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Impedance tomography: computational analysis based on finite element models of a cylinder and a human thorax.

A direct image reconstruction method of electrical impedance tomography (EIT) is evaluated using three-dimensional (3-D) finite element models of cylindrical and torso-shaped volume conductors. The cylindrical model is used to examine the effect of electrode configurations and the sensitivity to off-plane objects and to noise in the measured data. It is also used to validate the modeling procedures by comparison with experimental data acquired from a similar cylindrical tank filled with saline. Simulation results show only minor differences in performance between the various electrode configurations. In the second part, a realistic human thorax model constructed from CT images is used to evaluate monitoring of pulmonary edema by EIT. The conductivity, volume, and vertical position of an abnormal region in the lungs are varied to simulate the progress of edema. Dynamic EIT images are reconstructed from data computed for the inhomogeneous thorax (heart and lungs) as the reference set and a realistic amount of noise is added to reproduce the conditions in which the technique would be used in practice. Simulation results show that a 10 ml edema region with a conductivity equal to that of blood can be detected at a 40 dB signal-to-noise ratio (SNR). Detection of a smaller volume, in the order of 2 ml, should be possible by improving either the instrumentation to achieve 60 dB SNR or the performance of reconstruction algorithms.

Cardiography, Impedance↗

Method to localise myocardial infarction using magnetocardiography: simulation studies.

The work presents a method for localising regions of myocardial infarction (MI) using magnetocardiography, which is validated by simulation techniques. We have verified that the first two principal components of magnetocardiographic signals obtained from torso mapping within a normal group are very similar even in experimental measurements. So, if we have the temporal eigenvectors of a normal group, these can be used as an orthonormal basis for estimating the signals of a patient being tested. Analysis of the residual signals using singular value decomposition (SVD) allows the localisation of regions of MI. Comparisons are made with a similar method which uses spatial eigenvectors as its basis. It is shown that our approach is able to localise the equivalent current dipoles which generate MI even when they are not orthogonal to the spatial eigenvectors.

Computer Simulation↗

Magnetic field excitation of peripheral nerves and the heart: a comparison of thresholds.

Time-varying magnetic fields can theoretically excite the heart or peripheral nerves. Relative excitation thresholds of nerve and heart are compared using ellipsoidal representations of the human torso. Relative magnetic thresholds depend on the excitability of nerve and cardiac tissue, the geometric positions of anatomical features, stimulus waveform features and the direction and spatial distribution of the incident magnetic field. Minimum electric field thresholds for excitation of nerve and heart do not differ greatly. Nevertheless, nerve and heart magnetic thresholds may be disparate because of factors related to body geometry and the dependence of excitability on the stimulus waveform.

Heart↗

Cardiopulmonary monitoring by textile electrodes without subject-awareness of being monitored.

An automated system is developed to monitor cardiopulmonary functions during sleep using electrically conductive textiles. The system obviates the need to attach transducers or electrodes to the body surface, and the subject can follow his or her normal daily routine, wearing regular pajamas to bed. Part of the bed sheet consists of electrically conductive textiles under the positions of the head, torso and legs. Respiratory activity and electrocardiograms of diagnostic quality are observed by means of the electrodes while the subject is sleeping. Respiration is sensed by means of electrical capacitance in/around the thorax. Data acquisition and storage are fully automated; thus, the subject's awareness of being monitored is greatly reduced. This system could detect disorders of cardiopulmonary functions at an early stage, if used daily in the home with the concept of chronodiagnosis.

Bedding and Linens↗

Multichannel magnetocardiographic measurements with a physical thorax phantom.

Artificial dipolar sources were applied inside a physical thorax phantom to experimentally investigate the accuracy obtainable for non-invasive magnetocardiographic equivalent current dipole localisation. For the measurements, the phantom was filled with saline solution of electrical conductivity 0.21 S m-1. A multichannel cardiomagnetometer was employed to record the magnetic fields generated by seven dipolar sources at distances from 25 mm to 145 mm below the surface of the phantom. The inverse problem was solved using an equivalent current dipole in a homogeneous boundary element torso model. The dipole parameters were determined with a non-linear least squares fitting algorithm. The signal-to-noise ratio (SNR) and the goodness of fit of the calculated localisations were used in assessing the quality of the results. The dependence between the SNR and the goodness of fit was derived, and the results were found to correspond to the model. With SNR between 5 and 10, the average localisation error was found to be 9 +/- 8 mm, while for SNR between 30 and 40 and goodness of fit between 99.5% and 100%, the average error reduced to 3.2 +/- 0.3 mm. The SNR values obtained in this study were also compared with typical clinical values of SNR.

