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PubMed1996

Mechanical principles of compressive interbody fusion.

STUDY DESIGN: A biomechanical study on cadaveric lumbar spines was performed measuring interfragmentary forces and contact areas between intercorporal bone blocks and vertebral endplates. OBJECTIVES: To show the correct application of internal fixators to achieve interfragmentary compression between bone blocks and adjacent endplates. SUMMARY OF BACKGROUND DATA: Several researchers have previously tried to compress interbody bone blocks by internal fixator systems. Knowledge of the correct way to use the internal fixator systems for this purpose has been lacking. METHODS: Ten cadaveric lumbar spines were analyzed by instrumenting each motion unit with an intercorporal bone block and a dorsal transpedicular arbeitsgemeinschaft osteosynthesefragen internal fixator. Interfragmentary load and compression surface and their distribution were measured with a capacitive measuring mat. The internal fixator was loaded in compression in two different ways to determine the optimum mode of application. RESULTS: Simple compression of an internal fixator did not achieve sufficient interfragmentary forces and compression surfaces. Usually lordotic contouring of the instrumented spinal motion unit with a decrease in interfragmentary forces and width of compression surfaces developed. Preloading the fixator in slight kyphosis and compressing it in a second step achieved significantly improved interfragmentary forces and sufficient compression surfaces. CONCLUSIONS: Preloading an internal fixator in kyphosis and secondary compression is mandatory to get sufficient interfragmentary forces and compression surfaces between interbody bone blocks and adjacent vertebral endplates. The technique described provides a compressive interbody fusion and can be performed preserving the physiological shape of the spine.

Biomechanical Phenomena↗
PubMed1997

Histologic analysis of the lumbosacral nerve roots after compression in young and aged rabbits.

STUDY DESIGN: The histologic changes in the lumbosacral nerve roots of aged rabbits because of chronic (graded) and acute compression were compared with those seen in young rabbits. OBJECTIVES: To study differences in the process of recovery from nerve compression between the aged and the young. SUMMARY OF BACKGROUND DATA: Clinical findings often differ between nerve compressive lesions in young and aged patients. Little has been reported on the pathologic basis of this difference. METHODS: Forty-five Japanese white rabbits were used. The cauda equina and spinal nerve root were compressed with a device specifically designed for this purpose. Nerve compression was applied to the dura mater and nerve roots after partial laminectomy. The specimens were sampled at 1 month or 3 months after acute or graded nerve compression. RESULTS: An increase in small myelinated fibers, consistent with the process of regeneration, was observed by light microscopy; this difference was greater in the young group than in the aged group. Reactive degenerative changes, as seen by electron microscopy, were more often observed in the aged group than in the young group. CONCLUSIONS: These findings demonstrate the suppression of regeneration and the latent fragility of the aged neural tissue. This may explain the clinical findings observed in aged patients with degenerative lumbar lesions.

Age Factors↗
PubMed1988

A physiologic comparison of external cardiac massage techniques.

