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PubMed1983

[Experimental study on peripheral nerve lesions--compression neuropathy].

Compression is one of the most important causes of entrapment neuropathy. The experimental study described was performed to elucidate the pathogenesis of compression neuropathy in the sciatic nerves of 113 mongrel dogs. An apparatus, devised to compress the nerve constantly with the force of 15, 30 and 50 grams (27.6, 55.2, 92.0 mmHg), was applied to the sciatic nerve 4 cm distal to the sciatic tuberculum. The following observations were made on the 1st, 2nd, 3rd, 4th, 6th and 8th weeks. Macroscopic findings: The compressed site of the nerve was thinned and flattened. Adjacent portions both proximal and distal to the compressed site showed distinct swelling (prox. greater than dist.). Electrophysiological findings: In the 15-gram-compression group, the conductability was maintained up to the 8th week, but the motor nerve conduction velocity was reduced to approximately 60% of the control. In the 30-gram-compression group, the conductability of the compressed site was lost within one week. However, the conductability in the distal portion remained detectable. In the 50-gram-compression group, the conductability was completely lost within one week. Histological findings (H and E, Holmes and LFB stains): In the pseudoneuroma, the swelling of the individual axons was slight, but the arrangement of each axon and each funiculus was extremely sparse because of the exudate in the interstitial tissue. At the compressed site, axons were closely packed together with a concomitant decrease of interstitial tissue. In the 15-gram-compression group. Wallerian degeneration was localized in large myelinated fibers at the distal site. In the 30-gram-compression group, almost all the nerve fibers except for small ones showed degeneration. In the 50-gram-compression group, all fibers degenerated. Teased single fiber specimens: In the 15-gram-compression group, paranodal demyelination was seen from the 1st week. Up to the 8th week, such demyelination was more remarkable, and a bulbous deformity appeared at the proximal site of compression and Wallerian degeneration of the large myelinated fibers occurred at the distal site of compression. Microangiogram (India ink method): The internal microvessels decreased slightly in the 15-gram-compression group.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2006

Maintenance of graft compression in the adult cervical spine.

It is generally advised that the graft inserted in adult cervical spine should be pre-loaded with a compressive force or that the screws are inserted in a divergent orientation, in order to maximise compression and the chance of graft incorporation (Truumees et al. in Spine 28:1097-1102, 2003). However, there is little evidence that a compressive force is maintained once the force applicator has been removed, or that the divergent screws enhance compression. This study compared the maintenance of applied pre-load force, across cervical spine graft, between standard anterior plating technique with pre-load and divergent screws and a novel plate technique, which allows its application prior to removal of the force applicator. Six intact adult cadaveric human cervical spines were exposed by standard surgical technique. A Casper type distracter was inserted across the disc space of interest, the disc was removed. In 14 experiments, following the disc removal, an autologous iliac crest bone graft was inserted under distraction, together with a strain gauge pressure transducer. A resting output from the transducer was recorded. The voltage output has a linear relationship with compressive force. A standardised compressive force was applied across the graft through the "Casper type" distracter/compressor (7.5 kg, torque). The pre-load compressive force was measured using a torque drill. Then two different procedures were used in order to compare the final applied strain on the bone graft. In eight experiments (procedure 1), the "Casper type" distracter/compressor was removed and a standard anterior cervical plate with four divergent screws was inserted. In six experiments (procedure 2), a novel plate design was inserted prior to removal of the distracter/compressor, which is not possible with the standard plate design. A final compressive force across the graft was measured. For the standard plate construct (procedure 1), the applied compression force is significantly greater than resting (SO/SC)--P=0.01, but the compression force is not maintained once the compressor is removed (SO/SR)--P=0.27. Final bone graft compression after plate insertion is not significantly different to the resting state (SO/SF)--P=0.16 (Wilcoxon's sign test for paired observation). Application of the plate tended to offload the graft; the final compressive force is 170+/-100% less than the resting force. None of the applied force was maintained (mean 9.5+/-8.8%). For the new plate (procedure 2), the end compressive force (SF) measured across the graft was greater than the resting force (SO) (P<0.001). Further, the novel plate application increased the compressive force on the graft by 712+/-484%. The final bone graft compression using a novel plate, which allows its application prior to removal of the force applicator, is significant (SO/SF)--P=0.01. Here, 77+/-10% of the applied pre-load was maintained. The difference between the plates is significant (P<0.001). Conclusions are as follows: (1) Applied pre-load is not maintained across a graft once the force applicator is removed. (2) Divergent screws with a plate do not compress graft and rather tend to offload it. (3) Compressive force may be maintained if the plate is applied prior to the force applicator removal.

Biomechanical Phenomena↗

PubMed1997

Effect of lossy data compression on quantitative coronary measurements.

