How short-range adhesion slows down crack closure and contact formation.

While viscoelastic, adhesive contact rupture of simple indenters is well studied, contact formation has received much less attention. Here, we present simulations of the formation of contact between various power law indenters and an adhesive, viscoelastic foundation. For all investigated indenters, we find that the macroscopic relaxation time τ scales approximately with 1/ρ1.8, where ρ is the range of adhesion. The prolongation of contact formation with Tabor parameter is rationalized by the increased dissipation that short-range adhesion causes on a moving crack.

Detection of delayed cerebral ischemia (DCI) in subarachnoid haemorrhage applying near-infrared spectroscopy: elimination of the extracerebral signal by transcutaneous and intraparenchymatous measurements in parallel.

BACKGROUND: Detection of delayed cerebral ischemia (DCI) in high-grade subarachnoid haemorrhage (SAH) is an unsolved issue. Conventional near-infrared spectroscopy (NIRS) with optodes applied over the skin is controversial because the NIRS signal is contaminated by extracerebral tissue. The objective is to quantify and subtract the contribution from extracerebral tissue from the signal by using measurements in parallel with a NIRS brain tissue probe and conventional NIRS. METHODS: In a patient with high-grade SAH, two approaches for NIRS were applied. First, a conventional brain tissue probe for intracranial pressure (ICP) monitoring, supplied by optical fibres, was placed into the brain tissue 2 cm deep from the dura. Second, for conventional NIRS, a plaster-based patch carrying optodes (one emitter, two detectors) was attached to the skin. Central venous injections of 0.3 mg/kg body weight (bw) indocyanine green (ICG) were performed. ICG dye dilution curves obtained with the probe and patch were collected simultaneously and analysed for blood flow values. RESULTS: Twelve measurements in parallel with the probe and patch were performed. Mean cerebral blood flow (CBF) for the probe was higher (24.8 ± 9.1 ml/100 g/min) compared with the values obtained with the patch (for detector 1, extra-cerebral blood flow [ECBF] mean 5.1 ± 1.8 ml/100 g/min; p = 0.002; for detector 2, 6.6 ± 2.1 ml/100 g/min; p = 0.002). CBF values obtained with the probe correlated with blood flow values obtained with the patch (for CBF vs. ECBF detector 1, r = 0.72 [p = 0.008]; ECBF detector 2, r = 0.79 [p = 0.002]). CONCLUSIONS: Blood flow values obtained with conventional NIRS correlated significantly with absolute CBF values obtained directly within the brain tissue. Simultaneous measurements with the NeMo Probe and NeMo Patch allow quantification and subtraction of the contribution from extracerebral tissues from the signal obtained with conventional NIRS.

Neuromonitoring in intensive care: a new brain tissue probe for combined monitoring of intracranial pressure (ICP) cerebral blood flow (CBF) and oxygenation.

BACKGROUND: the benefits of monitoring cerebral blood flow (CBF) in stroke patients are apparent. New techniques combining near infrared spectroscopy (NIRS) and indocyanine green (ICG) dye dilution to estimate cerebral hemodynamics are available. However, with transcutaneous NIRS and optodes applied over the skin, the signal is contaminated by extracerebral tissues. The objective is to develop a new brain tissue probe for combined monitoring of intracranial pressure (ICP), CBF and cerebral blood volume (CBV). METHODS: conventional intraparenchymal probes for ICP monitoring are supplied with optical fibers. The light is coupled into the brain tissue and collected after absorption and scattering with a light detector. Venous injections of 0.2 mg/kgbw ICG are performed. The mean transit time of ICG (mttICG), CBF and CBV are calculated. RESULTS: with a prototype of the probe in a first patient with subarachnoid hemorrhage 6 pairs of repetitive measurements were performed. Mean values were for mttICG 5.6 ± 0.2 s, CBF 22.3 ± 2.8 ml/100 g/min and CBV 2.1 ± 0.3 ml/100 g. CONCLUSIONS: NIR spectroscopy allows the synchronous determination of multiple parameters with one single device. By measurements in parallel with the NeMo Probe and NIRS optodes placed over the skin, new algorithms can be developed to subtract the extracerebral contamination from the NIRS signal.

