Intra- and inter-individual variability in the mechanical properties of the human skin from in vivo measurements on 20 volunteers.

BACKGROUND/PURPOSE: The mechanical properties and behavior of the human skin in vivo are of medical importance, particularly to surgeons who have to consider the skin extension capabilities in the preparation of surgical acts. Variable data can be found in literature that result from diverse kinds of tests (in vivo, ex vivo, and postmortem) performed with different instruments. METHODS: This paper presents the results of in vivo measurements performed on a cohort of 20 healthy volunteers with an ultralight homemade uniaxial extensometer. Different anatomical zones were explored under different directions of solicitation in order to document inter- and intra-individual variability as well as skin anisotropy. RESULTS: The experimental data obtained are fitted with a phenomenological exponential model allowing the identification of three parameters characteristic of the tested skin behavior. These parameters can be related to the concept of skin extensibility used by surgeons. CONCLUSION: The inter- and intra-variability observed on that cohort confirms the need for a patient-specific approach based on the in vivo measurement of the mechanical behavior of the human skin of interest. Even the direction of higher skin stiffness is found to be individual-dependent. The capability of the extensometer used in this study to fulfill such measurement needs is also demonstrated.

Ultra-light extensometer for the assessment of the mechanical properties of the human skin in vivo.

BACKGROUND/PURPOSE: This paper aims to present an ultra-light extensometer device dedicated to the mechanical characterization of the human skin in vivo. METHODS: The device developed was conceived to be non-invasive, to work without any stand and to perform various uniaxial tensile tests with either effort or displacement control. We also use specific guarding tabs to make in vivo extension tests analogous to traction tests. RESULTS: Force-displacement curves are derived from the data provided by the device's sensors. The latter are converted into stress-strain curves thanks to complementary measurements of the skin thickness. We present typical experimental data and results that demonstrate the device ability to built stress-strain curves characteristic of the human skin behavior. An additional imaging unit records a sequence of images of the solicited skin area for further calculations of the displacement fields by digital image correlation. CONCLUSION: The analysis of the displacement and deformation fields validates the guarding tab efficiency and the capacity of the device to characterize the mechanical behavior of the human skin in vivo.

Fast contactless vibrating structure characterization using real time field programmable gate array-based digital signal processing: demonstrations with a passive wireless acoustic delay line probe and vision.

Vibrating mechanical structure characterization is demonstrated using contactless techniques best suited for mobile and rotating equipments. Fast measurement rates are achieved using Field Programmable Gate Array (FPGA) devices as real-time digital signal processors. Two kinds of algorithms are implemented on FPGA and experimentally validated in the case of the vibrating tuning fork. A first application concerns in-plane displacement detection by vision with sampling rates above 10 kHz, thus reaching frequency ranges above the audio range. A second demonstration concerns pulsed-RADAR cooperative target phase detection and is applied to radiofrequency acoustic transducers used as passive wireless strain gauges. In this case, the 250 ksamples/s refresh rate achieved is only limited by the acoustic sensor design but not by the detection bandwidth. These realizations illustrate the efficiency, interest, and potentialities of FPGA-based real-time digital signal processing for the contactless interrogation of passive embedded probes with high refresh rates.

Remote vibration measurement: a wireless passive surface acoustic wave resonator fast probing strategy.

Surface acoustic wave (SAW) resonators can advantageously operate as passive sensors which can be interrogated through a wireless link. Amongst the practical applications of such devices, structural health monitoring through stress measurement and more generally vibration characteristics of mechanical structures benefit from the ability to bury such sensors within the considered structure (wireless and battery-less). However, measurement bandwidth becomes a significant challenge when measuring wideband vibration characteristics of mechanical structures. A fast SAW resonator measurement scheme is demonstrated here. The measurement bandwidth is limited by the physical settling time of the resonator (Q/π periods), requiring only two probe pulses through a monostatic RADAR-like electronic setup to identify the sensor resonance frequency and hence stress on a resonator acting as a strain gauge. A measurement update rate of 4800 Hz using a high quality factor SAW resonator operating in the 434 MHz Industrial, Scientific and Medical band is experimentally demonstrated.

