Measurement of cerebral blood flow by transcranial Doppler ultrasonography in children presenting with autistic behavior. Preliminary results

Transcranial Doppler ultrasonographic recordings of the middle cerebral arteries were performed on eight children with autistic behavior compared to eight controls. Blood flow measurements were assessed at rest and during auditory and visual stimulations. The main result was obtained during the auditory stimulations and concerned the left artery blood flow which is lower in autistics than in controls in these conditions (p less than .02). This result confirms the possibility of a left hemisphere dysfunctioning in autistics and may be related to clinical features as language disabilities and paradoxical reactivity to auditory stimuli.     

Circulatory and hormonal changes induced by microgravity

The absence (or decrease) of the hydrostatic pressure during space flights (microgravity state) or simulations of weightlessness (by immersion, bed rest or head-down tilt) result in a body fluid shift and an engorgement of the central circulation where mechanoreceptors involved in plasma volume regulation are located. Their activation induces the initial (first hours) hormonal response with a decrease in plasma vasopressin, renin and aldosterone and probably an increase in a natriuretic factor (Gauer reflex). Prolonged exposure to microgravity leads to more complex and often hypothetical responses: cardiovascular deconditioning, modifications in secretion and circadian rhythms of above cited hormones. After 24 years of studies on approximately 200 astronauts our knowledge of cardiovascular and hormonal adaptation to space flight is still at the beginning.     

A method to synchronise cameras using the direct linear transformation technique

The aim of this paper is to present a method which enables the recordings of cameras that are not equipped with a synchronisation system to be synchronised a posteriori. Using the Direct Linear Transformation technique, this method estimates the phase difference between two cameras by minimising the reconstruction errors of a moving point. Once the phase difference value is known, one of the recordings is chosen as a reference and the second one is synchronised to the first by cubic spline interpolation.     

IL-33-Mediated Protection against Experimental Cerebral Malaria Is Linked to Induction of Type 2 Innate Lymphoid Cells,M2 Macrophages and Regulatory T Cells

Cerebral malaria (CM) is a complex parasitic disease caused by Plasmodium sp. Failure to establish an appropriate balance between pro- and anti-inflammatory immune responses is believed to contribute to the development of cerebral pathology. Using the blood-stage PbA (Plasmodium berghei ANKA) model of infection, we show here that administration of the pro-Th2 cytokine, IL-33, prevents the development of experimental cerebral malaria (ECM) in C57BL/6 mice and reduces the production of inflammatory mediators IFN-γ, IL-12 and TNF-α. IL-33 drives the expansion of type-2 innate lymphoid cells (ILC2) that produce Type-2 cytokines (IL-4, IL-5 and IL-13), leading to the polarization of the anti-inflammatory M2 macrophages, which in turn expand Foxp3 regulatory T cells (Tregs). PbA-infected mice adoptively transferred with ILC2 have elevated frequency of M2 and Tregs and are protected from ECM. Importantly, IL-33-treated mice deleted of Tregs (DEREG mice) are no longer able to resist ECM. Our data therefore provide evidence that IL-33 can prevent the development of ECM by orchestrating a protective immune response via ILC2, M2 macrophages and Tregs.     

A linear laser scanner to measure cross-sectional shape and area of biological specimens during mechanical testing

Measure of the cross-sectional area (CSA) of biological specimens is a primary concern for many biomechanical tests. Different procedures are presented in literature but besides the fact that noncontact techniques are required during mechanical testing, most of these procedures lack accuracy or speed. Moreover, they often require a precise positioning of the specimen, which is not always feasible, and do not enable the measure of the same section during tension. The objective of this study was to design a noncontact, fast, and accurate device capable of acquiring CSA of specimens mounted on a testing machine. A system based on the horizontal linear displacement of two charge-coupled device reflectance laser devices next to the specimen, one for each side, was chosen. The whole measuring block is mounted on a vertical linear guide to allow following the measured zone during sample tension (or compression). The device was validated by measuring the CSA of metallic rods machined with geometrical shapes (circular, hexagonal, semicircular, and triangular) as well as an equine superficial digital flexor tendon (SDFT) in static condition. We also performed measurements during mechanical testing of three SDFTs, obtaining the CSA variations until tendon rupture. The system was revealed to be very fast with acquisition times in the order of 0.1 s and interacquisition time of about 1.5 s. Measurements of the geometrical shapes yielded mean errors lower than 1.4% (n=20 for each shape) while the tendon CSA at rest was 90.29 ± 1.69 mm(2) (n=20). As for the tendons that underwent tension, a mean of 60 measures were performed for each test, which lasted about 2 min until rupture (at 20 mm/min), finding CSA variations linear with stress (R(2)>0.85). The proposed device was revealed to be accurate and repeatable. It is easy to assemble and operate and capable of moving to follow a defined zone on the specimen during testing. The system does not need precise centering of the sample and can perform noncontact measures during mechanical testing; therefore, it can be used to measure variations of the specimen CSA during a tension (or compression) test in order to determine, for instance, the true stress and transverse deformations.     