Under-reporting bicycle accidents to police in the COST TU1101 international survey: Cross-country comparisons and associated factors.

Police crash reports are often the main source for official data in many countries. However, with the exception of fatal crashes, crashes are often underreported in a biased manner. Consequently, the countermeasures adopted according to them may be inefficient. In the case of bicycle crashes, this bias is most acute and it probably varies across countries, with some of them being more prone to reporting accidents to police than others. Assessing if this bias occurs and the size of it can be of great importance for evaluating the risks associated with bicycling. This study utilized data collected in the COST TU1101 action "Towards safer bicycling through optimization of bicycle helmets and usage". The data came from an online survey that included questions related to bicyclists' attitudes, behaviour, cycling habits, accidents, and patterns of use of helmets. The survey was filled by 8655 bicyclists from 30 different countries. After applying various exclusion factors, 7015 questionnaires filled by adult cyclists from 17 countries, each with at least 100 valid responses, remained in our sample. The results showed that across all countries, an average of only 10% of all crashes were reported to the police, with a wide range among countries: from a minimum of 0.0% (Israel) and 2.6% (Croatia) to a maximum of a 35.0% (Germany). Some factors associated with the reporting levels were type of crash, type of vehicle involved, and injury severity. No relation was found between the likelihood of reporting and the cyclist's gender, age, educational level, marital status, being a parent, use of helmet, and type of bicycle. The significant under-reporting - including injury crashes that do not lead to hospitalization - justifies the use of self-report survey data for assessment of bicycling crash patterns as they relate to (1) crash risk issues such as location, infrastructure, cyclists' characteristics, and use of helmet and (2) strategic approaches to bicycle crash prevention and injury reduction.

Microstructural insight into pedestrian pelvic fracture as assessed by high-resolution computed tomography.

Pelvic and femoral neck bone surface strains were recorded in five full-body human cadaver vehicle-pedestrian impacts. Impacts were performed at 40 km/h using automotive front ends constructed to represent those used in previously reported finite element simulations. While experimental kinematics and bone strains closely matched model predictions, observed pelvic fractures did not consistently agree with the model, and could not be solely explained by vehicle geometry. In an attempt to reconcile injury outcome with factors apart from vehicle design, a proxy measure of subject skeletal health was assessed by high-resolution quantitative computed tomography (HRqCT) of the femoral neck. The incidence of hip/pelvis fracture was found to be consistent with low volumetric bone mineral density and low trabecular bone density. This finding lends quantitative support to the notion that healthy trabecular architecture is crucial in withstanding non-physiological impact loads. Furthermore, it is recommended that injury criteria used to assess vehicle safety with regard to pedestrians consider the increased susceptibility of elderly victims to pelvic fracture.

Different aprotinin applications influencing hemostatic changes in orthotopic liver transplantation.

The effect of different aprotinin applications on hemostatic changes and blood product requirements in orthotopic liver transplantation was investigated in a prospective, open, and randomized study. From November 1989 to June 1990, 13 patients received aprotinin as a bolus of 0.5 Mill. Kallikrein inactivator units (KIU) on three occasions in the course of an OLT, whereas 10 other patients were treated with continuous aprotinin infusion of 0.1-0.4 Mill. KIU/hr. Before and after reperfusion of the graft liver, signs of hyperfibrinolysis, measured by thrombelastography, were significantly lower in the infusion group. Tissue-type plasminogen activator (t-PA) activity increased during the anhepatic phase but to a significantly lesser extent in the infusion group. Blood product requirements during OLT were tendentiously higher in the bolus group but not significantly so. However, the use of packed red blood cells was significantly lower in the postoperative period, whereas there was no significant difference in fresh frozen plasma requirements between the two groups. All 23 patients have survived, and only one woman of each group required retransplantation due to severe host-versus-graft reactions. Furthermore, we investigated the perfusate of the graft liver in both groups and detected signs of a decreased t-PA release in the infusion group. Our results demonstrate an advantage of aprotinin given as continuous infusion over bolus application in OLT.

