Showing papers in "Medical Progress Through Technology in 1983"

Designing polyester vascular prostheses for the future.

Abstract: For 30 years polyester textile materials in tubular form have been used in vascular surgery for the replacement and by-pass of arteries. Initially such medical devices were implanted to maintain the distal blood flow of atherosclerotic patients for a number of months. Today, with prognoses in excess of 10 or 15 years, and with implantation in younger and younger patients, this particular end use is possibly one of the most demanding applications for a textile product. The paper describes the current manufacturing techniques and provides detailed information about the wide variety of filaments, yarns and fabrics used in the production of current commercial devices. By reviewing the mechanical and clinical performance of available designs against the criteria of an 'ideal' prosthesis, the objective of this paper is to assist surgeons in making clinical decisions, to provide the textile and medical products industries with directions for future design improvements, and to support standards writers in their formidable task of establishing a rational standard for vascular repair devices.

Topography of brain electrical activity: a bioengineering approach.

Abstract: The aim of this work is to describe a system for the mono- and bi-dimensional analysis of brain electrical activity. The analysis was carried on either by visual inspection of mono- and bi-dimensional data, or by automatic feature extraction from the bidimensional data. Because of the importance of visual inspection for the analysis of experimental data, particular care was devoted to optimize the displayed data perceptually. For automatic screening of large amounts of data (and to allow long term studies of clinical records), statistical facilities were also provided. One purpose of the system was to develop image processing algorithms oriented toward biomedical images, that could be easily implemented on special purpose, low cost hardware, like VLSI or microcomputer arrays. This was possible because of the modularity of the larger part of bidimensional processing, such as interpolation and statistical analysis. Results of an experiment on Visual Evoked Response are presented, showing that through abidimensional analysis of the recorded data the resolution achievable in the localization of brain electrical activity can be increased to less than 1 cm.

An electro-ocular switch for communication of the speechless.

Abstract: The designed EOG switch was based on the principle of the detection of the saccadal velocity producing a pulse above a certain selected value of the saccadal derivative. The EOG transducer is preferable above an eye switch designed on the infrared limbus-pupil reflection method because of two reasons, namely in its use for vertical eye movements and because of its low costs when composed with operational amplifiers (741) or with IC's. AC-coupling between the differential amplifier and the main amplifier excludes the effects of the well-known DC-drift during EOG recording on switching. An optocoupler at the output of the switch serves for the safety of the non-vocal handicapped during the communication process with the Handiwriter. Experience is obtained with the EOG switch connected with the Handiwriter system by one quadriplegic CVA patient and one quadriplegic ALS patient. A possible group of patients as candidates for using the EOG switch has been indicated in the discussion.

Direct accurate gas flow measurement in the patient: compensation for unavoidable error

Abstract: It is shown that the conditions for accurate flow measurement are not met if the resistant flow meter (e.g., Fleisch pneumotachograph or screen pneumotachograph) is attached directly at the mouth or endotracheal tube and the breath flows directly through it, firstly because its gas composition, temperature, and humidity change radically even within the course of one respiratory cycle, secondly because the expiratory peak flow of the patient being ventilated rapidly tends to become too high, and thirdly because the entire system is sensitive to turbulence. Methods are proposed to compensate continuously for the influence of the changing gas concentrations and to reduce expiratory peak flow without increasing resistance. With the resulting reduction in the error from 20% to about 2%, tidal volume can be more reliably determined, and the higher quality of primary data allows a more differentiated and more complex evaluation (N2-washout compartment analysis, VDS measurement, analysis of complicated patterns of spontaneous breathing or mechanical ventilation such as IMV, etc.).

Stroke volume in the dog: measurements by the impedance technique and thermodilution.

Abstract: The main objective of this paper was to assess the efficacy of a laboratory prototype cardio impedance meter, to determine stroke volume in experimental dogs, using Kubicek's classic model. A second objective, complementary to the first, was to evaluate the method itself, under the carefully controlled condition in which cardiac frequency was increased from the initial to the final value. Measurements were performed on ten mongrel dogs (average body weight = 15.2 kg, SD = 4.7), employing the standard thermodilution procedure as reference. Based on a total of 179 determinations (about 18 per animal), the following regression equation was obtained: SVd = (0.36 SVz + 3.94) ml where SVd = stroke volume by thermodilution, SVz = stroke volume by impedance, with a standard error of the estimate SEE = 4.26 ml, a coefficient of variation CV = 32.8%, and 0.84 as correlation r. Thus, the impedance technique overestimated consistently by an average factor in the order of 2. These conclusions were made: In the experimental dog, the impedancimetric method can measure non-invasively directional and relative changes in stroke volume; this permits the effect of several types of maneuvres to be followed on a beat-to-beat basis. The lack of accuracy would require the development of a more sophisticated mathematical model; however, a practical statistical expression for laboratory use is easily derivable, making the determination as if the measurement had been made with the thermodilution procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical impedance monitoring of the wound-healing process.