With the accepted use of (lossy) data compression at low compression factors (2, 3 and 4 on the Philips DCI), the question was posed whether higher lossy compression ratios can also be used without statistically affecting the results of quantitative coronary arteriography. In this study the influence of two data compression schemes (LOT and JPEG) at three different compression factors (5, 8 and 12) on coronary measurements was assessed with the Automated Coronary Analysis (ACA) package. A series of 30 original acquired digital images were compressed and decompressed at the different factors, and together with the original non-compressed images processed using the ACA package. In these images a total of 37 obstructed coronary segments were analyzed twice to assess the intra-observer variabilities in the obstruction and reference diameters and in the percent diameter stenosis. The results of the first and second measurements in each image were averaged, and from the differences in corresponding images with different compression ratios, the inter-compression variability was obtained. The results show that the intra-observer systematic errors in the absolute diameters are all small (< 0.07 mm), and statistically not significantly different. The intra-observer random errors for the compressed/decompressed series, however, were all larger (up to 0.21 mm) than for the original series (< 0.13 mm). Statistically significant differences in the intra-observer random errors were found for the JPEG compression scheme at a compression ratio of 5 and for the LOT scheme at a compression ratio of 12. The inter-compression systematic errors in the absolute diameter measurements were also small (< 0.07 mm) and not significant, while the random errors were found to be high in the range between 0.23 mm and 0.31 mm. Given the higher intra-observer variabilities for the compressed/decompressed image series as compared to original images, and the fact that all inter-compression variabilities were found to be so high, we must conclude that the higher compression ratios affect the results of QCA in a negative sense. In conclusion, the use of lossy data compression with JPEG or LOT compression schemes at ratios 5, 8 and 12 must be discouraged for QCA.

Algorithms↗

PubMed2005

Compression-dependent differences in hearing aid gain between speech and nonspeech input signals.

OBJECTIVE: A primary purpose of fitting hearing aids is to improve the audibility of speech; however, hearing aid gain is typically measured by using standardized nonspeech signals, e.g., swept pure tones, speech-weighted broadband noise, or modulated noise. When compression hearing aids are tested with these nonspeech input signals, the measured gain can be substantially different than if a real speech input signal were used. The purpose of this study was to systematically evaluate the effects of release time, compression ratio, and number of compression channels, as well as interactions of these parameters, on the gain difference between several common nonspeech hearing aid test signals and speech. It was hypothesized that the difference in hearing aid gain between static nonspeech signals and speech would increase as release time, compression ratio, and number of channels increased. DESIGN: Speech and several common nonspeech hearing aid test signals, matched at overall root-mean-square levels corresponding to average (65 dB SPL) and loud (80 dB SPL) conversational speech, were input into a master hearing aid circuit, and the gain of the circuit was measured in one-third octave bands. The hearing aid was programmed as a moderate-gain (23 dB) wide dynamic range compression instrument with a compression threshold of 50 dB SPL. The release time, compression ratio, and number of compression channels of the circuit were systematically adjusted by programming software. The one-third octave band gain differences between the nonspeech signals and speech were measured for all combinations of the compression settings. Multiple regression analysis was used to evaluate the effects of each compression parameter, and interactions of the parameters, on the gain difference between each nonspeech signal and speech. RESULTS: One-third octave band gain differences between nonspeech and speech signals (calculated as nonspeech signal minus speech signal) ranged from -3.1 to 10.4 dB, depending on frequency, nonspeech test signal, and input signal level. In most cases, the compression parameters accounted for more than 70% of the variance in gain differences between the speech and nonspeech signals. At an input level of 65 dB, increases in the release time and compression ratio led to an increase in the gain difference between most nonspeech signals and speech at most frequencies. Increases in the number of channels caused an increase in the gain difference when the spectra of the nonspeech signals differed from the speech spectrum. The effects of release time and number of channels increased as the compression ratio increased. At an 80 dB input level, increasing the compression ratio led to a decrease in the gain difference between the nonspeech signals and speech. Release time and number of channels had little to no effect at the higher input level. CONCLUSIONS: The compression parameters of release time, compression ratio, and number of compression channels explain most of the variance in differences in hearing aid gain between nonspeech and speech signals. It may be cumbersome, however, to quantitatively define this relationship for all hearing aid circuits. It is therefore recommended that hearing aid "use" gain or output be measured with a real speech signal. If a nonspeech signal must be used, then it should have spectral and temporal properties that are similar to speech.

Acoustic Stimulation↗

PubMed2005

SIMPLISMA and ALS applied to two-way nonlinear wavelet compressed ion mobility spectra of chemical warfare agent simulants.