Cardiology↗

Assessment of spatial resolution of pace mapping when using body surface potentials.

Using computer simulations and statistical methods, the resolution of pace mapping when used in combination with body surface potentials was systematically investigated. In an anatomical model of the human ventricular myocardium, pre-excitation sequences were initiated at 69 sites positioned along the atrioventricular (AV) ring and corresponding body surface potential maps (BSPMs) were calculated at 32 leads placed on the anterior torso. For each time after the onset of pre-excitation (every 4 ms to 40 ms) and each root-mean-square (RMS) noise level (5, 10, 20 and 50 microV), BSPMs were cros-correlated and the spatial resolution defined as the largest pacing site separation at which the differences in correlation coefficients were not statistically significant (level p > or = 0.05). The findings indicate that when random RMS noise of 5 microV was added to the simulated BSPMs, average spatial resolution over all 60 sites was at 20 ms after the onset of pre-excitation within 3.5 +/- 0.9 mm. The results provide theoretical evidence that statistical analysis of BSPMs obtained during pace mapping can offer improved means for subcentimetre identification of accessory pathways located along the AV ring.

Body Surface Potential Mapping↗

Comparison between electrocardiographic and magnetocardiographic inverse solutions using the boundary element method.

The accuracy of imaging cardiac sources using electrocardiographic and magnetocardiographic signals is influenced by thoracic inhomogeneities, e.g. the lungs and cardiac blood masses. The effects is investigated of such inhomogeneities on the body-surface potential maps (BSPM) and magnetic-field maps (MFM) inverse solutions for a single moving dipole as the source model and a realistic torso model as the volume conductor, by employing a node-based boundary element method. Using the same number and placement of the body-surface potential and magnetic field leads, a comparison is obtained of the numerical accuracy of body-surface potential and magnetic field leads. The results show that, with no noise added, the body-surface potential solution is less sensitive to the exclusion of the inhomogeneities than the magnetic field solution. The influence of noise on the BSPM and MFM localization is comparable for x (left-right) and y (foot-head) oriented dipoles, and the BSPM localisation is more accurate than the MFM localisation for z (anterior-posterior) oriented dipoles.

Electrocardiography↗

Application of the boundary element method to the solution of anisotropic electromagnetic problems.

The paper discusses the application of the boundary element method to the computation of the electric potential and magnetic field generated by bioelectric sources in an anisotropic inhomogeneous volume conductor, using a proper coordinate transformation. It is shown that the co-ordinate transformation generally not only affects the conductivity and geometry of the volume conductor under consideration, but also the current source term and the continuity relation on the interfaces bounding regions of different conductivity. To illustrate these results, the electric potentials in an anisotropic finite length cylinder and in an anisotropic volume conductor of irregular (torso) shape, computed by the boundary element method, are compared with the results obtained by the analytical solution and the finite element method, respectively.

Anisotropy↗

Multicentric malignant fibrous histiocytomas of the colon. Report of a case and review of the subject.

Malignant fibrous histiocytoma is a primitive mesenchymal tumor usually found in the soft tissues of the extremity or torso of adults. Only two previous reports of this lesion in the abdominal viscera are present in the world medical literature. A case is reported of three synchronous tumors in the rectum, colon, and omentum with the pathologic appearance of malignant fibrous histiocytoma. Although resected completely with a transverse colocolostomy and a low-anterior resection, the expected behavior of this tumor is one of aggressive local recurrence followed by distant metastasis. The clinical and pathologic characteristics of malignant fibrous histiocytoma are reviewed.

Adolescent↗

Segmental inertial parameters of the human trunk as determined from computed tomography.

