SEARCH · PubMed Health

Results for “COMPRESSION”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 721 records · Page 40Linked to original sources

PubMed2004

Spherical composite particles of rice starch and microcrystalline cellulose: a new coprocessed excipient for direct compression.

Composite particles of rice starch (RS) and microcrystalline cellulose were fabricated by spray-drying technique to be used as a directly compressible excipient. Two size fractions of microcrystalline cellulose, sieved (MCS) and jet milled (MCJ), having volumetric mean diameter (D50) of 13.61 and 40.51 microm, respectively, were used to form composite particles with RS in various mixing ratios. The composite particles produced were evaluated for their powder and compression properties. Although an increase in the microcrystalline cellulose proportion imparted greater compressibility of the composite particles, the shape of the particles was typically less spherical with rougher surface resulting in a decrease in the degree of flowability. Compressibility of composite particles made from different size fractions of microcrystalline cellulose was not different; however, using MCJ, which had a particle size range close to the size of RS (D50 = 13.57 microm), provided more spherical particles than using MCS. Spherical composite particles between RS and MCJ in the ratio of 7:3 (RS-MCJ-73) were then evaluated for powder properties and compressibility in comparison with some marketed directly compressible diluents. Compressibility of RS-MCJ-73 was greater than commercial spray-dried RS (Eratab), coprocessed lactose and microcrystalline cellulose (Cellactose), and agglomerated lactose (Tablettose), but, as expected, lower than microcrystalline cellulose (Vivapur 101). Flowability index of RS-MCJ-73 appeared to be slightly lower than Eratab but higher than Vivapur 101, Cellactose, and Tablettose. Tablets of RS-MCJ-73 exhibited low friability and good self-disintegrating property. It was concluded that these developed composite particles could be introduced as a new coprocessed direct compression excipient.

Cellulose↗

PubMed1996

Altered aggrecan synthesis correlates with cell and nucleus structure in statically compressed cartilage.

Previous studies have shown that static equilibrium compression of cartilage tissue in vivo and in vitro decreases chondrocyte synthesis of aggrecan molecules. In order to identify mechanisms of cellular response to loading, we have investigated alterations in cell and nucleus structure and the accompanying changes in the synthesis of aggrecan in statically compressed cartilage explants. Using glutaraldehyde fixation and quantitative autoradiography of compressed and radiolabeled cartilage disks we spatially localized newly synthesized aggrecan. Using stereological tools to analyze these same specimens we estimated the cell and nucleus volume, surface area and directional radii. We found that aggrecan synthesis was reduced overall in compressed tissue disks. However, the compression induced a spatial (radial) inhomogeneity in aggrecan synthesis which was not present in uncompressed disks. This spatial inhomogeneity appeared to be directly related to mechanical boundary conditions and the manner in which the load was applied and, therefore, may represent a spatially specific functional adaptation to mechanical loading. Coincident with reduced aggrecan synthesis, we observed reductions in cell and nucleus volume and radii in the direction of compression which were in approximate proportion to the reduction in tissue thickness. Cell and nucleus dimensions perpendicular to the direction of compression did not change significantly. Therefore the observed deformation of the cell and nucleus in statically compressed cartilage approximately followed the dimensional changes imposed on external specimen surfaces. The strong correlation observed between local changes in aggrecan synthesis and alterations in cell and nucleus structure also lend support to certain hypotheses regarding the intracellular signal transduction pathways that may be important in the biosynthetic response of chondrocytes to mechanical loading.

Aggrecans↗

PubMed2004

Prevention of deep-vein thrombosis after total hip and knee replacement. Low-molecular-weight heparin in combination with intermittent pneumatic compression.