Ion mobility spectrometry is a rapid scanning measurement method for which compression methods that facilitate the handling of large collections of data are beneficial. Peak distortion in reconstructed ion mobility spectra from linear wavelet compression is problematic in that artifact peaks may cause false positive alarms. Peak shifting also may cause false alarms if target peaks shift out of or interfering peaks shift into detection windows. Nonlinear wavelet compression (NLWC) preserves peak shape and can lessen the degree of distortion, shifting, and artifact peaks in the reconstructed spectra. NLWC was applied to achieve high compression and fidelity in the reconstructed spectra. Another benefit is that NLWC improves signal-to-noise ratios and thus the models built from compressed data are improved. By compressing both the drift time order and the spectrum acquisition order, greater compressions maybe achieved. A two-way nonlinear wavelet compression method that incorporates alternating least squares (2W-NLWC-ALS) algorithm was devised by applying ALS to partially reconstructed wavelet coefficients generated from two-way NLWC. The number of components in a data set can be determined automatically using ASIMPLISMA. The smaller ALS models are saved as the final compressed data and can be used to reconstruct the entire data set efficiently without maintaining the compressed wavelet coefficient matrix of the original data set. The 2W-NLWC-ALS algorithm provides greater compression ratios compared to regular wavelet compression and interpretable models. Using this method, large volumes of data can be acquired and easily evaluated through a simple compressed model. A compression ratio of 510 ppm, root-mean-square error (E(RMS)) of 6.3 mV (full-scale signal is usually 1 V or larger), and relative root-mean-square error (RE(RMS)) of 1.62% were achieved for data sets collected by CAM. A compression ratio of 46 ppm, E(RMS) of 9.2 mV, and RE(RMS) of 0.42% were achieved for data sets collected with an ITEMISER instrument. The 2W-NLWC-ALS algorithm is an efficient compression method that provides the benefits of a simple model.

Algorithms↗

PubMedDate not supplied

Swelling archives warrant closer look at compression.

Image compression is broadly categorized as lossless or lossy. With lossless compression, a compressed image can be decompressed and displayed as an exact digital replica of the original. With lossy compression, redundant pixel data are discarded during the compression process so that the compressed image is only an approximation of the original, therefore it cannot be returned to an original state. Although both types of compression are commonly used within the medical imaging community, institutions are much more likely to depend upon lossless compression for diagnostic purposes, even though lossy images, saved as a fraction of the original file size, are often diagnostically equivalent. With more and more digital modalities coming online and image studies growing ever larger, institutions failing to take full advantage of lossy compression are missing an opportunity to slow the growth of their image archives and IT infrastructure costs. Today, most PACS vendors include some form of image compression technology within their product offerings. Of 13 vendors sampled during an informal survey in June 2003, eight employ JPEG 2000 compression, which was incorporated into the DICOM standard in 2001, while the remainder use wavelet compression, which is the underlying methodology used in JPEG 2000. JPEG 2000 is an industry standard that enables image sharing across platforms and product lines. It also provides a single mechanism for creating lossless and lossy images, and gives institutions the flexibility to apply unique rates of compression to individual images based on modality, patient history, image size or other factors. Although it can be used judificiously to great advantage, compression is most often applied in an "across the board" manner to all images. The incorporation of JPEG 2000 within the DICOM standard does little to guarantee its longevity, or the quality of every JPEG 2000 implementation. At some point in time, especially as the demand for more compact, higher-quality lossy images grows, institutions will begin experimenting with and employing more advanced compression methods.

Data Compression↗

PubMed2004

Improved hemodynamic performance with a novel chest compression device during treatment of in-hospital cardiac arrest.

INTRODUCTION: The purpose of this pilot clinical study was to determine if a novel chest compression device would improve hemodynamics when compared to manual chest compression during cardiopulmonary resuscitation (CPR) in humans. The device is an automated self-adjusting electromechanical chest compressor based on AutoPulse technology (Revivant Corporation) that uses a load distributing compression band (A-CPR) to compress the anterior chest. METHODS: A total of 31 sequential subjects with in-hospital sudden cardiac arrest were screened with institutional review board approval. All subjects had received prior treatment for cardiac disease and most had co-morbidities. Subjects were included following 10 min of failed standard advanced life support (ALS) protocol. Fluid-filled catheters were advanced into the thoracic aorta and the right atrium and placement was confirmed by pressure waveforms and chest radiograph. The coronary perfusion pressure (CPP) was measured as the difference between the aortic and right atrial pressure during the chest compression's decompressed state. Following 10 min of failed ALS and catheter placement, subjects received alternating manual and A-CPR chest compressions for 90 s each. Chest compressions were administered without ventilation pauses at 100 compressions/min for manual CPR and 60 compressions/min for A-CPR. All subjects were intubated and ventilated by bag-valve at 12 breaths/min between compressions. Epinephrine (adrenaline) (1mg i.v. bolus) was given at the request of the attending physician at 3-5 min intervals. Usable pressure signals were present in 16 patients (68 +/- 6 years, 5 female), and data are reported from those patients only. A-CPR chest compressions increased peak aortic pressure when compared to manual chest compression (153 +/- 28 mmHg versus 115 +/- 42 mmHg, P < 0.0001, mean +/- S.D.). Similarly, A-CPR increased peak right atrial pressure when compared to manual chest compression (129 +/- 32 mmHg versus 83 +/- 40 mmHg, P < 0.0001). Furthermore, A-CPR increased CPP over manual chest compression (20 +/- 12 mmHg versus 15 +/- 11 mmHg, P < 0.015). Manual chest compressions were of consistent high quality (51 +/- 20 kg) and in all cases met or exceeded American Heart Association guidelines for depth of compression. CONCLUSION: Previous research has shown that increased CPP is correlated to increased coronary blood flow and increased rates of restored native circulation from sudden cardiac arrest. The A-CPR system using AutoPulse technology demonstrated increased coronary perfusion pressure over manual chest compression during CPR in this terminally ill patient population.

