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PubMed2004

Confined compression experiments on bovine nucleus pulposus and annulus fibrosus: sensitivity of the experiment in the determination of compressive modulus and hydraulic permeability.

The biphasic material properties for nucleus pulposus tissue in confined compression have not been reported previously, and are required for a better understanding of intervertebral disc function and to provide material properties for use in finite-element models. The aims of this study were to determine linear and non-linear material properties for nucleus pulposus and annulus fibrosus tissues in confined compression, to define the influence of swelling conditions on these properties, and to determine the changes in the compressive modulus and hydraulic permeability induced by the repetition of the stress-relaxation experiment after a return to swelling pressure equilibrium. Specimens from caudal bovine nucleus and annulus were tested in confined compression stress-relaxation experiments and analyzed to quantify the compressive modulus and hydraulic permeability using linear and non-linear biphasic models. Our results suggested the use of confined swelling pre-test condition and non-linear biphasic model, which provided the material parameters with lowest relative variance and water content most representative of physiological conditions. Smaller compressive modulus and higher hydraulic permeability were obtained for the nucleus (H(A0)=0.31+/-0.04 MPa, k(0)=0.67+/-0.09 x 10(-15)m(4)/Ns) than for the annulus (H(A0)=0.74+/-0.13 MPa, k(0)=0.23+/-0.19 x 10(-15)m(4)/Ns), with relatively weak non-linearities. Strains up to 20% resulted in material properties that were significantly altered upon retesting. These altered material properties are an effort to quantify non-recoverable damage that occurs in disc tissue and suggest that in vivo exposure of disc tissues to low strain-rate and high-deformation loading conditions which outpace biological repair may result in altered mechanical behaviors.

Animals↗
PubMed2002

Comparison of the equilibrium response of articular cartilage in unconfined compression, confined compression and indentation.

At mechanical equilibrium, articular cartilage is usually characterized as an isotropic elastic material with no interstitial fluid flow. In this study, the equilibrium properties (Young's modulus, aggregate modulus and Poisson's ratio) of bovine humeral, patellar and femoral cartilage specimens (n=26) were investigated using unconfined compression, confined compression, and indentation tests. Optical measurements of the Poisson's ratio of cartilage were also carried out. Mean values of the Young's modulus (assessed from the unconfined compression test) were 0.80+/-0.33, 0.57+/-0.17 and 0.31+/-0.18MPa and of the Poisson's ratio (assessed from the optical test) 0.15+/-0.06, 0.16+/-0.05 and 0.21+/-0.05 for humeral, patellar, and femoral cartilages, respectively. The indentation tests showed 30-79% (p<0.01) higher Young's modulus values than the unconfined compression tests. In indentation, values of the Young's modulus were independent of the indenter diameter only in the humeral cartilage. The mean values of the Poisson's ratio, obtained indirectly using the mathematical relation between the Young's modulus and the aggregate modulus in isotropic material, were 0.16+/-0.06, 0.21+/-0.05, and 0.26+/-0.08 for humeral, patellar, and femoral cartilages, respectively. We conclude that the values of the elastic parameters of the cartilage are dependent on the measurement technique in use. Based on the similar values of Poisson's ratios, as determined directly or indirectly, the equilibrium response of articular cartilage under unconfined and confined compression is satisfactorily described by the isotropic elastic model. However, values of the isotropic Young's modulus obtained from the in situ indentation tests are higher than those obtained from the in vitro unconfined or confined compression tests and may depend on the indenter size in use.

Animals↗
PubMed1997

Active compression-decompression cardiopulmonary resuscitation (ACD-CPR) compared with standard CPR in a manikin model--decompression force, compression rate, depth and duration.

