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PubMed1982

Non-invasive investigation of vascular compression in patients with thoracic outlet syndrome.

Three hundred and seventy-seven patients with brachial pain and 63 controls have been examined regarding presence of symptomatic compression of the brachial plexus and subclavian vessels (Thoracic Outlet Syndrome = TOS). Each patient was examined clinically and by Doppler flowmetry. Two hundred and thirty (61%) had moderate to pronounced compression of the brachial plexus and 11 (2.9%) isolated compression of the subclavian artery or vein. One hundred and twenty-nine patients had symptoms not related to TOS. The prevalence of TOS was almost twice as common in women as in men, 1.76:1. The TOS patients were younger than the non-TOS patients, P less than 0.05. There was a significant correlation between arterial compression measured by Doppler flowmetry and the presence of compression of the plexus, P less than 0.001. But the validity of this method was not satisfactory, giving both false positive and negative results. Furthermore, there was a very good correlation between arterial compression assessed clinically and by Doppler flowmetry, P less than 0.001. Thus, the diagnosis of TOS is still a clinical judgement, the Doppler technique adding very little and any significant vascular compression being easily detected by clinical assessment.

Adolescent↗

PubMed1995

The effect of cardiac compression on defibrillation efficacy and the upper limit of vulnerability.

INTRODUCTION: We determined the effects of decreasing the ventricular blood volume and altering cardiac geometry on defibrillation, the upper limit of vulnerability (ULV), and the relationship between them. METHODS AND RESULTS: In six pigs, fibrillation/defibrillation trials were performed with a left ventricular apex patch to a superior vena cava catheter electrode configuration and a biphasic waveform. Thirty trials each were performed on a compressed versus noncompressed (normal) heart. Compression was achieved using direct mechanical ventricular actuation. Dose-response curves were constructed, and the 50% probability points (ED50) were compared for leading edge voltage (LEV), leading edge current (LEI), and total energy (TE). In another 12 pigs, triplicate defibrillation thresholds (DFTs) and ULVs were determined for each heart state. The T wave was scanned with shocks in 10-msec steps for determining the ULV. Compression resulted in decreased ED50s for LEV (delta = 138 +/- 77 V, P < 0.05, mean +/- SD), LEI (delta = 1.57 +/- 0.7 A, P < 0.05), and TE (delta = 4.9 +/- 3.6 J, P < 0.05) compared to normal. In the second study, compression significantly reduced DFT (P < 0.02) and ULV (P < 0.02) for LEV, LEI, and TE compared to normal. The ULV tended to be lower than the DFT for the normal heart state (delta = 23 +/- 46 V LEV: P = NS). However, the ULV was significantly greater than the DFT for the compressed heart state (delta = 19 +/- 25 V LEV; P < 0.03). CONCLUSIONS: Shock delivery during cardiac compression improves defibrillation efficacy. Additionally, cardiac compression decreases both DFT and ULV, which supports the ULV hypothesis of defibrillation. Finally, maintaining the heart's geometric and volumetric state during ULV testing in paced rhythm and DFT testing in ventricular fibrillation moves the ULV higher than the DFT-the position predicted by the ULV hypothesis for defibrillation.

Animals↗

PubMed1989

Effects of nerve compression or ischaemia on conduction properties of myelinated and non-myelinated nerve fibres. An experimental study in the rabbit common peroneal nerve.

Compound action potentials of both myelinated (A) and non-myelinated (C) fibres in the common peroneal nerve of rabbits were studied during and after acute, graded compression of the nerve at 200 or 400 mmHg applied for 2 h or during ischaemia created by nitrogen inhalation or aortic occlusion. Compression of the nerve at 200 mmHg blocked the AI component (large myelinated fibres) after about 23 min, while compression at 400 mmHg shortened this time to 11 min. The A2 component (thinner myelinated fibres) had a lower conduction velocity and a higher resistance to compression. There was just a slight decrease in conduction velocity of the non-myelinated fibres when the nerves were compressed at 200 mmHg for 2 h. However, compression at 400 mmHg for 2 h induced a marked deterioration of amplitude and conduction velocity of the C-fibres. There was an incomplete restitution of function of A- and C-fibres during 2 h of recovery. The thinner myelinated fibres were more susceptible to deprivation of oxygen than the thicker ones, while non-myelinated fibres differed in response according to method of ischaemia induction. It is concluded that non-myelinated fibres are very resistant to compression and a very high pressure (greater than 400 mmHg) is needed to affect these fibres.

