Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Data Compression”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,495 records · Page 83Linked to original sources
PubMed2001

A novel method for controlled and reversible long term compression of the umbilical cord in fetal sheep.

1. In fetal sheep during late gestation the aims of the present study were to (1) develop a technique for inducing prolonged but reversible periods of controlled compression of the umbilical cord and (2) characterise the cardiovascular, endocrine and metabolic responses to this challenge. 2. Under 1-2 % halothane anaesthesia, 16 Welsh Mountain sheep fetuses were chronically instrumented at 118 +/- 2 days of gestation (term is ca 145 days) with an inflatable occluder cuff around the umbilical cord, amniotic and femoral vascular catheters and with transit-time flow probes around the contra-lateral femoral artery and an umbilical artery. At 125 days, umbilical blood flow was reduced by 30 % from a pre-determined 24 h baseline for 3 days by automated servo-controlled inflation of the occluder cuff (n = 8). The occluder was then deflated allowing return of umbilical blood flow to baseline. The remaining eight fetuses were used as sham-operated controls in which the occluder was not inflated throughout the protocol. Fetal cardiovascular variables were recorded at 8 s intervals and arterial blood samples taken for measurement of blood gases, glucose and lactate and plasma adrenaline, noradrenaline and vasopressin concentration throughout the study. 3. Automated servo-controlled inflation of the occluder cuff, programmed to reduce umbilical blood flow by 30 % from baseline, reduced umbilical blood flow by 30.2 +/- 1.7 %, with a coefficient of variation during compression of 6.5 +/- 1.1 %. Sustained partial compression of the umbilical cord produced falls in fetal arterial pH, P(a,O2), percentage O(2) saturation of haemoglobin, and hindlimb oxygen delivery, and increases in P(a,CO2), haemoglobin concentration, arterial blood oxygen carrying capacity and in blood glucose and lactate concentrations. While the reductions in P(a,O2), percentage saturation of haemoglobin and hindlimb oxygen delivery and the increase in P(a,CO2) were sustained throughout compression, the reduction in arterial pH and the increase in arterial oxygen carrying capacity had returned towards baseline values by 48 h compression. Fetal blood lactate concentrations reached a peak at 8 h of compression and, thereafter, were maintained at an elevated level relative to baseline. 4. Partial compression of the umbilical cord produced fetal hypertension, a reduction in femoral blood flow and, consequently, an increase in calculated fetal femoral vascular resistance for the duration of the challenge. In addition, the fall in heart rate measured in sham control fetuses by the end of the study, did not occur in cord-compressed fetuses. Cosinor analysis on 24 h rhythms of cardiovascular data indicated a significant increase in the amplitude of the 24 h rhythm in heart rate in cord-compressed fetuses relative to sham controls during the period of compression or sham-compression. Furthermore, cord compression led to an increase in fetal plasma noradrenaline, but not adrenaline and vasopressin concentrations relative to sham control fetuses. 5. In conclusion, a novel reversible method for controlled, long-term compression of the umbilical cord in sheep has been developed. The data show that sustained, partial compression of the umbilical cord produced moderate but sustained asphyxia, which resolved after the end of the compression period, and induced changes in fetal cardiovascular, endocrine and metabolic functions.

Animals↗
PubMed2000

Elastic registration of 3D cartilage surfaces from MR image data for detecting local changes in cartilage thickness.

The objective of this work was to develop and validate a computational method for the registration (matching) of 3D cartilage plates from MR image data sets. The technique tracks local cartilage thickness changes over time. A 3D elastic registration technique was applied that identifies corresponding points of the bone-cartilage interface in MR data sets of 3D-reconstructed cartilage plates. In a first rigid preregistration step, the surfaces are aligned, using the principal axes decomposition to correct for different joint positions and orientations in the MR scanner. In a second step, the surfaces are deformed elastically, based on geometric surface features, until they are sufficiently similar to identify corresponding surface points. The method was validated against artificially corrupted cartilage surfaces and MR data obtained from in vivo and in vitro compression experiments. The in vivo reproducibility was tested on patellar data sets of volunteers, with repositioning of the joint in between replicate acquisitions.