After total hip (THR) or knee replacement (TKR), there is still an appreciable risk of developing deep-vein thrombosis despite prophylaxis with low-molecular-weight heparin (LMWH). In a prospective, randomised study we examined the efficacy of LMWH in combination with intermittent pneumatic compression in patients undergoing primary unilateral THR or TKR. We administered 40 mg of enoxaparin daily to 131 patients combined with either the use of intermittent pneumatic compression or the wearing of graduated compression stockings. Compression ultrasonography showed no evidence of thrombosis after LMWH and intermittent pneumatic compression. In the group with LMWH and compression stockings the prevalence of thrombosis was 28.6% (40% after TKR, 14% after THR). This difference was significant (p < 0.0001). In the early post-operative phase after THR and TKR, combined prophylaxis with LMWH and intermittent pneumatic compression is more effective than LMWH used with graduated compression stockings.

Adult↗

PubMed2003

Efficient compression of fresnel fields for Internet transmission of three-dimensional images.

We compress phase-shift digital holograms (whole Fresnel fields) for the transmission of three-dimensional images. For real-time networking applications, the time required to compress can be as critical as the compression rate. We achieve lossy compression through quantization of both the real and imaginary streams, followed by a bit packing operation. Compression losses in the reconstructed objects were quantified. We define a speedup metric that combines space gains due to compression with temporal overheads due to the compression routine and the transmission serialization. We empirically verify transmission speedup due to compression using a special-purpose Internet-based networking application.

Journal Article↗

PubMed1997

Contamination of hospital compressed air with nitric oxide: unwitting replacement therapy.

BACKGROUND: Inhaled nitric oxide (NO) at levels between 5 and 80 ppm has been used experimentally to treat a variety of conditions. NO also is a common environmental air pollutant in industrial regions. As compressed hospital air is drawn from the local environment, we speculated that it may contain NO contamination, which, if present, would provide unwitting inhaled NO therapy to all subjects respiring this compressed gas. METHODS: NO levels were measured twice daily from ambient hospital air and compressed gas sources driving positive pressure ventilation from two adjacent hospitals and compared with NO levels reported daily by local Environmental Protection Agency sources. An NO chemiluminescence analyzer (Sievers 270B; Boulder, Colo) sensitive to > or =2 parts per billion was used to measure NO levels in ambient air and compressed gas. RESULTS: NO levels in ambient air and hospital compressed air covaried from day to day, and absolute levels of NO differed between hospitals with the difference never exceeding 1.4 ppm (range, 0 to 1.4 ppm; median, 0.07 ppm). The hospital with the highest usage level of compressed air had the highest levels of NO, which approximated ambient levels of NO. NO levels were lowest on weekends in both hospitals. We also documented inadvertent NO contamination in one hospital occurring over 5 days, which corresponded to welding activity near the intake port for fresh gas. This contamination resulted in system-wide NO levels of 5 to 8 ppm. CONCLUSION: Hospital compressed air contains highly variable levels of NO that tend to covary with ambient NO levels and to be highest when the rate of usage is high enough to preclude natural degradation of NO in 21% oxygen. Assuming that inhaled NO may alter gas exchange, pulmonary hemodynamics, and outcome from acute lung injury, the role of unwitting variable NO of hospital compressed air needs to be evaluated.

Air↗

PubMed2001

Influence of compression therapy on symptoms following soft tissue injury from maximal eccentric exercise.

STUDY DESIGN: A between groups design was used to compare recovery following eccentric muscle damage under 2 experimental conditions. OBJECTIVE: To determine if a compression sleeve donned immediately after maximal eccentric exercise would enhance recovery of physical function and decrease symptoms of soreness. BACKGROUND: Prior investigations using ice, intermittent compression, or exercise have not shown efficacy in relieving symptoms of delayed onset muscle soreness (DOMS). To date, no study has shown the effect of continuous compression on DOMS, yet this would offer a low cost intervention for patients suffering with the symptoms of DOMS. METHODS AND MEASURES: Twenty nonimpaired non-strength-trained women participated in the study. Subjects were matched for age, anthropometric data, and one repetition maximum concentric arm curl strength and then randomly placed into a control group (n = 10) or an experimental compression sleeve group (n = 10). Subjects were instructed to avoid pain-relieving modalities (eg, analgesic medications, ice) throughout the study. The experimental group wore a compressive sleeve garment for 5 days following eccentric exercise. Subjects performed 2 sets of 50 passive arm curls with the dominant arm on an isokinetic dynamometer with a maximal eccentric muscle action superimposed every fourth passive repetition. One repetition maximum elbow flexion, upper arm circumference, relaxed elbow angle, blood serum cortisol, creatine kinase, lactate dehydrogenase, and perception of soreness questionnaires were collected prior to the exercise bout and daily thereafter for 5 days. RESULTS: Creatine kinase was significantly elevated from the baseline value in both groups, although the experimental compression test group showed decreased magnitude of creatine kinase elevation following the eccentric exercise. Compression sleeve use prevented loss of elbow motion, decreased perceived soreness, reduced swelling, and promoted recovery of force production. CONCLUSIONS: Results from this study underline the importance of compression in soft tissue injury management.