Animals↗

PubMed1982

Multiple compression of powders in a tablet press.

Lactose, magnesium carbonate, phenacetin, microcrystalline cellulose and directly compressible starch compacts were repeatedly compressed in a tablet press, the tablets not being ejected from the die between compressions. When the interval between compressions was 1.3 s, all substances showed a decrease in the maximum force exerted by the tablet press, this being attributed to the formation of a structure of lower porosity. As the intervals between compressions is increased, the decrease in force is reduced, and in the case of microcrystalline cellulose and directly compressible starch, the force exerted at the second compression is greater than that exerted by the first.

Carbonates↗

PubMed1990

Effect of compression speed on the tensile strength of tablets of binary mixtures containing aspirin.

Mixtures of aspirin with sodium chloride, sucrose, Starch 1500 or Emcompress have been compressed to two maximum upper punch pressures at two compression speeds. Non-linear relationships between tensile strength and composition, and tablet porosity and composition were found in all cases. Tablets of the individual materials compressed at fast speed showed either little change or a reduction in tensile strength when compared with those compressed at slow speed. For mixtures of aspirin with Starch 1500, tablets compressed at fast speed were weaker and more porous than those compressed at slow speed. However, some mixtures of aspirin with sodium chloride, sucrose or Emcompress gave tablets with greater tensile strength and lower porosity when prepared at fast compression speed compared with tablets prepared at slow speed. This behaviour was attributed to the modification of the consolidation behaviour of the aspirin by the second material.

Aspirin↗

PubMed1995

Compression of lactose, glucose and mannitol granules.

The effect of the amount of granulation liquid, compression speed and maximum compression force on then compressibility and compactibility of lactose, glucose and mannitol granules was studied. The porosity based on the geometrical shape and the uniformity of weight of tablets was also studied. Lactose and mannitol granules showed a greater compressibility than glucose granules. Mannitol granules produced the hardest tablets and lactose and glucose the weakest. The change in the amount of granulation liquid caused changes both in the granule porosity and in the amount of binder; this was attributed to differences in tablet strength. All parameters studied were relatively insensitive to changing speeds of compression in the range used, except for the breaking force of mannitol tablets, which was greatest with the lowest speed of compression. All granule masses showed a relatively good continuous flow suitable for table production. Tablets compressed from lactose granules had the best uniformity of weight of the tablets studied.

Dosage Forms↗

PubMed1977

Induction of compression in the re-established visual projections on to a rotated tectal reimplant that retains its original topographic polarity within the halved optic tectum of adult goldfish.

1. The topographic pattern of re-established retinotectal projections following various surgical manipulations of the optic tectum was studied in adult goldfish with neurophysiological mapping methods. 2. Immediately following excision of the caudal half of the tectum, a piece of the tectal tissue was dissected from the remaining rostral half-tectum, and then reimplanted to the same half-tectum after either 180 or 90 degrees anticlockwise rotation around the dorsoventral axis in the first experimental group. 3. A majority (twenty-one out of twenty-three) of these operated fish, in which the reimplanted tectal tissue degenerated, showed no sign of a field compression: only the nasal half of the visual field (with a localized partial scotoma corresponding to the area of the degenerated reimplant) projected on to the remaining intact area of the rostral half-tectum. 4. In seven fish, the re-established visual projections on to the 180 or 90 degrees rotated reimplants showed a corresponding localized 180 or 90 degrees rotation with reference to the other projections on to the surrounding intact area of the same half-tectum. Only one of these seven fish showed also a compression in the re-established projections from the entire visual field on to the operated half-tectum with the 90 degrees rotated reimplant. 5. When a field compression was induced first in the intact rostral half-tectum following excision of the caudal half, and then a piece of the 90 degrees rotated tectal tissue was reimplanted later within the rostral half-tectum, the previously induced field compression persisted, regardless of whether the reimplanted tissue degenerated or survived. In the latter case, the compression in the re-established visual projections on to the surviving reimplant occurred according to the original topographic polarity of the 90 degrees rotated tectal tissue. 6. A field compression could also be induced within a rotated tectal reimplant, which retained its original polarity, as follows. A piece of the tectal tissue was dissected from the central area of the whole tectum, and then reimplanted after either 180 or 90 degrees rotation. When the reimplanted tectal tissue became reinnervated later, the caudal half of the operated tectum (including the posterior half of the reimplant) was excised. The re-established visual projections on to the remaining part of the halved reimplant within the rostral half-tectum showed later a field compression in accordance with the original topographic polarity of the 180 or 90 degrees rotated tectal tissue. 7. These results provide direct evidence for the compatibility between the retention of original topographic polarity by a reimplanted tectal tissue and the capability of the same tectal tissue to readjust to a disparity in size. 8. Histological examination of the operated half-tectum with a reimplant, stained by a modified rapid Golai method, revealed that the reimplanted tectal tissues retained highly organized cytoarchitectonic structures...

