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PubMed1999

Intermittent pneumatic compression of legs increases microcirculation in distant skeletal muscle.

Intermittent pneumatic compression has been established as a method of clinically preventing deep vein thrombosis, but the mechanism has not been documented. This study observed the effects of intermittent pneumatic compression of legs on the microcirculation of distant skeletal muscle. The cremaster muscles of 80 male rats were exposed, a specially designed intermittent pneumatic-compression device was applied to both legs for 60 minutes, and the microcirculation of the muscles was assessed by measurement of the vessel diameter in three categories (10-20, 21-40, and 41-70 microm) for 120 minutes. The results showed significant vasodilation in arterial and venous vessels during the application of intermittent pneumatic compression, which disappeared after termination of the compression. The vasodilation reached a maximum 30 minutes after initiation of the compression and could be completely blocked by an inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine (10 micromol/min). A 120-minute infusion of NG-monomethyl-L-arginine, beginning coincident with 60 minutes of intermittent pneumatic compression, resulted in a significant decrease in arterial diameter that remained at almost the same level after termination of the compression. The magnitude of the decrease in diameter in the group treated with intermittent pneumatic compression and NG-monomethyl-L-arginine was comparable with that in the group treated with NG-monomethyl-L-arginine alone. The results imply that the production of nitric oxide is involved in the positive influence of intermittent pneumatic compression on circulation. It is postulated that the rapid increase in venous velocity induced by intermittent pneumatic compression produces strong shear stress on the vascular endothelium, which stimulates an increased release of nitric oxide and thereby causes systemic vasodilation.

Animals↗

PubMed1993

Proteoglycan synthesis in fetal tendon is differentially regulated by cyclic compression in vitro.

The predominant proteoglycan in tensional regions of tendon is the small proteoglycan decorin. However, a fibrocartilaginous tissue containing large amounts of aggrecan and biglycan develops at points where tendon wraps under bone and is subjected to compressive loading in addition to tension. The hypothesis that local compression regulates the development of fibrocartilage in tendon was tested by assessing the effect of in vitro compressive loading on proteoglycan synthesis. Fetal bovine deep flexor tendon explants from the region which would have become fibrocartilage were subjected to 3 days of continuous cyclic uniaxial compression (unconfined) to 30% strain, at a frequency of 1 cycle/6 s (0.17 Hz). Compression was perpendicular to the long axis of the tendon. Large proteoglycan, biglycan, and decorin were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and [35S]sulfate incorporated into each proteoglycan was quantitated by liquid scintillation counting of gel slices. The primary effect of compression was to stimulate selectively synthesis of large proteoglycan and biglycan. Incorporation of [35S]sulfate into large proteoglycan was increased 100-300% and incorporation into biglycan was increased 50-150% in compressed tissue compared to matched uncompressed tissue segments. Incorporation into decorin was unchanged. A similar effect on radio-sulfate incorporation was seen following loading of tissue from the tensional region of tendon, which does not normally develop into fibrocartilage. Proteoglycans from compressed tissue were larger, due to slightly longer glycosaminoglycan chains. Disaccharide analysis showed that the C6S/C4S ratio was higher in both the large and the small proteoglycan populations from compressed tissue. Aggrecan mRNA levels were increased approximately fivefold in loaded tissue, and SDS-PAGE analysis of [3H]leucine-labeled core proteins indicated that large proteoglycan core protein synthesis was increased by compression. The selective changes in large proteoglycan and biglycan synthesis, and in the sulfate composition and size of the glycosminoglycan chains, are consistent with what might be expected during development of fibrocartilage in vivo. These observations support the hypothesis that compressive force can regulate the development of fibrocartilaginous tissue in tendon.

Animals↗

PubMed1997

Efficacy of compression of different capacitance beds in the amelioration of orthostatic hypotension.