This study used computed tomography (CT) imaging to determine in vivo mass, center of mass (CM), and moments of inertia (Icm) about the CM of discrete segments of the human torso. Four subjects, two males and two females, underwent serial transverse CT scans that were collected at 1-cm intervals for the full length of the trunk. The pixel intensity values of transverse images were correlated to tissue densities, thereby allowing trunk section mass properties to be calculated. The percentage of body mass observed by vertebral levels ranged from 1.1% at T1 to 2.6% at L5. The masses of the upper, middle, and lower trunk segments as percentages of body mass were estimated to be 18.5, 12.2, and 10.7%, respectively. The whole trunk mass was estimated to comprise 41.6% of the total body mass. Transverse vertebral CM values were found to lie anterior to their respective vertebral centroids by up to 5.0 cm in the lower thoracic region. For the upper, middle, and lower trunk segments, the average CM positions were found to be 25.9, 62.5, and 86.9% of the distance from the superior to inferior ends of the trunk. The upper and middle trunk CMs corresponded to approximately 4.0 cm anterior to T7/T8 vertebral centroid levels and 1.0 cm anterior to L3/L4 vertebral centroid levels, respectively. For the whole trunk, the CM was 52.7% of the distance from the xiphoid process and approximately 2.0 cm anterior to L1/L2 vertebral centroid levels. Variations in CM and Icm values were observed between subject, but these were within the range of previous reports of body segment parameters. Differences from previous studies were attributable to variations in boundary definitions, measurement techniques, population groups, and body states (live versus cadaver) examined. The disparity between previous findings and findings of this study emphasizes the need to better define the segmental properties of the trunk so that improved biomechanical representation of the body can be achieved.

Abdomen↗

Effects of rotational myocardial anisotropy in forward potential computations with equivalent heart dipoles.

Rotating fibers in the heart lead to a myocardium of inhomogeneous anisotropic conductivity. Besides affecting the activation isochrones, this anisotropy modifies the equivalent dipoles used in calculating extracardiac potentials, rendering them oblique rather than normal to the activation wavefront due to an added axial dipole component oriented along the fibers. Herein, however, consequences of the assumption usually made in forward potential calculations that the equivalent dipoles act in a myocardium that is homogeneous and isotropic are examined. A layered inner block representing the heart was placed inside an outer block representing an isotropic volume conductor. Fiber direction in the inner block rotated uniformly from layer to layer. Current dipoles of different orientations were placed in the inner block and the potentials calculated everywhere. Effects of the anisotropy of the inner block were gauged by computing an equivalent dipole that best fit the outer block surface potentials. For volume conductor conductivities close to that of the torso, the anisotropy diminished dipoles oriented along the fibers. Since the intraventricular blood masses in the heart also diminish such dipoles, these reductions of the axial component may explain the success of heart model simulations that ignore this component.

Anisotropy↗

Development of a collimator blurring compensation method using fine angular sampling projection data in SPECT.

Due to the collimator aperture, spatial resolution of SPECT data varies with source-to-detector distance. Since the radius of detector rotation is bigger when scanning larger patients, spatial resolution is degraded in these cases. Emitted gamma rays travel not only along the central axis of the collimator hole but also off-axis due to the collimator aperture. However, an off-axis ray at one angle would be a central-axis ray at another angle; therefore, raw projection data at one angle can be thought of as an ensemble of central-axis rays collected from a small arc equal to the collimator aperture. Thus, fine angular sampling can compensate for collimator blurring. By using a sampling pitch of less than half the collimator aperture angle, compensation was performed by subtracting the weighted sum of the projection data from the raw projection data. Collimator geometry and detector rotation radius determined the weighting function. Cylindrical phantom with four different-sized rods and torso phantom for Tl-201 cardiac SPECT simulation were used for evaluation. Aperture angle of the collimator was 7 degrees. Projection sampling pitch was 2 degrees. In both phantom studies, the proposed method showed improvement in contrast and reduction of partial volume effect, thereby indicating that the proposed method can compensate adequately for image blurring caused by the collimator aperture.

Artifacts↗

Lidocaine 0.5% spinal anaesthesia: a hypobaric solution for short-stay perirectal surgery.

The efficacy of subarachnoid injection of 8 ml lidocaine 0.5% was assessed in ten outpatients having perirectal surgery in the jackknife position. This solution is hypobaric, with a baricity 0.9985 +/- 0.0003 (mean +/- SD). Injections were made with the patient in the surgical position (with the upper torso at a 15 degrees downward inclination). Sensory level was tested by pinprick. Times to two-segment regression, to complete resolution of sensory analgesia, to urination, and to discharge from the recovery room were recorded. All injections produced effective anaesthesia for surgery. Lidocaine 0.5% behaves clinically as a hypobaric solution. Dermatomal levels remained low (T11 to L5) while the patients were in the surgical position (head down), but rose two to six dermatomes if the patient's head was elevated after surgery. Time to two-segment regression was 97 +/- 36 min, time until regression to S1 was 116 +/- 22 min, time to complete resolution of sensory blockade was 151 +/- 23 min, time to urination was 197 +/- 64 min, and time to discharge from the recovery room was 205 +/- 45 min. Lidocaine 0.5% provides effective spinal anaesthesia of short duration appropriate for outpatient surgical procedures. Dermatomal sensory spread of anaesthesia, and our measurements of specific gravity, indicate that this solution is hypobaric. It appears that changes in position can alter the spread of analgesia for at least one hour after injection and, thus, we caution against elevating the patient's head in the immediate postoperative period.

