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At least 973 records · Page 54Linked to original sources
PubMed1995

An optimal control model for analyzing human postural balance.

The question posed in this study is whether optimal control and state estimation can explain selection of control strategies used by humans, in response to small perturbations to stable upright balance. To answer this question, a human sensorimotor control model, compatible with previous work by others, was assembled. This model incorporates linearized equations and full-state feedback with provision for state estimation. A form of gain-scheduling is employed to account for nonlinearities caused by control and biomechanical constraints. By decoupling the mechanics and transforming the controls into the space of experimentally observed strategies, the model is made amenable to the study of a number of possible control objectives. The objectives studied include cost functions on the state deviations, so as to control the center of mass, provide a stable platform for the head, or maintain upright stance, along with a cost function on control effort. Also studied was the effect of time delay on the stability of controls produced using various control strategies. An objective function weighting excursion of the center of mass and deviations from the upright stable position, while taking advantage of fast modes of the system, as dictated by inertial parameters and musculoskeletal geometry, produces a control that reasonably matches experimental data. Given estimates of sensor performance, the model is also suited for prediction of uncertainty in the response.

Biomechanical Phenomena↗
PubMed2006

Ultrasound lung comets: a clinically useful sign of extravascular lung water.

Assessment of extravascular lung water is a challenging task for the clinical cardiologist and an elusive target for the echocardiographer. Today chest x-ray is considered the best way to assess extravascular lung water objectively, but this requires radiology facilities and specific reading expertise, uses ionizing energy, and poses a significant logistic burden. Recently, a new method was developed using echocardiography (with cardiac probes) of the lung. An increase in extravascular lung water-as assessed independently by chest computed tomography, chest x-ray, and thermodilution techniques-is mirrored by appearance of ultrasound lung comets (ULCs). ULCs consist of multiple comet tails originating from water-thickened interlobular septa and fanning out from the lung surface. The technique requires ultrasound scanning of the anterior right and left chest, from the second to the fifth intercostal space. It is simple (with a learning curve of < 10 examinations) and fast to perform (requiring < 3 minutes). ULC assessment is independent of the cardiac acoustic window, because the lung on the anterior chest is scanned. It requires very basic 2-D technology imaging, even without a second harmonic or Doppler. ULCs probably represent an ultrasonic equivalent of radiologic Kerley B-lines. On still-frame assessment, cardiogenic watery comets can be difficult to distinguish from pneumogenic fibrotic comets, although the latter are usually more localized and are not dissolved by an acute diuretic challenge. Functionally, ULCs are a sign of distress of the alveolar-capillary membrane, often associated with reduced ejection fraction and increased pulmonary wedge pressure. The ULC sign is quantitative, reproducible, and ideally suited to complement conventional echocardiography in the evaluation of heart failure patients in the emergency department (for the differential diagnosis of dyspnea), in-hospital evaluation (for tailoring diuretic therapy), home care (with portable ultrasound), and stress echocardiography lab (as a sign of acute pulmonary congestion during stress). In conclusion, ULCs represent a useful, practical, and appealingly simple way to image directly extravascular lung water.

Artifacts↗
PubMed2006

Raman spectroscopy in astrobiology.

Raman spectroscopy is proposed as a valuable analytical technique for planetary exploration because it is sensitive to organic and inorganic compounds and able to unambiguously identify key spectral markers in a mixture of biological and geological components; furthermore, sample manipulation is not required and any size of sample can be studied without chemical or mechanical pretreatment. NASA and ESA are considering the adoption of miniaturised Raman spectrometers for inclusion in suites of analytical instrumentation to be placed on robotic landers on Mars in the near future to search for extinct or extant life signals. In this paper we review the advantages and limitations of Raman spectroscopy for the analysis of complex specimens with relevance to the detection of bio- and geomarkers in extremophilic organisms which are considered to be terrestrial analogues of possible extraterrestial life that could have developed on planetary surfaces.

Biomarkers↗
PubMed1998

Blunt abdominal trauma in adults: role of CT in the diagnosis and management of visceral injuries. Part 2: Gastrointestinal tract and retroperitoneal organs.