Aged↗

PubMed2001

Fitting low ratio compression to people with severe and profound hearing losses.

OBJECTIVE: In this study, we aimed to determine the extent to which wide dynamic range compression and compression limiting could benefit severely and profoundly hearing-impaired adults. DESIGN: Subjects were fitted with multi-memory hearing aids incorporating frequency independent input-controlled compression with a 2:1 compression ratio and output-controlled compression limiting. The input compression threshold (CT) was varied to establish the lowest level that maintained audibility for conversational intensity speech without acoustic feedback oscillation. Where a low (40 to 57 dB SPL) CT was possible, this was compared with a moderate (65 to 74 dB SPL) level. The preferred input compression setting was subsequently compared with linear, compression-limited amplification in the same aids. In the three cases where 2:1 input compression could not be used, because of feedback or loudness insufficiency problems, compression limiting was compared with peak clipping. Field trials were conducted over a 2- or 3-mo period to establish preferences. RESULTS: Nine of the 16 subjects preferred the inclusion of the higher level input compression, and one preferred lower level input compression. Four subjects preferred linear, compression-limited amplification, one favored peak clipping, and one could not be satisfied with any of the options provided. CONCLUSIONS: 2:1 input compression was useful, and preferred by 10 of the subjects, but for nine subjects the preferred CT was relatively high. With a group 4-frequency average loss of 87 dB HTL, the results demonstrate that fast-acting, low compression ratio systems can be useful for losses traditionally regarded as the domain of linear amplification.

Adult↗

PubMed2001

A novel method for controlled and reversible long term compression of the umbilical cord in fetal sheep.

1. In fetal sheep during late gestation the aims of the present study were to (1) develop a technique for inducing prolonged but reversible periods of controlled compression of the umbilical cord and (2) characterise the cardiovascular, endocrine and metabolic responses to this challenge. 2. Under 1-2 % halothane anaesthesia, 16 Welsh Mountain sheep fetuses were chronically instrumented at 118 +/- 2 days of gestation (term is ca 145 days) with an inflatable occluder cuff around the umbilical cord, amniotic and femoral vascular catheters and with transit-time flow probes around the contra-lateral femoral artery and an umbilical artery. At 125 days, umbilical blood flow was reduced by 30 % from a pre-determined 24 h baseline for 3 days by automated servo-controlled inflation of the occluder cuff (n = 8). The occluder was then deflated allowing return of umbilical blood flow to baseline. The remaining eight fetuses were used as sham-operated controls in which the occluder was not inflated throughout the protocol. Fetal cardiovascular variables were recorded at 8 s intervals and arterial blood samples taken for measurement of blood gases, glucose and lactate and plasma adrenaline, noradrenaline and vasopressin concentration throughout the study. 3. Automated servo-controlled inflation of the occluder cuff, programmed to reduce umbilical blood flow by 30 % from baseline, reduced umbilical blood flow by 30.2 +/- 1.7 %, with a coefficient of variation during compression of 6.5 +/- 1.1 %. Sustained partial compression of the umbilical cord produced falls in fetal arterial pH, P(a,O2), percentage O(2) saturation of haemoglobin, and hindlimb oxygen delivery, and increases in P(a,CO2), haemoglobin concentration, arterial blood oxygen carrying capacity and in blood glucose and lactate concentrations. While the reductions in P(a,O2), percentage saturation of haemoglobin and hindlimb oxygen delivery and the increase in P(a,CO2) were sustained throughout compression, the reduction in arterial pH and the increase in arterial oxygen carrying capacity had returned towards baseline values by 48 h compression. Fetal blood lactate concentrations reached a peak at 8 h of compression and, thereafter, were maintained at an elevated level relative to baseline. 4. Partial compression of the umbilical cord produced fetal hypertension, a reduction in femoral blood flow and, consequently, an increase in calculated fetal femoral vascular resistance for the duration of the challenge. In addition, the fall in heart rate measured in sham control fetuses by the end of the study, did not occur in cord-compressed fetuses. Cosinor analysis on 24 h rhythms of cardiovascular data indicated a significant increase in the amplitude of the 24 h rhythm in heart rate in cord-compressed fetuses relative to sham controls during the period of compression or sham-compression. Furthermore, cord compression led to an increase in fetal plasma noradrenaline, but not adrenaline and vasopressin concentrations relative to sham control fetuses. 5. In conclusion, a novel reversible method for controlled, long-term compression of the umbilical cord in sheep has been developed. The data show that sustained, partial compression of the umbilical cord produced moderate but sustained asphyxia, which resolved after the end of the compression period, and induced changes in fetal cardiovascular, endocrine and metabolic functions.