Adult↗

Case report: intraoperative anaphylactoid reaction and hydroxyethyl starch in balanced electrolyte solution (Hextend).

PURPOSE: To report a first case of probable anaphylactoid reaction to 6% hydroxyethyl starch reconstituted in balanced electrolyte and glucose solution (Hextend). CLINICAL FEATURES: A 22-yr-old man was admitted for a partial nephrectomy. Near the end of the four-hour operation, an infusion of Hextend was initiated. Shortly thereafter, mechanical ventilation became difficult, peak inspiratory pressure increased to 55 cm H2O with audible wheezing over the patient's lungs. Blood pressure suddenly decreased to 68/46 mmHg. Multiple doses of phenylephrine, ephedrine and epinephrine were required to restore the patient's blood pressure. Postoperatively, a diffuse urticarial rash was apparent on his upper torso. The patient recovered uneventfully. His postoperative serum tryptase was 26.3 ng x mL(-1) (reference range, < 11.5 ng x mL(-1)) and the urine N-methyl-histamine was 2448 microg x g(-1) creatinine (reference range, 30-200 microg x g(-1) creatinine). Two months after the event, skin testing was conducted to test for possible allergy to latex, lidocaine, propofol, cisatracurium, succinylcholine, vecuronium, midazolam, fentanyl, ondansetron, neostigmine, and cephazolin, and all were negative. Hextend was also tested, starting with a 1:100,000 dilution and the results were negative. CONCLUSIONS: The temporal relationship of severe hypotension, bronchospasm and skin rash within ten minutes from administration of Hextend in this patient suggests an immediate hypersensitivity reaction to hetastarch. The elevated levels of serum tryptase and urinary N-methyl-histamine suggest that this hypersensitivity was mediated from mast cell degranulation. Negative skin testing suggests that the reaction was anaphylactoid.

Adult↗

[Effectiveness of preclinical emergency management. Fiction or fact?].

The current increase in the cost of health care must be considered as a severe threat to the prehospital emergency services system. Two examples have been selected--the patient with polytrauma and the patient in cardiac arrest--to demonstrate the dilemma between a need for objective data and the requirements of emergency patients. Study results obtained in trauma patients indicating that total prehospital time, including scene time, is correlated to patient outcome have led to the conclusion that at the scene treatment by emergency physicians may be dispensable. It has, however also been demonstrated that the time required for medical treatment at the scene is equivalent to 20% of the total scene time, thus representing only a fraction of the total prehospital time. Correlating the total prehospital time or scene time to outcome therefore appears absurd. The treatment principle of aggressive shock treatment in polytrauma needs critical reevaluation on the basis of results obtained by recent preclinical studies in patients with penetrating torso injuries. Small volume resuscitation could not be demonstrated to improve outcome in polytrauma patients, although a slight improvement in patients with brain injury may be assumed. Endotracheal intubation and early artificial ventilation are proven therapeutic principles in polytraumatized patients. Unfortunately, for ethical reasons randomised carefully controlled comparative studies can not be performed in polytrauma patients unless the patient is fully conscious. The importance of endotracheal intubation and artificial ventilation in unconscious trauma patients becomes apparent under conditions of anaesthesia where the application of the endotracheal tube averts regurgitation, aspiration and concomitant morbidity and mortality. The common causes of cardiovascular collapse and their pathomechanisms, as well as the mechanisms of cardiopulmonary resuscitation, have been widely investigated. Nevertheless, various aspects of their application are still controversial. The most recent study results have recommended initial ventilation prior to thoracic compression. New methods of assisting mechanical cardiopulmonary resuscitation, such as ACD CPR or vest CPR, have shown promising results in animal experiments. However, the importance of results obtained by preclinical randomised controlled investigations in humans need to be confirmed by further studies as to outcome. The efficacy of defibrillation in cases of ventricular fibrillation has been clearly demonstrated, particularly with a view to the interval between ventricular fibrillation and defibrillation. It has further been demonstrated that basic cardiopulmonary resuscitation preserves ventricular fibrillation and thus improves the chance of survival. The present generation of defibrillators has been further improved, particularly by the introduction of biphasic defibrillator wave forms, which may reduce the required energy, as well as possible complications, while offering an increase in the efficacy of defibrillation and a reduction in defibrillator size. Scientific emergency medicine is responsible not only for the development and validation of new methods and concepts, but in particular for their application under quality control conditions. Politicians require an improvement in the quality of the validation of emergency measures, although the instruments available for the investigation of these measures are known to be obsolete (experimental models, experimental design). Additionally, the financial support of research in emergency medicine suffers from being accourded low priority by public research funds such as the German Research Fund. However, in view of the rapid application of experimental results to daily practice it should be emphasized that patients also support research in emergency medicine via their direct financial contributions to the health insurance companies.