Orthostatic hypotension (OH) is the most disabling and serious manifestation of adrenergic failure, occurring in the autonomic neuropathies, pure autonomic failure (PAF) and multiple system atrophy (MSA). No specific treatment is currently available for most etiologies of OH. A reduction in venous capacity, secondary to some physical counter maneuvers (e.g., squatting or leg crossing), or the use of compressive garments, can ameliorate OH. However, there is little information on the differential efficacy, or the mechanisms of improvement, engendered by compression of specific capacitance beds. We therefore evaluated the efficacy of compression of specific compartments (calves, thighs, low abdomen, calves and thighs, and all compartments combined), using a modified antigravity suit, on the end-points of orthostatic blood pressure, and symptoms of orthostatic intolerance. Fourteen patients (PAF, n = 9; MSA, n = 3; diabetic autonomic neuropathy, n = 2; five males and nine females) with clinical OH were studied. The mean age was 62 years (range 31-78). The mean +/- SEM orthostatic systolic blood pressure when all compartments were compressed was 115.9 +/- 7.4 mmHg, significantly improved (p < 0.001) over the head-up tilt value without compression of 89.6 +/- 7.0 mmHg. The abdomen was the only single compartment whose compression significantly reduced OH (p < 0.005). There was a significant increase of peripheral resistance index (PRI) with compression of abdomen (p < 0.001) or all compartments (p < 0.001); end-diastolic index and cardiac index did not change. We conclude that denervation increases vascular capacity, and that venous compression improves OH by reducing this capacity and increasing PRI. Compression of all compartments is the most efficacious, followed by abdominal compression, whereas leg compression alone was less effective, presumably reflecting the large capacity of the abdomen relative to the legs.

Adult↗

PubMed1994

Wavelet compression and segmentation of digital mammograms.

An initial evaluation of Haar wavelets is presented in this study for the compression of mammographic images. Fifteen mammograms with 105 microns/pixel resolution and varying dynamic range (10 and 12 bits per pixel) containing clustered microcalcifications were compressed with two different rates. The quality and content of the compressed reconstructed images was evaluated by an expert mammographer. The visualization of the cluster was on the average good but degraded with increasing compression because of the discontinuities introduced by these types of wavelets as the compression rate increases. However, the artifacts in the decoded images were seen as totally artificial and were not misinterpreted by the radiologist as calcifications. The classification of the parenchymal densities did not change significantly but the morphology of the calcifications was increasingly distorted as the compression rate increased leading to lower estimates of the suspiciousness of the cluster and higher uncertainties in the diagnosis. The uncompressed and two sets of compressed images were also processed by a wavelet method to extract the calcifications. Despite the fact that the segmentation algorithm generated several false-positive signals in highly compressed images, all true clusters were successfully segmented indicating that the compression process preserved the features of interest. Our preliminary results indicated that wavelets could be used to achieve high compression rates of mammographic images without losing small details such as microcalcification clusters as well as detect the calcifications from either the uncompressed or compressed reconstructed data. Further research and application of multiresolution analysis to digital mammography is continuing.

Algorithms↗

PubMed1998

Pathology study of rabbit calf muscles after repeated compression.

: To elucidate the pathogenesis of chronic compartment syndrome, we examined pathological changes in the soleus (red) and extensor digitorum longus (EDL; white) muscles in Japanese white rabbits after repeated compression with a pneumatic tourniquet. Repeated tourniquet compression via cuff inflation was carried out on the rabbits, calves daily, for 2 h, then stopped for 30 min, and then applied for another 2 h. The contralateral hindlimb, which was not compressed, served as a control. Animals were allocated to 15 groups, with pressures of 40, 80, and 120 mmHg for periods of 1 day, 3 days, 1 week, 2 weeks, and 4 weeks. Skeletal muscle specimens in each group were studied by histopathological and histochemical (ATPase) methods. After compression for 1 day, regardless of pressure, and compression for 3 days in the 40-mmHg pressure group, edematous changes in regions with mild inflammation and increases in fiber diameter were observed in the muscles. After compression for 3 days in the 80- and 120-mmHg pressure groups, and after 1, 2, or 4 weeks in the 40-mmHg pressure group, a few necrotic fibers and scattered fibers with some mononuclear cell infiltrates indicative of early-stage necrosis were detected. In the groups with 80 or 120 mmHg pressure for 1, 2, or 4 weeks, muscle fibers exhibited marked degenerative changes, which were more pronounced in the 120-mmHg group than in the 80-mmHg group. The pathological changes were more pronounced in the soleus than in the EDL muscles, indicating that these two muscles differed in sensitivity to repeated compression. Additionally, average muscle wet weight and average fiber diameter for both types of muscle were increased in the 1-day and 3-day compression groups and decreased in the 1-week, 2-week, and 4-week compression groups. These findings clearly differ from those of previously reported single-compression experiments. Our findings indicate that repeated compression may cause serious muscle degeneration, particularly in red muscles.

