Peter Niederer

In Vivo Tracer Transport Through the Lacunocanalicular System of Rat Bone in an Environment Devoid of Mechanical Loading

Although diffusion has been shown to be the major contributing mechanism for molecular transport in the extravascular spaces of organs and soft tissues, it is unlikely that diffusion alone can account for molecular transport in the porous, yet relatively impermeable matrix of bone. Rather, it has been proposed that fluid flow induced by the deformations that bone is subjected to during daily activities may promote molecular transport through convective mixing of fluids or enhancement of molecular transport from the capillaries to the outermost osteocytes within a given osteon. As the relative contribution of diffusive and convective transport in the bone matrix has not yet been elucidated, we conducted experiments to study the primary role of diffusion for molecular transport within bone and to establish a baseline for fluid transport whereby mechanical loading effects are negligible. Procion red and microperoxidase were utilized as short-term (i.e., low MW, transported on the order of minutes) and long-term (i.e., comparatively high MW, transported on the order of hours) molecular tracers, respectively, to elucidate in vivo the pathways and extent of transport in the metacarpus and tibia of 60-day-old (i.e., skeletally immature) and 180-day-old (i.e., skeletally mature) animals. The tracers were introduced intravenously and the animals were maintained in an anesthetized state for the duration of the experiment to prevent physiological loading. In short-term studies, procion red tracer distribution was highly dependent on bone structure, demarcating spaces apposing the vascular pathways in the trabecular bone of immature animals and vascular and extravascular pathways (i.e., specifically, the lacunocanalicular system) within compact bone of mature animals. In longer term studies using microperoxidase, reaction product was concentrated in soft tissues as well as along a subperiosteal and subendosteal band of bone. In contrast, little peroxidase reaction product was observed in the metacarpal and tibial cortices of either immature or mature animals. Based on the results of these studies, diffusive transport mechanisms may suffice to insure an adequate supply of small molecules, such as amino acids, to osteocytes in the midcortex within minutes. In contrast, diffusion alone may not be efficient for transport of larger molecules. Thus, another mechanism of transport, such as convective transport by means of load-induced fluid flow, may be necessary to provide a sufficient supply of larger molecules, such as proteins to osteocytes for the maintenance of metabolic activity, as well as for activation or suppression of modeling processes.

The forces generated within the musculature of the left ventricular wall

Objectives: To test the hypothesis that two populations of myocardial fibres—fibres aligned parallel to the surfaces of the wall and an additional population of fibres that extend obliquely through the wall—when working in concert produce a dualistic, self stabilising arrangement. Methods: Assessment of tensile forces in the walls of seven porcine hearts by using needle probes. Ventricular diameter was measured with microsonometry and the intracavitary pressure through a fluid filled catheter. Positive inotropism was induced by dopamine, and negative inotropism by thiopental. The preload was raised by volume load and lowered by withdrawal of blood. Afterload was increased by inflation of a balloon in the aortic root. The anatomical orientation of the fibres was established subsequently in histological sections. Results: The forces in the fibres parallel to the surface decreased 20–35% during systolic shrinkage of the ventricle, during negative inotropism, and during ventricular unloading. They increased 10–30% on positive inotropic stimulation and with augmentation in preload and afterload. The forces in the oblique transmural fibres increased 8–65% during systole, on positive inotropic medication, with an increase in afterload and during ventricular shrinkage, and decreased 36% on negative inotropic medication. There was a delay of up to 147 ms in the drop in activity during relaxation in the oblique transmural fibres. Conclusion: Although the two populations of myocardial fibres are densely interwoven, it is possible to distinguish their functions with force probes. The delayed drop in force during relaxation in obliquely oriented fibres indicates that they are hindered in their shortening to an extent that parallels any increase in mural thickness. The transmural fibres, therefore, contribute to stiffening of the ventricular wall and hence to confining ventricular compliance.