Cartilage, Articular↗
PubMed1989

Bone creep-fatigue damage accumulation.

Creep and fatigue tests were performed on human femoral cortical bone and the results were compared to a cumulative damage model for bone fracture. Fatigue tests in tension, compression, and reversed loading with a tensile mean stress were conducted at 2 Hz and 0.02 Hz. Load frequency had a strong influence on the number of cycles to failure but did not influence the total time to failure. Bone displayed poor creep-fracture properties in both tension and compression. The fracture surfaces of the tensile creep specimens are distinctly different than those of the compressive specimens. The results suggest that tensile cyclic loading creates primarily time-dependent damage and compressive cyclic loading creates primarily cycle-dependent damage. However, data for load histories involving both tensile and compressive loading indicate lower time to failure than predicted by a simple summation of time-dependent and cycle-dependent damage.

Adult↗
PubMed2006

Usefulness of ocular compression during electroencephalography in distinguishing breath-holding spells and syncope from epileptic seizures.

Episodes of syncope or breath-holding spells are often misdiagnosed as epileptic events. The purpose of this study was to assess the usefulness of an electroencephalogram (EEG) with ocular compression to distinguish breath-holding spells and syncope from epileptic seizures. A retrospective analysis was performed on the EEG records of all children on whom ocular compression was performed from 2000 to 2003. Data from 116 patients with a clinical diagnosis consistent with either syncope or breath-holding spells were compared with a group of 46 patients with epilepsy. The RR interval during ocular compression was significantly higher in syncope patients compared with patients with epilepsy (P < .005). Using 2 seconds of asystole as the cutoff, the sensitivity of ocular compression was 26%, with 100% specificity. The change in RR interval from baseline to ocular compression also distinguished patients with breath-holding spells and syncope from patients with epilepsy. Even a small increase of 0.5 seconds in the RR interval demonstrated a sensitivity of 46%, with a specificity of 98%. Ocular compression performed during an EEG is useful in distinguishing patients with breath-holding spells and syncope from those with epileptic seizures. A requirement of a 2-second period of asystole with ocular compression excludes many patients. Our data indicate that an RR interval increase of 0.5 seconds over baseline identifies additional patients with increased vagal tone. Prompt and accurate diagnosis of the etiology of loss of consciousness might preclude the need for further extensive and expensive evaluation and reduce patient and parental distress.

Adolescent↗
PubMed1988

Interaction of contact velocity and cord compression in determining the severity of spinal cord injury.

Rate, depth, and duration of compression are the principal determinants of experimental spinal cord injury (SCI) severity. Since existing models do not allow independent control of these variables, the interaction of these factors has not been fully elucidated. The purpose of this study was to define the interactive relation of velocity (V) and compression (C) in SCI using a constrained stroke pneumatic impactor that allowed independent control of these variables. Computer simulation of previous weight-drop experiments using a lumped-mass model were compared with this series of impacts. After rigid stabilization of adjacent cervical vertebrae, the spinal cord (SC) in 48 male ferrets was compressed through the C6-C7 interspace. Maximum compression was 25%, 35%, 50%, or 65% of the SC diameter. Impacts were delivered at five velocities from 1.5 m/s to 6 m/s. Severity of injury was determined by pre and postinjury measurement of somatosensory evoked potentials (SEP) and blinded quantitation of histopathologic findings. Twenty-three of 48 animals (48%) had measurable SEP at 4 hs. No animal recovered SEP at 65% compression at any velocity, or at a velocity of 6 m/s for any level of compression. Recovery of SEP and histologic severity score correlated better with velocity-compression product, or maximum viscous response (VC) than with either V or C alone. The mean histologic severity score was higher in animals exhibiting no recovery of SEP. Modeling the viscoelastic elements of the SC using existing force-time and force-deflection data suggests that estimates of compression from current weight-drop techniques may be inaccurate. At low contact velocity, functional and anatomic damage is best predicted by maximum SC compression. However, as velocity increases, SCI severity becomes a function of the viscous response (VC), demonstrating the rate sensitivity of spinal cord tissue. Tolerance to SC compression decreases as the rate of deformation increases. This helps to explain apparent discrepancies between compression and severity of experimental SCI.

