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At least 523 records · Page 29Linked to original sources

PubMed2000

Clinical evaluation of wavelet-compressed digitized screen-film mammography.

RATIONALE AND OBJECTIVES: The authors compared diagnostic accuracy and callback rates with conventional screen-film mammograms and wavelet-compressed digitized images. MATERIALS AND METHODS: Sixty sets of mammograms (four views per case) were digitized at a spatial resolution of 100 microm. The images were wavelet compressed to a mean compression ratio of 8:1 and reviewed by three mammographers. Five regions were evaluated in each breast. Suspicion of malignancy was graded on a scale of 0% to 100%, and receiver operating characteristic (ROC) analysis was performed. Callback rates were calculated by using the American College of Radiology's Breast Imaging Reporting and Data System lexicon scale. RESULTS: The mean diagnostic accuracy with compressed and conventional images was 0.832 and 0.860, respectively. The upper 95% confidence bound for the difference in ROC areas was 0.061. The mean false-positive rate at a fixed sensitivity of 0.90 was 0.041 for compressed images and 0.059 for conventional images. The mean callback rates for normal, benign, and malignant regions were 0.023, 0.305, and 0.677, respectively, for compressed images and 0.036, 0.447, and 0.750, respectively, for conventional images. The upper 95% confidence bound for the (absolute) differences in callback rates was 0.012 for normal regions, 0.163 for benign regions, and 0.138 for malignant regions. CONCLUSION: Diagnostic accuracies were equivalent for both compressed and conventional images. The mean false-positive rate at fixed sensitivity was much better with the compressed images. However, the callback rates for malignant lesions were lower when the compressed images were used.

Breast Diseases↗

PubMed2001

Effectiveness of abdominal compression during helical renal CT.

RATIONALE AND OBJECTIVES: The authors performed this study to assess the effect of abdominal compression on opacification and distention of the proximal renal collecting system during helical computed tomography (CT). MATERIALS AND METHODS: Abdominal compression was applied during helical CT in 31 patients who were scanned 150 and 300 seconds after initiating a dynamic bolus injection of contrast material. Two reviewers assessed renal collecting system opacification and measured the maximal short-axis diameter of the collecting system at three locations: the upper pole, the lower pole, and the proximal ureter. A similar evaluation was performed in a control group of 29 patients who underwent CT without compression at 300 seconds after initiating the injection of contrast material. RESULTS: Both reviewers noted collecting system opacification at all locations in 52 of 56 noncompressed collecting systems scanned at 300 seconds, 57 of 59 compressed collecting systems scanned at 300 seconds, but only 26 of 59 compressed collecting systems scanned at 150 seconds. Measured collecting system distention was statistically significantly greater at 300 seconds in patents who received compression than in patients who did not (P = .0013). For patients who received compression, measured collecting system distention was statistically significantly greater on scans obtained at 300 seconds than on scans obtained at 150 seconds (P = .0001). CONCLUSION: Abdominal compression during renal helical CT produces a detectable increase in renal collecting system distention. In patients who receive compression, scanning at 300 seconds rather than at 150 seconds results in greater collecting system distention and more consistent opacification.

Abdomen↗

PubMed2001

Brain-stem compression in vertebrobasilar dolichoectasia. A multimodal electrophysiological study.

OBJECTIVE: To evaluate the effects of mechanical compression of the brain-stem in patients with vertebrobasilar dolichoectasia (VBD). METHODS: In the framework of a prospective, observational study that collected clinical and laboratory data in patients with VBD, we studied 20 patients with compression of the brain-stem due to ectatic, tortuous basilar or vertebral arteries. Patients with cerebral lesions other than small lacunae in the white matter of the cerebral hemispheres were excluded from the study. Patients underwent vestibular and auditory function testing, including brain-stem auditory evoked potentials (BAEPs), blink reflex (BR), somatosensory evoked potentials (SEPs), and motor evoked potentials (MEPs). RESULTS: Almost all of the patients complained of auditory or vestibular symptoms and none had symptoms or signs of impairment of long tracts or the facial and trigeminal nerves. The most consistent findings were BR abnormalities with prolongation of ipsilateral R1 latency in cases of compression of the pons (10/16) and prolongation of the R2 and R2c latencies with compression of the medulla oblongata (5/15). Subclinical impairment of corticospinal pathways was found in 13 out of 25 instances of compression, and this was more frequent with compression of the pons. Abnormal BAEPs or SEPs were less frequently encountered, and only in cases with compression of the pons. CONCLUSIONS: Neurovascular compression of the brain-stem, even with severe distortion, is seldom associated with overt clinical signs, whereas subclinical dysfunctions are relatively frequent. The central pathways of the BR and the corticospinal pathways are more susceptible to compression than acoustic and sensory pathways. BR, MEP and BAEP data provide a functional evaluation of the brain-stem and some cranial nerves, which is lacking in imaging studies. Functional investigations may be useful in the long-term management of these patients, since VBD may be progressive and surgical correction may be required at some stage.

