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At least 1,315 records · Page 73Linked to original sources
PubMed2002

Paraplegia as a complication of percutaneous vertebroplasty with polymethylmethacrylate: a case report.

STUDY DESIGN: A case report and review of the literature are presented. OBJECTIVE: To present the first case of paraplegia as a complication of percutaneous vertebroplasty with polymethylmethacrylate in osteoporotic compression fracture. SUMMARY OF BACKGROUND DATA: Complications of percutaneous vertebroplasty with polymethylmethacrylate (PMMA) for the treatment of osteoporotic compression fracture were found to be rare and minor, except in two cases of major neurologic complication. METHODS: The reported case is that of a 66-year-old woman with multilevel vertebral osteopenia and compression fractures. Percutaneous vertebroplasty using polymethylmethacrylate was performed at three vertebral bodies (L2, L1, and T11) using careful techniques including venography, large cannula, proper preparation and amount of polymethylmethacrylate, and continuous visualization with fluoroscopy. RESULTS: Immediately after surgery, the patient had complete motor and sensory deficits at T11. Computed tomography scan showed spinal cord compression caused by venous leakage of polymethylmethacrylate. In anticipation of recovery from paraplegia, posterior decompression was performed from L2 to T10. CONCLUSIONS: Percutaneous vertebroplasty with polymethylmethacrylate is not as simple and risk free as advocated in the literature. Careful safeguards and modifications are needed for the procedure, and new and physiologic material could be substituted for polymethylmethacrylate.

Aged↗
PubMed1997

Image transfer and computer-supported cooperative diagnosis.

The KAMEDIN system was designed as a low-cost communication tool as part of a computer-supported cooperative work project that included synchronized user interaction, telepointing and audioconferencing. During a five-month field trial, it was used for medical image transfer and cooperative diagnosis in 14 clinics and medical departments in Germany. During the field test, 297 teleconsultations were performed via ISDN and 875 MByte of data were transferred. An image compression ratio of 2-3 was obtained, so that the total quantity of data transferred corresponded to 14,000-21,000 magnetic resonance images or 3500-5250 computerized tomography images. Furthermore, 694 local sessions were conducted for the preparation of teleconsultations and the review of transferred images. Participants learned to handle the KAMEDIN system in a few hours. This was mainly owing to the design of the user-oriented graphical user interface and the restriction of the system to a set of essential image-processing functions.

Computers↗
PubMed2004

Cuff-compression of the proximal calf to reduce venous contamination in contrast-enhanced stepping-table magnetic Resonance angiography.

PURPOSE: To minimize venous overlay at the calf station in contrast-enhanced three-dimensional (3D) stepping-table magnetic resonance angiography (MRA) using a continuous cuff-compression technique during MR data acquisition. MATERIAL AND METHODS: Within 14 months, 32 patients suffering from symptomatic peripheral arterial occlusive disease (PAOD) with a bilateral ankle-brachial index (ABI) of 0.8 or below were consecutively enrolled in this study. Unilateral cuff-compression of the proximal calf was applied in the study group (n = 14). The control group (n = 18) underwent no compression. All patients underwent three-step 3D contrast-enhanced magnetic resonance angiography (3D CE-MRA) according to the institute's protocol. Venous contamination scores (vcs) at the calf station were blindly ranked by a 1 to 3 rating score (3 = major venous contamination). The vcs values of the control group were regarded as standard. Statistical significance between both groups was evaluated with a paired t test. RESULTS: Symmetric venous contamination was observed within the control group with a mean vcs of 2.2+/-0.6 on the left side and 2.2+/-0.7 on the right side with deltavcsleft-right of 0.1+/-0.2 (P>0.1). In the study group, asymmetric venous contamination was determined with vcsmean = 2.3+/-0.6 for the uncompressed side and vcsmean =1.4+/-0.5 for the compressed side and a deltavcsuncomp-comp of 0.9+/-0.5 (P<0.00005). The control group and the uncompressed side of the study group showed no significant difference in venous contamination (P > 0.1). CONCLUSION: Subdiastolic cuff-compression of the proximal calf is an easily applicable and inexpensive technique by which to reduce venous contamination of the calf station in stepping-table MR angiography and to improve evaluation of the infrapopliteal arteries.