Animals↗
PubMed2000

Cardiopulmonary resuscitation without ventilation.

Current resuscitation methods, although occasionally effective, rarely perform as well as initially anticipated. Some of the disappointment can be attributed to the difficulty of the task for many, including both professional and lay first responders. Significant attention has been paid recently to the need to simplify both the technique and the teaching of resuscitation. In considering simplification of the current resuscitation scheme, a logical start is an honest reappraisal of the importance and priorities of each of the once sacrosanct ABCs, specifically, establishment of an Airway, artificial Breathing (mouth-to-mouth breathing), and chest compressions for temporary Circulation. Experimental data continue to accumulate indicating that most important within this triad is circulation. Adequate oxygen exists within the blood during at least the first 10 mins of cardiac arrest. If circulation is provided to distribute such oxygen, no survival disadvantage results with chest compression-only basic life support (BLS) efforts. Even a totally occluded airway during the first 6 mins of cardiac arrest does not compromise survival if reasonable circulation is provided with chest compressions. Clinical studies support the same conclusion that what most influences survival in any BLS effort is circulation, not ventilation. Belgium investigators have shown equal survival rates among those treated with chest compressions plus ventilation and those who received chest compressions alone. Telephone dispatcher-guided BLS cardiopulmonary resuscitation (CPR) has likewise shown no survival disadvantage to chest compression-only CPR when compared with telephone-guided standard BLS CPR. Based on this reasoning, a new simplified BLS method has been proposed. "Staged" CPR consists of a strategy to initially teach laypersons a simplified approach to BLS, which requires only chest compressions and not mouth-to-mouth breathing. "Bronze" CPR, in which chest compression-only BLS is taught, was compared with the standard European Resuscitation Council BLS course for laypersons. Manikin "exit testing" at course completion has revealed significant advantages of the simplified approach compared with standard CPR courses for the lay public.

Animals↗
PubMed2003

Formats of image data files that can be used in routine digital light micrography. Part two.

This is part two of an article that describes the properties of the image data files that are encountered routinely in digital light micrography. In the current part of the article, the differences between saving image data as large intact files and smaller files that have had some information removed, i.e., using lossy compression, are related first. Subsequently, appropriate ways of configuring computers to deal with the large intact image data files are suggested. The structures of the image data files used for recording dynamic sequences and kinematic animations of series of digital light micrographs, i.e., movie formats, are then described. Finally, some information is supplied about choosing file formats for compressing both static and dynamic image data sets.

Computer Graphics↗
PubMed2002

DNA sequence compression using the burrows-wheeler transform.

We investigate off-line dictionary oriented approaches to DNA sequence compression, based on the Burrows-Wheeler Transform (BWT). The preponderance of short repeating patterns is an important phenomenon in biological sequences. Here, we propose off-line methods to compress DNA sequences that exploit the different repetition structures inherent in such sequences. Repetition analysis is performed based on the relationship between the BWT and important pattern matching data structures, such as the suffix tree and suffix array. We discuss how the proposed approach can be incorporated in the BWT compression pipeline.

Algorithms↗
PubMed2002

Medical management of hypopituitarism in patients with pituitary adenomas.

Hypopituitarism is a disease complex with variable clinical manifestations. Recent studies have improved our understanding of its pathophysiology, particularly in patients with pituitary adenomas. In that setting, hypopituitarism was previously considered a permanent and irreversible process, requiring life-long hormone replacement therapy. While this could be true in some instances, recent data demonstrated recovery of pituitary function in a large number of patients with hypopituitarism following surgical decompression. Mechanical compression of portal vessels and the pituitary stalk, by the expanding adenoma was postulated to be the predominant mechanism causing hypopituitarism in this setting. Since portal vessels also provide blood supply to the anterior lobe, ischemic necrosis of portions of the pituitary can occur as a result of increased and prolonged compression by the expanding adenoma. Recent data demonstrated increases in intrasellar pressure (ISP) in patients with pituitary macroadenomas, particularly those with hypopituitarism. The data showed that ISP measurements correlated positively with the serum prolactin levels but not with tumor sizes. It is postulated that increased ISP has predominant role in the pathogenesis of hypopituitarism in patients with pituitary adenomas while. The increase in ISP results in decreased blood flow through the portal vessels and the pituitary stalk. The latter will result in diminished delivery of hypothalamic hormones to the anterior pituitary and may also cause ischemia and/or necrosis in some portions of the normal gland. Recovery of pituitary function can thus be anticipated after surgical decompression, in patients who have viable pituitary cells. Understanding the pathophysiology of hypopituitarism and recognizing the probability for recovery of function should be emphasized in the management of patients with this disease. An important aspect of the management is patients' education about their disease, including the use of medic alert identification. The managing physician should appreciate the variable clinical manifestations of the disease and the possible occurrence of other associated neuroendocrine, neurological and neuro-ophthalmologic signs and symptoms. Treatment of hypopituitarism should not be rigid but instead, always individualized. Management should take into consideration the patients' age, sex, education, original disease process and clinical history.