Adolescent↗

PubMed1992

Fitting multichannel-compression hearing aids.

Multichannel hearing aids have been introduced recently in clinical practice. In this paper, some advantages and disadvantages of multichannel hearing aids are discussed. The advantages include an improved use of compression. However, the number of settings will be larger in multichannel hearing aids and exact knowledge of the goal to be pursued by compression is more necessary than ever. Inexactness of the definitions of these goals may have been a reason for the contradictory results in the studies on multichannel compression. A number of requirements must be fulfilled for a successful application of multichannel compression. One of these is detailed knowledge about the perception of suprathreshold signals. For that reason, an extension of the battery of tests commonly used in rehabilitative audiology is necessary. Another requirement is that the fitting strategy is determined by the purpose of applying compression. The objectives will be different for compression limiting and syllabic compression. A fitting procedure used in clinical practice has to take into account some limitations in the fitting time available. A number of possible fitting tools are discussed. Two strongly different fitting strategies for the same commercially available three-channel compression aid illustrate fundamental differences in fitting philosophy.

Audiometry, Pure-Tone↗

PubMedDate not supplied

Audio-visual perception of compressed speech by profoundly hearing-impaired subjects.

For many people with profound hearing loss conventional hearing aids give only little support in speechreading. This study aims at optimizing the presentation of speech signals in the severely reduced dynamic range of the profoundly hearing impaired by means of multichannel compression and multichannel amplification. The speech signal in each of six 1-octave channels (125-4000 Hz) was compressed instantaneously, using compression ratios of 1, 2, 3, or 5, and a compression threshold of 35 dB below peak level. A total of eight conditions were composed in which the compression ratio varied per channel. Sentences were presented audio-visually to 16 profoundly hearing-impaired subjects and syllable intelligibility was measured. Results show that all auditory signals are valuable supplements to speechreading. No clear overall preference is found for any of the compression conditions, but relatively high compression ratios (> 3-5) have a significantly detrimental effect. Inspection of the individual results reveals that compression may be beneficial for one subject.

Adolescent↗

PubMedDate not supplied

Effect of compression pressure on physical properties and dissolution characteristics of disintegrating tablets of propranolol microspheres.

Propranolol HCl was encapsulated with cellulose acetate butyrate by an emulsion-solvent evaporation method. Three direct compression diluents were blended with appropriate size fractions of the microspheres and each formulation was compressed at several pressures to give tablets that readily disintegrated in water. Tablets with microcrystalline cellulose (MC) as the diluent had the highest tablet crushing strength at any given compression pressure. Heckel plots of all the microsphere-diluent blends were nonlinear, indicating that the consolidation may result from crushing and rearrangement of the individual particles in addition to plastic deformation. Tablet properties and estimated yield pressures showed that MC was the most suitable diluent for compression of propranolol HCl microspheres. Drug release from compressed tablets was always faster than from uncompressed microspheres, but useful sustained-release characteristics were retained. Dissolution tests of MC formulations of the tableted microspheres showed increased release rate constants and decreased 50 per cent dissolution times compared to microspheres that had not been compressed. This result indicated that rupture of some of the microspheres had occurred. The drug release rate increased at higher compression pressures due to the rupture of a greater proportion of microspheres. Larger changes in release rate and t50 percent were observed with larger microspheres sizes. Generally, the least compression pressure that gives tablets with acceptable properties is preferred.