Animals↗

PubMed2000

A Conewise Linear Elasticity mixture model for the analysis of tension-compression nonlinearity in articular cartilage.

A biphasic mixture model is developed that can account for the observed tension-compression nonlinearity of cartilage by employing the continuum-based Conewise Linear Elasticity (CLE) model of Curnier et al. (J. Elasticity, 37, 1-38, 1995) to describe the solid phase of the mixture. In this first investigation, the orthotropic octantwise linear elasticity model was reduced to the more specialized case of cubic symmetry, to reduce the number of elastic constants from twelve to four. Confined and unconfined compression stress-relaxation, and torsional shear testing were performed on each of nine bovine humeral head articular cartilage cylindrical plugs from 6 month old calves. Using the CLE model with cubic symmetry, the aggregate modulus in compression and axial permeability were obtained from confined compression (H-A = 0.64 +/- 0.22 MPa, k2 = 3.62 +/- 0.97 x 10(-16) m4/N.s, r2 = 0.95 +/- 0.03), the tensile modulus, compressive Poisson ratio, and radial permeability were obtained from unconfined compression (E+Y = 12.75 +/- 1.56 MPa, v- = 0.03 +/- 0.01, kr = 6.06 +/- 2.10 x 10(-16) m4/N.s, r2 = 0.99 +/- 0.00), and the shear modulus was obtained from torsional shear (mu = 0.17 +/- 0.06 MPa). The model was also employed to predict the interstitial fluid pressure successfully at the center of the cartilage plug in unconfined compression (r2 = 0.98 +/- 0.01). The results of this study demonstrate that the integration of the CLE model with the biphasic mixture theory can provide a model of cartilage that can successfully curve-fit three distinct testing configurations while producing material parameters consistent with previous reports in the literature.

Cartilage, Articular↗

PubMed1996

Statistics of the log-compressed echo envelope.

Log compression of A lines to produce B-scan images in clinical ultrasound imaging systems is a standard procedure to control the dynamic range of the images. The statistics of such compressed images in terms of underlying scatterer statistics have not been derived. The statistics are analyzed for partially formed speckle using a general K distribution model of envelope statistics to derive the density function for the log-compressed envelope. This density function is used to elucidate the relation between the moments of the compressed envelope, the compression parameters, and the statistics of the scatterers. The analysis shows that the mean of the log-compressed envelope is an increasing function of both the backscattered energy and the effective scatterer density. The variance of the log-compressed envelope is a decreasing function of the effective scatterer density and is independent of the backscattered energy.

Computer Simulation↗

PubMed1998

The effect of compression ratio and release time on the categorical rating of sound quality.

Two experiments were carried out to determine how manipulating the compression ratio and release time of a single-band wide dynamic range hearing aid affects sound quality. In experiment I, compression ratio was varied over the range from linear to 10:1 (low compression threshold, attack time = 5 ms, release time = 200 ms). In experiment II, compression ratios of 1.5, 2, and 3:1 were combined with release times of 60, 200, and 1000 ms (attack time = 5 ms). Twenty listeners with sensorineural hearing loss rated the clarity, pleasantness, background noise, loudness, and the overall impression of speech-in-noise (Ventilation, Apartment, Cafeteria) processed through a compression hearing aid. Results revealed that increasing compression ratio caused decreases in ratings on all scales. Increasing release time caused ratings of pleasantness to increase, and ratings of background noise and loudness to decrease. At the 3:1 compression ratio, increasing the release time caused increases in ratings of clarity, pleasantness, and overall impression, and a decrease in background noise. Significant correlations were found between scales. Regression analysis revealed that the contributions of the scales of clarity, pleasantness, background noise, and loudness to the prediction of overall impression differed as a function of the competing noise condition.

Acoustic Stimulation↗

PubMed1990

Prevalence of vertebral compression fractures due to osteoporosis in ankylosing spondylitis.