During active compression-decompression cardiopulmonary resuscitation (ACD-CPR), the rescuer applies traction to the chest between compressions. Under experimental conditions, cardiac output increases, possibly through accentuated intrathoracal pressure fluctuations. ACD-CPR requires specific training and may be more complex to perform than standard CPR. The aim of this study was to characterize ACD-CPR performance compared with standard CPR by emergency care providers; in terms of decompression force, compression rate, depth and duration. Thirty-three ambulance paramedics were studied while performing standard CPR and ACD-CPR with the Ambu Cardiopump on a specially designed transducer-equipped manikin 9 months following initial training. The order of CPR performance was determined randomly by cross-over design. Performance data were recorded by a computer. The 2-min average active decompression force was 9.3 kg (interquartile range 2.5-15.3 kg) and six subjects (18%) met the manufacturers recommendation of 10-15 kg. External chest compression (ECC) rate decreased from 85 (70-101) to 76 (63-88) min-1 (P < 0.001), ECC depth decreased from 54 (50-58) to 45 (39-48) mm (P < 0.001) and compression duration from 40 (35-45) to 31% (28-33%) (P < 0.001) upon change from standard CPR to ACD-CPR. We conclude that the recommended level of decompression force was achieved by less than one fifth of study subjects. ACD-CPR when compared with standard CPR causes a consistent and significant reduction of compression rate, depth and duration. These are all factors of possible clinical significance. Training in ACD-CPR should address this issue, with special emphasis on optimal decompression force and ECC rate.

Adult↗
PubMed2003

Determining the compression behaviour of pharmaceutical powders from the force-distance compression profile.

The force-displacement curves obtained from an eccentric tablet machine were examined in a new way. The tendency of the material for plastic deformation, fragmentation and elasticity is expressed as numerical values, which are comparable between different materials. The dependence of these numerical values on the compression pressure was modelled. The accuracy of the displacement measurement was improved by filtering out noise from the measurement data by a novel method. The plastic deformation of the material near the force maximum of the compression cycle could be seen accurately from this precise displacement data. The elastic deformation of the tablet machine was also defined very precisely from the running machine. Tablets were made with an eccentric tablet machine using fixed lower and upper punch adjustments. This ensured that the speed of the upper punch and the theoretical height of the tablets were the same for all compactions. Therefore, only the properties of the materials determined the differences in the shape of the compression curves. The test materials used were alpha-lactose monohydrate, two grades of microcrystalline cellulose, maize starch and dicalcium phosphate dihydrate. The results showed that the use of accurate displacement measurement is essential in order, to see the small variations in the shape of the force-displacement curve near the force maximum of the compression cycle, and it made it possible to dynamically calibrate the elastic deformation of the eccentric tablet machine during compression. It turned out that the numerical values obtained with the new method described the plastic, brittle and elastic properties of the tested materials satisfactorily in a wide compression pressure range.

Compressive Strength↗
PubMed1990

Importance of compression onset rate for the degree of impairment of impulse propagation in experimental compression injury of the porcine cauda equina.

The effects of a rapid (0.05-0.1 seconds) and a slow (20 seconds) onset rate of cauda equina compression on impulse propagation, in terms of tail muscle electromyogram (EMG) amplitude, were analyzed in an experimental model of the pig cauda equina. Sham compression and compression at 50 mm Hg at either rapid or slow onset induced no or only minor functional impairment. Compression at 100 or 200 mm Hg induced impairment of the impulse propagation that was proportional to the applied pressure. The effects were more pronounced (P less than 0.01) for the rapid than for the slow onset of compression at both these pressure levels. An important factor for this observed difference in effects between the two employed onset rates seems to be the magnitude of intraneural edema formed outside the compression zone.

Animals↗
PubMed2000

Osteotomy, compression and reaming techniques for internal fixation of extracapsular hip fractures.

BACKGROUND: Many different surgical techniques, such as osteotomy, have been used in internal fixation of extracapsular hip fractures. OBJECTIVES: To compare different aspects of surgical technique in internal fixation of extracapsular hip fractures that have been subjected to randomised trials in adults. SEARCH STRATEGY: The Cochrane Musculoskeletal Injuries Group trials register, Medline, CENTRAL and reference lists of relevant articles were searched. Date of the most recent search: March 1999. SELECTION CRITERIA: All randomised and quasi-randomised trials investigating operative technique for the treatment of extracapsular hip fractures. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed trial quality, by use of an eleven item check list, and extracted data. Wherever possible and appropriate, results of outcome measures were pooled. MAIN RESULTS: All eight included trials were of only modest methodological quality. One trial of 65 patients undergoing fixation with a fixed nail-plate compared osteotomy versus anatomical reduction. There was a tendency to a reduced fixation failure rate after osteotomy. Four trials involving 465 patients undergoing fixation with a sliding hip screw (SHS) compared osteotomy versus anatomical reduction. Osteotomy was associated with an increased operative blood loss and length of surgery. There was also a tendency to an increased length of hospital stay and limb shortening for osteotomy. One trial of 200 patients undergoing fixation with a SHS compared results with or without compression across the fracture site. The only significant difference in outcomes was increased varus deformity in those fractures treated with compression. One trial of 19 patients reported reduced temperatures generated by a modified method of reaming the femoral head. Another study used oesophageal ultrasound to demonstrate reduced bone marrow intravascular embolism when a Gamma nail was inserted in 50 patients with, rather than without, a distal pressure venting hole in the femur. REVIEWER'S CONCLUSIONS: There is inadequate evidence to determine if any benefits exist for the routine use of osteotomy in conjunction with a SHS for the internal fixation of an unstable trochanteric femoral fracture. Osteotomy may be relevant if used in conjunction with a fixed nail plate. Based on the evidence of one trial only, there is inadequate evidence to support the application of compression across the fracture site of a trochanteric fracture during SHS fixation. Inadequate information exists for different reaming techniques during SHS or Gamma nail fixation to make definite conclusions.