Cellulose↗

PubMed1991

Influence of bone staple design on interfragmentary compression.

Staple fixation, most commonly thought of as static, has been studied with regard to effecting dynamic compression. Features of staple design that relate to the creation of interfragmentary compression have been analyzed, and a simple manipulative technique to effect compression is illustrated. Compressive forces of bone fixation staples were measured using pressure-sensitive film. Thirteen staple designs were tested in a wood-block model and in cadaveric bone. Staples with legs splayed outward produced higher compressive forces than standard staple designs. Internal beveling of the staple leg tips also produced high compressive forces, while external beveling produced distraction. Staples with legs tapered over their entire length produced compression, but caused splitting in the wood-block model. Our results show that outward splaying of the staple legs is a simple method to increase compression in any staple design.

Biomechanical Phenomena↗

PubMed2001

Evaluation of intermittent pneumatic compression devices.

Venous blood flow rate in the lower extremity after applying different pneumatic compression devices was evaluated. Five healthy individuals, aged 21-35, were recruited for this study. The ability of six different pneumatic compression devices to increase femoral venous blood flow velocity was analyzed and compared to that of active and passive foot dorsiflexion. Baseline venous blood flow velocity was measured using an ATL Duplex Doppler before leg compression. Venous blood flow velocity was then monitored before, during, and after each compression cycle. Average peak venous velocity increased >200% on dorsiflexion of the ankle. Among the investigated devices, the increase in venous velocity varied significantly. Design of compression chambers enabling compression on the lateral and medial aspects of the calf produced an increase in venous velocity closest to active foot dorsiflexion. Foot compression devices produced the smallest increase in venous velocity. The relative effectiveness of pneumatic compression devices, particularly with respect to increasing venous blood flow in the lower extremity, may correlate well with how closely the device simulates the physiologic contraction of the calf muscles. Clinical trials are needed to further compare the effectiveness of these devices, as other less readily measured factors play a role in thromboprophylaxis.

Adult↗

PubMed1995

Ultrasonographically guided manual compression of femoral artery injuries.

To determine the success and complication rates of ultrasonographically guided manual compression in patients with femoral arterial injuries after femoral arterial catheterization, we performed 53 sonographically guided compression repairs in 51 patients. Ultrasonographically guided compression repair was performed on 40 pseudoaneurysms in non-anticoagulated patients, seven pseudoaneurysms in anticoagulated patients, four arteriovenous fistulas on non-anticoagulated patients, and one pseudoaneurysm combined with an arteriovenous fistula. One pseudoaneurysm underwent two separate ultrasonographically guided compression repairs: once when the patient was anticoagulated and once after anticoagulants were withheld. Ultrasonographically guided compression repair was successful in 37 of 48 pseudoaneurysms (77%). Of the 40 pseudoaneurysms in non-anticoagulated patients, ultrasonographically guided compression repair was successful in 36 (90%). This repair technique failed in all seven pseudoaneurysms in anticoagulated patients. Ultrasonographically guided compression repair was successful in 13 of 16 (81%) multilobulated pseudoaneurysms but failed in all arteriovenous fistulas and the one case of pseudoaneurysm combined with an arteriovenous fistula. Ultrasonographically guided compression repair is a safe and effective alternative to surgery for the repair of pseudoaneurysms, including multilobulated pseudoaneurysms. The procedure does not appear to be effective in the anticoagulated patient or in patients with an arteriovenous fistula.

Aged↗

PubMed1999

[Learning cardiopulmonary resuscitation using conventional external cardiac massage or active compression-decompression in simulated cardiopulmonary resuscitation].

