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PubMed1998

Diffusion-weighted MR imaging of bone marrow: differentiation of benign versus pathologic compression fractures.

PURPOSE: To evaluate the usefulness of diffusion-weighted magnetic resonance (MR) imaging of bone marrow for differentiating between benign and pathologic vertebral compression fractures. MATERIALS AND METHODS: Thirty patients with 39 vertebral compression fractures were examined with MR imaging. Diffusion-weighted MR imaging was performed with a steady-state free precession sequence in 22 acute benign osteoporotic and/or traumatic fractures and 17 pathologic compression fractures. Biplanar radiographs, T1-weighted spin-echo (SE) MR images, and short inversion time inversion-recovery (STIR) MR images were available for all patients. The signal intensity characteristics were analyzed qualitatively and quantitatively (bone marrow contrast ratios and signal-to-noise ratios) for all sequences. RESULTS: At diffusion-weighted MR imaging, all benign vertebral compression fractures were hypo- to isointense to adjacent normal vertebral bodies. Pathologic compression fractures were hyperintense to normal vertebral bodies. Benign vertebral fractures had negative bone marrow contrast ratios at diffusion-weighted imaging, whereas pathologic vertebral fractures had positive values (P < .001). The difference in bone marrow contrast ratios for benign and pathologic compression fractures at T1-weighted SE and STIR imaging was not significant (P > .01). CONCLUSION: Diffusion-weighted MR imaging provided excellent distinction between pathologic and benign vertebral compression fractures.

Adult↗

PubMed2003

Rapid compressions in a captive bubble apparatus are isothermal.

Captive bubbles are commonly used to determine how interfacial films of pulmonary surfactant respond to changes in surface area, achieved by varying hydrostatic pressure. Although assumed to be isothermal, the gas phase temperature (Tg) would increase by >100 degrees C during compression from 1 to 3 atm if the process were adiabatic. To determine the actual change in temperature, we monitored pressure (P) and volume (V) during compressions lasting <1 s for bubbles with and without interfacial films and used P x V to evaluate Tg. P x V fell during and after the rapid compressions, consistent with reductions in n, the moles of gas phase molecules, because of increasing solubility in the subphase at higher P. As expected for a process with first-order kinetics, during 1 h after the rapid compression P x V decreased along a simple exponential curve. The temporal variation of n moles of gas was determined from P x V >10 min after the compression when the two phases should be isothermal. Back extrapolation of n then allowed calculation of Tg from P x V immediately after the compression. Our results indicate that for bubbles with or without interfacial films compressed to >3 atm within 1 s, the change in Tg is <2 degrees C.

Gases↗

PubMed1997

Diagnosis and management of left main stem bronchus compression.

There are four major variants of congenital vascular tracheal compression: innominate artery, aberrant subclavian, aorta or aortic arch anomaly, and pulmonary artery sling. These forms of vascular compression typically involve the trachea and/or the right main stem bronchus. We present eight cases of congenital vascular compression involving the left main stem bronchus. These cases represent a poorly understood variant of vascular tracheal compression. This variant represents approximately 10% of our pediatric tracheobronchial compression or stenosis patients. The finding, both noted endoscopically and now illustrated by magnetic resonance imaging, is caused by compression of the left main stem bronchus between the descending aorta and a portion of the pulmonary artery. Frequently, the descending aorta is in an abnormal anterior position with relation to the thoracic spine. Recognition of this entity is important in our experience and has influenced clinical management. In four of eight children, it required a surgical procedure directed toward the relief of the left main stem compression.

Abnormalities, Multiple↗

PubMedDate not supplied

Management of metastatic spinal cord compression.