Clinical trial with escalating doses of the antiepidermal growth factor receptor humanized monoclonal antibody EMD 72 000 in patients with advanced squamous cell carcinoma of the larynx and hypopharynx.

In this open uncontrolled phase I study, nine patients with stage III and IV squamous cell carcinoma of the head and neck (SCCHN) were treated with five administrations of the humanized antiepidermal growth factor receptor monoclonal antibody EMD 72000 in three consecutive ascending dose groups. Loading doses of 100 mg (group I), 200 mg (group II), and 400 mg (group III) were followed by four weekly maintenance doses of half the loading doses, i.e. 50, 100, and 200 mg, respectively. Two EMD 72000 administrations were scheduled before and three after surgery. The objectives of this trial were (a) to investigate the safety and toxicity of multiple EMD 72000 doses, (b) to determine the cumulative maximum tolerated dose of EMD 72000 at dosages between 300 mg and 1,200 mg, and (c) to determine the serum pharmacokinetics of EMD 72000. In total, 102 adverse events (AEs) were reported: five of toxicity grade 3, 18 of toxicity grade 2, 66 of toxicity grade 1, and 38 of toxicity grade 0. All AEs of toxicity grade 3 were considered to be not or remotely related to EMD 72000. The most frequent study drug-related AEs were fever and a transient elevation of liver enzymes. In all patients, the time to reach peak serum concentrations (tmax) was within 1-3 h of the start of each EMD 72000 infusion. Average peak serum concentrations (Cmax) after correction for dosage appeared to be dose-independent, whereas the half-life (t1/2) showed dose dependency. In conclusion, EMD 72000 was very well tolerated in patients with advanced stage SCCHN. The pharmacokinetic data from this trial suggest the feasibility of conducting future studies with weekly doses of 200 mg EMD 72000.

Biomechanical assessment of soft tissue cervical spine disorders and expert opinion in low speed collisions.

The multidisciplinary research of injury mechanisms and injury prevention requires the assessment of the technical and biomechanical circumstances of a collision; moreover, the causality assessment in the individual cases is facilitated by taking these aspects into account. In fact, only specially trained engineers and biomechanical experts are in a position to evaluate these relevant basic facts. In many crucial court cases, important technical factors such as collision angle, structural stiffness, extent of intrusion and the vehicle's velocity change are often ignored. The purely medical causality assessment is often based only on a coincidence of time of the 'accident' and the onset of the disorders. Unfortunately, statements about the 'accident speed' or the nebulous 'accident energy' are often made by clinicians with neither a proper collision documentation nor the necessary biomechanical and technical background. In order to overcome shortcomings of injury causality assessment as well as the terminology associated with soft tissue cervical spine injuries, a subdivision of the term 'accident severity' into four classes is proposed. Consequently, an 'accident severity assessment' can only be performed by a collaboration of four corresponding classes of experts, i.e. the engineer (dynamic loading of the vehicle), the biomechanical expert (biomechanical loading of the occupant), the physician (clinically diagnosable injuries), and eventually the psychiatrist (subjective sequelae individually experienced by the victim).

Comparison of car seats in low speed rear-end impacts using the BioRID dummy and the new neck injury criterion (NIC).

Long-term whiplash associated disorders (WAD) 1-3 sustained in low velocity rear-end impacts is the most common disability injury in Sweden. Therefore, to determine neck injury mechanisms and develop methods to measure neck-injury related parameters are of importance for current crash-safety research. A new neck injury criterion (NIC) has previously been proposed and evaluated by means of dummy, human and mathematical rear-impact simulations. So far, the criterion appears to be sensitive to the major car and collision related risk factors for injuries with long-term consequences. To further evaluate the applicability of NIC, four seats were tested according to a recently proposed sled-test procedure. 'Good' as well as 'bad' seats were chosen on the basis of a recently presented disability risk ranking list. The dummy used in the current tests was the Biofidelic Rear Impact Dummy (BioRID). The results of this study showed that NICmax values were generally related to the real-world risk of long-term WAD 1-3. Furthermore, these results suggested that NICmax calculated from sled tests using the BioRID dummy can be used for evaluating the neck injury risk of different car seats.

