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PubMed1990

Computer study of presynaptic inhibition controlling the spread of action potentials into axonal terminals.

1. The effect of presynaptic, axoaxonal inhibition, that exerts its action by producing a local conductance increase, on the behavior of action potentials at postsynaptic axon terminals is analyzed computationally. The significance of the location and strength of the presynaptic inhibition, as well as the morphology and membrane properties of the axonal terminals, are considered. 2. Keeping the specific properties of terminal membrane and axoplasm constant, the critical "silent" steady-state conductance change (gcrit) that blocks propagation is linearly scaled with the terminal diameter raised to the 3/2 power. At the midpoint of a 5 lambda long, 1 micron diameter axon that has the standard Hodgkin and Huxley (1952) kinetics at 18 degrees C (and an input conductance of 8.7 nS), gcrit is 72 nS. At 0 degrees C, gcrit = 200 nS, whereas at 30 degrees C gcrit = 30 nS. 3. The critical conductance change that blocks propagation depends steeply on the density of excitable channels (gNa) at the terminal. For a geometrically uniform terminal at 18 degrees C, the action potential can not be blocked by a local shunt when gNa greater than 600 mS/cm2. 4. An axoaxonal synapse in the proximity of the postsynaptic release site has graded control over the spike amplitude (and, therefore, over the postsynaptic output) at that site. Presynaptic inhibition located remotely from the release site has an all-or-none effect at the release site. 5. Inhibition is more effective in attenuating the spike at the terminal when it impinges onto a passive terminal rather than on an excitable one. 6. The detectability of the conductance increase as well as the change in action potential amplitude associated with the presynaptic inhibition is poor at only a short distance from the axoaxonal synapse. The presence of bottlenecks and varicosities at some axonal terminals enhances this decoupling effect even more. Thus presynaptic inhibition may reduce the potential near the output site of the affected axon significantly, without producing any noticeable conductance or voltage change at a distance of only several tens of micrometers (a few tenths of a space constant) away from it. 7. Varicosities and bottlenecks typically found along axonal terminals are the optimal loci for presynaptic inhibition to be most effective in attenuating the action potential at the terminal. Even with high density of excitable channels, propagation with such terminal geometry is insecure, and one, or few, quanta of inhibitory transmitter (a conductance change of several nanosiemens) can block propagation there.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1992

Visual increment and decrement threshold curves as a function of luminance range and noise in simulated computed tomographic scans.

OBJECTIVES: The effect of luminance range compression on the visual threshold of a target in a computed tomographic (CT) scan was investigated in eight experiments. METHODS: Both visual increment thresholds of a hot target and visual decrement thresholds of a cold target were obtained. Realistic noisy CT images simulating a scan reconstruction and partial volume blurring were tested as representative of complex medical images. Negative versions, high luminance versions, and noise-free versions of these CT images also were tested. RESULTS AND CONCLUSIONS: In all the noisy images, as the luminance range of the image was compressed, proportionately smaller physical luminance differences between the target and its local background were needed to reach visual threshold. However, the thresholds were the same in terms of the difference in CT numbers between target and background. Noise in terms of CT numbers sets the threshold for a wide range of display conditions. In the noise-free CTs, as the luminance range was compressed, the luminance differences between the target and background needed to reach threshold also decreased, but only marginally. However, in terms of CT numbers, the thresholds were increased.

Analysis of Variance↗
PubMed1992

A universal system for interactive image-directed neurosurgery.

Stereotactic methods confer great accuracy to intracranial target localization, but require strict adherence to a complex program of mechanical and computational maneuvers. A computerized, articulated, localizing 'arm' has been developed that frees the neurosurgeon of these constraints and provides a completely intuitive, 'user-friendly' interface. This universal system is independent of whatever localizing fiducial system is selected. The arm may be sterilized for intracranial use. A variety of intraoperative end effectors may be selected. The patient's CT/MR/PET scans are loaded into computer memory and a three-dimensional shaded surface wireframe diagram of the patient's head is displayed simultaneously with up to 3 independent sets of cross-referenced CT/MR/PET scan images on the intraoperative video screen. The arm's endpoint location and the directional vector are shown as cursors on the relevant scan slices, and change continuously as the surgeon moves the arm. Because the information is continuously updated, an unlimited number of targets and trajectories may be displayed throughout the operation. The arm has an ultimate design accuracy for end-point localization to within 0.1 mm throughout a target volume of 40 x 40 x 40 cm. The tested application accuracy of the first prototype model is 0.31 mm. In clinical use during 30 surgeries, its real-world application accuracy is 0.9 mm. This system provides stereotactic accuracy and universally compatible, intuitive, interactive operation.

Biopsy↗
PubMed1986

How to keep up with the medical literature: V. Access by personal computer to the medical literature.

