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At least 955 records · Page 53Linked to original sources

PubMed1989

[A method for evaluation of compressive ability in mastication by chewing gum containing polycarbonate microcapsules].

Evaluating masticatory ability is a fundamental subject in dentistry. However there is no sufficient clinical method for it. The purpose of this study was to evaluate compressive ability in mastication from compressive energy in mastication. To measure compressive energy from compressive transformation of a material before crushing, a new artificial material, CHEWING GUM CONTAINING POLYCARBONATE MICROCAPSULES, was originated. And by the material, a method for evaluation of compressive ability was made. The method was tested on 11 persons in the twenties (6 males, 5 females). The results were as follows: 1) The coefficient of variations of values that were measured 5 times on one male subject was 4.24%. 2) The distribution of values that were measured on 11 subjects ranged widely. The ratio of the minimum value to the maximum value on 9 adults of normal occlusion was 1 : 3.0. Compressive energy and occlusal contact area in mastication were calculated from these values. The results show that the method for evaluation of compressive ability is one of the new clinical methods for evaluation of masticatory function.

Adult↗

PubMed1999

[Value of compression therapy in treatment of deep venous thrombosis].

Therapy in the acute phase of deep vein thrombosis aims to prevent the longitudinal growth of the thrombus as well as the life-threatening complication of pulmonary embolism. Compression therapy is part of all revascularisative and conservative treatment strategies, but hardly mentioned in most of the literature. Clinical efficacy of a sufficient compression therapy in patients with acute deep vein thrombosis is marked by a quick ease of subjective complaints as well as a reduction of the edema. The long-term risk of deep vein thrombosis, the postthrombotic syndrome, is avoidable by the use of compression therapy. Clinical studies about the effectiveness in relation to the length of the thrombus and the incidence of pulmonary embolism are missing as well as studies about the selection of the best compression material. Recently compression pressures were experimentally measured between long and short stretch bandages and the skin in order to select bandage material. It can be concluded that long stretch bandages can be used in the treatment of acute phlebothrombosis in mobile out-patients. Short stretch bandages should be used in immobile patients in order to avoid high pressures between the skin and the bandages. Compression stockings (Class III) represent an equivalent alternative to compression bandages after the resolution of edema.

Acute Disease↗

PubMed1999

[Hard-copy (film) versus soft-copy (CRT) reading performance between compressed and uncompressed images: SOLs in abdominal CT images].

The objective of this study was to examine the feasibility of soft-copy (CRT) reading and suitable compression. Forty abdominal CT images with a space-occupying lesion (SOL) in liver and 40 normal images were selected for receiver-operating-curve (ROC) analysis. Each image was compressed by JPEG extended mode into 1/10 its original capacity, and then an expanded image was printed on film. Ten radiologists evaluated the presence of liver SOLs (primary and secondary tumors) on soft-copy (CRT) and hard-copy (film) images. Each radiologist reviewed four types of images (original and compressed hard-copy and original and compressed soft-copy images). Values of the area under the curve in the various ROC analyses were 0.858 (FILM) and 0.842 (CRT) for original images and 0.879 (FILM) and 0.846 (CRT) for compressed images. The results of ROC analysis showed better reading performance with hard-copy than soft-copy images, but the difference was not statistically significant. Compressed images showed a higher value (0.879) than original images (0.858), a difference that was statistically significant (p < 0.029) by the paired t-test but not by the jackknife method. The results indicate that soft-copy reading is a clinically acceptable alternative to hard-copy reading. We have had no difficulty in reading abdominal CT images compressed to 1/10 of the original size by the JPEG method. This study was supported in part by a grant from the Japanese Ministry of Health and Welfare.

Humans↗

PubMedDate not supplied

Acoustic analysis of speech through a hearing aid: consonant-vowel ratio effects with two-channel compression amplification.