Adenoma↗
PubMed1985

Neurogenic hypertension: etiology and surgical treatment. II. Observations in an experimental nonhuman primate model.

In a companion paper (Ann Surg 1985; 201(3):391-398), clinical data which suggest that neurogenic hypertension may be caused by arterial compression of the left medulla oblongata was presented. A chronic pathophysiologic animal model of neurogenic hypertension using a substitute for arterial pulsation, the neurovascular compression simulator (NCS), was developed. This paper presents data that demonstrate how development of hypertension in a nonhuman primate baboon (5 subject animals, 5 control animals) can be caused by the NCS, and the blood pressure can subsequently return to normal following cessation of NCS activity. These experiments show that pulsatile compression of the left ventrolateral medulla oblongata results in cardiovascular changes consistent with the sequence found in human neurogenic hypertension. Arteriosclerosis and arterial ectasia in the human contribute to arterial elongation and looping at the base of the brain. An arterial loop, by causing pulsatile compression of neural structures, elicits an increase in blood pressure initiated by an increase in cardiac output. This may be due to interference with the autonomic control of the heart and/or by alteration of the relative capacitance of the vascular system.

Animals↗
PubMedDate not supplied

Electromyographic analysis of the masseter and temporal muscles in oralized deaf individuals.

Deaf individuals show a number of difficulties related to the functionality of the stomatognathic system, mainly by reason of the little or no use of facial musculature during speech either due to the use of sign language or to the difficulty that these individuals have in articulating words. The stomatognathic system muscles play important roles in functions such as mastication, deglutition, and phonation. This study aimed to assess, by means of computerized bilateral electromyography (EMG), masseter and temporal muscles of 12 oralized deaf individuals in clinical activities that involve part of this masticatory musculature and compare this system's functionality with that of 12 normal listening individuals, performing the same activities. An 8-channel K6-I EMG Light Channel Surface Electromyography device was used (Myo-Tronics Co.Seattle, WA, USA), in addition to disposable double electrodes covered with silver chloride (Duotrodes; Myo-tronics Co., Seattle, WA) containing a conductor gel (Myogel- Myo-tronics Co., Seatlle, WA). The averaged rectified EMG values were normalized with reference to the EMG amplitude induced by a maximum bite force. The statistical analysis confirmed that there were any significant differences between the groups, clinical activities, and muscles, and also effects of interaction among them. The analysis made use of Variance Analysis (ANOVA). Significant differences (p < 0.01) for both muscles were found among the clinical conditions, with deaf individuals showing greater electromyographic activity for both muscles for the clinical activity protrusion. Deaf individuals showed a lower muscular activity for clinical activities that demanded a greater masseter and temporal muscular activity such as mastication, mouth opening and closing, and dental compression. Greater electromyographic values were found for both deaf individuals and healthy controls during clinical activities of mastication and dental compression. Based on the obtained data, we concluded that deaf individuals showed a lower activity of the masticatory musculature than healthy individuals; the differences were significant at the level of p < 0.01 between the performed clinical activities; and all deaf individuals and healthy controls showed greater electromyographic values for mastication and dental compression.

Adolescent↗
PubMed1982

Functional adaptation of bone in response to sinusoidally varying controlled compressive loading of the ovine metacarpus.