New multichannel near infrared spectrophotometry system for functional studies of the brain in adults and neonates

We have designed a versatile, multi-channel near-infrared spectrophotometry (NIRS) instrument for the purpose of mapping neuronal activation in the neonatal and adult brain in response to motor, tactile, and visual stimulation. The optical linearity, stability, and high signal to noise ratio (>70 dB) of the instrument were demonstrated using an in vitro validation procedure. In vivo measurements on the adult forearm were also performed. Changes in oxygenation, induced by arterial occlusion of the forearm, were recorded and were shown to compare well with measurements acquired using a conventional NIRS instrument. To demonstrate the capabilities of the instrument, functional measurements in adults and neonates were performed. The instrument exhibited the capability to differentiate with a spatial resolution in the order of cm, local activation patterns associated with a finger tapping sequence.

Statistical Analysis of the Angle of Intrusion of Porcine Ventricular Myocytes from Epicardium to Endocardium Using Diffusion Tensor Magnetic Resonance Imaging

Pairs of cylindrical knives were used to punch semicircular slices from the left basal, sub‐basal, equatorial, and apical ventricular wall of porcine hearts. The sections extended from the epicardium to the endocardium. Their semicircular shape compensated for the depth‐related changing orientation of the myocytes relative to the equatorial plane. The slices were analyzed by diffusion tensor magnetic resonance imaging. The primary eigenvector of the diffusion tensor was determined in each pixel to calculate the number and angle of intrusion of the long axis of the aggregated myocytes relative to the epicardial surface. Arrays of axially sectioned aggregates were found in which 53% of the approximately two million segments evaluated intruded up to ±15°, 40% exhibited an angle of intrusion between ±15° and ±45°, and 7% exceeded an angle of ±45°, the positive sign thereby denoting an epi‐ to endocardial spiral in clockwise direction seen from the apex, while a negative sign denotes an anticlockwise spiral from the epicardium to the endocardium. In the basal and apical slices, the greater number of segments intruded in positive direction, while in the sub‐basal and equatorial slices, negative angles of intrusion prevailed. The sampling of the primary eigenvectors was insensitive to postmortem decomposition of the tissue. In a previous histological study, we also documented the presence of large numbers of myocytes aggregated with their long axis intruding obliquely from the epicardial to the endocardial ventricular surfaces. We used magnetic resonance diffusion tensor imaging in this study to provide a comprehensive statistical analysis. Anat Rec, 290:1413–1423, 2007.

Optical properties of miniaturized endoscopes for ophthalmic use

Endoscopes for use in ophthalmology can now be manufactured with overall intraocular diameters smaller than 0.89 mm. Endoscopes based on gradient-index lenses yield a higher resolution than those making use of ordered fiber bundles having the same diameter. Likewise, endoscopes with optical elements having a diameter of 0.50 mm yield a higher resolution than those with smaller diameter (0.35 mm). Thanks to the miniaturization, a working channel can also be integrated within the tube of the endoscope instead of being a part of the illumination bundle. This allows the design of new endoscopic devices including various surgical instruments. Preference is given to an endoscope with an integrated aspiration/irrigation system or with a fiber for laser therapy. The potential phototoxicity of these systems is briefly discussed.

INFLUENCE OF VEHICLE FRONT GEOMETRY ON IMPACTED PEDESTRIAN KINEMATICS

A primary cause of severe injury experienced by a pedestrian who is impacted by the front of a vehicle consists in the head impact on the hood during the loading phase of the accident. Impact speed and vehicle front geometry are the most important factors which govern the severity of this impact. The aim of the present study is to analyse the motion patterns occuring during impact, particularly those of the head, and to identify a favourable front geometry in view of a reduced injury hazard. The investigations are based on impact tests performed on a sled with a vehicle front having a variable front geometry and at different impact speeds. The surrogate was a modified 572 ATD (HUMANOID) equipped with 18 accelerometers and whose head trajectory during impact was determined by high-speed cine-photogrammetry. Language: en

A novel ex vivo model for investigation of fluid displacements in bone after endoprosthesis implantation.