Metastatic spinal cord compression, diagnosed in 3-7% of cancer patients, is one of the most dreaded complications of metastatic cancer. It is an oncologic emergency, which must be diagnosed early and treated promptly to achieve the best results and avoid progressive pain, paralysis, sensory loss and sphincter incontinence. Patients who are ambulatory at the time of the diagnosis have a higher probability of obtaining good response to treatment and a longer survival. In clinical practice, back pain accompanies metastatic spinal cord compression in most cases, even in patients with no neurologic deficits. Magnetic resonance imaging is the best tool for diagnosing metastatic spinal cord compression and is able to identify spinal cord compression in 32-35% patients with back pain, bone metastases and normal neurologic examination. Moreover, magnetic resonance imaging gives the extension of the lesion, can diagnose other unsuspected clinical metastatic spinal cord compression sites, and is useful for the radiation oncologist in defining the target volume. Radiotherapy is the treatment of choice in most cases, whereas surgery is advised only in selected patients (ie, if stabilization is necessary, if radiotherapy has already been given in the same area, when vertebral body collapse causes bone impingement on the cord or nerve roots, when there are diagnostic doubts, or when computed tomography-guided percutaneous vertebral biopsy cannot be performed). Laminectomy should be abandoned in favor of more aggressive surgery (ie, posterior, anterior, and/or lateral approach, tumor mass resection, and stabilization of the spine). Generally, radiotherapy must be administered 7-10 days after surgery. The optimal radiation schedule has not been defined. However, as recently suggested by some clinical trials, even the hypofractionated radiotherapy regimens are effective and can be used without increasing radiation-induced myelopathy. Moderate doses of dexamethasone should be used in the early phases of therapy. After radiotherapy, spinal recurrence is generally found in sites different from the first compression area. A close post-treatment follow-up is suggested using clinical parameters (pain, motor and sphincter function), and magnetic resonance imaging should be performed only when a second metastatic spinal cord compression and/or myelopathy are clinically suspected.

Algorithms↗

PubMed2006

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

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

Adolescent↗

PubMed1999

Vertebral artery compression resulting from head movement: a possible cause of the sudden infant death syndrome.

OBJECTIVE: Vertebral artery compression causing brainstem ischemia has been suggested to underlie the sudden infant death syndrome. Vertebral artery distortion from neck movements has been demonstrated by angiography in infants, but direct evidence for arterial compression is lacking. In an attempt to demonstrate vertebral artery compression from head movement, we examined at postmortem the vertebral arteries of infants after neck extension or rotation. METHODS: The C1-C7 spinal column, together with a 2-cm rim of skull base, was removed from 20 infants dying from sudden infant death syndrome or other causes. In 5 cases the neck was extended, in 9 cases it was rotated 90 degrees to the right, and in 6 cases the neck was held in the neutral position. The neck was maintained in these positions during formalin fixation, and serial sections of selected blocks were examined microscopically. RESULTS: In 3 of 5 extended cases, bilateral vertebral artery compression was seen between the occipital bone and C1. In 3 of 9 rotated cases, the left vertebral artery was compressed adjacent to C1 before the artery entered the transverse foramen. No vertebral artery compression was seen in the necks held in the neutral position. CONCLUSIONS: The vertebral arteries of some infants can be compressed by neck movement. This could induce lethal brainstem ischemia in infants with inadequate collateral blood flow or with poor compensatory arterial dilatation, and may underlie some cases of sudden infant death syndrome.

Brain Ischemia↗

PubMed2004

Prospective randomized study comparing ultrasound-guided thrombin injection to compression in the treatment of femoral pseudoaneurysms.