Computed tomography plays an important role in the detection and management of blunt visceral injuries in adults. Current standard examination techniques enable detection of the majority of perforating or devascularizing bowel injuries, although diagnostic findings are often subtle and meticulous inspection is required. Computed tomography may demonstrate pancreatic contusions and lacerations and help in distinguishing minor traumatic lesions without involvement of the pancreatic duct (organ injury scale, grades I and II) from deep lacerations with ductal involvement (grades III and V). Computed tomography enables distinguishing renal contusions and minor cortical lacerations that can usually be managed conservatively (injuries of grades I-III) from corticomedullary lacerations and injuries of the major renal vessels (grades IV and V) that have a less favorable prognosis and more commonly require surgical repair. In addition, CT is well suited for the detection of active renal hemorrhage and guidance of transcatheter embolization treatment and delineation of preexisting benign or malignant pathologies that may predispose to posttraumatic hemorrhage. The radiologist's awareness of the diagnostic CT findings of abdominal visceral injuries as well as their clinical and surgical implications are important prerequisites for optimal patient management.

Abdominal Injuries↗
PubMedDate not supplied

Finding the biologically optimal alignment of multiple sequences.

OBJECTIVE: Deterministic annealing, which is derived from statistical physics, is a method for obtaining the global optimum in parameter space. During the annealing process, starting from high temperatures which are then lowered, deterministic annealing deterministically find the (global) optimum at each temperature. Thus, deterministic annealing is expected to be more computationally efficient than stochastic sampling strategies to obtain the global optimum. We propose to apply the deterministic annealing technique to the problem of efficiently finding the biologically optimal alignment of multiple sequences. METHODS AND MATERIAL: We take a strategy based on probabilistic models for aligning multiple sequences. That is, we train a probabilistic model using given training sequences and obtain their alignment by parsing, i.e. searching for the most likely parse of each sequence and gaps using the trained parameters of the model. In this scenario, we propose a new stochastic model, which is simple enough to be suited to multiple sequence alignment and, unlike existing stochastic models, say a profile hidden Markov model (HMM), allows us to use similarity scores between symbols (or a symbol and a gap). We further present a learning algorithm for our simple model by combining deterministic annealing with an expectation-maximization (EM) algorithm. We emphasize that our approach is time-efficient, even if the training is done through an annealing process. RESULTS: In our experiments, we used actual protein sequences whose three-dimensional (3D) structures are determined and which are all aligned based on their 3D structures. We compared the results obtained by our approach with those by other existing approaches. Experimental results clearly showed that our approach gave the best performance, in terms of the similarity to the structurally determined alignment, among the approaches tested. Experimental results further indicated that our approach was ten times more efficient in terms of actual computation time than a competing method.

Algorithms↗
PubMed1982

[Acquiring otoneurological results by computer. Evaluation after 2 years of experience].

Nearly all test performed in audiology and vestibulometry are based on quantitative paradigms and lead to results expressed in numerical form that are well suited for computer processing. Since 1980, the Oto-rhino-laryngology department of the Geneva University Hospital stores the complete patient record with all the results obtained in the otoneurological investigations (audiogram, impedance measurements, binaural tests, auditory-evoked potentials, electro-nystagmogram) on floppy disks using a PDP-11 micro-computer equipped with a low-speed printer and a Tektronix 4010 graphics terminal with an attached hard-copy unit. One of the main advantages of such a computer system is the gain in time for secretarial work such as patient record updating and archival. All test results are manually entered on a keyboard and the computer automatically produces reports with tables and graphs. The storage of patient files on floppy disks is fast, consumes little space and makes possible all types of statistical studies on the recorded clinical data. One should, however, be aware of the fact that the daily clinical use of even such a small computer system requires a solid technical infrastructure and lots of programming time. Nevertheless, the balance of our two years experience with this system is clearly positive and we foresee that the computer will become more and more an appreciated technical tool for several types of clinical work.

Electronystagmography↗
PubMed2004

Current state of ergonomics of operating rooms of Dutch hospitals in the endoscopic era.

Laparoscopic procedures are mostly performed in operating rooms which have been designed for conventional surgery. The ergonomic layout of these operating rooms is not suited for endoscopic surgery. This study reports on the current state of ergonomics of Dutch operating rooms for laparoscopic surgery. Number of trolleys, presence of ceiling-mounted booms, and number, positioning and size of monitors were recorded. The floor surface of operating rooms and lowest and highest positions of operating tables were documented. Positioning of the surgical team and monitors during laparoscopic surgery were assessed. Twenty-nine hospitals participated in this study. The average number of trolleys per hospital was 2.4. The mean height of the center of the monitors was 163 cm. Average floor surface of operating rooms was 37.45 m 2 . Only one of the 29 hospitals had a ceiling-mounted boom. The height of operating tables varied between 725 and 1215 mm. The floor space of current operating rooms is too small to allow use of space occupying technological systems. Less than 4% of operating rooms are equipped with permanent monitors mounted on booms. Operating tables cannot be lowered to a position which allows an ergonomic posture of the surgical team.