Adult↗

PubMed1997

Frictional work in double-sided tablet compression.

The aim of this study was to evaluate the friction during double-sided tablet compression. Dicalcium phosphate dihydrate and lactose were tabletted with a compaction simulator with symmetrical and asymmetrical double-sided sawtooth punch displacement profiles. The estimation of force transmission in a powder column was based on an exponential equation, including the material parameter consisting of both the friction coefficient and Poisson's ratio. This parameter was predetermined from a single-sided compression. A novel equation was derived from a previously presented equation for friction work in single-sided tablet compression. The basic assumption was drawn from the linearly decreasing movement of infinitely thin particle layers, which are produced as the compressing punch surface approaches the other punch. This calculation was also based on the assumption that the equilibrium point, where the particles do not move, is halfway between the punches in the symmetrical profile and at a distance proportional to the amplitudes of the asymmetrical upper and lower sawtooth profiles. The tensile strength of tablets compressed with single-double-sided profiles was identical, and thus the behavior of the materials studied under compression was independent of the compression profiles. The friction work values that were calculated with the proposed expression for double-sided profiles were close to the theoretical values, as estimated by calculations based on compressions with single-sided profiles. In conclusion, the novel mathematical expression opens new possibilities for the evaluation of friction in double-sided compression; for example, in rotary press tabletting.

Friction↗

PubMed1999

Effect of noise on the compressibility and diagnostic accuracy for caries detection of digital bitewing radiographs.

OBJECTIVES: To determine the effect of noise on the compressibility and the diagnostic accuracy for caries detection of digital bitewing radiographs. METHODS: Bitewing radiographs of patients were obtained with a storage phosphor (Digora, Soredex, Helsinki, Finland) and compressed at different JPEG compression levels (2, 27, 53 and 128). A just noticeable difference study was performed to select a compression level to study the added noise effect. Gaussian noise was added at low, medium, and high levels to both the original and compressed images. Seven observers examined the selected approximal surfaces to identify the caries depth. ROC analysis was performed together with ANOVA at P = 0.05. RESULTS: The compressibility of the images decreased as the noise level increased. ROC analysis revealed no significant difference between the original and compressed images within the same noise level (P > 0.06). With added noise compressed/decompressed images had a higher Az than the corresponding original images. CONCLUSIONS: JPEG compression at level 27 can be used without a significant deterioration in diagnostic accuracy. Compression at this level seemed to reduce the effect of noise to some extent.

Analysis of Variance↗

PubMed2002

Comparative evaluation of JPEG and JPEG2000 compression in quantitative digital subtraction radiography.

OBJECTIVES: The aim of this in vitro study was to compare the impact of JPEG and the novel JPEG2000 compression standard on quantitative digital subtraction radiography (DSR) and to determine the acceptable JPEG2000 compression ratios for DSR. METHODS: Nine dry pig mandible sections were radiographed three times ('Baseline', 'No change', and 'Gain') with standardized projection geometry. Bone gain was simulated by adding artificial bone chips (1, 4 and 15 mg). Images were registered, compressed by JPEG and JPEG2000 using compression ratios (CR) of 1 : 7, 1 : 16, 1 : 22, and 1 : 31, and then subtracted. Image distortion was assessed objectively by calculating average pixel error and peak signal to noise ratio. No change areas in compressed and subtracted 'No change-Baseline' images and bone gain volumes in compressed and subtracted 'Gain-Baseline' images were calculated for both compression standards and compared. RESULTS: JPEG introduced less distortion at low CRs, while JPEG2000 was superior at higher CRs. At CR of 1 : 7, no significant difference between JPEG and JPEG2000 was found. JPEG2000 yielded better results for no change measurements at higher CRs. Volumes of simulated bone gain were overestimated when JPEG and underestimated when JPEG2000 compression was used. CONCLUSIONS: At CR of 1 : 7 JPEG and JPEG2000 performed similarly, which indicates that CR of 1:7 in JPEG2000 can be used for DSR if images are registered before compression. At higher CRs, JPEG2000 is superior to JPEG but image distortions are too high for reliable quantitative DSR.