Axial speed of sound for the monitoring of injured equine tendons: a preliminary study

Equine superficial digital flexor tendons (SDFT) are often injured, and they represent an excellent model for human sport tendinopathies. While lesions can be precisely diagnosed by clinical evaluation and ultrasonography, a prognosis is often difficult to establish; the knowledge of the injured tendon's mechanical properties would help in anticipating the outcome. The objectives of the present study were to compare the axial speed of sound (SOS) measured in vivo in normal and injured tendons and to investigate their relationship with the tendons' mechanical parameters, in order to assess the potential of quantitative axial ultrasound to monitor the healing of the injured tendons. SOS was measured in vivo in the right fore SDFTs of 12 horses during walk, before and 3.5 months after the surgical induction of a bilateral core lesion. The 12 horses were then euthanized, their SDFTs isolated and tested in tension to measure their elastic modulus and maximal load (and corresponding stress). SOS significantly decreased from 2179.4 ± 31.4 m/s in normal tendons to 2065.8 ± 67.1 m/s 3.5 months after the surgical induction, and the tendons' elastic modulus (0.90 ± 0.17 GPa) was found lower than what has been reported in normal tendons. While SOS was not correlated to tendon maximal load and corresponding stress, the SOS normalized on its value in normal tendons was correlated to the tendons' elastic modulus. These preliminary results confirm the potential of axial SOS in helping the functional assessment of injured tendon.     

Reproducibility of a non-invasive ultrasonic technique of tendon force measurement,determined in vitro in equine superficial digital flexor tendons

A non-invasive ultrasonic (US) technique of tendon force measurement has been recently developed. It is based on the relationship demonstrated between the speed of sound (SOS) in a tendon and the traction force applied to it. The objectives of the present study were to evaluate the variability of this non-linear relationship among 7 equine superficial digital flexor (SDF) tendons, and the reproducibility of SOS measurements in these tendons over successive loading cycles and tests. Seven SDF tendons were equipped with an US probe (1 MHz), secured in contact with the skin overlying the tendon metacarpal part. The tendons were submitted to a traction test consisting in 5 cycles of loading/unloading between 50 and 4050 N. Four tendons out of the 7 were submitted to 5 additional cycles up to 5550 N. The SOS-tendon force relationships appeared similar in shape, although large differences in SOS levels were observed among the tendons. Reproducibility between cycles was evaluated from the root mean square of the standard deviations (RMS-SD) of SOS values observed every 100 N, and of force values every 2 m/s. Reproducibility of SOS measurements revealed high between successive cycles: above 500 N the RMS-SD was less than 2% of the corresponding traction force. Reproducibility between tests was lower, partly due to the experimental set-up; above 500 N the difference between the two tests stayed nevertheless below 15% of the corresponding mean traction force. The reproducibility of the US technique here demonstrated in vitro has now to be confirmed in vivo.     

True stress and Poisson's ratio of tendons during loading

Excessive axial tension is very likely involved in the aetiology of tendon lesions, and the most appropriate indicator of tendon stress state is the true stress, the ratio of instantaneous load to instantaneous cross-sectional area (CSA). Difficulties to measure tendon CSA during tension often led to approximate true stress by assuming that CSA is constant during loading (i.e. by the engineering stress) or that tendon is incompressible, implying a Poisson's ratio of 0.5, although these hypotheses have never been tested. The objective of this study was to measure tendon CSA variation during quasi-static tensile loading, in order to assess the true stress to which the tendon is subjected and its Poisson's ratio. Eight equine superficial digital flexor tendons (SDFT, about 30cm long) were tested in tension until failure while the CSA of each tendon was measured in its metacarpal part by means of a linear laser scanner. Axial elongation and load were synchronously recorded during the test. CSA was found to linearly decrease with strain, with a mean decrease at failure of -10.7±2.8% (mean±standard deviation). True stress at failure was 7.1-13.6% higher than engineering stress, while stress estimation under the hypothesis of incompressibility differed from true stress of -6.6 to 2.3%. Average Poisson's ratio was 0.55±0.12 and did not significantly vary with load. From these results on equine SDFT it was demonstrated that tendon in axial quasi-static tension can be considered, at first approximation, as an incompressible material.