Fracture Fixation, Internal↗
PubMed2005

Intradiscal pressure measurements in normal discs, compressed discs and compressed discs treated with axial posterior disc distraction: an experimental study on the rabbit lumbar spine model.

Intervertebral disc (IVD) pressure measurement is an appropriate method for characterizing spinal loading conditions. However, there is no human or animal model that provides sufficient IVD pressure data. The aim of our study was to establish physiological pressure values in the rabbit lumbar spine and to determine whether temporary external disc compression and distraction were associated with pressure changes. Measurements were done using a microstructure-based fibreoptic sensor. Data were collected in five control rabbits (N, measurement lying prone at segment L3/4 at day 28), five rabbits with 28 days of axial compression (C, measurement at day 28) and three rabbits with 28 days of axial compression and following 28 days of axial distraction (D, measurement at day 56). Disc compression and distraction was verified by disc height in lateral radiographs. The controls (N) showed a level-related range between 0.25 MPa-0.45 MPa. The IVD pressure was highest at level L3/4 (0.42 MPa; range 0.38-0.45) with a decrease in both cranial and caudal adjacent segments. The result for C was a significant decrease in IVD pressure (0.31 MPa) when compared with controls (P=0.009). D showed slightly higher median IVD pressure (0.32 MPa) compared to C, but significantly lower levels when compared with N (P=0.037). Our results indicate a high range of physiological IVD pressure at different levels of the lumbar rabbit spine. Temporary disc compression reduces pressure when compared with controls. These data support the hypothesis that temporary external compression leads to moderate disc degeneration as a result of degradation of water-binding disc matrix or affected active pumping mechanisms of nutrients into the disc. A stabilization of IVD pressure in discs treated with temporary distraction was observed.

Animals↗
PubMed2006

Effect of particle size and compression force on compaction behavior and derived mathematical parameters of compressibility.

PURPOSE: To analyze the influence of inherent densification and deformation properties of paracetamol on the mathematical parameters derived from Heckel, Walker, Kawakita, and Adams equations and to correlate these with single particle nominal fracture strength and bulk compression parameters using confined compression on a fully instrumented rotary tablet press. MATERIALS AND METHODS: Force-displacement data were captured during in-die compression for four different particle size fractions (150-250, 300-450, 500-650, and 700-1,000 microm) of paracetamol each at compression force of 5.2, 8.6, and 17.3 kN. Nominal single particle fracture strength was obtained by micro tensile testing. RESULTS: Apparent mean yield pressure (Py) from Heckel analysis was significantly affected by the applied pressure, and was influenced by elastic energy and Young's modulus. The single particle fracture strength correlated to parameters obtained from Heckel, Walker, Kawakita, and Adams equations. Results obtained from bulk compression and single particle measurements were consistent with, and polynomially related to Py, Kawakita (1/b), and Adams parameter (tau0'). CONCLUSIONS: Values of Py, 1/b, and tau0' obtained from Heckel, Kawakita, and Adams equations, respectively, can be interpreted as a measure of single particle nominal fracture strength during confined compression loading. Walker and Adams parameters were less affected, than Heckel and Kawakita parameters, by the applied pressure.

Acetaminophen↗
PubMed1995

Abdominal compressions increase vital organ perfusion during CPR in dogs: relation with efficacy of thoracic compressions.