Algorithms↗

PubMed1997

Effects of compression bandaging on leg pulsatile blood flow.

Leg external compression bandaging is the mainstay of venous ulcer treatment, yet little is known about the impact of therapeutic compression levels on arterial haemodynamics. In this study, the effect of foot-to-knee, four-layer compression bandaging on below-knee arterial pulsatile blood flow was assessed by nuclear magnetic resonance flowmetry. In 14 healthy supine subjects bilateral flow measurements at five below-knee sites without compression, and after compressing one leg to an average malleolar sub-bandage pressure of 40.7 +/- 4.0 mmHg, revealed a potentially important new phenomenon. The forefoot-to-knee compression bandaging caused a highly significant (P < 0.001) increase in the bandaged leg pulsatile blood flow owing to increases in both peak flow and pulse width. It is hypothesized that arteriolar vasodilatation, induced either myogenically by reduced transmural pressure or by vasodilatory substance release triggered by increased venous shear stress, produce the observed compression-related phenomenon. Whatever the mechanism(s), the finding of a compression-associated pulsatile flow increase suggests a previously undiscovered arterial linkage, which may play a role in the well-documented beneficial effects of compression bandaging in venous ulcer treatment. A possible impact of the arterial flow-pulse increase is speculated to effect venous ulcer outcome via a decrease in leucocyte effects in the distal microvasculature, as a consequence of the more vigorous haemodynamic state.

Adult↗

PubMed2000

The effect of medical elastic compression stockings with different slope values on edema. Measurements underneath three different types of stockings.

BACKGROUND: Medical elastic compression stockings are widely used in venous diseases. Their effects on the venous system have been shown in the past. Up to now, little is known about the slope or stiffness factor of stockings. OBJECTIVE: To evaluate the effect of different slope and stiffness factors of medical elastic compression stockings on the venous system. METHODS: Examinations were carried out in 29 legs of 25 different patients (12 men, 13 women) with a mean age of 66.0 years. All patients were known with chronic venous insufficiency. On all these patients three different elastic medical compression stockings were tested; one with a low slope, one with a high slope, and one with a low slope but a higher pressure at the ankle. The tests were carried out by determining capillary filtration rate (CFR) with air-plethysmography (APG) while wearing the stockings. RESULTS: The mean value of the CFR without wearing a stocking was 4.65 ml/min (SD = 1.68), with Compriform (low slope, 30 mmHg) the mean CFR was 3.54 ml/min (SD = 1.22), with Bellavar (high slope, 30 mmHg) a mean CFR of 3.15 ml/min (SD = 1.17) was found, and the mean CFR related to Fast-fit (low slope, 34.5 mmHg) was 3.02 ml/min (SD = 1.12). There is a highly statistically significant difference in CFR between no stockings and wearing a stocking (paired Student's t-test; P < 0.01). Regarding the individual stocking, there is a highly statistically significant difference in CFR between the Compriform and the other two stockings (paired Student's t-test; P < 0.01). Between Bellavar and the Fast-fit the difference was not statistically significant. CONCLUSIONS: There is a statistically significant difference in CFR, and consequently in the development of edema, between not wearing an elastic compression stocking and wearing an elastic compression stocking. There is also a statistically significant difference in CFR between elastic compression stockings with the same compression, but a low slope profile and a high slope profile. Stockings with a low slope, but a higher compression may perform as well as stockings with a higher slope but a lower compression in reducing the CFR. In patients with a strong tendency to develop edema it may be advisable to prescribe stockings with a high slope profile.

Adult↗

PubMed2005

Compression therapy for chronic venous insufficiency.