On the basis of recent investigation, controversy has arisen regarding which of several cardiopulmonary resuscitation methods optimizes hemodynamics. The present study was designed to compare five recently described chest compression techniques: high-impulse manual chest compression at 150/min, mechanical compression at 60/min with simultaneous ventilation, mechanical compression at 60/min with simultaneous ventilation and either systolic or diastolic abdominal compression, and pneumatic vest compression at 60/min. Eight dogs were chronically instrumented with electromagnetic flow probes in the ascending and descending aorta while matched micromanometers measured aortic, left ventricular, and pleural pressures. At study, each dog was anesthetized with morphine, intubated, and the heart was fibrillated by rapid ventricular pacing. The five cardiopulmonary resuscitation methods were performed randomly in each preparation within 7 to 10 minutes of arrest. In four dogs, brachiocephalic blood flow was computed as total cardiac output minus descending aortic blood flow, and in all dogs coronary perfusion pressure was calculated as mean diastolic aortic pressure minus mean diastolic left ventricular pressure. Average cardiac output for seven studies was 662 +/- 61 ml/min with high-impulse manual compression, 340 +/- 46 ml/min with mechanical compression and simultaneous ventilation, 336 +/- 45 ml/min with mechanical compression and simultaneous ventilation with systolic abdominal compression, 366 +/- 52 ml/min with mechanical compression and simultaneous ventilation with diastolic abdominal compression, and 196 +/- 29 ml/min with vest resuscitation (high-impulse manual compression significantly greater than other techniques by multivariate analysis, p less than 0.05). Brachiocephalic blood flow generally followed cardiac output and was statistically the greatest with high-impulse manual compression at 273 +/- 47 ml/min (p less than 0.05). Finally, high-impulse manual compression provided the highest coronary perfusion pressure of 31 +/- 4 mm Hg (p less than 0.05) compared to 23 +/- 2 mm Hg for mechanical compression and simultaneous ventilation, 23 +/- 2 mm Hg for mechanical compression and simultaneous ventilation with systolic abdominal compression, 23 +/- 3 mm Hg for mechanical compression and simultaneous ventilation with diastolic abdominal compression, and 11 +/- 2 mm Hg for vest resuscitation. These data demonstrate that high-impulse manual compression generated physiologically and statistically superior hemodynamics when compared with other methods in this model of cardiopulmonary resuscitation.

Animals↗
PubMed2005

Percutaneous balloon compression for the treatment of trigeminal neuralgia: results in 56 patients based on balloon compression pressure monitoring.

OBJECT: Percutaneous balloon compression is an effective and technically simple method for treating trigeminal neuralgia (TN). Nevertheless, dysesthesias (10-20%) and masseter muscle weakness (66%) following the procedure have been noted. The purpose of this study was to evaluate the results of testing TN with percutaneous balloon compression aided by intraluminal pressure monitoring. METHODS: In this study the authors review the results and complications associated with percutaneous balloon compression by using intraluminal pressure monitoring data obtained in 65 procedures performed in 56 consecutive patients over 4 years. The mean patient age was 71 years (range 37-92 years), and the mean follow-up duration was 17 months (range 3-38 months). The mean intraluminal compression pressure was (1160 +/- 62 mm Hg), and the mean duration of compression was 1.15 +/- 0.27 minutes. The trigeminal depressor response was observed in 60 (92%) of 65 procedures, and initial pain relief occurred in 92% of patients. The recurrence rate in patients who had initial relief was 16% (nine of 56). The mean time until recurrence in patients who experienced pain relief after surgery was 13 months (range 3-23 months). Mild numbness immediately after surgery was observed in 83% of patients. At the most recent evaluation, 17% of patients reported persistent, nontroublesome numbness and none had moderate or severe numbness. Minor dysesthesia was present in two patients (4%). Mild masseter muscle weakness occurred in 24% of patients and resolved within a maximum period of 1 year. No patient experienced anesthesia dolorosa, corneal keratitis, or other cranial nerve deficits. These morbidity rates are lower than the incidence reported in the literature when pressure monitoring is not used. CONCLUSIONS: These data show that by monitoring compression pressure and limiting the duration of compression, it is possible to reduce the incidence of dysesthesias, severe numbness, and masseter weakness after surgery without increasing the rate of recurrent pain in patients with classic TN.

Adult↗
PubMed1999

Medical image compression based on a morphological representation of wavelet coefficients.

Image compression is fundamental to the efficient and cost-effective use of digital medical imaging technology and applications. Wavelet transform techniques currently provide the most promising approach to high-quality image compression which is essential for diagnostic medical applications. A novel approach to image compression based on the wavelet decomposition has been developed which utilizes the shape or morphology of wavelet transform coefficients in the wavelet domain to isolate and retain significant coefficients corresponding to image structure and features. The remaining coefficients are further compressed using a combination of run-length and Huffman coding. The technique has been implemented and applied to full 16 bit medical image data for a range of compression ratios. Objective peak signal-to-noise ratio performance of the compression technique was analyzed. Results indicate that good reconstructed image quality can be achieved at compression ratios of up to 15:1 for the image types studied. This technique represents an effective approach to the compression of diagnostic medical images and is worthy of further, more thorough, evaluation of diagnostic quality and accuracy in a clinical setting.