Access to the medical literature through personal computers is now readily available and can greatly reduce logistical barriers to using recently published journal articles to support clinical decisions. In this article, we describe many of the options available to clinicians who wish to do their own computer searching of MEDLINE, the largest of the electronic services for the biomedical literature. The "bare bones" computer equipment needed includes a terminal or personal computer, a modern and telephone line, and a printer. Access to MEDLINE is then gained through subscribing to any of a burgeoning number of database vendors. A comparison of 17 permutations and combinations of software and vendors shows that the software and vendors vary substantially in efficiency, cost, and ease of use. Direct subscription to MEDLINE is least expensive, PaperChase is the simplest service to use, and Colleague and Medis provide both MEDLINE access plus full-text journals online. Basic search techniques are illustrated for three clinical problems.

Computers↗
PubMed1991

[Eyeglass frame for detection of eye, head movements and pupillary diameter].

Up till now, the simultaneous recording of the movements of the eyes, the movements of the head and the diameter of the pupil required the combined use of several apparatus. In this paper we present a new apparatus developed for the simultaneous recording of the movements of the eyes and of the head, and the diameter of the pupil. The apparatus consists of a portable frame (weight 215 g) a 19" rack containing electronics, and a PC for storing and analyzing the recorded data. In comparison with other systems providing similar measuring possibilities the present apparatus has the advantage of smaller dimensions and lower weight.

Computer Terminals↗
PubMed1991

Visual load of working with visual display terminals--introduction of VDT to newspaper editing and visual effect.

In the Japanese newspaper industry, since the late 1970s, computerization has been started in large scale. The system, called Computerized Typesetting System (CTS), has been introduced. With this system, all information in the newspaper is input into a computer, called up on a cathode ray display (CRT) to edit, and then output to film or printing plates by CTS. Thus, the work of newspaper production has undergone a major transformation from industrial work to clerical work. It was reported that newspaper production staff working with VDTs complained more than staff working with the older key system about visual and physical problems which affected their job and their daily life. The complaint rates were highest for editors, who used VDT constantly throughout the day. This study was performed to clarify the health impact of VDT use and to prevent health disorders caused by the introduction of CTS. It is concluded that 5 m corrected vision and sphere refraction of CTS workers who used CTS over 2 or 4 hr daily, significantly became worse in a year after the introduction. Therefore, it is indicated that the control of CTS work time is important to prevent the visual disorder.

Adult↗
PubMed1990

Congenital malformations among children of women working with video display terminals.

In a case-base study among 214,108 commercial and clerical employees in Denmark the potential effect of the use of video display terminals on the risk of congenital malformations in pregnancy was investigated. The study base was identified by means of register linkage of the Medical Birth Register and the National Register of In-Patients. In the source population 24,352 pregnancy outcomes were registered, 661 of which with congenital malformations entered the case group, and a base sample of 2252 pregnancies was drawn. Data concerning the use of video display terminals, job stress, ergonomic factors, exposure to organic solvents, and life-style factors were obtained from postal questionnaires. The results of this study did not support the hypothesis that the use of video display terminals during pregnancy is associated with an increased risk of congenital malformations.

Adolescent↗
PubMedDate not supplied

[Modular project of the Picture Archiving and Communication System (PACS). Preliminary clinical experience. II].

In the previous paper in this volume the PAC System installed in the Radiology Department of the University of Trieste has been described and its advantages and limitations have been analyzed, mainly from an operational point of view. This paper deals with the clinical evaluation of the system in ordinary operative conditions. A series of cases with specific characteristics was monitored in order to reveal different performances in both diagnostic process and conclusions using the PACS viewing console (DW) vs. conventional CRT film images on alternators. In a first test, 100 routine (not pre-selected) brain CT cases were independently analyzed by 4 radiologists, each of them giving 2 interpretations of the same case, one based on film and the other on PACS. The data were analyzed by conventional statistical methods, showing a substantial agreement of the results obtained with the 2 modalities. A second test concerned the evaluation of 100 lumbar intervertebral disks by CT, with the same procedure as above. Four radiologists were again asked to decide on film and PACS images about normality, protusion, or herniation of the disks. The results demonstrate the possibility of adequately reporting on the PACS monitor and stress the need of an adequate training period and the efficacy of the image processing capabilities of the system.

Brain Diseases↗
PubMed1992

The effects of continuous exposure to 20-kHz sawtooth magnetic fields on the litters of CD-1 mice.

Mated CD-1 mice were exposed to 20-kHz sawtooth magnetic fields similar to those associated with video display terminals (VDT). Four groups of animals were continuously exposed from day 1 to day 18 of pregnancy to field strengths of 0, 3.6, 17, or 200 microT. There were no less than 185 mated dams in each exposure group. On day 18, the dams were sacrificed and assessed for weight gain and pregnancy. The litters were evaluated for numbers of implantations, fetal deaths and resorptions, gross external, visceral and skeletal malformations, and fetal weights. There were no less than 140 pregnant females in each group, and there were no significant differences between any of the exposure groups and the sham group (0 microT) for any of the end points. The results of this study do not support the hypothesis that the 20-kHz VLF magnetic fields associated with video display terminals are teratogenic in mammals.

Abnormalities, Radiation-Induced↗
PubMed1989

Microcomputer-controlled administration of vasodilators following cardiac surgery: technical considerations.