Pressure aberrations inside the spinal canal during rear-end impact.

Minor soft tissue injuries of the cervical spine increasingly pose problems in public health. Such injuries are conveyed particularly often in rear-end automobile collisions at low impact speeds and it has been established that they may be associated with long-term impairment. As a possible cause for this type of injury it has been hypothesized that pressure pulses induced in cervical fluid compartments during the impact could damage the membrane of spinal nerve cells. To date, animal as well as cadaver experiments performed support this hypothesis. A theoretical analysis has been undertaken in order to investigate the pressure and flow pulse emerging in a cervical fluid compartment under conditions representing rear-end impacts with a Dv of 15 km/h. Using the finite element (FE) method, a three-dimensional model of the cervical spine was developed. The model consists of eight vertebrae (C1-T1), the intervertebral discs, the intervertebral joints, all the major ligaments, most of the neck muscles and the head. Additionally, a typical venous blood vessel was included. To determine the pressure behaviour inside the blood vessel, fluid-structure interaction was taken into account. For the time interval including the development of the S-shape, the pressure pulses were calculated and found to be in qualitative agreement with the reported measurements. The shear stresses acting on the vessel wall can be determined from the associated flow pulses. An extrapolation of the results into the interstitial space where nerve cells are located at this stage does not allow assessment of whether a damage threshold may be reached.

Biomechanical assessment of soft tissue neck injuries in cases with long sick leave times.

A database was established by collecting 919 cases of claimed cervical spine disorders (CSDs) sustained in automotive accidents. All cases had a sick leave time of more than 4 weeks. Data was obtained from a major Swiss accident insurer. An assessment scheme was developed that took into account technical, medical, and biomechanical aspects. All cases were evaluated according to this scheme. The overall biomechanical assessment, that stated the extent to which the symptoms claimed could be explained by the impact, was found to be significantly influenced by the patient's history of CSD in terms of preexisting damage or preexisting symptoms. In 52% of the assessed cases, the CSD claimed could be explained with a combination of neck loading and also by considering the patient's medical history. Performing a solely technical analysis of the collision circumstances or a purely medical evaluation based on a Quebec Task Force (QTF) grade alone are insufficient to assess the accident-related explicability of claimed CSD. Biomechanically relevant individual factors have to be considered.

Transverse and normal interfacial stiffness of solids with randomly rough surfaces.

Using a theoretical approach and computer simulations, we calculate the normal stiffness K(perpendicular) and the transverse stiffness K(parallel) of the interface between two contacting isotropic solids with randomly rough surfaces and Poisson ratio ν. The theoretical predictions for K(perpendicular) agree well with the simulations. Moreover, the theoretical result for the ratio K(perpendicular)/K(parallel) is (2 - ν)/(2 - 2ν), as predicted by Mindlin for a single circular contact region. Finally, we compare the theory to experimental ultrasonic data.

Simple microscopic theory of Amontons's laws for static friction.

A microscopic theory for the ubiquitous phenomenon of static friction is presented. Interactions between two surfaces are modeled by an energy penalty that increases exponentially with the degree of surface overlap. The resulting static friction is proportional to load, in accordance with Amontons's laws. However, the friction coefficient between bare surfaces vanishes as the area of individual contacts grows, except in the rare case of commensurate surfaces. An area independent friction coefficient is obtained for any surface geometry when an adsorbed layer of mobile atoms is introduced between the surfaces. The predictions from our simple analytic model are confirmed by detailed molecular dynamics simulations.

Whiplash injury: cases with a long period of sick leave need biomechanical assessment.