Journal Article↗
PubMed1992

The electrode system in impedance-based ventilation measurement.

In this paper, we determined which electrode types, sizes, and locations were best suited for impedance-based ventilation measurement. Optimal electrodes provide high signal-to-(motion) artifact ratio (SAR) and reliability by meeting the following criteria: 1) low baseline impedance, 2) high adhesion, 3) good physical stability, 4) large effective area, 5) thin with high flexibility. We compared 14 electrodes from two main groups: adhesive-gel and conductive rubber electrodes. Adhesive-gel electrodes are easy to apply, make good body contact, and do not slip during the course of an experiment. We found that higher SAR's are obtained when electrode area is increased by connecting several small electrodes together rather than by using a single electrode with a larger area. The peak SAR is achieved when two electrode arrays (area = 70 cm2) are centered at the 8th intercostal spaces on opposite midaxillary lines. To determine the optimal electrode locations, we placed 32 electrodes on the trunk and recorded impedance between 171 electrode combinations on ten normal adult subjects. Based on these data, we conclude that the SAR's are highest when one electrode is placed on the midpoint between the left and right second intercostal spaces on the sternum and the other electrode is placed in the opposite position on the back.

Adult↗
PubMed2004

Verbal communication in MR environments: effect of MR system acoustic noise on speech understanding.

PURPOSE: To assess the masking effect of magnetic resonance (MR)-related acoustic noise and the effect of passive hearing protection on speech understanding. MATERIALS AND METHODS: Acoustic recordings were made at 1.5 T at patient and operator (interventionalist in the MR suite) locations for relevant pulse sequences. In an audiologic laboratory, speech-to-noise ratios (STNRs) were determined, defined as the difference between the absolute sound pressure levels of MR noise and speech. The recorded noise of the MR sequences was played simultaneously with the recorded sentences at various intensities, and 15 healthy volunteers (seven women, eight men; median age, 27 years) repeated these sentences as accurately as possible. The STNR that corresponded with a 50% correct repetition was used as the measure for speech intelligibility. In addition, the effect of passive hearing protection on speech intelligibility was tested by using an earplug model. RESULTS: Overall, speech understanding was reduced more at operator than at patient location. Most problematic were fast gradient-recalled-echo train and spiral k-space sequences. As the absolute sound pressure level of these sequences was approximately 100 dB at patient location, the vocal effort needed to attain 50% intelligibility was shouting (>77 dB). At operator location, less effort was required because of the lower sound pressure levels of the MR noise. Fast spoiled gradient-recalled-echo and echo-planar imaging sequences showed relatively favorable results with raised voice at operator location and loud speaking at patient location. The use of hearing protection slightly improved STNR. CONCLUSION: At 1.5 T, the level of MR noise requires that large vocal effort is used, at the operator and especially at the patient location. Depending on the specific MR sequence used, loud speaking or shouting is needed to achieve adequate bidirectional communication with the patient. The wearing of earplugs improves speech intelligibility.

Acoustics↗
PubMed1992

Measurements of blood flow and exchanging water space in breast tumors using positron emission tomography: a rapid and noninvasive dynamic method.

A noninvasive dynamic method for the measurement of blood flow, using 15O-labeled water and positron emission tomography, has been developed and used to study 20 patients with breast carcinoma. The mean tumor flow was 29.8 +/- 17.0 (SE) ml/dl/min of tissue, while normal breast flow was 5.6 +/- 1.4 ml/dl/min of tissue. The exchanging water space of tissue known as the volume of distribution of the tracer (Vd) was also derived. This is defined as the volume of water in tissue that exchanges with a unit volume of water in arterial blood during the period of the study (7 min). The mean tumor Vd was 0.56 +/- 0.15 ml/ml while normal breast Vd was 0.14 +/- 0.05 ml/ml. The low value in normal breast is partly due to the high fat content of the tissue. The mean flow per unit of exchangeable volume was similar in tumor (52.8 +/- 22.0) and normal breast tissue (45.2 +/- 20.0). This suggests that the major discrepancy seen in measured values of flow between breast tumors and normal breast principally reflects the different composition of the two tissues. This method is rapid and suited for studying the reactivity of human tumor vasculature, so extending studies are being performed on animal tumors.