Abstract: The healing process was studied of five surgical wounds in sheep caused by the implantation of pacemaker electrodes in the vaginal or vulvar submucosa, while the electrodes were being used for impedometric measurements of the tissue surrounding them. Separate measurements of conductance (G) and capacitance (C) were carried out at frequencies ranging from 10 Hz to 100 kHz. The highest specific conductance at 100 kHz (mumho/cm) was observed on the 3rd postoperative day - 3095 +/- 172 SEM (n = 5), at which time the wound area was considerably swollen. Thereafter, the conductance gradually decreased and stabilized in 17-20 days at 2194 +/- 54 when the healing process was terminated. The decreasing impedance angle and tissue phase angle indicated that during the healing process cell volume decreased and cell density increased.

Technology--an unfulfilled promise for the handicapped.

Abstract: Rehabilitation engineering emphasizes the application of the physical, medical, allied health and social sciences to ameliorate the handicaps of persons with disabilities. A handicap is the consequence of a disability that interferes with a person's life goals in daily living, vocation, avocation and recreation. The degree of a handicap depends on the interaction of a disability and a particular environment as well as on the nature of the life goals of persons with a disability. Thus, technology can reduce a handicap by overcoming functional barriers, but it may increase a handicap by raising a person's life goals to a level that cannot yet technically be achieved, or if developed, effectively delivered. The design-development-production process and the special problems inherent in the development and distribution of technical devices for handicapped persons are discussed. The dependence of the service-delivery system on adequate information and effective evaluation of devices in meeting the needs of handicapped persons is critically examined. Recommendations to overcome barriers that interfere with the availability of the products of technology for persons with disabilities are presented. A description of research areas of technology for the handicapped is also presented.

High-sensitivity, high-linearity, low-leak, self-balanced impedance cardiograph.

Abstract: An impedance cardiograph (so-called cardioimpedance meter) with the following characteristics is described: preadjustable current generator range of 0-4 mA rms at 100 kHz, crystal-controlled; sensitivity up to 50 V/omega with a resolution of 2 m omega; maximum nonlinearity of 2%; 0.7 microA arms of maximum leak current at 50 Hz; flat frequency response between 0 and 19 Hz. The instrument is self-balanced, using Arenson's bridge [1] with minor modifications, and is also able to operate as a plethysmograph, respirograph, and as an intracardiac Z-meter. Preliminary test as an impedance cardiograph yielded a correlation coefficient better than 0.8 when the stroke volume was evaluated by Kubicek's method and compared with values obtained using thermodilution.

A method for two dimensional multi-segmental kinematic and kinetic analysis of normal and pathological human gait.

Abstract: The application of an integrated gait analysis system in clinical research is described. With this system it is possible to analyse the walking pattern of various groups of patients with regard to foot-floor contact, kinematics and kinetics, using a Selspot system. In order to study various groups of patients an extensive body-segment model adapted to the variety in patient groups is dealt with and is related to data from the literature. Special attention has been paid to the analysis or errors in the quantities used in kinematics and kinetics. The various sources of errors leading to inaccuracy of the data describing the walking pattern are discussed.

Optical communication aids in rehabilitation

Abstract: Two types of low-cost optical communication aids for non-vocal paralyzed patients are described: one based on reflection via mirrors and the other based on refraction via prisms. The recognition by the partner, when the handicapped person looks straight via the mirror/prism into his eyes, is crucial in the selection of the corresponding symbol in this communication process. The configurations in which the mirrors/prisms are arranged in aids of one- or two-dimensions, respectively. Preceding the choice of an advanced eye-controlled aid, eye defects can be detected using two-dimensional aids. Both types of optical communicators have been used in rehabilitation. The prism-aids appeared to be preferable to mirror-devices and to ETRAN-window in the communication process for speech replacement or in playing simple games.

A method for optimization of pulse sequences in NMR-imaging

Abstract: The diagnostic quality of NMR-images is very much dependent on the pulse sequences and the associated parameters. Therefore, one could use pulse sequences as 'electronic contrast media', if one knew the interrelation between the appearance of pathological alterations in NMR-images and the pulse sequences used. A method is demonstrated which allows a simulation of NMR experiments in the computer, based upon two measurements of one single plane with different recovery times. During this procedure, proton density-, T1- and T2-pictures are calculated and a systematic parameter variation can be done with any programmed pulse sequence equation, by calculating new pictures with different contrast. Even virtual images which cannot be achieved by real NMR experiments can be created. In some cases these virtual images have advantages over real NMR-pictures which are demonstrated. The method may be helpful by answering the questions about optimal parameters and may be one step towards a standardization in NMR-imaging.