Algorithms↗
PubMed1995

A compression mechanism for sequence databases to improve the efficiency of conventional tools.

This paper describes a method to compress molecular biology databases that are characterized by an increasing proportion of data derived from genome projects. The performance of our tool has been tested on various data files of the EMBL nucleotide sequence database. The best compression ratios were achieved on EST (Expressed Sequence Tags) data, typically derived from large-scale sequence projects. The compression of sequence database updates was tested in combination with the common Unix compression program 'compress'. Our tool improved the efficiency of 'compress' on average by 16%.

Base Sequence↗
PubMed2004

Dual domain watermarking for authentication and compression of cultural heritage images.

This paper proposes an approach for the combined image authentication and compression of color images by making use of a digital watermarking and data hiding framework. The digital watermark is comprised of two components: a soft-authenticator watermark for authentication and tamper assessment of the given image, and a chrominance watermark employed to improve the efficiency of compression. The multipurpose watermark is designed by exploiting the orthogonality of various domains used for authentication, color decomposition and watermark insertion. The approach is implemented as a DCT-DWT dual domain algorithm and is applied for the protection and compression of cultural heritage imagery. Analysis is provided to characterize the behavior of the scheme under ideal conditions. Simulations and comparisons of the proposed approach with state-of-the-art existing work demonstrate the potential of the overall scheme.

Algorithms↗
PubMed2005

Storage and transmission of microarray images.

With the recent explosion of interest in microarray technology, massive amounts of microarray images are currently being produced. The storage and transmission of these types of data are becoming increasingly challenging. This article reviews the latest technologies that allow for the compression and storage of microarray images in dedicated database systems.

Data Compression↗
PubMed2006

Electromyographic analysis of physical examination tests for type II superior labrum anterior-posterior lesions.

Physical examination tests that place tension on the long head of the biceps may best reproduce symptoms in patients with type II superior labrum anterior-posterior (SLAP) lesions. The objective of this study is to compare the normalized electromyographic signal of the long head of the biceps for SLAP lesion physical examination tests. The active compression test, anterior-superior SLAP test, biceps load test II, biceps tension test, and pain provocation test were performed on 13 subjects while biceps electromyographic data were recorded. The active compression test and biceps tension test had significantly higher electromyographic signals than the other tests. We found no significant differences when comparing forearm supination and pronation within individual tests. Because the active compression and biceps tension tests maximize muscle activation on the long head of the biceps, they may be the best physical examination tests by which to identify type II SLAP lesions.

Adult↗
PubMed2002

Structural Response of Lower Leg Muscles in Compression: A Low Impact Energy Study Employing Volunteers, Cadavers and the Hybrid III.

Little has been reported in the literature on the compressive properties of muscle. These data are needed for the development of finite element models that address impact of the muscles, especially in the study of pedestrian impact. Tests were conducted to characterize the compressive response of muscle. Volunteers, cadaveric specimens and a Hybrid III dummy were impacted in the posterior and lateral aspect of the lower leg using a free flying pendulum. Volunteer muscles were tested while tensed and relaxed. The effects of muscle tension were found to influence results, especially in posterior leg impacts. Cadaveric response was found to be similar to that of the relaxed volunteer. The resulting data can be used to identify a material law using an inverse method.

Journal Article↗
PubMed2000

Analysis of the compression mechanics of pharmaceutical agglomerates of different porosity and composition using the Adams and Kawakita equations.

PURPOSE: To analyze the mechanics of some pharmaceutical agglomerates during uniaxial confined compression by using compression parameters derived from the Heckel, Kawakita and Adams equations, and to study the influence of these compression parameters on the tablet-forming ability of agglomerates. METHODS: Force and displacement data sampled during in-die compression of agglomerates was used to calculate compression parameters according to the Heckel (sigmay), Kawakita (1/b and a), and Adams (tau0') equations. Mechanical strength of single agglomerates as well as the air permeability and tensile strength of tablets prepared from them were also determined. RESULTS: Sigmay- from the Heckel equation did not differ between agglomerates of different porosity. Both 1/b and tau0' varied with agglomerate porosity and composition. These two compression parameters were linearly related to each other. No general correlation was found between 1/b and tau0' and the strength of single agglomerates. The two parameters were related to the intergranular pore structure and tensile strength of tablets formed from the agglomerates. CONCLUSIONS: 1/b and tau0' may be interpreted as measures of the agglomerate shear strength during uniaxial confined compression, and as such they may be used as indicators of the tabletting performance of the agglomerates.