OBJECTIVE: To determine the prevalence of vertebral compression fractures due to osteoporosis in patients with ankylosing spondylitis. DESIGN: Prospective study of 111 consecutive patients; patients with vertebral compression fractures were entered into a case-control study. SETTING: Outpatient clinic at the centre for rheumatic diseases, Glasgow. PATIENTS: 111 Consecutive patients with ankylosing spondylitis. Patients with compression fractures were matched for age and sex with two controls selected from the rest of the group. Patients with biconcave vertebral fractures were also studied. MAIN OUTCOME MEASURES: Assessments of spinal deformity and mobility and analysis of lateral radiographs of spines for presence of syndesmophytes. RESULTS: Fifteen patients with compression fractures and five with biconcave fractures were studied. Compared with the controls the patients with compression fractures had increased formation of syndesmophytes in the lumbar spine, whereas those with biconcave fractures had increased formation throughout the spine. Patients with compression fractures also had a greater degree of spinal deformity (distance from wall to tragus 24.5 cm v 12.7 cm in controls), less spinal mobility (20 v 45.6 degrees of flexion), and reduced chest expansion (2 cm v 3cm). CONCLUSION: Vertebral compression fractures due to osteoporosis are a common but frequently unrecognised complication of ankylosing spondylitis and may contribute to the pathogenesis of spinal deformity and back pain.

Adolescent↗

PubMed1997

A systematic review of compression treatment for venous leg ulcers.

OBJECTIVE: To estimate the clinical and cost effectiveness of compression systems for treating venous leg ulcers. METHODS: Systematic review of research. Search of 19 electronic databases including Medline, CINAHL, and Embase. Relevant journals and conference proceedings were hand searched and experts were consulted. MAIN OUTCOME MEASURES: Rate of healing and proportion of ulcers healed within a time period. STUDY SELECTION: Randomised controlled trials, published or unpublished, with no restriction on date or language, that evaluated compression as a treatment for venous leg ulcers. RESULTS: 24 randomised controlled trials were included in the review. The research evidence was quite weak: many trials had inadequate sample size and generally poor methodology. Compression seems to increase healing rates. Various high compression regimens are more effective than low compression. Few trials have compared the effectiveness of different high compression systems. CONCLUSIONS: Compression systems improve the healing of venous leg ulcers and should be used routinely in uncomplicated venous ulcers. Insufficient reliable evidence exists to indicate which system is the most effective. More good quality randomised controlled trials in association with economic evaluations are needed, to ascertain the most cost effective system for treating venous leg ulcers.

Bandages↗

PubMed1989

Image data compression in magnification hand radiographs.

A study was conducted on the use of an irreversible compression technique, Fourier quantization, to reduce the amount of digital data needed for an image. The effect of image compression was studied in radiographs obtained to diagnose subperiosteal bone resorption. Magnification radiographs of 44 hands were digitized to an array size of 4,096 X 4,096 X 12 bits. Selected subregions containing a single middle phalanx were compressed and reconstructed. A subset of the resultant 12-bit uncompressed and 8-, 7-, and 6-bit compressed images were read by four radiologists whose responses were analyzed with receiver operating characteristic (ROC) techniques. There were 81 images used in the ROC analysis, of which 48 were normal and 33 showed subperiosteal resorption. No statistically significant loss of diagnostic quality was detected for 8- or 7-bit compressed images, with average compression ratios of 16:1 and 28:1, respectively. Diagnostic quality was lost with 6-bit images, with an average compression ratio of 107:1.

Arthritis↗

PubMed1990

Outcome analysis of patients with normal compression US examinations.

Prior studies have documented the accuracy of compression ultrasound (US) for use in evaluating patients with clinically suspected deep venous thrombosis (DVT) of the lower extremity. A normal compression US examination is considered indicative of no thrombotic disease, and anticoagulant therapy is withheld. There are no long-term data supporting treatment decisions based solely on normal compression US results. The authors undertook a long-term (8-33-month) review of 1,111 normal compression US examinations performed on 1,022 patients. Outcome analysis obtained through review of imaging records, inpatient charts, and death certificates failed to document sequelae of untreated DVT in all but five patients with negative examinations. Three patients again presented with clinical symptoms of DVT that were subsequently documented with compression US, and two patients reportedly died of pulmonary embolism with no documentation of DVT several months after the initial negative study. Because of the clinical acceptance of this test and the subsequent increased demand for its use, compression US has quadrupled the yearly detection rate of DVT at the authors' institution. With the results of prior controlled studies and this favorable outcome analysis study, compression US is recommended as the diagnostic modality of choice for suspected DVT.

Adolescent↗

PubMed1990

Clinical evaluation of irreversible image compression: analysis of chest imaging with computed radiography.