Programmed electrical stimulation of the heart: how, when and where.

Abstract: In the last 15 years programmed electrical stimulation of the heart has been used to evaluate the site of origin, mechanisms and pathways of tachycardias and to select the best therapeutic approach for each particular patient. Recently, it has also been used increasingly to try to identify patients at risk of sudden arrhythmic death. The method of programmed electrical stimulation of the heart is reviewed and its indications are considered; the type of centres that should be performing these studies is also discussed.

Permeation of lipophilic drugs through synthetic elastomers.

Abstract: Permeability studies were carried out with three lipophilic drugs, namely, phenytoin and primidone (both widely used in the treatment of epilepsies and convulsive disorders), and dapsone (a sulfone antimicrobial agent used in the treatment of leprosy and to a lesser extent in dermatitis herpetiformis) through silica-filled poly(dimethyl siloxane) (Silastic) membranes, and anisotropic membranes of poly(ether-urethane)/poly(dimethyl siloxane) block copolymer (Avcothane, Cardiothane). These polymers are used in medical implants and in various cardiovascular devices. While both polymers were permeable to the drugs, the transport properties differed significantly. In the case of the poly(dimethyl siloxane) there was an initial large burst effect, followed by an exponential decrease in the rate of drugs released through the polymer films, although with dapsone the release rate became essentially constant between 100-180 h at 37 degrees C. In the case of the anisotropic films of the poly(ether-urethane)/poly(dimethyl siloxane) block copolymer, the permeabilities were much higher. Significantly, phenytoin exhibited essentially constant rate (zero-order) kinetics between 25-150 h, showing only a moderate burst effect that is probably not significant therapeutically. Importantly, dapsone showed neither a burst effect nor any significant time lag, and the release followed constant rate (zero-order) kinetics between 12-80 h, followed by only a moderate decrease in drug concentration up to 140 h (the experimental end-point). The diffusion coefficients calculated from initial desorption data at 37 degrees C for the poly(ether-urethane)/poly(dimethyl siloxane) block copolymer are as follows: phenytoin = 8.6 X 10(-9) cm2/s, primidone = 2.8 X 10(-9) cm2/s, and dapsone = 2.4 X 10(-8) cm2/s.(ABSTRACT TRUNCATED AT 250 WORDS)

A computer-based system for the study of ECG/VCG variability

Abstract: A description is given of a computer-based system for electrocardiogram and vectorcardiogram analysis. Its main purpose is to provide a basic research and study tool of the variability occurring in electrocardiographic activity when the observation time is of the order of 30 min. System/operator interaction is designed to allow the user to validate or correct the identifications executed by the program. Special attention is given to graphic representation techniques suitable for synthesizing a great many numerical results. Data acquisition and analysis are performed by two different PDP 11 systems. The acquisition programs are written in ASSEMBLER, the analysis programs are in FORTRAN. Intermediate files are structured by a data compression technique. At present the program is oriented to study normal subjects. A new version to study bundle-branch blocks is now available.

The influence of novel platelet aggregation inhibitors on human blood platelet clustering and retention effected by some polymer materials, in vitro.

Abstract: Human blood platelet clustering and retention in vitro induced by medical grade Cuprophane and Silastic and by non-medical grade polyethylene and Mylar, are discussed. The influence of synthetic compounds on polymer-induced platelet clustering and retention has been evaluated, interpreted in terms of physicochemical parameters, and correlated with ADP- and human alpha-trombin-stimulated aggregation; the Pearson product-moment correlation coefficient for a series of bis (alkylnipecotoylamino) alkanes was computed at r = 0.98 between (i) mylar-induced cluster formation and (ii) ADP-effected aggregation, and at r = 0.94 in corresponding correlations with thrombin as an inducing agent. All experiments were carried out in vitro. Due to the paucity of polymer specimens meeting the stipulated specifications, several evaluations had to be limited to triplicate and duplicate determinations.

Technology and Society.

Abstract: Technology has had a great impact on changes in life-style during the past. Urgent requirements concerning alimentation, health care, traffic and communication have been met by means of technology. The physical, sensory and intelligent strength of man have been multiplied by the utilization of natural resources, and the average lifetime has been increased considerably. However, technology is always combined with undesired side-effects, such as environmental pollution and cost explosion, as long as it has to meet the increasing requirements of mankind. Physicists and engineers were paying attention to these side-effects long before the so-called critical intelligentsia appeared on the scene. It is noteworthy that, especially in Germany, the natural sciences could never be integrated into culture. As a result of this, many scholars argue against technology without presenting solutions for the actual problems that are at present created by the ever-increasing numbers of people in the world and their high demands. Only science and technology can help to overcome these difficulties if they are applied in a reasonable way.