Reactive-homeostasis as a cybernetic model of the silhouette effect of denial of pregnancy.

In a woman presenting a pervasive denial of pregnancy, it happens that abdominal swelling is significantly reduced if not completely absent. In such cases, the announcement of the pregnancy to the unaware woman by a physician is often sufficient to trigger the spontaneous appearance of a normal silhouette of pregnancy with abdominal prominence. The pregnancy announcement acts as an input signal applied to the regulation mechanisms of the body with the consequence that the output signal; i.e. the silhouette of the pregnant woman; turns spontaneously from an abnormal shape to a normal one. By applying a system-based analysis to these observations, the brain appears clearly to be responsible for this disorder through instructions sent to the body by the nervous system. The silhouette effect is thus shown to be a cybernetic disorder as opposed to a functional one. The existence of unexpected information-and-semantic pathways throughout the human body is also revealed by this spontaneous transition. A reactive-homeostasis model is then proposed in which symptoms result from an abnormal but coherent regulation of the functioning of the body caused by an unconscious mechanism by the brain to escape paradoxical realities. Spontaneous recovery is then a consequence of the paradoxical situation dissolution induced by the pregnancy announcement. This concept of reactive-homeostasis prompts us to investigate human disorders in complementary categories; i.e. cybernetic versus functional. Such an enlarged point of view may improve our knowledge of aetiology and suggest new perspectives for therapeutics research.

Vibration amplitude of a tip-loaded quartz tuning fork during shear force microscopy scanning.

This Note reports on experimental results obtained with a recently published vision method for in-plane vibration measurement [Sandoz et al., Rev. Sci. Instrum. 78, 023706 (2007)]. The latter is applied to a tip-loaded quartz tuning fork frequently used in scanning probe microscopy for shear-force monitoring of the tip-sample distance. The vibration amplitude of the tip-loaded prong is compared to that of the free one and the damping induced by tip-surface interactions is measured. The tuning-fork behavior is characterized during approaches from free space to surface contact. Tip-surface contact is clearly identified by a drastic reduction in the prong vibration amplitude. However, no differences were observed between hydrophilic and hydrophobic surfaces. Experiments reported here show that the vibration amplitude of the quartz tuning fork in free space is a good estimate of the vibration amplitude of the tip interacting with the sample surface during shear force sample-tip feedback. The experimental setup for measuring the amplitude is easily integrated in an inverted microscope setup on which the shear force microscope is installed for simultaneous scanning probe and optical microscopy analysis of the sample.

Spectroscopic OCT by grating-based temporal correlation coupled to optical spectral analysis.

Spectroscopic optical coherence tomography (spectroscopic OCT) is an echographic-like optical method for biomedical functional imaging. Current spectroscopic optical coherence tomography (OCT) methods rely on a posteriori numerical calculation. We present an alternative for optically accessing the spectroscopic information in OCT, that is, without postprocessing, by using a grating-based correlation and a wavelength demultiplexing system. Spectrally resolved A-scan is directly recorded on the image sensor. Due to the grating-based system, no correlation scan is necessary. The signal is registered in the wavelength-depth plane on a 2D camera that provides a large number of resolved points. In the frame of this paper, we present the principle of the system as well as demonstration results. Advantages and drawback of this system compared to others are discussed.

Position referencing in optical microscopy thanks to sample holders with out-of-focus encoded patterns.

This article introduces smart sample holders for optical microscopy. Their purpose is to allow the absolute determination of the position of the observed zone with respect to the sample holder itself and with a high accuracy. It becomes then straightforward to find a given zone of interest by positioning coarsely the microscope slide to the same position coordinates. Furthermore images recorded during different observation sessions; i.e. for slightly different positions; can be processed numerically in order to superimpose them with a high accuracy. Thus the slight deviations of the microscope slide position and orientation due to the different observations are compensated numerically and a perfect superimposition of the recorded images is performed. Then accurate site-by-site image comparisons become possible even for images recorded during different observation sessions and over a long period of time. The subpixel capability of the proposed method is demonstrated and those smart microscope slides constitute a new tool for live cell experiment. In practise, an encoded geometrical pattern used as position reference is inserted in a plane parallel to the surface receiving the tissue section or sample. Then the transition of the focus position from the tissue section to the position reference requires only a vertical adjustment and does not affect the lateral coordinates of observation. The numeric processing of the image of the position reference pattern allows the retrieval of the lateral coordinates that are also used for the tissue section image. Thus each image is recorded with a set of position coordinates that defines accurately the position of the observed area with respect to the sample holder itself.