Animals↗

PubMed2000

Evaluation of JPEG and wavelet compression of body CT images for direct digital teleradiologic transmission.

PURPOSE: To determine acceptable levels of JPEG (Joint Photographic Experts Group) and wavelet compression for teleradiologic transmission of body computed tomographic (CT) images. MATERIALS AND METHODS: A digital test pattern (Society of Motion Picture and Television Engineers, 512 x 512 matrix) was transmitted after JPEG or wavelet compression by using point-to-point and Web-based teleradiology, respectively. Lossless, 10:1 lossy, and 20:1 lossy ratios were tested. Images were evaluated for high- and low-contrast resolution, sensitivity to small signal differences, and misregistration artifacts. Three independent observers who were blinded to the compression scheme evaluated these image quality measures in 20 clinical cases with similar levels of compression. RESULTS: High-contrast resolution was not diminished with any tested level of JPEG or wavelet compression. With JPEG compression, low-contrast resolution was not lost with 10:1 lossy compression but was lost at 3% modulation with 20:1 lossy compression. With wavelet compression, there was loss of 1% modulation with 10:1 lossy compression and loss of 5% modulation with 20:1 lossy compression. Sensitivity to small signal differences (5% and 95% of the maximal signal) diminished only with 20:1 lossy wavelet compression. With 10:1 lossy compression, misregistration artifacts were mild and were equivalent with JPEG and wavelet compression. Qualitative clinical findings supported these findings. CONCLUSION: Lossy 10:1 compression is suitable for on-call electronic transmission of body CT images as long as original images are subsequently reviewed.

Humans↗

PubMed2006

Rescuer fatigue: standard versus continuous chest-compression cardiopulmonary resuscitation.

OBJECTIVES: Continuous chest-compression cardiopulmonary resuscitation (CCC-CPR) has been advocated as an alternative to standard CPR (STD-CPR). Studies have shown that CCC-CPR delivers substantially more chest compressions per minute and is easier to remember and perform than STD-CPR. One concern regarding CCC-CPR is that the rescuer may fatigue and be unable to maintain adequate compression rate or depth throughout an average emergency medical services response time. The specific aim of this study was to compare the effects of fatigue on the performance of CCC-CPR and STD-CPR on a manikin model. METHODS: This was a prospective, randomized crossover study involving 53 medical students performing CCC-CPR and STD-CPR on a manikin model. Students were randomized to their initial CPR group and then performed the other type of CPR after a period of at least two days. Students were evaluated on their performance of 9 minutes of CPR for each method. The primary endpoint was the number of adequate chest compressions (at least 38 mm of compression depth) delivered per minute during each of the 9 minutes. The secondary endpoints were total compressions, compression rate, and the number of breaks taken for rest. The students' performance was evaluated on the basis of Skillreporter Resusci Anne (Laerdal, Wappingers Falls, NY) recordings. Primary and secondary endpoints were analyzed by using the generalized linear mixed model for counting data. RESULTS: In the first 2 minutes, participants delivered significantly more adequate compressions per minute with CCC-CPR than STD-CPR, (47 vs. 32, p = 0.004 in the 1st minute and 39 vs. 29, p = 0.04 in the 2nd minute). For minutes 3 through 9, the differences in number of adequate compressions between groups were not significant. Evaluating the 9 minutes of CPR as a whole, there were significantly more adequate compressions in CCC-CPR vs. STD-CPR (p = 0.0003). Although the number of adequate compressions per minute declined over time in both groups, the rate of decline was significantly greater in CCC-CPR compared with STD-CPR (p = 0.0003). The mean number of total compressions delivered in the first minute was significantly greater with CCC-CPR than STD-CPR (105 per minute vs. 58 per minute, p < 0.001) and did not change over 9 minutes in either group. There were no differences in compression rates or number of breaks between groups. CONCLUSIONS: CCC-CPR resulted in more adequate compressions per minute than STD-CPR for the first 2 minutes of CPR. However, the difference diminished after 3 minutes, presumably as a result of greater rescuer fatigue with CCC-CPR. Overall, CCC-CPR resulted in more total compressions per minute than STD-CPR during the entire 9 minutes of resuscitation.

Adult↗

PubMed2002

Tolerance of the cervical spine to eccentric axial compression.