PURPOSE: To compare in a randomized prospective study the treatment of femoral pseudoaneurysms with ultrasound-guided thrombin injection versus ultrasound-guided compression. METHODS: Thirty consecutive patients (22 men; mean age 67+/-8 years, range 53-82) with iatrogenic femoral pseudoaneurysms were randomized to treatment with either ultrasound-guided compression (n=15) or injection of bovine thrombin (n=15). The primary outcome measure was thrombosis of the pseudoaneurysm within 24 hours. Secondary outcome measures were complications and hospitalization time (LOS). RESULTS: Thrombosis within 24 hours was achieved in 15 (100%) patients given thrombin versus 2 (13%) in the compression group (p<0.001). Of 13 pseudoaneurysms failing the initial compression treatment, 7 were retreated, 4 successfully. Thus, only 6 (40%) lesions were thrombosed within 48 hours after 1 or 2 compression sessions. The other 9 cases were successfully treated with thrombin injection. LOS was 2.8+/-1.5 days and 3.5+/-2.4 days in the thrombin and compression groups, respectively (p>0.05). No complications were noted in either group. CONCLUSIONS: Ultrasound-guided thrombin injection induces a fast, effective, and safe thrombosis of postcatheterization pseudoaneurysms. The technique is clearly superior to compression treatment and is recommended as the therapy of choice.

Aged↗

PubMed2002

Bale compression and hydrogen phosphide fumigation to control cereal leaf beetle (Coleoptera: Chrysomelidae) in exported rye straw.

Control of larvae and adults of cereal leaf beetle, Oulema melanopus (L.), by bale compression and hydrogen phosphide fumigation was studied in rye straw, Secale cereale L., in Aurora, OR. Natural mortality of larvae after transport was 4.0 +/- 1.0% (mean +/- SEM). Compression (105 kg/cm2) of larvae in standard bales (122 cm long) of rye straw resulted in 100% mortality. Compression of adults in standard bales plus storage of the compressed bales (56 cm long) for 1 d in a freight container resulted in 100% mortality. A KD50 of 102 ppm hydrogen phosphide for 1 h was estimated from the probit regression line developed from dose-response data at 21 degrees C in basic laboratory tests. The LD50s and LD99s were 163 and 6,910 ppm for 2-h exposures and were 18 and 42 ppm for 6-h exposures at 21 degrees C, respectively. A tested close of 400 ppm for 24 h at 21 degrees C resulted in 100% mortality of the adults. Larvae (n = 10,560) and adults (n = 18,602) did not survive exposure to bale compression followed by hydrogen phosphide fumigation (60 g/28.3 m3) for 3 d in rye straw loaded in freight containers in large-scale tests. Copper plate corrosion values indicating the severity of exposure to hydrogen phosphide were 13 and 12, and mean temperatures of five locations in the freight container were 25 and 26 degrees C in large-scale tests with the larvae and adults, respectively. Hydrogen phosphide concentrations were > or = 400 ppm throughout the 3-d fumigation for larvae and during the first day of fumigation for adults. We propose that cereal leaf beetle can be controlled by a single treatment of bale compression followed by a 1-d storage period or by a fumigation in which 400 ppm hydrogen phosphide is maintained for 1 d at 21 degrees C or above. We confirmed that a multiple quarantine treatment of bale compression) followed by a 3-d fumigation will control cereal leafbeetle in exported rye straw.

Animals↗

PubMed2000

Percutaneous injection of thrombin for the treatment of pseudoaneurysms after catheterization: an alternative to sonographically guided compression.

OBJECTIVE: The purpose of our study was to determine the efficacy of percutaneous thrombin treatment for iatrogenic pseudoaneurysms of the femoral artery in comparison with sonographically guided compression repair. SUBJECTS AND METHODS: Twenty-three pseudoaneurysms occurring after catheterization were treated percutaneously with an initial injection of 1.0 mL of thrombin solution via a 22-gauge spinal needle under continuous sonographic guidance. Four patients required the additional injection of 1.0-4.0 mL of thrombin for complete thrombosis. Repeated sonography was performed 24 hr after injection. Additionally, we compared our results with those of a control group by reviewing the imaging findings and medical records of 16 patients who underwent sonographically guided compression of iatrogenic pseudoaneurysms between January 1998 and July 1998. RESULTS: Twenty-two of 23 pseudoaneurysms occurring after catheterization were successfully treated with percutaneous thrombin injection. One recurrence was identified 24 hr after injection in a patient who experienced a significant complication. Procedure time was limited to 15 min with an overall success rate of 96%. Retrospectively, 18 iatrogenic pseudoaneurysms were identified in 16 patients. Six (60%) of 10 pseudoaneurysms were successfully compressed under sonographic guidance, with an average time to thrombosis of 32 min. Compression was unsuccessful for four pseudoaneurysms with an average compression time of 45 min. Compression could not be performed in seven patients (39%). The overall success rate of sonographically guided repair was 60%. CONCLUSION: Preliminary evidence suggests that sonographically guided percutaneous thrombin injection is a safe and effective method of treatment for iatrogenic pseudoaneurysms and offers significant advantages over conventional sonographically guided compression.