A total of 668 cases of cervical spine disorders (CSD) sustained in automotive collisions were analysed. All cases had a minimum sick leave duration of 4 weeks. To evaluate these cases a scheme was developed that takes into account technical, medical, and biomechanical aspects. For each case, the delta-v value of the underlying collision was estimated, the medical files were analysed, and a QTF (Québec Task Force) grade was assigned. In addition, the medical history of the patient was reviewed. It was found that the QTF grade for patients with pre-existing damage of the neck or pre-existing signs differed significantly from those patients without such a history. The overall assessment, which stated the extent to which the symptoms claimed could be explained by the impact, was also found to be significantly influenced by a history of neck injury. The results of the study showed that in about 50% of the cases where the technical analysis alone would not suggest that the symptoms shown could be explained by the impact, those symptoms could be explained when patient history and the collision circumstances were taken into consideration. It also found that medical evaluation based on a QTF grade alone cannot assess the explicability of claimed CSD without taking into account the collision circumstances. Therefore, the assessment of critical individual relevant biomechanical factors is necessary.

Time-resolved flow cytometry for the measurement of lanthanide chelate fluorescence: II. Instrument design and experimental results.

A time-resolved flow cytometer capable of measuring a luminescence with a decay time in the range of 10 microseconds to 2 ms, typical for some lanthanide chelates, is presented. The instrument permits acquisition of conventional light scatter and prompt fluorescence signals as well as detection of slowly decaying luminescence by a photon counting unit for a selectable time period of 1 microsecond to 1 ms. During photon counting, the laser beam is turned off by an acoustooptic deflector. The design of a flow chamber with an average geometrical light collection efficiency of 35% over a distance of 1.7 mm is presented and analyzed by ray tracing. A pulse processing system featuring digital integration of the conventional signals and a transputer system for the acquisition and the transfer of the measured parameter values to a host computer is described. Instrument function is verified with lyophilized human lymphocytes stained for the CD8 antigen with dye-loaded liposomes. Quantitation of cell-associated europium chelate fluorescence, displaying a decay time of 1.6 ms, is demonstrated. Elimination of fast decaying background emission generated by DNA-associated ethidium bromide is shown. The background generated by instrument components in the time-gated measurement channel is characterized, and measures for its complete elimination are discussed.

Comparison Tests of BioRID II and RID 2 with Regard to Repeatability, Reproducibility and Sensitivity for Assessment of Car Seat Protection Potential in Rear-End Impacts.

The objective of our study was to investigate the properties of the BioRID II and RID2 dummies regarding repeatability and reproducibility as well as their suitability to identify the protection potential of different car seats. For repeatability and reproducibility tests, three BioRID II and three RID 2 dummies at current build levels were seated on a rigid bench seat equipped with a head restraint, and mounted on a HyGe-type sled. The test velocity was prescribed by the proposed ISO-Pulse. For testing the interaction of the dummies with varying car seat geometries and mechanical properties and their ability to assess the protection potential of the seats, three seat types with passive and one seat with an active head restraint system from different car manufacturers were used. The seats were chosen due to their injury protection potential, indicated by accident field data and results of seat evaluation tests. One BioRID II equipped with a T1-load cell and one RID2 were positioned side-by-side on identical seats for each test. The tests were performed at velocities prescribed by the ISO-Pulse (deltav 16km/h / 8 g max.)and a more severe pulse (deltav 24km/h / 13 g max.). The dummy responses were interpreted by applying all currently proposed whiplash injury criteria (e.g. NIC, N(km), NDC, LNL). A comparison of these criteria shows their sensitivity for identification of the respective seat protection potential. This study examines the repeatability, reproducibility, kinematics and sensitivity of these two dummies in sled tests as well as their suitability with regard to the different injury criteria. The RID2 exhibited better repeatability and reproducibility than the BioRID II, because of its simpler mechanical design. The dummies did not give a consistent ranking of the low-speed, rear-end impact protection potentials of the four seat evaluated. More experience is needed to decide which dummy, injury criteria and limits should be used to assess the whiplash protection potential of seat designs.

The poststenotic vessel segment during dynamic exercise: effect of oral isosorbide-dinitrate.