To obtain carried load, quantitative data relating functional adaptation of bone to controlled, sinusoidally-varying, compressive loading of constant amplitude was applied to the right metacarpal bones via Steinmann's pins inserted through the metaphyses in 13 sheep. Loading was applied for two 1-hr periods/day at 24 cycle/minute, through-out a test period of 28 days. The amplitude of the applied loading was varied from test to test, giving peak stresses on the mid-diaphyseal cross-section that ranged from 2.2-8.3 N/mm2. In the mid-diaphyseal region, the bone responded by periosteal apposition, with maximum proliferation usually occurring on the medio- and laterovolar borders and relatively little new bone on the dorsal and volar aspects. The cross-sectional areas of new bone was roughly proportional to the applied stress, with a maximum increase of approximately 8% in the most highly stressed bones. There was also evidence that periosteal resorption had occurred, presumably as the first step in the apposition process. A significantly increased level of intracortical activity was found in the right metacarpus as compared with the contralateral bone.

Adaptation, Physiological↗
PubMed1992

The role of transcranial Doppler in carotid artery surgery.

In order to evaluate the usefulness of transcranial Doppler (TCD) in carotid artery surgery, 90 patients who underwent carotid endarterectomy were studied. Transcranial Doppler was performed preoperatively with digital compression of the carotid artery and intraoperatively at the time of cross-clamping, together with routine EEG monitoring. The percentage residual middle cerebral artery velocity (%MCAV) during carotid artery compression or cross-clamping was considered. The intraoperative %MCAV at cross-clamping was compared with the values obtained in the preoperative examination during the compression test and with the EEG data; the EEG records were blindly reviewed by a neurologist and divided into three groups: group A, normal; group B, moderate anomalies and group C, major anomalies. There were no significant differences between preoperative %MCAV (compression test) and intraoperative %MCAV (cross-clamping) by separate analysis of the data related to systolic, diastolic and mean velocity. The systolic, diastolic, mean %MCAV and the Gosling index after cross-clamping were then compared with the EEG data: no significant differences were seen between groups A and B; on the other hand, in all patients with major EEG anomalies (group C) the %MCAV at TCD was reduced to 0. In conclusion, preoperative TCD associated with carotid artery compression appears a safe and useful way of identifying patients at risk of cerebral ischaemia during carotid artery cross-clamping. Patients with no residual flow at intraoperative TCD need to be considered as presenting a very high risk of ischaemia and in this group the use of a shunt is mandatory.

Aged↗
PubMed1991

Compression of the ambulatory ECG by average beat subtraction and residual differencing.

We implemented a method for compression of the abulatory ECG that includes average beat subtraction and first differencing of residual data. Our previous investigations indicated that this method is superior to other compression methods with respect to data rate as a function mean-squared-error distortion. Based on previous results we selected a sample rate of 100 samples per second and a quantization step size of 35 microV. These selections allow storage of 24 h of two-channel ECG data in 4 Mbytes of memory with a minimum rms distortion. For this sample rate and quantization level, we show that estimation of beat location and quantizer location can significantly affect compression performance. Improved compression resulted when beats were located with a temporal resolution of 5 ms and coarse quantization was performed in the compression loop. For the 24-h MIT/BIH arrhythmia database our compression algorithm coded a single-channel of ECG data with an average data rate of 174 bits per second.

Algorithms↗
PubMed2003

Thoracic outlet: assessment with MR imaging in asymptomatic and symptomatic populations.