Adult↗

PubMed2000

Detection of masses and clustered microcalcifications on data compressed mammograms: an observer performance study.

OBJECTIVE: To evaluate observers' ability to detect breast masses and clustered microcalcifications depicted on data compressed mammograms, an observer performance study was performed. MATERIALS AND METHODS: Eight observers assessed 60 mammographic images obtained in six modes, ranging from noncompressed to a maximum data compression level of 101:1. Observers were asked to rate the images on a scale of 0 to 100 for the likelihood of the presence of a mass and also independently for the likelihood of the presence of clustered microcalcifications. In addition, observers were asked to rate their subjective assessment of the quality of each image for the detection of a mass and separately for the detection of microcalcifications. Receiver operating characteristic analyses were performed. RESULTS: The average area under the receiver operating characteristic curve, A(z), for the detection of clustered microcalcifications decreases significantly at the highest data compression level when compared with the noncompressed and two lowest levels of data compression (p < 0.01), and a trend test of the average area under the receiver operating characteristic curve for all observers is statistically significant (p < 0.05). No statistically significant differences among or between any of the data compression level modes for the detection of masses were detected. CONCLUSION: At a high level of mammogram data compression, observer performance was degraded for the detection of clustered microcalcifications. Detection of masses was not affected by the data compression methods and levels used in this study.

Breast Neoplasms↗

PubMed1988

The effect of specific compression settings on phoneme identification in hearing-impaired subjects.

In this study, some aspects of single-channel compression have been investigated in 15 hearing-impaired subjects and 4 normal-hearing listeners. Phoneme perception as a function of the compression-threshold level was measured for two hearing aids with input-dependent compression, differing in compression ratio and compression recovery time. Phoneme-identification scores, obtained by different hearing aids under similar conditions, did not differ significantly. However, there was a small but significant increase in identification scores for the lowest setting of the compression threshold. Some qualitative differences in the patterns of confusion could also be established. There are indications that compression reduces the relative contribution of frication and enhances the contribution of the second formant of vowels in phoneme perception.

Adolescent↗

PubMed1999

Use of a loudness model for hearing aid fitting: II. Hearing aids with multi-channel compression.

A model for predicting loudness for people with cochlear hearing loss was applied to the problem of the initial fitting of a multi-channel compression hearing aid. The fitting was based on two constraints: (1) The specific loudness pattern evoked by speech of a moderate level (65 dB SPL) should be reasonably flat (equal loudness per critical band), and the overall loudness should be similar to that evoked in a normal listener by 65-dB speech (about 23 sones for binaural listening); (2) Speech with an overall level of 45 dB SPL should just be audible in all frequency bands from 500 Hz up to about 4 kHz, provided that this does not require compression ratios exceeding about 3. These two constraints were used to determine initial values for the gain, compression ratio and compression threshold in each channel of a multi-channel compression system. This initial fitting was based entirely on audiometric thresholds; it does not require suprathreshold loudness measures. The fitting method was evaluated using an experimental fast-acting four-channel compression system. The initial fitting was followed by an adaptive procedure to 'fine tune' the fitting, and the aids were then used in everyday life. Performance was evaluated by use of questionnaires and by measures of speech intelligibility. Although the fine tuning resulted in modest changes in the fitting parameters for some subjects, on average the frequency response shapes and compression ratios were similar before and after the fine tuning. The fittings led to satisfactory loudness impressions in everyday life and to high speech intelligibility over a wide range of levels. It was concluded that the initial fitting method gives reasonable starting values for the fine tuning.