Coronary vasomotion of normal, stenotic, and poststenotic vessel segments was studied in 18 patients with coronary artery disease at rest, during submaximal bicycle exercise, and 5 min after sublingual nitroglycerin or oral isosorbide-dinitrate (ISDN) spray. Patients were divided into two groups: group 1 consisted of 10 patients with no premedication prior to exercise, and group 2 consisted of 8 patients receiving 120 mg long-acting ISDN orally 1 h before the procedure. Quantitative coronary arteriography was carried out in biplane projection using a semi-automatic computer system. The normal vessel segment showed a trend toward a small increase in cross-sectional area during exercise in both groups (+3% in group 1 and +4% in group 2, both NS). After sublingual nitroglycerin following exercise, there was a significant increase in group 1 (+29%, p less than 0.001 vs rest) but not after ISDN spray in group 2 (+5%, NS vs rest). The stenotic vessel segment showed exercise-induced stenosis narrowing in group 1 (-31%, p less than 0.01 vs rest) which was prevented by oral ISDN (+6%, NS vs rest). After exercise, sublingual administration of nitroglycerin or ISDN spray was associated with no significant change in stenosis area in either group. The poststenotic vessel segment showed no significant vasomotion during exercise in both groups (area change +6% in group 1 and +7% in group 2), but poststenotic luminal area increased after sublingual nitroglycerin (group 1: +15%, p less than 0.01 vs rest) or ISDN spray (group 2: +15%, p less than 0.05 vs rest). The mean pulmonary artery pressure increased during exercise from 22 to 39 mmHg (p less than 0.001) in group 1 and from 14 to 27 mmHg (p less than 0.001) in group 2. At rest (p less than 0.001) and during exercise (p less than 0.01) mean pulmonary pressure was lower in group 2 than in group 1. Thus, it is concluded that coronary vasomotion of the poststenotic vessel segment is only minimal during exercise and is not affected by coronary vasomotion of the stenotic vessel segment. Pretreatment with oral ISDN did not influence coronary vasomotion of the poststenotic vessel segment, but prevented exercise-induced stenosis narrowing. In the untreated patients, vasoconstriction of the stenotic vessel segment is limited to the site of the stenosis, and it appears that there is no release of vasoactive substances with vasoconstrictive influences on the poststenotic segment.

Validation of a new automatic system for biplane quantitative coronary arteriography.

In a collaboration between the University of Texas (software) and the University of Zürich (hardware) a compact, automatic system for biplane quantitative coronary arteriography was developed. The system is based on a 35 mm film projector, a slow-scan CCD-camera (image digitizing) and a computer workstation (Apollo DN 3000, image storage and processing). A new calibration procedure based on two fixed reference points in the center of the image intensifier was used (isocenter technique). Contour detection of coronary arteries was carried out in biplane projection using a geometric-densitometric edge-detection algorithm. The proximal and distal luminal areas, as well as the minimal luminal area of the stenotic vessel segment were determined. Accuracy and precision were determined from precision drilled holes in a plexiglas cube which were filled with 50%, 75% and 100% contrast medium. The diameter of the holes ranged from 0.5 to 5.0 mm. The mean difference and the standard deviation of the differences between the true and the measured diameters were 0.12 +/- 0.14 mm for plane A and 0.26 +/- 0.17 mm for plane B, respectively. After a second order correction the mean difference amounted to 0.02 +/- 0.09 mm for plane A and 0.02 +/- 0.12 mm for plane B, respectively. Intra- and interobserver variability were evaluated in 5 patients (age 60 +/- 10 years) with coronary artery disease using 16 normal and 5 stenotic vessel segments (cross-sectional area ranging from 0.8 to 8.7 mm2). Two independent observers analyzed the same vessel segment twice. Intraobserver variability expressed as the standard error of estimate in percent of the mean angiographic vessel area (SEE) amounted to 2.1% for observer 1 and 4.4% for observer 2, respectively. Interobserver variability expressed as SEE was 4.1% for measurement 1 and 3.6% for measurement 2, respectively.