Cervical spine injury resulting from compressive impact loading is a particularly devastating musculoskeletal injury due to the frequency of neurologic involvement. The objective of this research was to investigate the effect of axial eccentricity on the tolerance of the cervical spine. Two functional spinal unit segments (3 adjacent vertebra and their intervening discs and soft-tissues) were dissected from the lower cervical spine of twenty-four human cadaver cervical spines and randomly assigned to one of three loading groups. The eight specimens were tested to failure in compression, compression-flexion, and compression-extension under displacement control on a high-rate MTS load frame. The resulting six-axis loads were measured and evaluated by injury mechanism (group). Statistically distinct (p < 0.01) injury mechanisms, in terms of measured axial eccentricity, were produced by each of the eccentric axial compression inputs (compression-flexion, compression-extension, and compression). The axial force at failure for the compression and compression-extension loading environments were nearly equal and significantly (p < 0.01) larger (4-times) than their counterpart in the compression-flexion group. Failure data were compared with the neck injury criteria (Nij) recently proposed by the NHTSA using the 50th percentile male and 5th percentile female injury reference values. The compression and compression-extension mechanisms produced Nij values near 1.0. The compression-flexion series resulted in significantly lower Nij values at failure (approx. 0.3, p < 0.01). The results of this study provide tolerance data for the cervical spine subjected to different compressive loading environments and may be used to enhance injury reference computations facilitating neck injury prevention.

Journal Article↗

PubMed2001

Fixed and dynamic urethral compression for the treatment of post-prostatectomy urinary incontinence: is history repeating itself?

PURPOSE: We reviewed the evolution of appliances and devices used for treating post-prostatectomy urinary incontinence. MATERIALS AND METHODS: We used the MEDLINE to search the literature from 1966 to March 2000 and then manually searched bibliographies to identify studies that our initial search may have missed. RESULTS: The evolution of treatment for post-prostatectomy urinary incontinence may be traced back to the 18th century. Two main schools of thoughts simultaneously evolved. The first fixed urethral compression devices were constructed to enable urethral obstruction by fixed resistance. This outlet resistance allows voiding after intra-abdominal and intravesical pressure is elevated but it is sufficient to prevent leakage between urinations. The other school of thought preferred creation of dynamic urethral compression in which outlet resistance is not fixed but may be decreased when voiding is desired or elevated between urinations. Therapeutic fixed and dynamic urethral compression interventions may be further divided into external or internal compressive devices or procedures. External fixed compression devices may be traced back to antiquity. A penile clamp, similar to the later Cunningham clamp, and a truss designed to compress the urethra by external perineal compression were presented in the Heister textbook of surgery, Institutiones Chirurgicae, as early as 1750. Dynamic compressive devices applied externally were developed much later, such as the first artificial urinary sphincter, described by Foley, in 1947 and the Vincent apparatus, described in 1960. The modern era of fixed urethral compression began in 1961 with Berry. Acrylic prostheses impregnated with bismuth to allow radiographic visualization were produced in various shapes and sizes, and used to compress the urethra against the urogenital diaphragm. In 1968 the University of California-Los Angeles group under the direction of Kaufman began to use cavernous crural crossover to compress the bulbous urethra (Kaufman I). Later 2 other modifications were described, including approximation of the crura in the midline using a polytetrafluoroethylene mesh tape (Kaufman II) and an implantable silicone gel prosthesis (Kaufman III). With the advent of the artificial urinary sphincter pioneered by Scott in 1973 interest in passive urethral compression disappeared in favor of the implantation of an inflatable circumferential prosthetic sphincter. Recently there has been a trend back to passive urethral compression. Synthetic bolsters have been described that passively compress the bulbar urethra to achieve urinary incontinence after radical prostatectomy. CONCLUSIONS: Much creativity has been dedicated to solve the complex and challenging problem of post-prostatectomy urinary incontinence. Devices used for treating this condition may be grouped according to the mechanism of action and how they are applied. Passive urethral compression, long abandoned in favor of dynamic implantable sphincters, has reemerged. Further research in this field may determine which school of thought may provide the best solution for treating post-prostatectomy urinary incontinence.

History, 18th Century↗

PubMed2002

Nerve vasculature changes induced by serotonin under chronic cauda equina compression.