Aged↗
PubMed2005

Missing the forest for the trees: phylogenetic compression and its implications for inferring complex evolutionary histories.

Phylogenetic tree reconstruction is difficult in the presence of lateral gene transfer and other processes generating conflicting signals. We develop a new approach to this problem using ideas borrowed from algorithmic information theory. It selects the hypothesis that simultaneously minimizes the descriptive complexity of the tree(s) plus the data when encoded using those tree(s). In practice this is the hypothesis that can compress the data the most. We show not only that phylogenetic compression is an efficient method for encoding most phylogenetic data sets and is more efficient than compression schemes designed for single sequences, but also that it provides a clear information theoretic rule for determining when a collection of conflicting trees is a better explanation of the data than a single tree. By casting the parsimony problem in this more general framework, we also conclude that the so-called total-evidence tree--the tree constructed from all the data simultaneously--is not always the most economical explanation of the data.

Algorithms↗
PubMedDate not supplied

[Ventral compression spondylodesis using internal fixator instrumentation--a biomechanical study].

Pseudarthrosis is said to be a main complication in anterior interbody fusion. It is usually the result of an insufficient mechanical stability which hinders bony incorporation of intervertebral bone grafts. In order to improve stability dorsal transpedicular instrumentation should be carried out to achieve interfragmentary compression between bone block and adjacent vertebral endplate. Using human lumbar spine cadavers and a capacitive measuring mat an experimental study was completed to find out in which way an internal fixator has to be used to achieve this goal. The collected data showed that simple compression of the fixator by reducing the distance between the Schanz-screws did not produce sufficient interfragmentary compression. Preloading the fixator in kyphosis and compression in a second step improved the results significantly. Using this technique a compressive interbody fusion can be attained.

Adolescent↗
PubMedDate not supplied

Effect of in vitro mechanical compression on Epilysin (matrix metalloproteinase-28) expression in hypertrophic scars.

Epilysin, designated matrix metalloproteinase (MMP)-28, is the newest member of this family of proteases expressed by keratinocytes in response to an injury. MMP-28's physiological role and specific substrates are unknown, but its expression pattern suggests that it may serve a role in both tissue homeostasis and wound healing. The aim of this preliminary study was to observe the presence of MMP-28 protein in normotrophic and hypertrophic scars and to evaluate the effect of in vitro mechanical compression on its expression. Biopsies from normotrophic and hypertrophic scars resulting from burns were divided into two samples, one to be used as control (uncompressed) and the other to be compressed in an oxygenated organ chamber for 24 hours in the presence of a serum-free medium, using an electromechanical load transducer (stable pressure = 35 mmHg). Analysis of MMP-28 protein secretion, assessed by Western blot and beta-casein zymography in scar conditioned media, revealed that normotrophic scar did not release MMP-28 in any condition while hypertrophic scar released active MMP-28 both in control conditions and after compression. MMP-28 immunohistochemistry revealed a light protein presence in normotrophic scar keratinocytes and a strong MMP-28 positivity in hypertrophic scar keratinocytes in control conditions, while compression increased MMP-28 staining in normotrophic scar and induced a significant reduction of the protein presence in hypertrophic scar keratinocytes. As it has been suggested that MMP-28 may restructure the skin basal membrane (Saarialho-Kere et al., 2002), our data indicate that mechanical compression directly acts to modulate the remodeling phase of wound healing, altering release and activity of MMP-28 in hypertrophic scars.

Adolescent↗
PubMed2006

Video compression using spatiotemporal regularity flow.

We propose a new framework in wavelet video coding to improve the compression rate by exploiting the spatiotemporal regularity of the data. A sequence of images creates a spatiotemporal volume. This volume is said to be regular along the directions in which the pixels vary the least, hence the entropy is the lowest. The wavelet decomposition of regularized data results in a fewer number of significant coefficients, thus yielding a higher compression rate. The directions of regularity of an image sequence depend on both its motion content and spatial structure. We propose the representation of these directions by a 3-D vector field, which we refer to as the spatiotemporal regularity flow (SPREF). SPREF uses splines to approximate the directions of regularity. The compactness of the spline representation results in a low storage overhead for SPREF, which is a desired property in compression applications. Once SPREF directions are known, they can be converted into actual paths along which the data is regular. Directional decomposition of the data along these paths can be further improved by using a special class of wavelet basis called the 3-D orthonormal bandelet basis. SPREF -based video compression not only removes the temporal redundancy, but it also compensates for the spatial redundancy. Our experiments on several standard video sequences demonstrate that the proposed method results in higher compression rates as compared to the standard wavelet based compression.