In this study, the consonant-vowel ratio (CVR) changes associated with varying the compression ratio and crossover frequency of two-channel syllabic compression amplification were examined. Consonant-vowel syllables were recorded at 60 and 75 dB SPL input levels to the hearing aid under 13 different amplification conditions: 12 compression conditions and a condition that used linear amplification in both channels. Syllables consisted of voiceless stops, fricatives, and affricates combined with the vowels /a/, /i/, and /u/. Acoustic analysis of the processed syllables indicated that the CVR was generally increased with compression, compared to linear amplification, and that the effects were greatest for amplification with compression in the high-frequency channel. In addition, higher CVRs were obtained when the crossover frequency was raised. Compression in the low-frequency channel had the least effect on CVR. As previous research has indicated that CVR may serve as a cue to the perception of some consonant sounds by people with hearing impairment, the results suggest the need for caution with the application of high-frequency channel compression until the perceptual effects are fully investigated.

Hearing Aids↗

PubMed2000

[Compression therapy in deep venous thrombosis].

External compression, both intermittent by pneumatic pumps and continuous by anelastic or elastic bandages and by graduate compression stockings, play a pivotal role in prophylaxis of Deep Venous Thrombosis (DVT). The use of external compression in DVT therapy and in prophylaxis of pulmonary embolism (PE) and of post-thrombotic syndrome has not been validated as well as in DVT prophylaxis. The pathophysiologic properties of the external compression and the most recent evidences about the early mobilization of the patients with DVT and about Low Molecular Weight Heparin (LMWH) therapy suggest the advantages of the external compression. The authors review the most important clinical investigations about early use of external compression in DVT joined with pharmacological therapy: the results have been the reduction of the growth of the thrombus, the reduction of PE ratio, the prevention of the post-thrombotic syndrome, the indirect improvement of the quality of life. Finally the authors confirm the recommendations about the use of physical therapy with early mobilization and external compression joined with LMWH anticoagulation in DVT.

Anticoagulants↗

PubMed2001

Tracheobronchial compression of vascular origin. Review of experience in infants and children.

BACKGROUND: Tracheobronchial compression of vascular origin is an uncommon but important cause of respiratory distress in infants and children. We reviewed our surgical experience with 31 children, presenting vascular tracheobronchial compression. METHODS: Thirty-one children, with a median age of seven months, were operated on for airway and/or oesophageal compression secondary to vascular anomalies. Diagnostic findings, mainly established by bronchoscopy and angiography, revealed several pathologic disorders such as right aortic arch with aortic diverticulum in 10, double aortic arch in five, innominate artery compression in six, arteria lusoria in four, and pulmonary artery sling in one patient. Five children developed tracheobronchial compression after previous repair of a complex congenital heart disease. Clinical symptoms on admission were dominantly stridor, recurrent airway infection, dyspnea, respiratory distress and upper digestive complaints such as dysphagia and gastroesophageal reflux. RESULTS: Surgical relief was successful in 30 patients. Only one child with palliated tetralogy of Fallot and pulmonary artery sling died because of intractable extensive tracheobronchial stenosis. Late follow-up over three to 90 months showed a symptom-free evolution in most patients, including one reoperation for recurrent compression and one late death. CONCLUSIONS: Tracheobronchial compression by vascular structures in childhood is uncommon and may be masked by nonspecific respiratory symptoms, resulting in an often delayed diagnosis. Once imaging studies have clearly delineated the causal pathologic vascular structures, surgical correction is often straightforward and effective, in spite of the common presence of tracheobronchial malacia.

Airway Obstruction↗

PubMedDate not supplied

Evaluation of compressed lung CT image quality using quantitative analysis.