Adenosine Triphosphatases↗

PubMed1993

Active compression-decompression resuscitation: analysis of transmitral flow and left ventricular volume by transesophageal echocardiography in humans. Cardiopulmonary Resuscitation Working Group.

OBJECTIVES: This study was designed to test the hypothesis that active compression-decompression cardiopulmonary resuscitation increases transmitral flow and end-decompression left ventricular volume over levels achieved with standard manual cardiopulmonary resuscitation. BACKGROUND: Recently, cardiopulmonary resuscitation incorporating active compression and decompression of the chest has been demonstrated to improve hemodynamic status in a canine model and in humans after cardiac arrest. METHODS: The active compression-decompression device was applied midsternum in five consecutive patients and results compared sequentially (in random order) with those of standard manual cardiopulmonary resuscitation. Both techniques were performed at 80 compressions/min with a 1.5- to 2-in. (3.8 to 5.1 cm) compression depth and a 50% duty cycle. Transesophageal echocardiographic data obtained in each patient included the velocity-time integral of transmitral pulsed Doppler recordings and two-dimensional images of the left ventricle in the long-axis view. Planimetric volume measurements of the left ventricle were obtained at both end-compression and end-decompression. RESULTS: No difference was observed in end-compression volume between the two techniques (p = 0.81). Increased end-decompression volume (active compression-decompression technique 81.3 +/- 12.5 vs. standard technique 69.4 +/- 10.8, p < 0.05), stroke volume (active compression-decompression technique 32.6 +/- 6.8 vs. standard technique 17.6 +/- 5.2, p < 0.05) and velocity-time integral of transmitral flow (active compression-decompression technique 15.8 +/- 4.3 vs. standard technique 7.8 +/- 2.3, p < 0.05) were found in the active compression-decompression group. The transmitral velocity-time integral was highly correlated with left ventricular stroke volume (r = 0.90). CONCLUSIONS: Improved transmitral flow, end-decompression left ventricular volume and stroke volume are seen with active compression-decompression resuscitation, suggesting a biphasic cardiothoracic cycle of flow. Active decompression of the chest appears to be a beneficial adjunct to standard cardiopulmonary resuscitation.

Aged↗

PubMed2005

Task-based model/human observer evaluation of SPIHT wavelet compression with human visual system-based quantization.

RATIONALE AND OBJECTIVE: The set partitioning in hierarchical trees (SPIHT) wavelet image compression algorithm with the human visual system (HVS) quantization matrix was investigated using x-ray coronary angiograms. We tested whether the HVS quantization matrix for the SPIHT wavelet compression improved computer model/human observer performance in a detection task with variable signals compared to performance with the default quantization matrix. We also tested the hypothesis of whether evaluating the rank order of the two quantization matrices (HVS versus default) based on performance of computer model observers in a signal known exactly but variable task (SKEV) generalized to model/human performance in the more clinically realistic signal known statistically task (SKS). MATERIALS AND METHODS: Nine hundred test images were created using real x-ray coronary angiograms as backgrounds and simulated arteries with filling defects (signals). The task for the model and human observer was to detect which one of the four computer simulated arterial segments contained the signal, four alternative-forced-choice (4 AFC). We obtained performance for four model observers (nonprewhitening matched filter with an eye filter, Hotelling, Channelized Hotelling, and Laguerre Gauss Hotelling model observers) for both the SKEV and SKS tasks with images compressed with and without the HVS quantization matrix. A psychophysical study measured performance from three human observers for the same conditions and tasks as the model observers. RESULTS: Performance for all four model observers improved with the use of the HVS quantization scheme. Improvements ranged from 5% (at compression ratio 7:1) to 50% (at compression ratio 30:1) for both the SKEV and SKS tasks. Human observer performance improvement averaged across observers ranged from 6% (at compression ratio 7:1) to 35% (at compression ratio 30:1) for the SKEV task and from 2% (at compression ratio 7:1) to 38% (at compression ratio 30:1) for the SKS task. Addition of internal noise to the model observers allowed for good prediction of human performance. CONCLUSIONS: Use of the HVS quantization scheme in the SPIHT wavelet compression led to improved model and human observer performance in clinically relevant detection tasks in x-ray coronary angiograms. Model observer performance can be reliably used to predict the human observer performance for the studied tasks as a function of SPIHT wavelet image compression. Our results further confirmed that model observer performance in the computationally more tractable SKEV task can be potentially used as a figure of merit for the more clinically realistic SKS task with real anatomic backgrounds.