PURPOSE: To compare the dynamic modifications of the thoracic outlet in asymptomatic volunteers and symptomatic patients and assess the presence and location of vasculonervous compressions in these two populations. MATERIALS AND METHODS: Thirty-five healthy volunteers and 54 patients with clinical symptoms of thoracic outlet syndrome (TOS) underwent magnetic resonance (MR) imaging of the thoracic outlets with their arms alongside their bodies and after a postural maneuver. Measurements were obtained at the interscalene triangle (thickness of anterior scalene muscle, interscalene angle), at the costoclavicular space (minimum costoclavicular distance, distance between inferior border of subclavius muscle and the anterior chest wall, maximum thickness of subclavius muscle, angle between first rib shaft and horizontal), and at the retropectoralis minor space (distance between posterior border of pectoralis minor muscle and posterior lining of axilla at the passage of the axillary vessels, thickness of pectoralis minor muscle). The presence and location of vasculonervous compressions were also assessed. Group data were analyzed with the Student t test. RESULTS: Patients with TOS had a smaller costoclavicular distance after the postural maneuver (P <.001), a thicker subclavius muscle in both arm positions (P <.001), and a wider retropectoralis minor space after the postural maneuver (P <.001) than did volunteers. Venous compressions after the postural maneuver were observed in 47% of volunteers and 63% of patients at the prescalene space, in 54% of volunteers and 61% of patients at the costoclavicular space, and in 27% of volunteers and 30% of patients at the retropectoralis minor space. Arterial and nervous compressions, respectively, were seen in 72% and 7% of patients. No arterial or nervous compression was seen in volunteers. Except for venous thrombosis, vasculonervous compressions were demonstrated only with arm elevation. Only three thoracic outlet measurements differed significantly in both populations. CONCLUSION: MR imaging appeared helpful in demonstrating the location and cause of arterial or nervous compressions.

Adult↗
PubMed1983

Suspected epidural compression of the spinal cord and cauda equina by metastatic carcinoma. Clinical diagnosis and survival.

Data from 133 patients with cancer and suspected compression of the spinal cord or cauda equina was reviewed. Although there were differences in presenting symptoms and signs between the group of 62 patients with compression and the 71 without, no single symptom or sign discriminated adequately between the two groups. Multiple logistic regression was used to try to develop an index of signs and symptoms which could identify those without compression, thereby sparing them a myelogram. Eight characteristics, in combination, proved most effective as an index, but they were not perfect predictors of patients with block. Final diagnoses in the group without compression were: vertebral metastases 35%, carcinomatous meningitis 24%, plexopathy and/or neuropathy 21%, other 30% (10% had two diagnoses). Sixty-six percent of those with compression and 50% of those without compression died within six months, although patients rarely survived for much longer.

Adolescent↗
PubMed1983

Children's item and other errors on time-compressed, sequenced rhyming words.

This investigation provided normative data for the performance of 36 M and 36 F children in 3 groups averaging 8, 10, and 12 yrs old, presented time-compressed (TC) rhyme sequences under multitalker masking and no masking conditions. Analysis of both item and order errors yielded significant effects for TC and masking conditions. These effects were consistent with findings for stimuli previously found useful in assessing auditory perceptual problems, thereby supporting the diagnostic potential of these stimuli. Analysis of the order errors also yielded several higher-order interactions which appeared to be clinically negligible but supportive of the suggestion that order errors may be especially sensitive to subtle pathological problems.

Adolescent↗
PubMed2003

Axial compression generated by cortical and cancellous lag screws in the equine distal phalanx.

Lag screw fixation using single 4.5 mm cortical bone screws is a recommended technique for repair of mid-sagittal plane fractures of the distal phalanx in adult horses. However, implant infection and technical difficulties in obtaining adequate interfragmentary compression have made this surgical procedure somewhat controversial. We hypothesized that use of larger diameter screws would result in increased axial compression and improved stability of this fracture. Paired distal phalanges from the forelimbs of 10 adult horses were collected at necropsy and divided in half in the midsagittal plane. Using a randomized block study design, four types of bone screws (4.5 mm cortical, 5.5 mm cortical, 6.5 mm cancellous pre-tapped, and 6.5 mm cancellous non-tapped) were inserted to a depth of 15 mm. During screw insertion, the axial force generated under the screw head was measured with a load washer containing a piezoelectric force transducer, while torque of insertion was recorded with a torsional testing machine. The 6.5mm screw inserted after pre-tapping generated significantly greater axial force (2781 N) than the 4.5 mm (1522 N), 5.5 mm (2073 N) or 6.5 mm non-tapped (2295 N) screws. The relationship between maximal applied torque and axial force generated was linear for each screw type. Each unit of torque applied during insertion of cortical screws resulted in a greater increase in axial compression, as compared to cancellous screws. These data suggest that use of larger diameter screws would result in improved interfragmentary compression of distal phalangeal fractures.

Animals↗