The goals of this study were (1) to evaluate the quality of compressed lung CT images obtained using high resolution CT (HRCT: 2 mm slice thickness) for degree of compression and conventional CT (10 mm slice thickness) images by using physical and subjective evaluations, and (2) to analyze the distortion of density distribution on lung CT images using histogram analysis for each compression ratio. The coding method was performed according to the Joint Photographic Experts Group (JPEG). We physically evaluated the quality of compressed lung CT images using the peak signal-to-noise ratio (PSNR) as given by the square root of the ratio of the peak value of the gray level squared to the mean square error (dB) and subjectively evaluated the CT images using the mean opinion score (MOS). The acceptable compression ratio for diagnosis was about 1:6 to 1:7 for conventional CT images and about 1:4 to 1:5 for HRCT images as determined by MOS. The PSNR corresponding to acceptable compression ratios was about 50 dB. The difference in density distribution between HRCT and conventional CT was statistically significant (Friedman test: p<0.02) in histogram analysis. Results suggested that, in comparison with conventional CT, a high compression ratio was not suitable for HRCT.

Algorithms↗

PubMed2001

[Experimental study of compression by Herbert screw in carpal scaphoid fracture].

PURPOSE OF THE STUDY: The purpose of this experimental work was to obtain a radiographical assessment of the effect of the compression achieved with the Herbert screw due to its different thread diameters by comparing the real and expected reduction of interfragment gap (IFG) on cadaver bones. To better understand and define the limits of this "self-compressing" effect and to study the usefulness of screw sizes smaller than the scaphoid, we measured the maximal and mean reduction of IFG without using the instrumentation. MATERIAL AND METHODS: Twelve scaphoids were obtained from fresh cadavers. The scaphoid holes were drilled and tapped in the largest axis of the scaphoid, in a central position parallel to an anti-rotation wire. A transverse osteotomy was made in the mid third of the scaphoid to simulate a Schernberg grade III fracture. The real IFG reduction was defined as the difference between the gap measured before and after screwing. The expected IFG reduction was defined by multiplying the number of screw turns by the pitch height per turn. RESULTS: On the reduction average, a Herbert screw produced a 1.1 mm IFG reduction. The maximal reduction IFG measured was 1.5 mm. For 7 cases, the real IFG reduction was larger than expected, for 4 cases it was smaller than expected and for 1 case the difference was considered negligible. The Fisher test did not demonstrate any significant statistical difference between the real and expected IFG reduction for all scaphoids. The operator perceived a subjective sensation of compression after one screw turn that continued up through the last turn. DISCUSSION: The Herbert screw develops maximal compression force when all the screw threads are totally anchored in the bone. The interfragment gap closes linearly, bringing the two bone fragments together. However, failure can result if the gap is too wide (>2 mm), the screw is poorly positioned, or there is an inappropriate correspondence between screw length and diameter and scaphoid size. Unlike spongy bone screws, the Herbert screw has a round non-conical tip thread and a shallow thread that do not bring the bone fragments together. The perception of compression corresponds to the passage of the screw through the spongy bone and not to real narrowing of the gap between the fragments. In clinical practice, because of the use of instrumentation for open surgery in carpal scaphoid fracture, it is not necessary to rely on these data, but they can be useful for percutaneous screw insertion without a guidewire and without prior compression or for another localization. Peroperative radiographs should be obtained to assess the quality of the screw position and check reduction and the reality of the compression.

Aged↗

PubMed2003

The role of tenascin-C in adaptation of tendons to compressive loading.

Although most tendon regions are subjected primarily to high tensile loads, selected regions, primarily those that directly contact bones that change the direction of the tendon, must withstand high compressive loads as well. Compressed tendon regions differ from regions subjected to primarily tensile loads: they have a fibrocartilaginous structure with spherical cells surrounded by a matrix containing aggrecan and collagen types I and II, in contrast regions not exposed to compression have a fibrous structure with spindle shaped fibroblasts surrounded by a matrix of dense, longitudinally oriented type I collagen fibrils. The spherical shape of cells in fibrocartilagenous regions indicates these cells are more loosely attached to the matrix than their spindle-shaped counterparts in fibrous regions, a feature that may help to minimize cell deformation during tendon compression. We hypothesized that expression of tenascin-C, an anti-adhesive protein, is part of the adaptation of tendon cells to compression that helps establish and maintain fibrocartilaginous regions. To test this hypothesis we compared tenascin-C content and expression in compressed (distal) versus uncompressed (proximal) segments of bovine flexor tendons. Immunohistochemistry and immunoblot analyses showed that tenascin-C content was increased in the distal tendon where it co-distributed with type II collagen and aggrecan. Tendon cells from the distal segments expressed more tenascin-C than did cells from the proximal segments for up to four days in cell culture, indicating that increased tenascin-C expression is a relatively stable feature of the distal cells. These observations support the hypothesis that tenascin-C expression is a cellular adaptation to compression that helps establish and maintain fibrocartilagenous regions of tendons.