Algorithms↗

PubMed2002

A comparison of two compression algorithms and the detection of caries.

OBJECTIVES: To assess the effect of two compression algorithms (JPEG and wavelet) on the detection of approximal caries. METHODS: Fifteen bitewing radiographs were generated using 100 posterior teeth mounted in blocks. The images were produced on conventional films (Ektaspeed Plus) and scanned at 300 d.p.i. Digital images were then compressed 9:1 with JPEG and wavelet methods. Nine observers detected the presence and depth of approximal caries recorded on a 5-point confidence scale and a 4-point depth scale from images viewed in random order. Histological examination provided the true depth of the lesions. Data were analysed by means of ANOVA. The null hypothesis was that there is no significant difference between the two compression algorithms and the original uncompressed images. RESULTS: JPEG performed significantly worse than the original and the wavelet algorithm (P<0.001) for the detection of dentinal lesions. However, no significant differences were found for the detection of sound surfaces, enamel lesions, and lesions up to the DEJ between JPEG-compressed images and each of the other two modalities. There was also no significant difference between the wavelet-compressed images and the original for all lesion depths. CONCLUSIONS: At a compression ratio of 9:1, there were no significant differences among the original images, JPEG and wavelet compressed images for the detection of enamel caries. JPEG-compressed images performed inferiorly to the original and wavelet-compressed images for the detection of dentinal lesions. Wavelet compression is a better choice than JPEG at the compression ratio investigated in this study.

Algorithms↗

PubMed1996

Effects of single-band syllabic amplitude compression on temporal speech information in nonsense syllables and in sentences.

The effects of single-band amplitude compression on the use by subjects with normal hearing of temporal speech information were assessed using speech stimuli that had been processed to remove most spectral information before being compressed. The resulting signal-related-noise (SRN) stimuli isolated the effects of compression on the temporal information in speech by making it impossible for subjects to identify stimulus items on the basis of spectral speech information. Subjects with normal hearing listened to /aCa/ SRN disyllables that had been subjected to single-band compression at various combinations of compression ratio (CR) and time constants (TC). Performance was reduced only in the most severe compression condition (CR = 8; TC = 50), and then only slightly. Additional testing showed that subjects could use both periodicity and compression-overshoot artifactual information--in addition to envelope information--to identify the compressed /aCa/ stimuli. When a list of 10 context-controlled sentences was converted to SRN and compressed at CR = 8 and TC = 50, the ability of subjects with normal hearing to identify the sentences was significantly affected. Results established that (a) subjects with normal hearing differ widely in their abilities to use temporal information for speech identification, even after training; (b) subjects can learn to use both temporal envelope and periodicity information for identification if disyllables, even though; (c) subjects with normal hearing need envelope but not periodicity information to identify SRN sentences in a closed set. These results suggest that single-band compression at CR = 8 and TC = 50 would be undesirable for persons with limited ability to resolve speech spectral information. It is currently not known how less severe compression conditions would affect envelope information in sentences.

Adult↗

PubMed1999

Long cotton wool rolls as compression enhancers in macrosclerotherapy for varicose veins.

BACKGROUND: Macrosclerotherapy in combination with compression has proven to be safe and effective in the treatment of varicose veins. Local compression is increased by pads, according to Laplace law. Firm rolls of cotton wool are fixed over the course of the entire vein to increase local compression and to reduce complications. Additional compression is given by a combination of a class I (daytime and nighttime) and class II (daytime only) medical compression hosiery. PURPOSE: To evaluate the effectiveness and side effects of sclerocompression therapy with cotton wool rolls in combination with medical compression hosiery. METHOD: Prospective study with 100 patients (120 legs) with primary varicose veins, which are treated with polidocanol as sclerosant with the empty vein technique. Immediately after the injection, a long cotton wool roll is placed over the entire vein and fixed. Additional compression is obtained with class I and class II medical compression hosiery. The interface pressure on the skin, just under the cotton wool roll, is measured on 12 legs with the aid of an interface pressure measuring instrument (Oxford Pressure Monitor). RESULTS: Good sclerosing results are obtained in all patients. Side effects are classified as early and late. In 16 patients, minor side effects which needed no treatment are observed. In only 3 cases (2.5%), intravascular blood clots (2) and phlebitis (1) needed incision and expression. The mean interface pressure of all measuring sensors under the cotton wool roll is 84 mm/Hg (68 to 122 mm/Hg). CONCLUSION: This study proves the high effectiveness of a cotton wool roll compression right at the place of treatment. By using these long cotton wool compression rolls, the compression part of sclerocompression therapy becomes more effective and much easier to perform.