STUDY OBJECTIVE: Abdominal compressions can be interposed between the thoracic compressions of standard CPR (SCPR). The resulting interposed abdominal compression CPR (IAC-CPR) may increase blood pressures and patient survival, particularly if applied as a primary technique after in-hospital cardiac arrest. We used a predominant cardiac compression canine model to study the effects of IAC-CPR on blood pressures and total and vital organ perfusion as a function of time after cardiac arrest and efficacy of SCPR. DESIGN: In a crossover design, we measured blood pressures and total and regional blood flow (radioactive microspheres) during 6-minute episodes of mechanical SCPR and IAC-CPR, both early (4 to 16 minutes) and late (18 to 30 minutes) after induction of ventricular fibrillation in eight dogs (weight, 25 to 33 kg) under neuroleptanalgesia/anesthesia. RESULTS: During IAC-CPR, the ascending aortic-right atrial pressure gradient increased (P < .05), and retrograde pressure pulses contributed to the rise of ascending aortic pressure. Within 2 minutes after the start of IAC-CPR, end-tidal CO2 fraction increased by 0.6 +/- 0.4 vol% (P < .05), suggesting enhanced venous return. IAC-CPR enhanced (P < .05) total forward blood flow (574 +/- 406 versus 394 +/- 266 mL/minute during SCPR for the early phase) and vital organ perfusion (including myocardium), in both early and late phases. The IAC-CPR-induced augmentation of blood flow was greater if perfusion was relatively high during SCPR. CONCLUSION: Compared with predominant cardiac compressions alone (SCPR), the addition of interposed abdominal compressions (IAC-CPR) improves total and vital organ oxygen delivery through enhanced venous return and perfusion pressures.

Abdomen↗
PubMed2000

American College of Cardiology/European Society of Cardiology International Study of Angiographic Data Compression Phase III: measurement of image quality differences at varying levels of data compression.

OBJECTIVES: We sought to investigate up to which level of Joint Photographic Experts Group JPEG) data compression the perceived image quality and the detection of diagnostic features remain equivalent to the quality and detectability found in uncompressed coronary angiograms. BACKGROUND: Digital coronary angiograms represent an enormous amount of data and therefore require costly computerized communication and archiving systems. Earlier studies on the viability of medical image compression were not fully conclusive. METHODS: Twenty-one raters evaluated sets of 91 cine runs. Uncompressed and compressed versions of the images were presented side by side on one monitor, and image quality differences were assessed on a scale featuring six scores. In addition, the raters had to detect pre-defined clinical features. Compression ratios (CR) were 6:1, 10:1 and 16:1. Statistical evaluation was based on descriptive statistics and on the equivalence t-test. RESULTS: At the lowest CR (CR 6:1), there was already a small (15%) increase in assigning the aesthetic quality score indicating "quality difference is barely discernible-the images are equivalent." At CR 10:1 and CR 16:1, close to 10% and 55%, respectively, of the compressed images were rated to be "clearly degraded, but still adequate for clinical use" or worse. Concerning diagnostic features, at CR 10:1 and CR 16:1 the error rate was 9.6% and 13.1%, respectively, compared with 9% for the baseline error rate in uncompressed images. CONCLUSIONS: Compression at CR 6:1 provides equivalence with the original cine runs. If CR 16:1 were used, one would have to tolerate a significant increase in the diagnostic error rate over the baseline error rate. At CR 10:1, intermediate results were obtained.

Adult↗
PubMed1991

Effect of moisture content on compression properties of two dextrose-based directly compressible diluents.

Moisture sorption characteristics and the effect of moisture content on the compression properties of two dextrose-based directly compressible diluents, namely, Emdex (diluent A) and Sweetrex (diluent B) were studied. Both diluents sorbed moisture rapidly at relative humidities greater than 60%. For both the diluents, pressures required to compress tablets to the same relative density decreased with increasing moisture content. Yield pressures calculated from linear Heckel plots obtained from the compression data of both diluents reflected decreasing values with increasing moisture content. Three-way surface profile graphs of moisture content versus tablet parameters such as crushing force, relative density, and compression pressure give a unique overall picture of the compression properties of a diluent and offer the tablet formulator a useful tool for diluent comparison.

Chemical Phenomena↗
PubMed2000

American College of Cardiology/ European Society of Cardiology international study of angiographic data compression phase III. Measurement Of image quality differences at varying levels of data compression.