Adaptation, Physiological↗

PubMed2002

[Statistical study of the wavelet-based lossy medical image compression technique].

Medical digital images have informational redundancy. Both the amount of memory for image storage and their transmission time could be reduced if image compression techniques are applied. The techniques are divided into two groups: lossless (compression ratio does not exceed 3 times) and lossy ones. Compression ratio of lossy techniques depends on visibility of distortions. It is a variable parameter and it can exceed 20 times. A compression study was performed to evaluate the compression schemes, which were based on the wavelet transform. The goal was to develop a set of recommendations for an acceptable compression ratio for different medical image modalities: ultrasound cardiac images and X-ray angiographic images. The acceptable image quality after compression was evaluated by physicians. Statistical analysis of the evaluation results was used to form a set of recommendations.

Angiography↗

PubMed1992

[Changes in retinal blood flow volume in experimental retinal vein compression].

The authors quantitated the retinal blood flow volume during and immediately after experimental compression of the temporal retinal vein in 5 Macaca fuscata monkey eyes. The hydrogen clearance method was used to quantitate the retinal blood flow volume. After placing a microelectrode on the retinal surface, we measured the blood flow volume 4 times at a 15-minute interval. This value served as a baseline for the experiments. Next we compressed the temporal retinal vein near the disc with a 25-gauge needle with a rounded tip under guidance by an indirect ophthalmoscope. We measured the blood flow volume during compression. The compression was maintained for 3 minutes. Further blood flow determination was performed 7 minutes after release of compression and was repeated 4 times at a 15-minute interval. During compression of the temporal retinal vein, the retinal blood flow volume in the area served by the vein decreased by an average of 35%. The flow volume recovered rapidly and remained stable after release of compression. There was no reactive hyperemia. This model appears useful to elucidate the retinal circulation of branch retinal vein occlusion.

Animals↗

PubMedDate not supplied

Characteristics of nerve root compression caused by degenerative lumbar spinal stenosis with scoliosis.

BACKGROUND CONTEXT: In degenerative lumbar spinal stenosis with scoliosis (DLS), many authors stated that nerve root compression is almost always seen on the concave side of the scoliosis, and L4 and L5 nerve roots are the most often involved. However, there are few reports on the relationship between nerve root compression and the pattern of scoliosis. PURPOSE: To investigate the factors that may contribute to radiculopathy in DLS and their association with the pattern of the scoliosis. STUDY DESIGN: Retrospective analysis. METHODS: Twenty-two consecutive patients with DLS with radiculopathy were examined. The symptomatic nerve roots were determined by pain distribution, neurological findings and nerve root infiltration using lidocaine. The compressive factors were diagnosed by magnetic resonance imaging or myelography, discography, computed tomography after myelography or discography and radiculography. The pattern of scoliosis was determined in plain radiographs. We evaluated the correlation between the affected nerve root and the compressive factors or the pattern of the scoliosis. RESULTS: The L3 root was affected in 23% of patients; L4 root in 68%, L5 root in 55% and S1 root in 18%. L3 and L4 roots were more compressed by foraminal or extraforaminal stenosis on the concave side of the curve, whereas L5 and S1 roots were commonly affected by lateral recess stenosis on the convex side. The Cobb angle and the lateral slip of the cases in which L3 or L4 root was affected were significantly larger than in cases in which L5 or S1 root was compressed. CONCLUSIONS: In the treatment of radiculopathy caused by DLS, it is important to bear in mind that L3 or L4 roots were more strongly compressed by foraminal or extraforaminal stenosis at the concave side of the curve, whereas L5 or S1 nerve roots were affected more by lateral recess stenosis at the convex side of the curve.