Animals↗

PubMed1999

Compressed air as a source of inhaled oxidants in intensive care units.

Exhaled gas from mechanically ventilated preterm infants was found to have similar oxidant concentrations, regardless of lung disease, leading to the hypothesis that wall outlet gases were an oxidant source. Oxidants in compressed room air and oxygen from wall outlets were assessed in three hospitals. Samples were collected by flowing wall outlet gas through a heated humidifier and an ice-packed condenser. Nitric oxide (NO) was measured in intensive care room air and in compressed air with and without a charcoal filter using a Sievers NOA280 nitric oxide analyzer (Boulder, CO). Oxidants were measured by spectrophotometry and expressed as nMol equivalents of H2O2/mL. The quantity of oxidant was also expressed as amount of Vitamin C (nMol/mL) added until the oxidant was nondetectable. This quantity of Vitamin C was also expressed in Trolox Equivalent Antioxidant Capacity (TEAC) units (mMol/L). Free and total chlorine were measured with a Chlorine Photometer. Oxidants were not found in compressed oxygen and were only found in compressed air when the compression method used tap water. At a compressed room air gas flow of 1.5 L/min, the total volume of condensate was 20.2 +/- 1 mL/hr. The oxidant concentration was 1.52 +/- 0.09 nMol/mL equivalents of H2O2/mL of sample and 30.8 +/- 1.2 nMol/hr; 17.9% of that found in tap water. Oxidant reduction required 2.05 +/-0.12 nMol/mL vitamin C, (1.78 +/- 0.1 x 10(-3) TEAC units). Free and total chlorine in tap water were 0.3 +/- 0.02 mg/mL and 2.9 +/- 0.002 mg/mL, respectively. Outlet gas contained 0.4 +/- 0.06 mg/mL and 0.07 + 0.01 mg/mL total and free chlorine, respectively; both 14% of tap water. When a charcoal filter was installed in the hospital with oxidants in compressed air, oxidants were completely removed. Nursery room air contained 12.4 +/- 0.5 ppb NO; compressed wall air without a charcoal filter, 8.1 +/- 0.1 ppb and compressed air with a charcoal filter 12.5 +/- 0.5 ppb. A charcoal filter does not remove NO. (Table 3) We recommend that all compressed air methods using tap water have charcoal filters at the compression site and the gases be assessed periodically for oxidants.

Administration, Inhalation↗

PubMed2001

[Medical compression therapy].

In order to evaluate the correlation between the pressure exerted by compression stockings and a resulting improvement in venous hemodynamics, we carried out an open, randomized, prospective study on 22 patients (11 women and 11 men with an average age of 55.1 [10.3]) with chronic venous insufficiency (CVI) in the clinical stages C1-4, Ep, AS, Ap, PR. Dynamic strain gauge plethysmography was used to measure the acute effect on venous hemodynamics of 9 different compression stockings in compression class 2 (A-D). At the same time when venous function parameters were monitored, we also measured the pressure exerted by the compression stockings during rest and exercise. With all compression stockings the average resting pressure fulfilled in reclined patients the specifications for compression class 2 (25-35 mmHg at the ankle, CEN). The compression stockings lengthened venous refill time t0 in a statistically significant degree. The improvement in venous function was correlated with the ratios of maximal working pressure to resting pressure while standing (r = 0.97, p < 0.001). Compression stockings belonging to the same compression class vary in their acute effect on venous hemodynamics. The efficiency of the different therapeutic compression stockings was largely dependent on the amount of fabric stretch, which can be characterized in vivo with the ratio of maximum exerted pressure during movement to that while standing still. A knowledge of the hemodynamic effectivity of the various compression stockings allows the optimal stocking selection for each patient and his individual clinical situation.

Adult↗

PubMed2002

Survival and neurologic outcome after cardiopulmonary resuscitation with four different chest compression-ventilation ratios.