Acoustic Stimulation↗

PubMed2002

Effects of high-frequency emphasis and compression time constants on speech intelligibility in noise.

The objectives of the study were to evaluate the effect of different settings with regard to speech intelligibility in noise both objectively and subjectively and thus determine a favoured setting of compression time parameters, pre-set program (high-frequency emphasis) or combination for each individual user in a prospective study. Another objective was to evaluate the relationship between patient characteristics (e.g. slope of hearing loss) and favoured settings. In total, 38 subjects divided over five audiological centres were fitted with the Philips Spaceline D71-40 BTE digital hearing aid. Subjects were asked to compare three predefined compression algorithms with different time constants, slow (indicated by the manufacturer as AVC), intermediate (NORMAL) and fast (SYLLABIC) over two 4-week periods using the intermediate setting in both comparisons and randomizing over the fast and slow conditions. A randomization determined whether a subject started with the comfort-oriented pre-set program (AUTO) or the speech intelligibility-oriented setting with high-frequency emphasis (SPIN). In a third 4-week period, the pre-sets AUTO and SPIN were compared using the setting of the compression time constants that gave the best results during the first two periods. Comparisons were made using a standard speech-in-noise test with three types of noise: continuous speaker noise, modulated ICRA-4 noise, and car noise. The patients were also asked to fill in a Dutch translation and adaptation of the APHAB questionnaire to indicate their impression of performance. The results indicate that no compression algorithm, pre-set or combination is favoured overall. The largest improvement in speech-in-noise scores was found with syllabic compression. The advantageous effect of high-frequency emphasis after optimization of compression timing is small. The APHAB showed that users tend to prefer the SPIN setting. We found no relationship between favoured compression or pre-set and the degree or steepness of the hearing loss User preference and best performance in noise do not always coincide. Acclimatization may play a role. It could be advisable to let a user listen to a subjectively less favoured condition for at least some time if an optimal setting for speech intelligibility in noise is preferred over comfort.

Acoustic Stimulation↗

PubMed1983

Axial compression in femoral neck osteotomies. A biomechanic study in human cadaver hips.

The risk of applying compression to a sliding-screw-plate osteosynthesis in the treatment of femoral neck fractures was evaluated in an experimental study of 40 femoral neck osteotomies. Ten pairs of bones from autopsied women between 70 years and 79 years of age were compared to 10 pairs of bones from autopsied women of more than 80 years of age. The compression was applied intermittently but measured continuously. The results showed a diphasic curve. When the maximum axial compression force was reached, any attempt to apply further compression resulted in a rapid fall in pressure at the site of the osteotomy. The median of the maximum axial compression force was 971 N, ranging from 275 N to 1756N. The maximum axial compression forces were significantly lower in bones from women of more than 80 years of age compared to bones from women in the seventh decade. The clinical implication of the study is that compression of femoral neck fractures by a sliding-screw-plate system may be hazardous in patients with brittle bone, e.g. women over 80 years of age.

Age Factors↗

PubMed2003

The effect of compression, stretching, and cooking temperature on free oil formation in mozzarella curd.