Aged↗

PubMed2003

Efficacy of Class 1 elastic compression stockings in the early stages of chronic venous disease. A comparative study.

AIM: The aim of this study was to compare the efficacy of Class 1 (10-15 mmHg at the ankle) compression stockings with that of reference stockings of identical appearance during the early stages of chronic venous disease (CVD). METHODS: A prospective multi-center randomized double blind crossover study was conducted on 2 groups of female patients presenting with CVD with a CEAP classification of C1-3SEp As1-5. The efficacy of Class 1 compression stockings was evaluated with respect to global painful discomfort (visual analog scale), each symptom of CVD, the daily behavior of the patient, changes in the volume of the legs, and the functioning of the venous pump (D-PPG). The compliance level of each patient was measured by the number of days that she wore the stockings for at least 6 hours, and tolerance was measured by the reporting of ensuing undesirable events. RESULTS: A total of 125 patients were included in the study and were analyzed for intent to treat. Highly significant differences favoring Class 1 compression stockings were noted with respect to both global painful discomfort and each symptom of CVD with the exception of paresthesia. The relief of symptoms that resulted from the use of the Class 1 compression stockings was twice that which resulted from the use of the reference stockings. Differences that favored the Class 1 compression stockings were also observed with respect to 2 quality-of-life factors (mood and daily work activity). Good compliance in the use of the stockings was reported for 95% of the patients, and tolerance was higher for the Class 1 compression stockings group than for the reference group. CONCLUSION: The regular wearing of Class 1 graduated elastic compression stockings during a 15-day period results in a significant improvement in the symptomatology of early-stage chronic venous disease, i.e., in the relief of global painful discomfort as well as in quality-of-life criteria. A high level of patient compliance in the wearing of the stockings was achieved in this study.

Adolescent↗

PubMed2005

A web service-based Grid portal for Edgebreaker compression.

BACKGROUND: In health applications, and elsewhere, 3D data sets are increasingly accessed through the Internet. To reduce the transfer time while maintaining an unaltered 3D model, adequate compression and decompression techniques are needed. Recently, Grid technologies have been integrated with Web Services technologies to provide a framework for interoperable application-to-application interaction. OBJECTIVES: The paper describes an implementation of the Edgebreaker compression technique exploiting web services technology and presents a novel approach for using such services in a Grid Portal. The Grid portal, developed at the CACT/ISUFI of the University of Lecce, allows the processing and delivery of biomedical images (CT--computerized tomography--and MRI--magnetic resonance images) in a distributed environment, using the power and security of computational Grids. METHODS: The Edgebreaker Compression Web Service has been deployed on a Grid portal and allows compressing and decompressing 3D data sets using the Globus toolkit GSI (Globus Security Infrastructure) protocol. Moreover, the classical algorithm has been modified extending the compression to files containing more than one object. RESULTS AND CONCLUSIONS: An implementation of the Edgebreaker compression technique and related experimental results are presented. A novel approach for using the compression web service in a Grid portal allowing storing and preprocessing of huge 3D data sets, and subsequent efficient transmission of results for remote visualization is also described.

Algorithms↗

PubMed2005

[Use of compressed images for medical checkups: comparison between radiologists' subjective quality assessment and diagnostic usefulness].

With the increasing demand on picture archiving and communication systems (PACS) to handle larger numbers of images, much research has been conducted on the utilization of lossy compression for efficient communication and storage in PACS systems. The receiver operating characteristics (ROC) method is commonly used to determine the appropriate compression ratio of lossy images. However, conducting an ROC experiment is impractical at actual medical facilities because it is difficult to prepare and interpret images with different compression ratios for each modality, body part, and acquisition method. On the other hand, experienced radiologists have the ability to subjectively assess the level of image quality required for interpretatior and quantitative analysis. Therefore, by simply viewing images, they are able to determine the appropriate criteria for image quality and derive a practical compression ratio for each application. The present study focused on lossy compression as employed in teleradiology systems for medical checkups. Experiments comparing radiologists' subjective assessment of compressed images against the diagnostic results obtained using these images were conducted in order to investigate appropriate compression ratios and efficient methods for determining them.