Adult↗
PubMed1992

[Postoperative lumbar discitis].

The authors report our experience on 19 cases of discitis developed after operations for herniated lumbar disc. Because of the negativity of the neuroradiological studies in the acute stage, the recognition of the typical syndrome (severe back pain, spasm of the paravertebral lumbar muscles, limited spinal motility, fever) beginning 3-30 days post-operatively and the study of some laboratory tests (elevated Erythrocyte sedimentation rate (ESR) and midly to moderately elevated white blood cells (WBC) are very important for diagnosis. The first radiographic findings (disc space narrowing, ecc.) are detectable only 4 to 6 weeks after the first symptoms; other X-ray findings are not seen post-operatively before 6 months-2 years. The CT-scan is diagnostic of discitis only when the following three specific signs are present: a) anterior paravertebral soft tissue swelling with obliteration of paravertebral fat planes; b) fragmentation or erosion of vertebral end plates; c) paravertebral fluid collection (abscess). In our experience a period of immobilization of the spine with a plaster body jackets and the use of adequate antibiotic therapy are the more effective treatment. Undoubtedly the discits are the results of an infection that must be prevented adhering to the aseptic principles not only during surgery but also during the procedures performed in the radiology suite.

Adult↗
PubMedDate not supplied

Neurobiological and endocrine correlates of individual differences in spatial learning ability.

The polysialylated neural cell adhesion molecule (PSA-NCAM) has been implicated in activity-dependent synaptic remodeling and memory formation. Here, we questioned whether training-induced modulation of PSA-NCAM expression might be related to individual differences in spatial learning abilities. At 12 h posttraining, immunohistochemical analyses revealed a learning-induced up-regulation of PSA-NCAM in the hippocampal dentate gyrus that was related to the spatial learning abilities displayed by rats during training. Specifically, a positive correlation was found between latency to find the platform and subsequent activated PSA levels, indicating that greater induction of polysialylation was observed in rats with the slower acquisition curve. At posttraining times when no learning-associated activation of PSA was observed, no such correlation was found. Further experiments revealed that performance in the massed water maze training is related to a pattern of spatial learning and memory abilities, and to learning-related glucocorticoid responsiveness. Taken together, our findings suggest that the learning-related neural circuits of fast learners are better suited to solving the water maze task than those of slow learners, the latter relying more on structural reorganization to form memory, rather than the relatively economic mechanism of altering synaptic efficacy that is likely used by the former.

Analysis of Variance↗
PubMedDate not supplied

Disobliteration of the aorto-iliac (-femoral) arteries with the plaque cracker, using the retroperitoneal approach.

The aorto-iliac disobliteration technique using the LeVeen plaque cracker is described and the results in 70 patients (operated on at the Elisabeth Hospital, Sluiskil, The Netherlands), are presented. The early mortality rate for the series was 4.3%. There were two cases of haemorrhage due to adventitial damage, within two weeks of the operation. The 5 year patency rate was 100%. The LeVeen disobliteration technique is a considerable improvement in the conventional open or half closed endarterectomy. The operation is shorter, and simpler. Also it is ideally suited for combination with the retroperitoneal approach. The technique can be easily combined with disobliterations distal to the groin. The relative advantages and disadvantages of the closed disobliteration and synthetic graft methods are discussed together with the reasons why the closed disobliteration technique seems to be the method of choice in those patients without aneurysms or excessive calcification.

Adult↗
PubMed1996

Consideration in selecting crops for the human-rated life support system: a Linear Programming model.

A Linear Programming model has been constructed which aids in selecting appropriate crops for CELSS (Controlled Environment Life Support System) food production. A team of Controlled Environment Agriculture (CEA) faculty, staff, graduate students and invited experts representing more than a dozen disciplines, provided a wide range of expertise in developing the model and the crop production program. The model incorporates nutritional content and controlled-environment based production yields of carefully chosen crops into a framework where a crop mix can be constructed to suit the astronauts' needs. The crew's nutritional requirements can be adequately satisfied with only a few crops (assuming vitamin mineral supplements are provided) but this will not be satisfactory from a culinary standpoint. This model is flexible enough that taste and variety driven food choices can be built into the model.

Crops, Agricultural↗
PubMed1995

Control of the necrosed tissue volume during noninvasive ultrasound surgery using a 16-element phased array.

