deteriorate with time, automated experiment control and faster data acquisition and storage provides more dependable data than manual methods. Subsequent analysis is much more convenient when the data has been stored along with parameters values and labels in a standard format on a digital bulk storage device such as a magnetic tape or disk.
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