Compression therapy provides a means to treat venous stasis, venous hypertension, and venous edema. Different methods of compression therapy have been described periodically over the last 2,000 years. In addition to static compression, specialized compression pumps have been developed and a technique of massage called manual lymphatic drainage has emerged to treat primary and secondary lymphedema. Objectives of compression therapy are to reduce the swollen limb to minimum size, maintain that size, and allow the patient to participate in the care of his limb whenever possible. Reduction therapy is achieved by limb elevation, compression pumps as necessary, and compression wraps. Maintenance therapy largely consists of compression wraps or compression stockings. Nonelastic devices have found a place in treating severe lymphedema but it should be emphasized that periodic follow-up must be done during maintenance therapy so that adjunctive maintenance measures can be added as needed.

Bandages↗

PubMedDate not supplied

A biomechanical comparison of equine third metacarpal condylar bone fragment compression and screw pushout strength between headless tapered variable pitch and AO cortical bone screws.

OBJECTIVES: To compare bone fragment compression and the mechanical pushout strength and stiffness of 6.5-mm Acutrak Plus (AP) and 4.5-mm AO cortical (AO) bone screws after stabilization of a simulated equine third metacarpal (MC3) bone complete lateral condylar fracture. STUDY DESIGN: In vitro biomechanical paired study of screw insertion variables, bone fragment compression, and screw pushout tests using a bone screw stabilized simulated lateral condylar fracture model. SAMPLE POPULATION: Six pairs of cadaveric equine MC3s. METHODS: Metacarpi were placed in a fixture and centered on a biaxial load cell in a materials testing system to measure torque, compressive force, and time for drilling, tapping, and screw insertion. Fragment compression was measured with a pressure-sensing device placed between the simulated fracture fragments during screw insertion for fragment stabilization. Subsequently, screws were pushed out of the stabilized bone fragments in a single cycle to failure. A paired t test was used to assess differences between site preparation, screw insertion, fragment compression, and screw pushout variables, with significance set at P <.05. RESULTS: Measured drilling variables were comparable for AO and AP specimens. However, the AP tap had significantly greater insertion torque and force. Mean maximum screw insertion torque was significantly greater for AO screws. For fragment compression, AP screws generated 65% and 44% of the compressive pressure and force, respectively, of AO screws. AP screws tended to have higher overall pushout strength. Pushout stiffness was similar between both screw types. CONCLUSION: The 6.5-mm tapered AP screw generated less interfragmentary compressive pressure and force but had similar pushout stiffness. Evaluation of failure patterns demonstrated that AP screws had greater pushout strength compared with 4.5-mm AO screws for fixation of a simulated complete lateral condylar fracture. CLINICAL RELEVANCE: The 6.5-mm tapered AP screw should provide ample holding strength but would provide less interfragmentary compression than 4.5-mm AO screws for repair of complete lateral condylar fractures in horses.

Animals↗

PubMed2000

The efficacy of the new SCD response compression system in the prevention of venous stasis.

OBJECTIVE: The current commercially available sequential intermittent pneumatic compression device used for the prevention of deep venous thrombosis has a constant cycle of 11 seconds' compression and 60 seconds' deflation. This deflation period ensures that the veins are filled before the subsequent cycle begins. It has been suggested that in some positions (eg, semirecumbent or sitting) and with different patients (eg, those with venous reflux), refilling of the veins may occur much earlier than 60 seconds, and thus a more frequent cycle may be more effective in expelling blood proximally. The aim of the study was to test the effectiveness of a new sequential compression system (the SCD Response Compression System), which has the ability to detect the change in the venous volume and to respond by initiating the subsequent cycle when the veins are substantially full. METHODS: In an open controlled trial at an academic vascular laboratory, the SCD Response Compression System was tested against the existing SCD Sequel Compression System in 12 healthy volunteers who were in supine, semirecumbent, and sitting positions. The refilling time sensed by the device was compared with that determined from recordings of femoral vein flow velocity by the use of duplex ultrasound scan. The total volume of blood expelled per hour during compression was compared with that produced by the existing SCD system in the same volunteers and positions. RESULTS: The refilling time determined automatically by the SCD Response Compression System varied from 24 to 60 seconds in the subjects tested, demonstrating individual patient variation. The refilling time (mean +/- SD) in the sitting position was 40.6 +/- 10. 0 seconds, which was significantly longer (P <.001) than that measured in the supine and semirecumbent positions, 33.8 +/- 4.1 and 35.6 +/- 4.9 seconds, respectively. There was a linear relationship between the duplex scan-derived refill time (mean of 6 readings per leg) and the SCD Response device-derived refill time (r = 0.85, P <. 001). The total volume of blood (mean +/- SD) expelled per hour by the existing SCD Sequel device in the supine, semirecumbent, and sitting positions was 2.23 +/- 0.90 L/h, 2.47 +/- 0.86 L/h, and 3.28 +/- 1.24 L/h, respectively. The SCD Response device increased the volume expelled to 3.92 +/- 1.60 L/h or a 76% increase (P =.001) in the supine position, to 3.93 +/- 1.55 L/h or a 59% increase (P =. 001) in the semirecumbent position, and to 3.97 +/- 1.42 L/h or a 21% increase (P =.026) in the sitting position. CONCLUSIONS: By achieving more appropriately timed compression cycles over time, the new SCD Response System is effective in preventing venous stasis by means of a new method that improves on the clinically documented effectiveness of the existing SCD system. Further studies testing its potential for improved efficacy in preventing deep venous thrombosis are justified.