OBJECTIVES: We sought to investigate up to which level of Joint Photographic Experts Group (JPEG) data compression the perceived image quality and the detection of diagnostic features remain equivalent to the quality and detectability found in uncompressed coronary angiograms. BACKGROUND: Digital coronary angiograms represent an enormous amount of data and therefore require costly computerized communication and archiving systems. Earlier studies on the viability of medical image compression were not fully conclusive. METHODS: Twenty-one raters evaluated sets of 91 cine runs. Uncompressed and compressed versions of the images were presented side by side on one monitor, and image quality differences were assessed on a scale featuring six scores. In addition, the raters had to detect pre-defined clinical features. Compression ratios (CR) were 6:1, 10:1 and 16:1. Statistical evaluation was based on descriptive statistics and on the equivalence t -test. Results At the lowest CR (CR 6:1), there was already a small (15%) increase in assigning the aesthetic quality score indicating "quality difference is barely discernible-the images are equivalent.' At CR 10:1 and CR 16:1, close to 10% and 55%, respectively, of the compressed images were rated to be "clearly degraded, but still adequate for clinical use' or worse. Concerning diagnostic features, at CR 10:1 and CR 16:1 the error rate was 9.6% and 13.1%, respectively, compared with 9% for the baseline error rate in uncompressed images. CONCLUSIONS: Compression at CR 6:1 provides equivalence with the original cine runs. If CR 16:1 were used, one would have to tolerate a significant increase in the diagnostic error rate over the baseline error rate. At CR 10:1, intermediate results were obtained.

Adult↗
PubMed1999

Lossy compression should not be used in certain imaging applications such as chest radiography. For the proposition.

Computational techniques are frequently used to compress image data so that transmission and storage requirements are reduced. If the computational techniques result in no loss in image resolution, the technique is referred to as lossless compression. Greater compression of data may yield some loss in spatial or temporal resolution, and is referred to as lossy compression. In some radiologic examinations [e.g., gastrointestinal (GI) studies], some resolution loss may be tolerable, whereas in others (chest examinations and mammography) it conceivably could result in missed pathology. Without lossy compression, however, data requirements can be overwhelming for transmission, storage and retrieval of images such as chest films. The unanswered question, addressed in this Point/Counterpoint issue, is whether some degree of lossy compression can be tolerated in chest radiography.

Humans↗
PubMed1999

Ankle arthrodesis: internal non-compression arthrodesis versus internal compression arthrodesis.

Ankle arthrodesis is still considered to be the standard treatment for most disabling types of ankle arthritis, but fusion methods are varied. We report our experience of ankle arthrodesis and compare a group of 34 cases treated by Blair's non-compression arthrodesis to another group of 32 cases treated by internal compression arthrodesis using two crossed screws. The same surgeon performed all the operations. The Blair's non-compression arthrodesis group included 21 males and 13 females with an average age of 42 y/o (range 18-70 y/o) and an average follow up period of 38.6 months (range 26-62 months). The union rate was 91.2% and the average union time was 5.6 months (range 2-10 months). There were three cases of non-union. The cross-screw compression arthrodesis group included 20 males and 12 females with an average age of 45 y/o (range 20-86 y/o) and an average follow up period of 38.3 months (range 15-81 months). The union rate was 96.9% and the average union time was 2.7 months (range 1.5-4.4 months). There was one case of non-union. We conclude that our cross-screws compression arthrodesis with its shorter fusion time was found to be superior to the Blair's non-compression arthrodesis.

Adult↗
PubMed2000

Compression ultrasonography of the leg veins in patients with clinically suspected pulmonary embolism: is a more extensive assessment of compressibility useful?

We performed a multi-center study in consecutive patients with suspected pulmonary embolism to compare the diagnostic accuracy of a two-point compression ultrasonography (only the common femoral vein and popliteal vein) with an extensive examination of compressibility (from the common femoral vein until the trifurcation of calf veins). A total of 479 patients underwent the two-point compression ultrasonography. The prevalence of pulmonary embolism was 32%. The sensitivity and specificity of this procedure were 23% (95% CI 19-26) and 98% (95% CI 96-99), respectively. Extensive compression ultrasonography was performed in 461 (96%) of these 479 patients and showed comparable accuracy indices (sensitivity 25%, 95% Cl 20-28 and specificity 97%, 95% CI 95-99). We conclude that compression ultrasonography has a limited sensitivity for the detection of thrombosis in patients with acute pulmonary embolism within 24 h of presentation. A more extensive assessment of compressibility of the leg veins in these patients has no additional value as compared to the two-point assessment.

Adult↗