STUDY OBJECTIVE: The optimal ratio of chest compressions to ventilations during cardiopulmonary resuscitation (CPR) is unknown. We determine 24-hour survival and neurologic outcome, comparing 4 different chest compression-ventilation CPR ratios in a porcine model of prolonged cardiac arrest and bystander CPR. METHODS: Forty swine were instrumented and subjected to 3 minutes of ventricular fibrillation followed by 12 minutes of CPR by using 1 of 4 models of chest compression-ventilation ratios as follows: (1) standard CPR with a ratio of 15:2; (2) CC-CPR, chest compressions only with no ventilations for 12 minutes; (3) 50:5-CPR, CPR with a ratio of 50:5 compressions to ventilations, as advocated by authorities in Great Britain; and (4) 100:2-CPR, 4 minutes of chest compressions only followed by CPR with a ratio of 100:2 compressions to ventilations. CPR was followed by standard advanced cardiac life support, 1 hour of critical care, and 24 hours of observation, followed by a neurologic evaluation. RESULTS: There were no statistically significant differences in 24-hour survival among the 4 groups (standard CPR, 7/10; CC-CPR, 7/10; 50:5-CPR, 8/10; 100:2-CPR, 9/10). There were significant differences in 24-hour neurologic function, as evaluated by using the swine cerebral performance category scale. The animals receiving 100:2-CPR had significantly better neurologic function at 24 hours than the standard CPR group with a 15:2 ratio (1.5 versus 2.5; P =.007). The 100:2-CPR group also had better neurologic function than the CC-CPR group, which received chest compressions with no ventilations (1.5 versus 2.3; P =.027). Coronary perfusion pressures, aortic pressures, and myocardial and kidney blood flows were not significantly different among the groups. Coronary perfusion pressure as an integrated area under the curve was significantly better in the CC-CPR group than in the standard CPR group (P =.04). Minute ventilation and PaO (2) were significantly lower in the CC-CPR group. CONCLUSION: In this experimental model of bystander CPR, the group receiving compressions only for 4 minutes followed by a compression-ventilation ratio of 100:2 achieved better neurologic outcome than the group receiving standard CPR and CC-CPR. Consideration of alternative chest compression-ventilation ratios might be appropriate.

Animals↗

PubMed2000

Compression and walking versus bed rest in the treatment of proximal deep venous thrombosis with low molecular weight heparin.

OBJECTIVE: The purpose of this randomized controlled trial was to evaluate the benefits of compression and walking exercises in comparison with bed rest in the acute stage of proximal deep venous thrombosis (DVT). METHODS: Forty-five patients with proximal DVT that was proved with compression ultrasound scan or phlebography were randomized into three groups. Group A consisted of 15 patients who received inelastic compression bandages (Unna boots on the lower leg, adhesive bandages on the thigh), and group B consisted of 15 patients who received thigh-length compression stockings, class II. Group C consisted of 15 patients who underwent bed rest and no compression. All patients received dalteparin, 200 IU/kg per body weight, subcutaneously every 24 hours. The clinical characteristics of the three groups were comparable. Primary end points were the reduction of pain assessed daily with the Visual Analogue Scale and the Lowenberg test, the reduction of leg circumference at the ankle and calf levels, and the improvement of clinical scores. The daily walking distance was measured with a pedometer. Safety parameters were ventilation-perfusion scans and duplex ultrasound scans performed on days 0 and 9. RESULTS: The daily walking distance was between 600 and 12,000 m in the compression groups and averaged 66 m in the bed rest group. The pain level showed a statistically significant reduction starting after the second day in the compression groups (A and B) and after 9 days in the bed rest group C (P <.05). The same was true for the measurement of leg circumference. Improvement of the clinical scores was significantly better in the compression groups compared with the bed rest group (P <.01). There was no significant difference concerning the occurrence of new pulmonary emboli and regression of thrombus diameter. Progression of thrombi in the femoral vein was greater and occurred more frequently in the bed rest group than in the other two groups (P = not significant). CONCLUSION: Mobile patients with acute proximal DVT treated with low molecular weight heparin should be encouraged to walk with compression bandages or medical compression stockings. The rate of resolution of pain and swelling is significantly faster when the patient ambulates with compression. The risk of pulmonary embolism is not significantly increased by this approach.

Acute Disease↗

PubMed2006

Bulk characterization of pharmaceutical powders by low-pressure compression II: effect of method settings and particle size.