Adult↗

PubMed1999

Assessment of an EMG-based method for continuous estimates of low back compression during asymmetrical occupational tasks.

Variables, such as peak and accumulated moments and spine compression forces, have been shown to be risk factors for occupational low back pain. Estimates of these forces during prolonged, dynamic, asymmetric tasks using biomechanical models is complex and time-consuming. A simple technique for continuous measurement of these variables over a prolonged period is needed to measure the distribution of spinal loading during both sagittal plane lifts and complex asymmetrical jobs. The aim of this study was to determine whether a linear normalization of erector spinae EMG to spine compression force, called compression normalized EMG (CNEMG), could be used to estimate spinal loading for simulations of asymmetrical occupational tasks. The estimates of spine compression force obtained using the normalized EMG are presented in the form of an amplitude probability distribution function and are compared with estimates of a three-dimensional biomechanical model. The per cent time a worker spends above particular levels of spinal loading of interest, such as the NIOSH action limit for compression, are displayed. Five males performed simulated occupational tasks. The exposure time at a specific level of spine compression force for a combination of three tasks, estimated by CNEMG, was, on average, within 6.5% of the time calculated by the biomechanical model. However, if the task combination was dominated by an axial twisting moment, then the difference was, on average, 13.4%. The difference in magnitude of spine compression at a specific probability was, on average, 14.9% and when axial trunk twist dominated, 30.7%. It is concluded that CNEMG can estimate probability at a specific level of spine compression force when the task combination is characterized by a predominant extensor moment in the sagittal plane. Estimates of spine compression at a specific probability, and estimates obtained during task combinations dominated by an axial twisting moment, are poor.

Adult↗

PubMed2007

Stem-righting mechanism in gymnosperm trees deduced from limitations in compression wood development.

BACKGROUND AND AIMS: In response to inclination stimuli, gymnosperm trees undergo corrective growth during which compression wood develops on the lower side of the inclined stem. High compressive growth stress is generated in the compression wood region and is an important factor in righting the stem. The aims of the study were to elucidate how the generation of compressive growth stress in the compression wood region is involved in the righting response and thus to determine a righting mechanism for tree saplings. METHODS: Cryptomeria japonica saplings were grown at inclinations of 0 degrees (vertical) to 50 degrees. At each inclination angle, the growth stress on the lower side of the inclined stem was investigated, together with the degree of compression-wood development such as the width of the current growth layer and lignin content, and the upward bending moment. KEY RESULTS: Growth stress, the degree of compression wood development, and the upward moment grew as the stem inclination angle increased from 0 to 30 degrees, but did not rise further at inclinations > 30 degrees. CONCLUSIONS: The results suggest the following righting mechanism for gymnosperm saplings. As the stem inclination is elevated from 0 to 30 degrees, the degree of compression wood development increases to force the sapling back to its original orientation; at inclinations > 30 degrees, the maximum degree of compression wood is formed and additional time is needed for the stem to reorient itself.

Cryptomeria↗

PubMed1990

Cardiopulmonary resuscitation with interposed abdominal compression after asphyxial or fibrillatory cardiac arrest in pigs.