OBJECTIVE: To compare medical students' simulated learning of two different techniques of cardiopulmonary resuscitation (CPR). One was conventional external cardiac massage (ECM) and the other was active compression-decompression (ACD-CPR). MATERIAL AND METHODS: The study group (group S) comprised 111 students enrolled in their fourth year of medical studies who had no prior experience of CPR. Group R, the control group, was made up of 32 medical residents in anesthesiology and post-anesthetic intensive care. Before the study, group S received 5 hours of theoretical classes on CPR and both groups saw a video explaining each technique just before performing the test. All subjects applied each method to an adult dummy for one minute. The variables evaluated were frequency of complete and effective thoracic compressions and the body weight of the resuscitator. RESULTS: Each group performed similarly using the two techniques in terms of frequency of total compressions achieved. For each technique, the number of effective compressions achieved by group S (49.4 +/- 22.9 with ECM and 42.5 +/- 20.7 with ACD-CPR) was significantly lower (p < 0.05) than the number attained by group R (71.2 +/- 18.6 with ECM and 58.8 +/- 12 with ACD-CPR). Group R's frequency of effective compressions was significantly higher (p < 0.05) with CPR than with ACD-CPR. Body weight had no influence on the number of total compressions or efficacy in group R, whereas lower body weight in group S was significantly related to lower frequency of effective compressions with ECM p < 0.05). Neither group achieved a frequency of 80 total compressions in one minute. CONCLUSIONS: With the present teaching method, the medical students' performance was poor for both types of CPR and was affected by body weight. The residents' performance was less effective with ACD-CPR, a technique that was new to them, than with conventional ECM, with which they were expert and on which body weight had no impact.

Adult↗

PubMed2000

Methods and limits of digital image compression of retinal images for telemedicine.

PURPOSE: To investigate image compression of digital retinal images and the effect of various levels of compression on the quality of the images. METHODS: JPEG (Joint Photographic Experts Group) and Wavelet image compression techniques were applied in five different levels to 11 eyes with subtle retinal abnormalities and to 4 normal eyes. Image quality was assessed by four different methods: calculation of the root mean square (RMS) error between the original and compressed image, determining the level of arteriole branching, identification of retinal abnormalities by experienced observers, and a subjective assessment of overall image quality. To verify the techniques used and findings, a second set of retinal images was assessed by calculation of RMS error and overall image quality. RESULTS: Plots and tabulations of the data as a function of the final image size showed that when the original image size of 1.5 MB was reduced to 29 KB using JPEG compression, there was no serious degradation in quality. The smallest Wavelet compressed images in this study (15 KB) were generally still of acceptable quality. CONCLUSIONS: For situations where digital image transmission time and costs should be minimized, Wavelet image compression to 15 KB is recommended, although there is a slight cost of computational time. Where computational time should be minimized, and to remain compatible with other imaging systems, the use of JPEG compression to 29 KB is an excellent alternative.

Humans↗

PubMed2002

Benefits of syllabic input compression for users of cochlear implants.

Ten users of multielectrode cochlear implants participated in an evaluation of the perceptual effects of input-signal compression. A syllabic compressor was introduced into the microphone circuit of Spectra-22 or SPrint sound processors. The post-compression gain was adjusted to provide similar loudness for speech at an average level of 65 dBA with compression either enabled or disabled. Sentence recognition was measured at three levels. Averaged across all listeners, statistically significant score increases were obtained at each level with compression enabled (45 dBA: 19.6 percentage points, p < .0001; 55 dBA: 16.6 percentage points, p < .0001; 70 dBA: 3.1 percentage points, p = .031). A test of speech intelligibility in noise showed no significant effect of compression. Generally, participants in the trial reported improved perception of low-level sounds with compression, although a few disliked the increased loudness of some background noises. Some participants suggested that the ability to enable or disable compression with a manual switch would be helpful. Overall, the results show that input compression can improve the performance of these sound processors for users of cochlear implants, especially when listening to speech at low levels.

Adult↗

PubMed2003

Progressive changes in arterial oxygenation during one-lung anaesthesia are related to the response to compression of the non-dependent lung.