Algorithms↗
PubMed1986

External pneumatic calf compression reduces deep venous thrombosis in patients with ruptured intracranial aneurysms.

We evaluated the ability of intermittent external pneumatic calf compression to prevent deep venous thrombosis after subarachnoid hemorrhage from ruptured intracranial aneurysms. Fifty-six subarachnoid hemorrhage patients not given external pneumatic calf compression were compared with 90 patients who had calf compression after their subarachnoid hemorrhages. Both groups of patients were on strict bedrest for 7 to 21 days after aneurysm rupture, and both received epsilon-aminocaproic acid, 30 to 36 g/day intravenously, until operation. The risk factors in the two groups were similar, and the nursing and medical care did not seem to differ. Of patients without external pneumatic compression, 18% had venographically proven deep venous thrombi, which contrasts with 6% of patients receiving calf compression. This was a significant difference (P less than 0.05; chi 2). These retrospective data suggest that external pneumatic calf compression helps to prevent deep venous thrombosis in patients with subarachnoid hemorrhage when delayed operation, bedrest, and antifibrinolytic agents are used.

Adult↗
PubMed2004

Elimination of the friction effects in unconfined compression tests of biomaterials and soft tissues.

The mechanical properties of biomaterials and soft tissues are determined conventionally using unconfined compression tests. In such tests, frictionless specimen/platen contact in unconfined compression tests has to be assumed in determining the material properties of the materials. Previous theoretical analysis demonstrated, however, that the effects of the friction at the specimen/platen contact interface on the measured stress responses are non-negligible. In this study, a computational approach was proposed to eliminate the effects of friction. The friction coefficient between the specimen and the compression platens is measured first. Using a finite element model, the stress-strain relationship, without the influence of the friction effects, can be derived from the experimental data obtained in conventional unconfined compression tests. In order to validate the proposed approach, unconfined compressive tests of rubber have been performed.

Algorithms↗
PubMed2006

Local fluorouracil chemotherapy interferes with neural and behavioral recovery after brain tumor-like mass compression.

In this study, we investigated the impact of intracerebral delivery of chemotherapy on functional recovery from focal cortical tissue displacement, characteristic of brain tumors. Unilateral focal brain compression was induced by epidural implantation of an inverted hemisphere-shaped bead over the sensorimotor cortex. Microinjections of a total of 1mg chemoagent fluorouracil or the same volume of saline were made into the compressed cortex. Behavioral tests of forelimb sensorimotor function were conducted during 4 weeks' observation. Rats subjected to any of the three types of lesions, saline microinjection plus cortical compression, chemoagent microinjection alone, or chemoagent microinjection combined with cortical compression, demonstrated significant behavioral deficits in several sensorimotor tasks, compared with saline-microinjected control animals. In placing tests, behavioral deficits elicited by each single treatment were worsened by combined treatment with chemoagent microinjection and focal cortical compression. Concurrently, local delivery of chemoagent into the compressed cortex induced increased cortical tissue loss, necrosis and apoptosis. These data indicate that local chemotherapy exacerbates compression-induced neurological impairment, and a model of controlled focal cortical compression may provide a valuable means to improve anti-cancer therapeutic designs with reduced deterioration of brain function.

Animals↗
PubMed1999

Influence of automatic gain control parameter settings on speech understanding of cochlear implant users employing the continuous interleaved sampling strategy.