The purpose of this study was to compare the efficacy of standard cardiopulmonary resuscitation and cardiopulmonary resuscitation with interposed abdominal compression for restoration of spontaneous circulation in an asphyxial and fibrillatory arrest model. Twenty-eight pigs weighing 19-27 kg were randomly allocated to two arrest groups. Each of these two groups was then subdivided into a treatment group and a control group resulting in four groups of seven pigs each. In the control groups standard cardiopulmonary resuscitation was performed with a pneumatically driven chest compressor at a rate of 80 beats per min. The animals' lungs were ventilated at a respiratory rate of 20 breaths per min independently of chest compression. In the treatment group, in addition to standard cardiopulmonary resuscitation, manual interposed abdominal compression was applied at the midabdomen in the second half of the relaxation phase using a blood pressure cuff to measure and standardize the compressions. Following asphyxial cardiac arrest of 3 min, none of the seven animals could be resuscitated with standard cardiopulmonary resuscitation, whereas all seven animals could be resuscitated with interposed abdominal compression and standard cardiopulmonary resuscitation after 240 +/- 84 s. Following fibrillatory cardiac arrest of 4 min, none of the seven animals that received standard cardiopulmonary resuscitation and countershocks could be resuscitated. In the group that received standard cardiopulmonary resuscitation and interposed abdominal compression spontaneous circulation was achieved in all animals in 244 +/- 117 s. End-diastolic arteriovenous pressure difference, which correlates with coronary blood flow, was significantly higher with interposed abdominal compression during resuscitation from both forms of cardiac arrest. The results of our study indicate that cardiopulmonary resuscitation with interposed abdominal compression in the second half of the relaxation phase improves diastolic arteriovenous pressure difference and resuscitation success in comparison with that following standard cardiopulmonary resuscitation. The use of interposed abdominal compression during basic cardiac life support should be investigated further in patients.

Abdomen↗

PubMed1999

Unintended inhalation of nitric oxide by contamination of compressed air: physiologic effects and interference with intended nitric oxide inhalation in acute lung injury.

BACKGROUND: Compressed air from a hospital's central gas supply may contain nitric oxide as a result of air pollution. Inhaled nitric oxide may increase arterial oxygen tension and decrease pulmonary vascular resistance in patients with acute lung injury and acute respiratory distress syndrome. Therefore, the authors wanted to determine whether unintentional nitric oxide inhalation by contamination of compressed air influences arterial oxygen tension and pulmonary vascular resistance and interferes with the therapeutic use of nitric oxide. METHODS: Nitric oxide concentrations in the compressed air of a university hospital were measured continuously by chemiluminescence during two periods (4 and 2 weeks). The effects of unintended nitric oxide inhalation on arterial oxygen tension (n = 15) and on pulmonary vascular resistance (n = 9) were measured in patients with acute lung injury and acute respiratory distress syndrome by changing the source of compressed air of the ventilator from the hospital's central gas supply to a nitric oxide-free gas tank containing compressed air. In five of these patients, the effects of an additional inhalation of 5 ppm nitric oxide were evaluated. RESULTS: During working days, compressed air of the hospital's central gas supply contained clinically effective nitric oxide concentrations (> 80 parts per billion) during 40% of the time. Change to gas tank-supplied nitric oxide-free compressed air decreased the arterial oxygen tension by 10% and increased pulmonary vascular resistance by 13%. The addition of 5 ppm nitric oxide had a minimal effect on arterial oxygen tension and pulmonary vascular resistance when added to hospital-supplied compressed air but improved both when added to tank-supplied compressed air. CONCLUSIONS: Unintended inhalation of nitric oxide increases arterial oxygen tension and decreases pulmonary vascular resistance in patients with acute lung injury and acute respiratory distress syndrome. The unintended nitric oxide inhalation interferes with the therapeutic use of nitric oxide.

Administration, Inhalation↗

PubMed1997

Effects of intermittent pneumatic compression on venous haemodynamics and fibrinolytic activity.