The aim of the present study was to investigate the effect of punch and die diameter, sample size, compression speed, and particle size on two low-pressure compression-derived parameters; the compressed density and the Walker w parameter. The excellent repeatability of the low-pressure compression method allowed small effects of variations in punch and die diameter and sample size to be demonstrated on a high significance level. Changing the compression speed, however, did not cause a significant effect in the compressed density, whereas a decrease in w was seen. The effect of particle size was studied by compressing and tapping different grades of calcium carbonate, lactose, and microcrystalline cellulose. The low-pressure compression-derived parameters were compared to tapped densities and to Compressibility Indexes obtained by tapping volumetry. Even though the relationship between particle size and the low-pressure compression-derived parameters appeared to be more complicated, a similar trend was observed. It was concluded that the low-pressure compression method provides a useful alternative to the more sample-consuming methods providing flow-related information.

Algorithms↗

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↗

PubMed2004

Experimental spinal stenosis: relationship between degree of cauda equina compression, neuropathology, and pain.

STUDY DESIGN: An analysis of pathologic changes after different degrees of cauda equina compression. OBJECTIVES: To explore the association between the degree of the cauda equina compression and the extent of pathologic change, expression of tumor necrosis factor (TNF-alpha), and neuropathic pain. To compare with distal nerve compression injury. SUMMARY OF BACKGROUND DATA: Compression of the cauda equina reduces blood flow in compressed nerve roots and causes TNF-alpha expression and neuropathological change. In peripheral nerve, expression of TNF-alpha in Schwann cells is associated with primary demyelination without pain while TNF-alpha expression by macrophages is associated with axonal (Wallerian) degeneration and pain. METHODS: Two square-shaped pieces of silicon were placed into the fourth and sixth epidural space in rats. Various sized silicon was used in each group (mild, moderate, and strong compression groups), while no silicon was used in the sham-operated group. Mechanical allodynia was determined by the von Frey test. Comparisons of the number of TNF-alpha- and apoptosis-positive cells were made using immunohistochemistry. RESULTS: There was no significant mechanical allodynia observed in any group. Some nerve roots showed demyelination following mild cauda equina compression. Axonal degeneration was observed in the moderate and strong cauda equina compression groups. TNF-alpha-immunoreactive cells were increased in all compression groups. Apoptosis of dorsal root ganglion cells was less than apoptosis in the spinal cord. CONCLUSION: Mild cauda equina compression induces TNF-alpha expression and demyelination. Moderate and strong cauda equina compression induces TNF-alpha expression and degeneration associated with macrophage invasion. Neither demyelination nor degeneration in the cauda equina induced mechanical allodynia. Nerve lesions proximal to the dorsal root ganglion do not produce significant mechanical allodynia. Dorsal root ganglion apoptosis may be important for pain.

Animals↗

PubMed2005

Estimating the compressive strength of the porcine cervical spine: an examination of the utility of DXA.

STUDY DESIGN: The failure strength of porcine spinal units was correlated with vertebral size and bone mineralization. The accuracy of the resulting predictive equations was tested with an independent sample of spinal units. OBJECTIVES: To determine if dual energy x-ray absorptiometry (DXA)-obtained measures of bone mineralization can be used to accurately predict the compressive tolerance of porcine spinal units. SUMMARY OF BACKGROUND DATA: Porcine spinal units are often used in place of cadaveric tissues, and normalization is used to improve the transferability of model results. In compressive testing, normalization can be performed to the estimated compressive strength. Bone mineralization measures have been shown to be positively correlated with compressive tolerance and have been used to predict the tolerance of human spinal units. However, the accuracy of these predictive equations has not been assessed with an independent sample. METHODS: Twenty porcine cervical spinal units were scanned (DXA) to obtain measures of bone mineral content (BMC) and bone mineral density (BMD). The units were compressed to failure, and the failure loads were correlated with the measured bone mineralization and endplate area of the spinal unit. The regression equations were used to predict the compressive tolerance of an independent sample of spinal units. RESULTS: BMC (P = 0.078) and BMD (P = 0.2834) were not significantly correlated to compressive strength. Endplate area was the most highly correlated variable, with an r of 0.5329. The use of a predictive equation including BMC on the second independent sample resulted in errors of estimation of 1.4 +/- 1.2 kN, corresponding to 13% of the average compressive strength. In comparison, the use of an equation employing endplate area alone resulted in estimation errors of 11%. CONCLUSIONS: Measures of BMC/BMD did not enhance predictions of compressive strength and will not reduce errors in compressive load normalization in a porcine model. The poor correlations found between BMC and compressive strength may be due to the non-load-bearing anterior processes of the porcine cervical spine.

Absorptiometry, Photon↗