OBJECTIVE: The purpose of the present study was to gather data on the influence of compression ratio and attack and release times of slow-acting front-end automatic gain control (AGC) systems on speech understanding of cochlear implant users in various listening situations. The data should allow evaluation of the usefulness of front-end AGC in body-worn speech processors. DESIGN: Subjects were 12 experienced postlingually deafened adult users of the Med-El Combi-40 multichannel cochlear implant. Six different front-end configurations, including a linear setting, the standard AGC of the Med-El Combi-40 processor, and four slow-acting dual front-end AGCs (use of two instead of one level detector for improved transient handling), were evaluated in two experiments. In experiment 1, tests were performed at 55, 70 and 85 dB SPL, roughly corresponding to soft, medium and loud speech. Experiment 2 was intended to evaluate the quality of transient handling of the six configurations. In this experiment an intense transient ("chink") at 100 dB SPL was spliced onto the beginning of each sentence (presented at 85 dB SPL). RESULTS: At 55 dB SPL subjects performed significantly more poorly with the linear setting than with the AGC settings, but no differences in performance could be found for the AGC settings. At 70 dB SPL subjects showed the poorest performance with the high compression ratio dual front-end AGCs. No differences in performance of the six front-end configurations were found at 85 dB SPL. In the presence of intense chinks, performance of the standard AGC dropped significantly. CONCLUSIONS: The results indicate that slow-acting front-end AGC can be used effectively in speech processors for cochlear implants to expand the range of input levels that are audible for the cochlear implant user, without any need to adjust a processor control, and that incorporation of an additional fast-acting AGC component can improve performance under conditions where intense transients occur.

Adult↗
PubMed2005

A comparison of CPR delivery with various compression-to-ventilation ratios during two-rescuer CPR.

BACKGROUND: The number of chest compressions required for optimal generation of coronary perfusion pressure remains unknown although studies examining compression-to-ventilation ratios higher than 15:2 (C:V) in animals have reported higher C:V to be superior for return of spontaneous circulation and neurologic outcome. We examined human performance of two-rescuer CPR using various C:V. METHODS: Thirty six EMT-Basic students in their final week of training performed two-rescuer CPR using C:V of 15:2, 30:2, 40:2, 50:2, and 60:2 on a recording resuscitation manikin. Compression and ventilation variables were recorded by computer while the number of pauses for ventilations and the hands-off time (time not spent performing chest compressions) were abstracted by hand. Data were analyzed by ANOVA and significant differences from the standard treatment of C:V = 15:2 were assessed by Tukey's HSD post hoc test. FINDINGS: The number of compressions delivered per minute increased with increasing C:V while the hands-off time and pauses for ventilations decreased. All comparisons were significantly different from C:V = 15:2 (P < 0.001). The ventilation numbers decreased with increasing C:V although mean minute volume exceeded 1l for all C:V. INTERPRETATION: A 15:2 compression-to-ventilation ratio when performed during two-rescuer CPR results in 26s of hands off time each minute while only delivering 60 compressions. Alternative C:V ratios of 30:2, 40:2, 50:2, and 60:2 all exceed the AHA recommended 80 compressions/min while still delivering a minute volume in excess of 1l.

Cardiopulmonary Resuscitation↗
PubMed1996

Finite element modeling of the C4-C6 cervical spine unit.

This study was conducted to develop a detailed, three-dimensional, anatomically accurate finite element model of the human cervical spine structure using close-up computed tomography scans and to validate against experimental data. The finite element model of the three vertebra segment C4-C6 unit consisted of 9178 solid elements and 1193 thin shell elements. The force-displacement response under axial compression correlated well with experimental data. Because of the inclusion of three levels in the spinal structure, it was possible to determine the internal mechanics of the various components at each level. The applicability of the model was illustrated by adopting appropriate material properties from literature. Results indicated that, the stresses in the anterior column were higher compared to the posterior column at the inferior level, while the opposite was found to be true at the superior level. The superior and inferior endplate stresses were higher in the middle vertebral body compared to the adjacent vertebrae. In addition, the stresses in the cancellous core of the middle, unconstrained vertebral body were higher. The present three-dimensional finite element model offers an additional facet to a better understanding of the biomechanics of the human cervical spine.

Adult↗