Pneumatic intermittent compression is an effective method to prevent postoperative venous thromboembolism. Its efficacy has been ascribed to both a haemodynamic action (increase of blood flow velocity) and a stimulation of endogenous fibrinolytic activity [via the production of tissue-type plasminogen activator (t-PA) by the vascular endothelium]. The relative contribution of these two effects is still debated. In a randomized, cross-over study in ten healthy volunteers, we compared the haemodynamic and fibrinolytic effects of two different pneumatic intermittent compression devices: a classical, low-pressure, whole-leg boots system, and a novel, high-pressure, plantar compression system. The study was performed at rest, to compare haemodynamics and fibrinolytic activity modifications, and under induced venous leg stasis, in order to compare the two compression systems in experimental conditions mimicking laparoscopic surgery. Our data show that (1) a pneumatic compression device that exerts its compression on the plantar venous plexus only induced an increase of venous blood peak velocity and flow in the common femoral vein that is very similar to that induced by the classical whole-leg boots compression system; (2) the venous stasis induced by an external pressure mimicking the conditions of laparoscopic surgery further increased the absolute velocity and flow increase, with the two intermittent compression systems tested; (3) no changes of t-PA or plasminogen activator-inhibitor 1 antigens were observed with either pneumatic compression device. In conclusion, the present study indicates that the antithrombotic effect of mechanical prophylaxis is probably mainly due to its ability to increase venous peak velocity and flow, especially under venous stasis conditions.

Adult↗

PubMed1982

CPR with simultaneous compression and ventilation at high airway pressure in 4 animal models.

CPR with simultaneous chest compression and ventilation at high airway pressure (SCV-CPR) improves blood flow in some studies but not in others, perhaps because of differences in the animal models employed. To resolve such discrepancies, we compared SCV-CPR to standard CPR in 4 mechanically different canine models, using both small and large dogs and small and large compression pads. The 4 groups were: large dogs receiving chest compression through a large pad (model A), large dogs receiving chest compression through a small pad (model B), small dogs receiving chest compression through a large pad (model C), and small dogs receiving chest compression through a small pad (model D). Cardiac output (CO) during CPR was determined by a specially modified indicator dilution method. Models A, B, and C all had similar mean COs of 14 ml/min . kg body weight during standard CPR, and 27 ml/min . kg during SCV-CPR. However, in model D, there was no significant difference during standard vs. SCV-CPR, and the mean output was 33 ml/min . kg. We conclude that in models A, B, and C, little direct heart compression occurred and the higher intrathoracic pressure pulses produced by SCV-CPR improved blood flow. However it seems likely that there was effective cardiac compression in model D. In the absence of direct cardiac compression, SCV-CPR provides an alternative means of generating satisfactory flow in a mechanically appropriate animal model.

Animals↗

PubMed1999

Aspiration and transtracheal jet ventilation with different pressures and depths of chest compression.

OBJECTIVE: To evaluate aspiration prophylaxis during cardiopulmonary resuscitation (CPR) using transtracheal jet ventilation (TJV) with different pressure-depths of chest compression and chest compression alone without mechanical ventilation. DESIGN: Prospective, animal study. SETTING: Animal research laboratory, Chang Gung Memorial Hospital, Kaohsiung Medical Center, Taiwan. SUBJECTS: Mongrel dogs (n = 10) weighing 8 to 12 kg. INTERVENTIONS: Eight mongrel dogs were anesthetized, paralyzed, and ventilated transtracheally with a jet ventilator at frequencies varied from 600 to 10 cycles/min. The airway pressures below and above the jetting port were measured. The mouth of the dog was filled with barium and chest radiographs were taken 10 mins after chest compression with 20-pound pressure and 5-cm depth in group 1 and 10-pound pressure and 3-cm depth in group 2 at each different jet frequency. Two additional dogs underwent the same procedures but received only chest compression without TJV. MEASUREMENTS AND MAIN RESULTS: Pulmonary aspiration was not noted in the chest radiographs from either group. The airway pressure changes between groups were not significantly affected by difference in pressures and depths of chest compression at the same jetting frequency. However, pulmonary aspiration occurred in the two dogs that received chest compression alone without TJV. CONCLUSIONS: Application of TJV during chest compression with different pressures and depths caused no pulmonary aspiration in dogs at frequencies between 600 and 10 cycles/min. The protection against aspiration disappeared if the dogs received only chest compression without TJV. The mechanism of preventing pulmonary aspiration in TJV is thought to be due to forceful unidirectional gas outflow through the larynx and higher airway pressure in the carina than in the upper airway. The airway pressures were not affected by different chest compression pressures and depths because the larynx stayed open during TJV and the air outflow could freely move out without increasing the pressure in the airway.

Animals↗