Hypertension in the early postoperative period after cardiopulmonary bypass is associated with increased morbidity, and is commonly managed by the infusion of short-acting vasodilators. Automatic arterial blood pressure control by closed-loop infusion has been shown to be superior to manual control in several studies. The investigators have developed a closed-loop arterial pressure control system based on the Atari 1040ST microcomputer (Atari, Sunnyvale, CA). The program uses a proportional-integral-derivative control algorithm, developed from that described by Sheppard and his colleagues. The arterial waveform is sampled digitally, and the waveform analysis routine incorporates several artifact detection and rejection functions. Additional safety features are provided in the computer-infusion pump subroutine, which cause alarms to be activated if computer-pump communication fails to occur within a specified time period. A novel feature of this system is the clinical staff's use of a "mouse" to enter data and control the program, which makes keyboard skills unnecessary. This system is in routine service in the cardiac intensive care unit (CICU), both for direct clinical use and for research into various aspects of arterial pressure control, and has proved to be acceptable to the clinical staff.

Algorithms↗
PubMed1990

[Monocrystalline aluminum dental implants in animals: a study of the peri-implant tissue].

After the extraction of two molars in a dog's jaw, a single crystal alumina screw was implanted. Monthly radiographs were taken and analyzed by means of a video display computer (VDC) to obtain densitometric informations about the interface. After one year implantation, the bone segment containing the prosthesis was fixed in 4% paraformaldehyde, embedded in methacrylate and sectioned by a microtome saw. The results in light microscopy with ordinary and polarized light, in SEM and X-ray microanalysis, show the presence of a thick connective tissue layer interposed between the screw and the bone. The histological findings confirm the results obtained through the VDC analysis of the radiographic images.

Absorptiometry, Photon↗
PubMed1987

An algorithm for planning stereotactic brain implants.

A computer software package was developed for the planning and execution of brain biopsy and radioactive implant procedures with the BRW Stereotaxic System. With the application of computer graphics and a zero-one integer variable programming algorithm, an implant plan with accompanying isodose distributions and stereotactic coordinates can be easily accomplished at the time of the operation when the computer imaging terminal and a printer/plotter is placed in the operating room.

Algorithms↗
PubMed1990

Steady flow of a viscous fluid through a network of tubes with applications to the human arterial system.

The paper presents a finite-element model for the analysis of steady flow of a viscous fluid through a connected system of elastic tubes with the aim of simulating the conditions of blood flow through the human arterial system. The governing equations of the model are non-linear in character and are solved through an iterative computational procedure. This model is capable of incorporating the effects of stenosis on flow and pressure. Typical results are presented and discussed. Quantitative results have been obtained on blood flow through a model of the human arterial system corresponding to the sets of prescribed conditions at the terminations. Also computational results on the effect of stenosis in typical arteries of the system are presented.

Aorta↗
PubMedDate not supplied

Three-dimensional computer reconstruction of the distribution of neuromuscular junctions in the thyroarytenoid muscle.

Microinjections of botulinum toxin have recently been shown to be effective in the treatment of strabismus, and it has also been suggested that microinjections of this myoneural blocking agent might be of value in the treatment of spastic dysphonia. The success of such a microinjection technique would rely on a precise knowledge of the distribution of myoneural junctions in the thyroarytenoid muscle. In view of this potential application as well as the need for such information in reinnervation procedures, we have used computer graphics to reconstruct the three-dimensional distribution of motor end-plates in the thyroarytenoid muscle. Three cat and one human (fresh autopsy specimen) larynges were frozen and sectioned on a cryostat. Serial sections were then processed for the histochemical localization of acetylcholinesterase activity to demarcate the neuromuscular junctions. An X-Y digitizer was used to reference the position of the motor end-plates in each serial section, and the three-dimensional distribution of the neuromuscular junctions was reconstructed on a computer graphics terminal. The results are discussed in regard to their applicability to clinical treatment of spastic dysphonia and other disorders of phonation.

Animals↗
PubMed1989

Interhemispheric connections differ between symmetrical and asymmetrical brain regions.

Coronal sections from the brains of male Wistar rats that underwent corpus-callosectomy in adulthood were stained with Cresyl Violet for Nissl substance or by the Fink-Heimer method for terminal axonal degeneration. Measurements of volumetric asymmetry of neocortical region SM-I were made, and the per cent of terminal degeneration computed. As in previous studies, there was a negative correlation between asymmetry coefficient and total (right plus left) architectonic volume, indicating that symmetrical brain regions are larger than the average of the corresponding regions in asymmetrical brains. It was also found that as volumetric asymmetry increased, the per cent of axonal termination decreased, partly as a result of a decrease in the number of patches of callosal axonal termination. These results are interpreted in the light of what is known about the ontogenesis of callosal connectivity, and mechanisms for the development of architectonic asymmetry in the cerebral cortex are postulated.

Animals↗
PubMedDate not supplied

Identifying the savings potential of bedside terminals.

Savings estimates from using bedside terminal systems must be unit and shift-specific to properly determine which functional areas offer savings potential, the potential savings on different shifts, and which nursing units have the greatest savings potential.

Computer Terminals↗