BACKGROUND: Arterial oxygenation can change during one-lung ventilation for reasons that are not fully understood. METHODS: We studied patients during anaesthesia and one-lung ventilation, with an inspiratory oxygen fraction of 0.8. Arterial blood gas values were recorded every 10 s with a continuous intra-arterial sensor. The non-dependent lung was compressed several times during the surgical procedure, using a retractor. The change in Pa(O(2)) during and after compression of the non-dependent lung was measured. RESULTS: Pa(O(2)) increased significantly when the non-dependent lung was compressed, and decreased when the compression was released. The first compression of the non-dependent lung transiently increased Pa(O(2)), but the effect of the second compression on oxygenation was more marked and persistent. Pa(O(2)) increased by more than 13 kPa at 10 min after the second compression in four patients (responder group). Arterial oxygenation improved markedly in patients in this group during the surgical procedure. CONCLUSION: Oxygenation can improve during one-lung ventilation in some patients. This improvement is partly related to a marked increase in Pa(O(2)) during compression of the non-dependent lung.

Aged↗

PubMed1992

[Indications, technique and results of monosegmental dorsal spondylodesis in wedge compression fractures (grade II) of the thoracolumbar spine].

The management of wedge compression fractures of the thoracolumbar spine remains a controversial subject. Although there is an increasing tendency for operative intervention of spinal injuries, non-operative treatment of compression fracture has been the method of choice. The compression fracture is a fracture occurring during compressive forces of the anterior column due to flexion mechanisms. The more severe the compressive fracture, the more likely it will be to present, in an addition to anterior wedging, a failure of the posterior column indicating tension forces at that level. These fractures, defined as mechanically unstable and classified as compression fractures Grade II, are concentrated in the thoracolumbar region. Between June 1987 and July 1990 14 patients with compression fractures Grade II were treated posteriorly with one level internal fixation. Of the 14 patients, 9 had stabilization with plates and cerclage wire, 5 with an internal fixator. All patients received a localized fusion. In order to permit a more reliable analysis of the results of our stabilizing procedures, a comparison was made with a series of 11 cases with equivalent fractures treated non-operatively between 1986 and 1989. At clinical and radiographic follow-up evaluation, the results in the operative group were much more favourable, both subjective and objective, than in the non-operative group. We derive from these results that in thoracolumbar compression fractures Grade II, posterior one level stabilization and fusion is a recommendable surgical procedure.

Adult↗

PubMed1989

[Effects of experimental compression of the brainstem on the circulatory and the respiratory parameters in the rabbit].

Circulatory and respiratory changes following a mechanical compression of the brainstem of the rabbit were studied. Under light ether anesthesia, the animal was tracheostomized, immobilized by pancuronium bromide, and mechanically ventilated, following which the skull was fixed and suboccipital craniotomy was performed, and finally the brainstem was exposed. The site of compression was selected as (A): 3mm lateral, 3mm rostral, (B): 2mm lateral and (C): 3mm lateral, 3mm caudal, of the obex, respectively. After inhalation of ether was discontinued and elimination of the effect of muscle relaxant was confirmed, the direct compression with glass stick of 0.8mm in diameter was carried out. In each point, vertical compression of 1mm, 2mm and 3mm, was performed stereotaxically. In each depth of the compression, 3 to 4 animals were studied. The blood pressure was measured directly in the femoral artery and the respiratory changes by impedance pneumography. The circulatory changes, biphasic change of arterial pressure and/or transient bradycardia occurred earlier than the respiratory changes in 2mm and 3mm depth of the compression in all 3 points. CO2 response curve with rebreathing method was obtained before and 15 minutes after the compression to evaluate the degree of damage of the medullary respiratory center. The depression of CO2 response curve was observed only in 3mm compression depth at the point (A). It is concluded from this study that excessive invasion of the brainstem during the suboccipital craniotomy under controlled ventilation could be detected through the observation of the changes in circulatory parameters.

Animals↗