The effect of the extent and rate of compression and stretching on free oil formation in Mozzarella cheese curd was investigated at 55, 65, and 75 degrees C. Confocal laser scanning microscopy was used to determine the maximum cross-sectional diameter, cross-sectional area, elongation factor (maximum divided by minimum cross-sectional diameter), and circularity of fat globules in the cheese curd at the different temperatures, and after stretching or compression. Free oil was not significantly affected by the rate of biaxial compression from 50 to 2000 mm/min at 65 degrees C, the rate of tensile stretching from 1000 to 2500 mm/min at 60 degrees C, or the extent of biaxial compression from 40 to 80% of the original height at 1000 mm/min and 65 degrees C. Increasing the rate of stretching from 1000 to 2500 mm/min increased the elongation factor from 1.91 to 2.61. Cross-sectional area, maximum diameter, and circularity were not affected by the rate of biaxial compression. The extent of curd compression had no effect on the milk fat globule size and shape. Increasing the extent of stretching at 60 degrees C and at 1000 mm/min increased the free oil content (on a fat basis) from 23.8% (curd stretched by 1.4x) to 32.3% (stretched by 4.6x) and the elongation factor of the globules, but did not affect any of the other globule parameters. Increasing the temperature of the cooking-stretching water increased the cross-sectional area, diameter of the globules, and free oil content from 24.1% at 55 degrees C to 34.5% at 75 degrees C for curd compressed to 50% height at 1000 mm/min.

Cheese↗

PubMed2000

Rotational compression of the vertebral artery at the point of dural penetration. Case report.

Vertebrobasilar insufficiency (VBI) due to vertebral artery (VA) compression occurs in a significant number of patients. Rotational compression of the VA usually occurs below C-2, where the artery is pinched during head rotation, leading to thrombus formation and subsequent cerebellar infarction. Although this problem has been reported to occur at the atlantooccipital levels, a review of the literature revealed no published cases of VA compression at the point of dural penetration, which is located above the atlantooccipital membrane. The authors report the case of a 30-year-old woman who presented with signs and symptoms of VBI. Dynamic angiography demonstrated left-sided VA compression at the site at which dural penetration had occurred, proximal to the posterior inferior cerebellar artery. Surgical decompression of the left VA at the point of dural penetration relieved the symptoms, and postoperative dynamic angiography demonstrated complete resolution of the positional compression of the left VA. Because of these findings, an additional possible location for rotational compression of the VA is described, namely, the point of dural penetration. The authors suggest a method of surgically treating rotational VA compression at this site.

Adult↗

PubMed2006

Cochlear implant speech processor placement and compression effects on sound sensitivity and interaural level difference.

The purpose of this investigation was to determine the impact of commonly recommended cochlear implant (CI) speech processor placements on microphone output both with and without single channel front-end compression. The impact of this compression use on interaural level difference (ILD) magnitude was also evaluated for the ear-level position. Finally, pilot localization data collected with and without single channel front-end compression was collected on seven bilateral cochlear implant recipients. The results revealed that differences in signal audibility due to clinical placement of CI speech processors in ear, shoulder, and collar positions can at least partially be offset through the use of front-end compression. These data also revealed that compression impacted ILD cues. Preliminary data indicated that some bilaterally implanted subjects were able to take advantage of the enhanced ILD cues when compression was turned off, while other bilaterally implanted subjects did not localize better in the compression-off condition.

Acoustic Stimulation↗

PubMed2000

Measuring the compression of mortality.

Compression of mortality is measured here in four ways: 1) by standard deviation of the age at death above the mode; 2) by standard deviation of the age at death in the highest quartile; 3) by the inter-quartile range; and 4) by the shortest age interval in which a given proportion of deaths take place. The two first-mentioned are directed at old ages, while the other two measure compression over the entire age range. The fourth alternative is recommended as the most suitable for general use and offers several variations, called the C-family of compression indicators. Applied to historical and modern populations, all four measures show convincingly that the secular transition from high to low mortality has been accompanied by general and massive compression of mortality. In recent decades, however, this development has come close to stagnation even when life expectancy continues to increase. This has happened at a level where compression is still so incomplete that the shortest age interval in which 90% of deaths occur, is 35 years. It seems unrealistic to expect human mortality ever to be compressed into so narrow an age interval that the survival curve would even approximately rectangular. It is considered useful to monitor changes in the compression of mortality because the indicators describe relevant aspects of the length of life and may acquire new significance as indicators of population heterogeneity.

Age Factors↗