Focused high-power ultrasound beams are well suited for noninvasive local destruction of deep target volumes. In order to avoid cavitation and to utilize only thermal tissue damage, high frequencies (1-5 MHz) are used in ultrasonic surgery. However, the focal spots generated by sharply focused transducers become so small that only small tumors can be treated in a reasonable time. Phased array ultrasound transducers can be employed to electronically scan a focal spot or to produce multiple foci in the desired region to increase the treated volume. In this article, theoretical and experimental studies of spherically curved square-element phased arrays for use in ultrasonic surgery were performed. The simulation results were compared with experimental results from a 16-element array. It was shown that the phased array could control the necrosed tissue volume by using closely spaced multiple foci. The phased array can also be used to enlarge a necrosed tissue volume in only one direction at a time, i.e., lateral or longitudinal. The spherically curved 16 square-element phased array can produce useful results by varying the phase and amplitude setting. Four focal points can be easily generated with a distance of two or four wavelengths between the two closest peaks. The maximum necrosed tissue volume generated by the array can be up to sixteen times the volume induced by a similar spherical transducer. Therefore the treatment time could be reduced compared with single transducer treatment.

Biophysical Phenomena↗
PubMed1996

Metamorphosis and pattern formation in Hydractinia echinata, a colonial hydroid.

There are several reasons why Hydractinia echinata Hydrozoa, Cnidaria) is excellently suited to study developmental processes. In the laboratory fertilization takes place every morning in the seawater in thousands of eggs. Cleavage starting synchronously leads to a ciliated planula larva within 2 to 3 days. Onset of metamorphosis from the larval to the polyp stage must be triggered externally. There are several agents known to induce or to interfere with induction of metamorphosis thus allowing access to the biochemical basis of this process. The pattern of the resultant polyp can be influenced by certain treatments during the process of metamorphosis allowing access to a process of proportioning. The colony develops by elongation of hollow tubes at the base of the polyps, termed stolons on which in more or less regular intervals new polyps emerge. Two (main) types of polyps are formed allowing to study spacing by lateral inhibition and lateral dependence of each other. In the present paper current data and hypotheses concerning all these topics are discussed.

Animals↗
PubMed1999

Value of dynamic susceptibility contrast magnetic resonance imaging in the evaluation of intracranial tumors.

The degree of tumor malignancy generally correlates to tumor grade, and the direct measurement of tumor vasculature is desired. Dynamic susceptibility contrast magnetic resonance imaging can provide relative cerebral blood volume and, therefore, is one of the most reliable methods to evaluate tumor vasculature in vivo. Tumor vessel size is extremely variable due to complex tumor angiogenesis, and the gradient-echo echo-planar imaging (GE-EPI) technique, which is sensitive to the total vascular bed, is well suited for this purpose. As many studies have shown, dynamic susceptibility contrast magnetic resonance imaging is more useful for grading glioma than conventional magnetic resonance imaging. We found that this technique can also provide supplementary information to differentiate between malignant lymphoma and glioma because the absence of tumor neovascularization of malignant lymphoma leads to low rCBV, which is in contrast to those of malignant gliomas. Indeed, this technique can be used for the differentiation of extra-axial tumors such as between meningioma and neurinoma. Recently, this technique has been focused toward determining the stereotactic biopsy site, monitoring the embolization of effect in meningioma, or evaluation of treatment effects after radiation therapy. However, the value of tumor rCBV is affected by many conditions such as the T1 relaxivity effects of gadolinium in the extravascular space. To establish the usefulness of this technique, further examination will be needed.

Adult↗
PubMed2004

Motor rehabilitation using virtual reality.

Virtual Reality (VR) provides a unique medium suited to the achievement of several requirements for effective rehabilitation intervention. Specifically, therapy can be provided within a functional, purposeful and motivating context. Many VR applications present opportunities for individuals to participate in experiences, which are engaging and rewarding. In addition to the value of the rehabilitation experience for the user, both therapists and users benefit from the ability to readily grade and document the therapeutic intervention using various systems. In VR, advanced technologies are used to produce simulated, interactive and multi-dimensional environments. Visual interfaces including desktop monitors and head-mounted displays (HMDs), haptic interfaces, and real-time motion tracking devices are used to create environments allowing users to interact with images and virtual objects in real-time through multiple sensory modalities. Opportunities for object manipulation and body movement through virtual space provide frameworks that, in varying degrees, are perceived as comparable to similar opportunities in the real world. This paper reviews current work on motor rehabilitation using virtual environments and virtual reality and where possible, compares outcomes with those achieved in real-world applications.

Journal Article↗