Algorithms↗
PubMed2002

Compressive tolerance of the maturing cervical spine.

While a number of experiments have reported injury thresholds for the adult cervical spine in compression, the compressive failure tolerance of the child spine has not been characterized. In order to develop useful safety measures for children, the biomechanical effects of maturation must be evaluated. Hence, this study examined the effects of spinal development on the compressive mechanics of the cervical spine. An animal model was used due to the lack of human tissues in the pediatric age range. Twenty-two fresh cadaveric baboon cervical spines (all male) were dissected into two functional spinal unit segments: Occiput-C2, C3-C5, C6-T1. The specimens ranged in age from 1 to 30-human equivalent years based upon radiographic assessment of their skeletal maturity. Dynamic (1.0-m/sec) haversine displacement inputs up to 70% strain were imparted on each specimen and the resulting loads were recorded. Significant increases in the compressive failure load were observed with increased maturation of the spinal tissues (ANOVA, p = 0.003). Differences were also observed between the spinal levels examined. The lower cervical spine, C6-T1, had the smallest failure load for specimens greater than 8-human-equivalent years, while the upper cervical spine was the most susceptible to injury at less than 8-human-equivalent years. The compressive failures generated are consistent with those observed clinically, consisting of primarily burst fractures and physis (growth plate) failures. These data clearly suggest that spinal compressive tolerance is directly related to maturation. Therefore, through scaling, these data may provide tolerance values applicable to anthropomorphic test dummies and computational models aimed at injury prevention for the pediatric occupant.

Journal Article↗
PubMed2005

Quality measurement of lossy compression in medical imaging.

At the time when most of image data in hospitals are stored in digital form using picture archiving and communication systems (PACS), telemedicine goes through its boom, and demand for data storage and bandwidth requirements increases, lossy compression techniques become necessity. This review article summarizes different methods for quality measurement of image compression in radiology. After brief compression techniques description, technical and medical measurements (including Receiver Operating Characteristic Curves) of image compression are described. Employing of these methods in practice and their results are shown on sample studies. The article concludes with basic recommendations for experimental protocols when performing quality measurement of medical images.

Image Processing, Computer-Assisted↗
PubMed2006

Biomechanical comparison of two different periarticular plating systems for stabilization of complex distal humerus fractures.

BACKGROUND: Complex intra-articular distal humerus fractures are relatively uncommon injuries but are fraught with poor outcomes such as malunion, elbow stiffness and deformity. Various types of internal fixation screw-plate constructs have been developed to improve fixation. Specifically, a 90 degrees offset periarticular system lowers the profile on the lateral epicondyle, yet it is unclear how this design compares to other plate constructs. This study compared the mechanical stiffness and plate surface strains between two types of constructs for stabilization of complex distal humerus fractures. METHODS: Identical bi-columnar segmental intra-articular fractures were created in ten epoxy composite left humeri. Models were randomly assigned to two groups (n=5/group) with either parallel plates or perpendicular plates. Rosette strain gages were placed at the most distal possible space on the lateral plate for both constructs. Models were mechanically tested with estimates of physiologic loads in flexion, extension, varus, valgus axial compression and axial torsion. Data for mechanical stiffness, transverse plate strain and longitudinal plate strain were compared with a one-way ANOVA (P<0.05). FINDINGS: There was no statistical difference in stiffness in any direction. The longitudinal strain for the 90 degrees construct was significantly lower in axial compression. The 180 degrees system demonstrated significantly lower transverse strains during axial torsion. INTERPRETATION: Both systems demonstrated similar mechanical stiffness theoretically providing similar fracture stabilization. Plate strain differences may affect fragment position, but it is unclear how much plate loading occurs in vivo. Surgeon experience and preference may dictate the choice of a plate construct for this fracture configuration.

Biomechanical Phenomena↗
PubMed1984

The physiology of external cardiac massage: high-impulse cardiopulmonary resuscitation.