Tissue perfusion and mass transport in the vicinity of implant surfaces prior to integration or bonding may play a crucial role in modulating cellular activities associated with bone remodeling, in particular, at early stages of the integration process. Furthermore, fluid displacements have been postulated to transduct mechanical stress signals to bone cells via loading-dependent flow of interstitial fluid through the lacunocanalicular network of bone. Thus, an understanding and new possibilities for influencing these processes may be of great importance for implant success. An ex vivo model was developed and validated for investigation of fluid displacements in bone after endoprosthesis implantation. This model serves to explicate the effects of surgical intervention as well as mechanical loading of the implant–bone construct on load-induced fluid flow in the vicinity of the implant. Using this model, we intend to quantify perfusion and extravascular flow dynamics in the vicinity of implants and define optimal conditions for enhancing molecular transport of osteotropic agents from the implant surface to apposing bone as well as from the blood supply to the implant surface. Furthermore, the elucidation of main transport pathways may help in understanding the distribution of wear particles in bone surrounding implant, a process which has been postulated to cause osteolysis and implant loosening.

Linking left ventricular function and mural architecture: what does the clinician need to know?

The myocardium has a unique architecture, which converts the linear pull of a striated but involuntary muscle into a constrictive action. The left ventricle has also to balance the need to restrict the diameter of its chamber, thereby minimising mural tension, while providing at the same time a wall thick enough to achieve systemic pressure within the cavity. The precise architectural arrangement of the cardiomyocytes that fulfils these requirements is currently a topic of considerable debate. There is a divide between proponents of a counter-wound, single myocardial band,1 and those who describe an arrangement of clefts around thinner lamellar units.2 ,3 In seeking to contribute to this debate, we present here a description of the changes that occur in surface geometry of the ventricle. We will show how the strain indexes of the wall, including mural thickening, are mathematically bound together by this geometry, irrespective of the internal architecture of the wall. We will then relate these indexes to demonstrable features of cardiomyocytic orientation and function.4 In so doing, we provide a relatively simple explanation for left ventricular (LV) twist that does not rely on the presence of a unique myocardial band. We will also reinforce the observation of MacIver and Townsend that hypertrophy of the left ventricle can falsely normalise its ejection fraction (EF) despite falling contractility.5 We conclude by addressing other significant aspects of mural architecture.nnInitially, we will regard the LV myocardium as a structure of fixed mass and so, at physiological pressures, of fixed volume. It envelops the cavity, and its surfaces are illustrated in figure 1. The magnitudes of changes in the inner and outer dimension of the wall, and of the distance between them, which is the mural thickness, are linked mathematically by the geometry of this very …

Crashworthiness and Compatibility of Low Mass Vehicles in Collisions

Reducing the weight of vehicles could be a strong means of reducing fuel consumption in urban traffic. Published accident and injury statistics however show an inverse correlation of vehicle mass against injury severity in car to car collisions, above all in head-on collisions. This inverse correlation is in part caused by current crash test standards, where compatibility in collisions between cars of different size and weight is not a requirement. Compatibility in frontal collisions demands for significantly different deceleration-time curves in rigid barrier impacts for cars with different weight. Low mass vehicles (LMV) must meet compatibility criteria to comply with current injury criteria in real car to car collisions. Cars designed according to compatibility criteria can change future accident and injury statistics in a way that injury severity in LMVs can be reduced significantly. (A) For the covering abstract see IRRD 893297.

COMPUTER ASSISTED SINGLE-VIEW PHOTOGRAMMETRY FOR ACCIDENT SCENE DOCUMENTATION

Accurate documentation of traffic accidents is a prerequisite for accident research as well as traffic jurisdiction. As an important part of accident documentation, stereo-photogrammetry is recognised to be an excellent tool for providing accurate and complete scaled maps of accident scenes. However, due to its relatively high expense, it is usually only applied in cases of severe accidents. In contrast, single-view photogrammetry which is based on photographs taken with non-metric cameras and on on-the-job calibration requires little installation at the accident scene and provides adequate accuracy, because camera calibration and plotting of scaled maps can be performed by making use of computer-assisted image analysis. As the method basically consists in a simple perspective rectification single-view photogrammetry as such is restricted to plane accident sites. In this paper the method is demonstrated and its accuracy discussed.