STUDY DESIGN: An analysis of nerve vascular changes in nerve roots induced by serotonin in chronically compressed nerve roots. OBJECTIVES: To assess the hypotheses that serotonin might have a vasoconstrictive effect in chronically compressed nerve roots. SUMMARY OF BACKGROUND DATA: The 5-hydroxytryptamine 2A receptor is involved in serotonin-induced activation or sensitization of sensory nerve terminals. Serotonin exerts complex effects on pain and hyperalgesia through various receptor subtypes located at various levels of the pain transmission system. Serotonin induces endothelium-dependent contraction in vascular diseases. However, there is no knowledge regarding a response of nerve vasculature induced by serotonin in chronically compressed nerve roots. METHODS: A total of 45 dogs were used. A plastic balloon was placed under the lamina L7 and inflated to 10 mm Hg and left for 1 week. Four experimental groups were used: no operation (Group A, n = 15), the balloon was placed under the lamina but not inflated (Group B, n = 10), the balloon was inflated to 10 mm Hg for 1 week and the pressure was released just before the measurement (Group C, n = 10), and the balloon was inflated to 10 mm Hg for 1 week and inflation was maintained during the measurements (Group D, n = 10). The blood vessels of the second or third sacral nerve were defined after an intra-arterial injection of 0.5 micromol/L or 1.0 micromol/L serotonin using a specially designed operation microscope equipped with a video camera. In all groups 0.5 micromol/L serotonin (each group, n = 5) or 1.0 micromol/L serotonin (each group, n = 5) was injected. In Group A (n = 5) saline was injected. The measurements of diameter of observed blood vessels and blood flow index were performed on video recordings. All statistical assessments were performed by Wilcoxon signed-ranks test and Fisher's PLSD. RESULTS: In Group A, the diameter of blood vessels and blood flow did not change after administration of saline. In the noncompression groups (Groups A and B) the diameter of blood vessels and blood flow increased after injection of 0.5 micromol/L serotonin. In compression groups (Groups C and D) the blood vessels contracted after injecting 0.5 micromol/L serotonin and blood flow decreased. There was a significant difference in the diameter of blood vessels and blood flow between noncompression and compression groups (P < 0.01). There was no difference regarding diameter of blood vessels between released compression (Group C) and maintained compression during measurement group (Group D). In all groups blood vessels contracted and blood flow decreased after injecting 1.0 micromol/L. In electron microscopic observation tight junction of endothelial cells was destroyed in chronically compression nerve roots. DISCUSSION: The present study demonstrated that serotonin had a vasodilative effect on the intact nerve roots, whereas there was a vasoconstrictive effect to the chronically compressed nerve roots. There was no difference in the diameter of blood vessels between released compression and maintained compression during measurement group. Results suggested that dysfunction of endothelial cells induced by serotonin rather than mechanical compression itself might lead to contraction of blood vessels under chronic compression. CONCLUSION: Serotonin had a vasoconstrictive effect on the chronically compressed nerve roots.

Animals↗

PubMed2006

Neuronal loss and expression of neurotrophic factors in a model of rat chronic compressive spinal cord injury.

STUDY DESIGN: An experimental animal study about neuronal loss and the expression of neurotrophic factors in the chronic compressive spinal cords. OBJECTIVES: To investigate neuronal loss and the expression of neurotrophic factors in the chronic compressive spinal cords of rats, and to evaluate effects of decompressive procedures for the neuronal loss. SUMMARY OF BACKGROUND DATA: Chronic compression of spinal cords induces the loss of motor neurons in the anterior horn. However, the precise mechanism of this neuronal loss is not still understood completely. Furthermore, it is uncertain whether decompressive procedures prevent this neuronal loss or not. METHODS: A thin expanding polymer sheet was implanted microsurgically underneath T7 laminae of rats. After 6, 9, 12, and 15 weeks, the thoracic spinal cord was harvested and examined histopathologically. The expression of neurotrophic factors, including NGF, BDNF, NT-3, GDNF, CNTF, and VEGF, was analyzed using semiquantitative RT-PCR, enzyme immunoassay, and immunohistochemistry. Decompressive surgery was performed through the removal of T7 laminae and the compression materials 6, 9, and 12 weeks after starting compression. Three weeks later, respectively, the neuronal loss in the anterior horn was estimated. RESULTS: The spinal cords were progressively flattened by the expanding of the implanted polymer sheet, and the number of motor neurons in the anterior horn decreased, especially from 6 to 9 weeks after starting compression. Semiquantitative RT-PCR analysis showed that the expression of NGF and BDNF mRNAs was decreased significantly in the spinal cords of 12-week compression group compared with the 6-week compression group and that NGF mRNA expression was up-regulated significantly in the 6-week compression group relative to the 6-week control group. Any changes of expression of other neurotrophic factors were not significant. Since BDNF, not NGF, has been known to be one of the powerful survival factors for spinal motoneurons, we investigated the levels of BDNF protein in the compressive spinal cords using enzyme immunoassay and immunohistochemistry. We demonstrated the level of BDNF protein in the compressive spinal cords was increased 6 weeks after compression but declined after 12 weeks. The decompressive procedure in the 6 weeks after compression prevented neuronal loss, but the same procedure in the 9 or 12 weeks was ineffective. CONCLUSIONS: From the point of view of neuronal loss, decompressive surgery at an earlier stage, when compensatory mechanisms including the up-regulation of BDNF might be still effective, could provide better therapeutic results against chronic mechanical compressive spinal cord lesions.