In intact chronically instrumented dogs, left ventricular dynamics were studied during cardiopulmonary resuscitation (CPR). Electromagnetic flow probes measured cardiac output and coronary blood flow, ultrasonic transducers measured cardiac dimensions, and micromanometers measured left ventricular, right ventricular, aortic, and intrathoracic pressures. The dogs were anesthetized with morphine, intubated, and fibrillated by rapid ventricular pacing. Data were obtained during manual external massage with dogs in the lateral and supine positions. Force of compression was varied from a peak intrathoracic pressure of 10 to 30 mm Hg, and compression rate was varied from 60 to 150/min. Increasing force of compression increased stroke volume up to a peak intrathoracic pressure of approximately 20 mm Hg, beyond which stroke volume remained constant or declined. Stroke volume appeared to result primarily from direct transmission of manual compression force to the heart rather than from positive intrathoracic pressure because peak cardiac or vascular pressures or the change in these pressures were consistently two to four times greater than the corresponding intrathoracic pressures during manual compression. With increasing compression rate, stroke volume remained relatively constant, and total cardiac output increased significantly: 425 +/- 92 ml/min at 60/min, 643 +/- 130 ml/min at 100/min, and 975 +/- 219 ml/min at 150/min (p less than .05). Left ventricular dimensions decreased minimally at higher manual compression rates. In four patients undergoing CPR, systolic and diastolic arterial blood pressure increased with faster compression rates, correlating well with data obtained in the dog. Dynamic coronary blood flow in canine experiments decreased to zero or negative values during compression. Antegrade coronary flow occurred primarily during noncompression periods and seemed to be related to diastolic aortic perfusion pressure; coronary flow at a compression rate of 150/min averaged 75% of control. Therefore stroke volume and coronary blood flow in this canine preparation were maximized with manual chest compression performed with moderate force and brief duration. Increasing rate of compression increased total cardiac output while coronary blood flow was well maintained. Direct cardiac compression appeared to be the major determinant of stroke volume during manual external cardiac massage.

Animals↗
PubMed2003

A role for the interleukin-1 receptor in the pathway linking static mechanical compression to decreased proteoglycan synthesis in surface articular cartilage.

Loading of articular cartilage during weight bearing is essential for the maintenance of cartilage function. Although certain cyclic loading protocols stimulate extracellular matrix synthesis, constant or static compression decreases proteoglycan and collagen synthesis in cartilage explants. The goal of this study was to determine whether the compression-induced decrease in proteoglycan synthesis involves an interleukin-1 (IL-1) signaling pathway. Cartilage explants were compressed 50% in the presence of IL-1 receptor antagonist (IL-1ra), and the incorporation of [35S]sulfate into macromolecules was measured. IL-1ra increased sulfate incorporation in compressed cartilage but not in cartilage maintained at the in situ thickness (0% compression). IL-1alpha and IL-1beta mRNAs were detected in cartilage compressed 50% for at least 3h, while nitric oxide synthase II mRNA was only detected in cartilage compressed 50% for 6h. The data support a role for the IL-1 receptor in the pathway linking static compression to reduced proteoglycan synthesis.

Animals↗
PubMed1996

Extensible biosignal (EBS) file format: simple method for EEG data exchange.

Increasing use of computer technology in EEG research requires the creation of standardized data formats to transmit, exchange, analyze or modify mainly EEG/MEG as well as mere general polygraphic data. The extensible biosignal file format (EBS) has been designed for easy use. The concept of the EBS format is a simple structure of variable size, consisting of one fixed and two variable headers and a data section. In the variable header, any information can be stored in attributes. The data are archived in one of 3 organizational forms: channel order, temporal order, or compressed. The format supports various data types, multiple biosignals (ECG, EEG, MEG, polygraph), annotations, processing history, location diagrams (CGM), 16 hit ISO 10646 character set, random access to large amounts of data, global or private extensions, self-identification, and multiple tools for conversion, modification and visualization which are freely available in source code.

Brain↗
PubMed2001

Effects of intermittent pneumatic compression of the calf and thigh on arterial calf inflow: a study of normals, claudicants, and grafted arteriopaths.