Animals↗

[Fractures of the scapula].

Two thirds of the fractures of the scapula refer to its body, one third to its neck, and one forth to the glenoid. They are indicative of high-energy blunt trauma. Traffic injuries are their main cause. Associated ipsilateral upper torso injuries are common and have to be considered!Scapular fractures may be classified as being extra- or intraarticular. Extraarticular fractures concern the scapular body, its processes, or the scapular neck. A fracture of the surgical neck of the scapula accompanied by an injury to the coracoclavicular connection is regarded as a "floating shoulder". In this case the broken suspension of the glenoid has to be reconstructed. Most intraarticular fractures are of the Bankart variety, where a shoulder dislocation spreads an oblique fragment of the glenoid. They should be treated by internal fixation, if the size of the fragment is bigger than 16 mm. Where surgery is advisable, an appropriate approach has to be chosen depending on the type of the fracture. The anterior approach of Neer and the dorsolateral approach of Brodsky are very suitable. As a basic principle dislocated or unstable fractures of the scapular processes and of the glenoid should be treated by internal fixation, since their functional result may be less than fair if they are treated conservatively. Most other fractures heal uneventful under a conservative regimen.

Accidents, Traffic↗

[The significance of delayed diagnosis of lesions in multiply traumatised patients. A study of 1,187 shock room patients].

BACKGROUND: Multislice computed tomography (CT) technology has improved the diagnosis of relevant lesions within the phase of primary treatment of severely injured patients. The lack of time in this phase and the complexity of the multiple injuries there is still a risk that lesions will be missed at this stage. The purpose of this study was to evaluate the incidence, causes, implications and significance when injuries are not diagnosed until later. METHODS: The data were documented prospectively in the context of a quality management system for the care of severely injured patients in a primary urban trauma centre. Missed injuries were defined as any lesions that had not been recognised by the time the patient was admitted to the ICU. RESULTS: During a 44-month period 1,187 (ISS 21+/-17) patients were enrolled in the study, all of whom were admitted from May 1998 to April 2002 after attending the emergency room. In total 64 (4.9%) missed injuries were detected in 58 (ISS 30+/-16) patients; 26 of the 64 missed injuries were located on the torso, 8 injuries in the head and neck region, and 30 on the arms and legs. The missed injuries were categorised as follows: 1. Lesion not seen in diagnostics (n=15). 2. Incomplete diagnostics (n=8). 3. Primarily unsuspicuous examination (n=35). 4. Diagnostics interrupted due to hemodynamic instability (n=6). CONCLUSION: Despite intensified and standardised diagnostic procedures prescribed for use in trauma centres, injuries are still missed in severely injured patients. About 30% of lesions that are not diagnosed until after the patient has left the emergency room have clinically significant, but not lethal, consequences for the patient. Great importance attaches to the follow-up investigation on the intensive care station, so that lesions that have initially been overlooked can be diagnosed and treated as soon as possible so as to keep the complication rate low.

Adolescent↗

Distal mdx muscle groups exhibiting up-regulation of utrophin and rescue of dystrophin-associated glycoproteins exemplify a protected phenotype in muscular dystrophy.

Unique unaffected skeletal muscle fibres. unlike necrotic torso and limb muscles, may pave the way for a more detailed understanding of the molecular pathogenesis of inherited neuromuscular disorders and help to develop new treatment strategies for muscular dystrophies. The sparing of extraocular muscle in Duchenne muscular dystrophy is mostly attributed to the special protective properties of extremely fast-twitching small-diameter fibres, but here we show that distal muscles also represent a particular phenotype that is more resistant to necrosis. Immunoblot analysis of membranes isolated from the well established dystrophic animal model mdx shows that, in contrast to dystrophic limb muscles, the toe musculature exhibits an up-regulation of the autosomal dystrophin homologue utrophin and a concomitant rescue of dystrophin-associated glycoproteins. Thus distal mdx muscle groups provide a cellular system that naturally avoids myofibre degeneration which might be useful in the search for naturally occurring compensatory mechanisms in inherited skeletal muscle diseases.

Animals↗