Animals↗

PubMed1994

Displaying radiologic images on personal computers: image storage and compression--Part 2.

This is part 2 of our article on image storage and compression, the third article of our series for radiologists and imaging scientists on displaying, manipulating, and analyzing radiologic images on personal computers. Image compression is classified as lossless (nondestructive) or lossy (destructive). Common lossless compression algorithms include variable-length bit codes (Huffman codes and variants), dictionary-based compression (Lempel-Ziv variants), and arithmetic coding. Huffman codes and the Lempel-Ziv-Welch (LZW) algorithm are commonly used for image compression. All of these compression methods are enhanced if the image has been transformed into a differential image based on a differential pulse-code modulation (DPCM) algorithm. The LZW compression after the DPCM image transformation performed the best on our example images, and performed almost as well as the best of the three commercial compression programs tested. Lossy compression techniques are capable of much higher data compression, but reduced image quality and compression artifacts may be noticeable. Lossy compression is comprised of three steps: transformation, quantization, and coding. Two commonly used transformation methods are the discrete cosine transformation and discrete wavelet transformation. In both methods, most of the image information is contained in a relatively few of the transformation coefficients. The quantization step reduces many of the lower order coefficients to 0, which greatly improves the efficiency of the coding (compression) step. In fractal-based image compression, image patterns are stored as equations that can be reconstructed at different levels of resolution.

Algorithms↗

PubMed2005

Transient response of compressed electrorheological fluid.

Transient behaviors of a compressed electrorheological (ER) fluid based on zeolite and silicone oil have been experimentally investigated. The ER fluid is purely compressed between two parallel plates. Compressive speed and voltage amplitude effects on the transient process and randomly applied on/off voltages have been studied. Through normalizing compressive stress of the ER fluid, the characteristic compressive strain and the response time constant corresponding to the rise of compressive stress have been fitted with exponential equations. Results show that the rising time of the transient compressive stress is greatly affected by the compressive speed and the compressive strain position applying voltages, while the amplitude of the applied voltage has little effect on the rising time. The obtained transient compressive strain for the compressive stress to rise to its stable value is much smaller than that working in the transient process of ER fluids under shearing. The decay time and decay strain of compressive stress are much less than for stress rising. The half decay compressive strain is as small as 0.0003 in the experiment. Results show that the response time of compressed ER fluids is quick enough for the usual working conditions of squeezing ER dampers.

Journal Article↗

PubMed2006

Decreased incidence of left common iliac vein compression in patients with abdominal aortic aneurysms.

OBJECTIVE: Compression of the left common iliac vein (LCIV) by the right common iliac artery is an anatomic variant that may increase the risk for LCIV thrombosis. The incidence of LCIV compression in patients with abdominal aortic aneurysms (AAA) is unknown, however. The aim of this descriptive anatomic study was to determine (1) the incidence of LCIV compression in patients with and without AAA and (2) if endovascular AAA repair acutely alters the incidence of LCIV compression and, hence, the risk of LCIV thrombosis. METHOD: A retrospective analysis of medical records and helical computed tomography (CT) scans was conducted in 100 AAA patients and 100 non-AAA patients (n = 200). Medical records were reviewed for symptoms and risk factors for deep vein thrombosis, and data were reported according to the Joint Society Reporting Standards for acute lower-extremity venous thrombosis. The minor diameters of the aorta, inferior vena cava, and common iliac arteries and veins were measured. For AAA patients, measurements were obtained from preoperative and 30-day postoperative CT scans. RESULTS: The mean age of the study cohort was 38 years (range, 17 to 85 years) for non-AAA subjects and 73 years (range, 51 to 89 years) for AAA subjects. The mean acute lower-extremity venous thrombosis risk factor score was low for both patient groups (non-AAA, 0.82 +/- 0.12; AAA, 2.63 +/- 0.14). Mean compression of the LCIV was 37.8% (range, 0% to 74.8%) for non-AAA patients but only 27.3% (range, 0% to 74.2%; P < .0006) for AAA patients. Of non-AAA patients with venous compression, the right common iliac artery was the compressing structure in 87% of cases. However, of AAA patients with venous compression, the left common iliac artery was the compressing structure in 76% of cases. There was no statistically significant change in the degree of compression of the LCIV before and after endovascular repair (27.3% vs 25.1%, respectively) nor was there a change in the structure that compressed the LCIV. CONCLUSION: Patients with AAA were found to have more tortuous iliac arteries that led to less anatomic compression of the LCIV compared with nonaneurysmal patients. Furthermore, the left common iliac artery was found to compress the LCIV in most of the AAA patients, and the right iliac artery was found to compress the LCIV in most non-AAA patients. Endovascular AAA repair did not acutely alter these anatomic findings. Patients with AAA may therefore be at lower risk of developing LCIV thrombosis owing to the nature of their anatomy.

Adolescent↗