BACKGROUND: Recent data indicate that intermittent pneumatic compression (IPC) of the foot may offer benefits in patients with intermittent claudication exceeding those of standard medications approved by the Food and Drug Administration. IPC of the foot (IPC(foot)) and calf (IPC(calf)) increases flow velocity in infrainguinal arterial bypass grafts and thus may prevent arterial thrombosis. Our aim was to evaluate the acute effects of IPC of the thigh (IPC(thigh)), IPC(calf), and IPC of the thigh and calf (IPC(calf + thigh)) in healthy controls, claudicants, and arteriopaths who have undergone infrainguinal bypass grafting for critical or subcritical limb ischemia. METHODS: Sixteen limbs of normals (group A), 17 limbs of claudicants (group B), and 16 limbs of arteriopaths (group C) who had undergone infrainguinal autologous revascularization were studied. Blood flow was measured in the limbs of normals and claudicants in the popliteal artery and in the grafts of revascularized limbs by using duplex ultrasonography. Mean velocity (mV), peak systolic velocity, end diastolic velocity (EDV), pulsatility index (PI), and volume flow (Q) were measured in the sitting position at rest and within 10 seconds from the delivery of IPC(thigh), IPC(calf), and IPC(calf + thigh), IPC was delivered at maximum inflation and deflation pressures of 120 mm Hg and 0 mm Hg, respectively; inflation and deflation times of 4 and 16 seconds, respectively; and a proximal inflate delay of 1 second (calf compression preceding that of thigh). RESULTS: In all 3 groups with all IPC modes, the Q, mV, and EDV increased while PI decreased (P <.05). IPC(thigh) was less effective than IPC(calf), but still increased Q (by 114%, 57%, and 59.8% in groups A, B, and C, respectively) and EDV, while decreasing PI in all 3 groups (P <.05). IPC(calf + thigh) was the most efficient mode, generating an increase in the median Q of 424% in controls, 229% in claudicants, and 317% in grafted arteriopaths. The addition of IPC(thigh) to IPC(calf) increased the mV and Q in group A (P < or = .044); the mV, Q, and EDV in group B (P < or = .03), and mV and PI by 24% and -27% in group C, respectively. CONCLUSIONS: IPC applied to the thigh, either alone or in combination with IPC(calf), generates native arterial and infrainguinal autologous graft flow enhancement. The paucity of conservative methods available for lower limb blood flow augmentation may allow IPC of the lower limb to emerge as a reliable, noninvasive therapeutic option, ameliorating claudication and assisting infrainguinal bypass graft flow. IPC(thigh) adds to the armamentarium of currently known IPC options (foot or calf) promoting its applicability and efficacy.

Adult↗
PubMed2005

Temperature dependence of the crystal structure and g-values of [(HC(Ph2PO)3)2Cu](ClO4)2.2H2O: influence of dynamic Jahn-Teller coupling and lattice strain interactions.

The temperature dependence of the X-ray crystal structure and powder EPR spectrum of [(HC(Ph(2)PO)(3))(2)Cu](ClO(4))(2).2H(2)O is reported, and the structure at room temperature confirms that reported previously. Below approximately 100 K, the data imply a geometry with near elongated tetragonal symmetry for the [(HC(Ph(2)PO)(3))(2)Cu](2+) complex, but on warming the two higher Cu-O bond lengths and g-values progressively converge, and by 340 K the bond lengths correspond to a compressed tetragonal geometry. The data may be interpreted satisfactorily assuming an equilibrium among the energy levels of a Cu-O(6) polyhedron subjected to Jahn-Teller vibronic coupling and a lattice strain. However, agreement with the experiment is obtained only if the orthorhombic component of the lattice strain decreases to a negligible value as the temperature approaches 340 K.

Journal Article↗
PubMed1999

Coding of sound pressure level in the barn owl's auditory nerve.

Rate-intensity functions, i.e., the relation between discharge rate and sound pressure level, were recorded from single auditory nerve fibers in the barn owl. Differences in sound pressure level between the owl's two ears are known to be an important cue in sound localization. One objective was therefore to quantify the discharge rates of auditory nerve fibers, as a basis for higher-order processing of sound pressure level. The second aim was to investigate the rate-intensity functions for cues to the underlying cochlear mechanisms, using a model developed in mammals. Rate-intensity functions at the most sensitive frequency mostly showed a well-defined breakpoint between an initial steep segment and a progressively flattening segment. This shape has, in mammals, been convincingly traced to a compressive nonlinearity in the cochlear mechanics, which in turn is a reflection of the cochlear amplifier enhancing low-level stimuli. The similarity of the rate-intensity functions of the barn owl is thus further evidence for a similar mechanism in birds. An interesting difference from mammalian data was that this compressive nonlinearity was not shared among fibers of similar characteristic frequency, suggesting a different mechanism with a more locally differentiated operation than in mammals. In all fibers, the steepest change in discharge rate with rising sound pressure level occurred within 10-20 dB of their respective thresholds. Because the range of neural thresholds at any one characteristic frequency is small in the owl, auditory nerve fibers were collectively most sensitive for changes in sound pressure level within approximately 30 dB of the best thresholds. Fibers most sensitive to high frequencies (>6-7 kHz) showed a smaller increase of rate above spontaneous discharge rate than did lower-frequency fibers.