Endoscopy↗

PubMed1991

[Experimental study on brain damage by extracerebral compression; alteration of cerebral circulation and microvascular architectures].

Effects of extracerebral compression on cerebral circulation and microvascular architectures were investigated in 23 adult cats. Brain compression was produced by inserting 12 steel balls (5 mm in diameter) into the extradural space through a burr hole at the left temporal bone. One ball was inserted every 10 minutes. Mean arterial blood pressure (MABP), intracranial pressure (ICP) and cerebral blood flow (CBF) were measured continuously. Cerebral perfusion pressure (CPP) and cerebrovascular resistance (CVR) were then calculated. Microvascular architectures of the brain were studied by scanning electron microscopy (SEM) with cerebrovascular casting methods. CBF decreased significantly on the compressed side though CPP remained unchanged till 5 balls had been inserted. CVR increased correlatively to the numbers of balls on the compressed side while remaining unchanged during insertion of the balls on the contralateral side. In SEM study, flection and interruption of capillaries and compressed phenomenon of veins were most remarkable on the compressed side. Alterations of microvascular architectures correspond to cortical deformity in degree. These data show that increase of CVR correlating to alteration of microvascular architectures plays an important role in decrease of CBF in a compressed brain. It is thus suggested that intracranial mass lesion causing deformity of the brain must be removed in order to avoid further brain tissue damage due to microvascular lesions.

Animals↗

PubMed1990

Sequential gradient pneumatic compression enhances venous ulcer healing: a randomized trial.

The treatment of venous ulcers has remained largely unchanged for centuries. The application of properly applied graduated compression bandages, the use of graduated compression stockings, and surgery have been shown to achieve healing. However, some ulcers persist despite appropriate management. A randomized study was undertaken to compare two regimens of treatment for such patients. Both regimens included ulcer debridement, cleaning, nonadherent dressing, and graduated compression stockings. In one regimen, sequential gradient intermittent pneumatic compression was applied for 4 hours each day. Only one of 24 patients in the control group had complete healing of all ulcers compared with 10 of 21 patients healed in the intermittent pneumatic compression group. The median rate of ulcer healing in the control group was 2.1% area per week compared to 19.8% area per week in the intermittent pneumatic compression group. The results indicate that sequential gradient intermittent pneumatic compression is beneficial in the treatment of venous ulcers.

Adult↗

PubMed1990

Axillary artery compression and thrombosis in throwing athletes.

A 28-year-old major league baseball pitcher sustained an axillary artery thrombosis which was successfully treated with intraarterial urokinase. Subsequent angiography and duplex scanning with the arm elevated in the pitching position demonstrated inducible compression of the axillary artery by the humeral head as well as compression at the thoracic outlet. To determine the incidence of axillary and subclavian artery compression and to investigate the mechanism of injury, brachial artery blood pressures and duplex scans of the subclavian and axillary arteries were performed in both the neutral position and the throwing position in the 92 extremities of 19 major league baseball pitchers, 16 non-pitching major league players, and 11 nonathlete controls. A drop in blood pressure of greater than 20 mm Hg was noted in the position in 56% of extremities tested, with a loss of a detectable blood pressure in 13%. Compression of the axillary artery by the humeral head was documented in 83% of extremities, but in only 7.6% was a greater than 50% stenosis inducible. No statistical difference was found in the incidence of arterial compression between the three groups tested or between their dominant and nondominant extremities. Dissection of the axillary artery in two cadavers documented that abduction and external rotation of the arm causes compression of the axillary artery by the humeral head, which acts as a fulcrum. We conclude that the repetitive mechanical trauma of the throwing motion can cause intermittent compression and contusion of the axillary artery by the humeral head and predisposes the athlete who throws to thrombosis of the axillary artery.

Adult↗