To implement a picture archiving and communication system, clinical evaluation of irreversible image compression with a newly developed modified two-dimensional discrete cosine transform (DCT) and bit-allocation technique was performed for chest images with computed radiography (CR). CR images were observed on a cathode-ray-tube monitor in a 1,024 X 1,536 matrix. One original and five reconstructed versions of the same images with compression ratios of 3:1, 6:1, 13:1, 19:1, and 31:1 were ranked according to quality. Test images with higher spatial frequency were ranked better than those with lower spatial frequency and the acceptable upper limit of the compression ratio was 19:1. In studies of receiver operating characteristics for scoring the presence or absence of nodules and linear shadows, the images with a compression ratio of 25:1 showed a statistical difference as compared with the other images with a compression ratio of 20:1 or less. Both studies show that plain CR chest images with a compression ratio of 10:1 are acceptable and, with use of an improved DCT technique, the upper limit of the compression ratio is 20:1.

Humans↗

PubMed1991

Venous thrombosis in patients who have undergone major hip or knee surgery: detection with compression US and impedance plethysmography.

To compare the sensitivity, specificity, and predictive values of compression ultrasonography (US) in postoperative orthopedic patients with those of (a) impedance plethysmography in postoperative patients and (b) compression US in symptomatic outpatients, the authors performed an investigator-blinded cohort study. One hundred thirty-four consecutive inpatients who had undergone elective knee-replacement surgery or surgery for a fractured hip and 65 consecutive outpatients with clinically suspected venous thrombosis who had undergone venography were evaluated. Compression US allowed detection of 11 of 21 (52.4%) proximal-vein thrombi but was insensitive to calf-vein thrombi in the orthopedic patients. Compression US had a significantly greater specificity and positive predictive value than impedance plethysmography for all thrombi in orthopedic patients; compression US also had greater sensitivity. The sensitivity of compression US for proximal-vein thrombi was significantly higher (92.1%) in symptomatic outpatients than in orthopedic patients. The authors conclude that compression US has significant advantages over impedance plethysmography in the detection of proximal-vein thrombi in patients who have undergone hip- or knee-replacement surgery.

Hip Joint↗

PubMed1998

Airway compression in children with abnormal thoracic configuration.

PURPOSE: To assess the clinical and imaging findings in children with severe tracheal or bronchial compression caused by abnormal thoracic configuration. MATERIALS AND METHODS: Clinical and imaging findings, care, and outcome were reviewed in six patients with airway compression caused by abnormal thoracic configuration. Radiographs and magnetic resonance (MR) images were available in all patients. RESULTS: Mechanisms of airway compression included alteration of mediastinal anatomy and direct airway compression secondary to a narrow anteroposterior chest diameter. In three patients, the trachea was compressed at the level of the thoracic inlet. In the other three patients, the left main bronchus was compressed. Four patients underwent surgery for the thoracic deformity, with resolution of airway symptoms. In all four patients, the presence, location, and cause of airway obstruction determined at MR imaging were confirmed at surgery. CONCLUSION: Abnormal thoracic configuration, in addition to causing restrictive lung disease, can cause respiratory distress secondary to severe compression of the central airways.

Adolescent↗

PubMed1998

Detection of subtle abnormalities on chest radiographs after irreversible compression.

PURPOSE: To assess the effect of wavelet-based compression of posteroanterior chest radiographs on detection of small uncalcified pulmonary nodules and fibrosis. MATERIALS AND METHODS: Computed tomography (CT) of the chest was used to identify 20 patients with normal posteroanterior chest radiographs, 20 with a solitary uncalcified pulmonary nodule 1-2 cm in diameter, and 20 with fibrotic disease. A double-blind protocol for readings of original images and images compressed at 40:1 and 80:1 was analyzed by using the nonparametric receiver operating characteristic to measure differences in diagnostic accuracy and their statistical significance. RESULTS: There was no substantial difference in the overall diagnostic accuracy (measured by the area under the curve index) for both nodules and fibrosis between images compressed at 40:1 and 80:1 and uncompressed images. Readers tended to perform better on images compressed at 40:1 compared with uncompressed images. The "high-sensitivity" portion of the 80:1 compression curve for nodules was below that for the uncompressed curve, although this was not statistically significant. CONCLUSION: Lossy compression of chest radiographs at 40:1 can be used without decreased diagnostic accuracy for detection of pulmonary nodules and fibrosis. There is no statistically significant difference in diagnostic accuracy at 80:1 compression, but detection ability is decreased.

Algorithms↗