Acoustic Stimulation↗
PubMed1990

Electrocardiographic ambulatory monitoring with a real-time analysis system.

The analysis of records collected during long-term ambulatory electrocardiographic monitoring has traditionally involved the review of massive data, either manually or with the aid of interactive scanning computers. Many factors complicate this analysis, including the use of analog tape for storage of electrocardiographic waveforms, the need to analyze 100,000 waveforms from an average 24-hour study, and the need to deal with an interface that compresses 24 hours of data into as little as 6 minutes on a screen. Today, the computer incorporated in the monitor can scrutinize each cardiac cycle in real time. The system produces a statistical report based on every heart beat and also performs data reduction and storage of electrocardiograph samples. To assess real-time analysis we examined data collected from the Circadian CircaMed ambulatory electrocardiography system. We found that it could detect and quantify simple or complex ventricular ectopic beats, brady- or tachyarrhythmic events, and ST-segment deviation. One hundred fifty patients 21 to 85 years old with symptoms or clinical finding suggestive of ischemia, cardiac arrhythmia, or conductive defects were referred to our electrocardiography laboratory for ambulatory monitoring. The results demonstrate that this system can detect the full range of cardiac disease found with the traditional method. Of the 150 patients, ambulatory electrocardiographic tests were positive in 93 (62%). In addition, we developed a methodology for lead placement when using two bipolar leads, as is typical for ambulatory electrocardiography. We present a procedure for determining the optimum lead placement that is based on the patient's history and a 12-lead electrocardiogram.

Adult↗
PubMed2000

Injurious mechanical compression of bovine articular cartilage induces chondrocyte apoptosis.

A bovine cartilage explant system was used to evaluate the effects of injurious compression on chondrocyte apoptosis and matrix biochemical and biomechanical properties within intact cartilage. Disks of newborn bovine articular cartilage were compressed in vitro to various peak stress levels and chondrocyte apoptotic cell death, tissue biomechanical properties, tissue swelling, glycosaminoglycan loss, and nitrite levels were quantified. Chondrocyte apoptosis occurred at peak stresses as low as 4.5 MPa and increased with peak stress in a dose-dependent manner. This increase in apoptosis was maximal by 24 h after the termination of the loading protocol. At high peak stresses (>20 MPa), greater than 50% of cells apoptosed. When measured in uniaxial confined compression, the equilibrium and dynamic stiffness of explants decreased with the severity of injurious load, although this trend was not significant until 24-MPa peak stress. In contrast, the equilibrium and dynamic stiffness measured in radially unconfined compression decreased significantly after injurious stresses of 12 and 7 MPa, respectively. Together, these results suggested that injurious compression caused a degradation of the collagen fibril network in the 7- to 12-MPa range. Consistent with this hypothesis, injurious compression caused a dose-dependent increase in tissue swelling, significant by 13-MPa peak stress. Glycosaminoglycans were also released from the cartilage in a dose-dependent manner, significant by 6- to 13-MPa peak stress. Nitrite levels were significantly increased above controls at 20-MPa peak stress. Together, these data suggest that injurious compression can stimulate cell death as well as a range of biomechanical and biochemical alterations to the matrix and, possibly, chondrocyte nitric oxide expression. Interestingly, chondrocyte programmed cell death appears to take place at stresses lower than those required to stimulate cartilage matrix degradation and biomechanical changes. While chondrocyte apoptosis may therefore be one of the earliest responses to tissue injury, it is currently unclear whether this initial cellular response subsequently drives cartilage matrix degradation and changes in the biomechanical properties of the tissue.

Animals↗