Recovery and half-life of von Willebrand factor-cleaving protease after plasma therapy in patients with thrombotic thrombocytopenic purpura.

Plasma exchange using fresh-frozen plasma (FFP) for replacement was given to two brothers during a relapse of thrombotic thrombocytopenic purpura (TTP). A constitutional deficiency of von Willebrand factor(vWF)-cleaving protease had been previously established in both patients. No inhibitor of vWF-cleaving protease was present in patients' plasmas. They received plasma exchange for four and three consecutive days, respectively. In both patients, the activity of vWF-cleaving protease after the first plasmapheresis session was evaluated and was found to be virtually identical to anticipated activity calculated from predicted patient plasma volume and volume of exchanged plasma. Pathologic platelet counts and lactate dehydrogenase levels were normalized in both patients within 4-6 days. The biologic half-life of vWF-cleaving protease was determined in these patients following the last plasma exchange. The respective half-lives of 3.3 and 2.1 days represent the lowest known clearance rates of proteases in circulating human plasma. Another patient with relapsing TTP was treated with plasma exchange and/or plasma infusion for 10 consecutive days during the first relapse, 221-231 days after the initial TTP event. Pharmacokinetic studies of vWF-cleaving protease were performed after plasma exchange on day 221 and after plasma infusion on day 231. High level of an IgG in patient plasma, capable of completely inhibiting protease activity in an equal volume of normal plasma, had been established prior to first plasmapheresis. There was no measurable protease activity at any time during plasma therapy. Following plasma exchange, the level of the inhibitor was transiently slightly depressed. After 10 days of plasma therapy, the concentration of the inhibitor in patient plasma was increased about 5-fold. We suggest that, in contrast to protease deficient patients without circulating inhibitor, complementary therapy including immunosuppressive treatment, vincristine and/or splenectomy is indicated in patients with acquired inhibitors of vWF-cleaving protease. Testing for vWF-cleaving protease inhibitor may be useful in predicting the response to plasma exchange in patients with TTP.

Wavelet transform as a processing tool in white-light interferometry.

Results of the application of wavelet transform for signal processing in white-light interferometry are reported. The mother wavelet frequency is chosen to be the light-source correlogram 1's, and accurate phase measurements are obtained from simple correlation computations. The fringe envelope is also addressed and permits a complete analysis of coherence-limited fringe patterns. Miscalibrations of phase shift and mean wavelength are also considered.

Deficient activity of von Willebrand factor-cleaving protease in chronic relapsing thrombotic thrombocytopenic purpura.

In patients with thrombotic thrombocytopenic purpura (TTP), excessive intravascular platelet aggregation has been associated with appearance in plasma of unusually large von Willebrand factor (vWF) multimers. These extremely adhesive vWF multimers may arise due to deficiency of a "depolymerase" cleaving vWF to smaller molecular forms, either by reducing the interdimeric disulfide bridges or by proteolytic degradation. We studied the activity of a recently described vWF-cleaving protease in four patients with chronic relapsing TTP. Diluted plasma samples of TTP patients were incubated with purified normal human vWF in the presence of a serine protease inhibitor, at low ionic strength, and in the presence of urea and barium ions. The extent of vWF degradation was assayed by electrophoresis in sodium dodecyl sulfate-agarose gels and immunoblotting. Four patients, that included two brothers, with chronic relapsing TTP displayed either substantially reduced levels or a complete absence of vWF-cleaving protease activity. In none of these patient plasmas was an inhibitor of or an antibody against the vWF-cleaving protease established. Our data suggest that the unusually large vWF multimers found in TTP patients may be caused by deficient vWF-cleaving protease activity. Deficiency of this protease may be inherited in an autosomal recessive manner and seems to predispose to chronic relapsing TTP. The assay of the vWF-cleaving protease activity may be used as a sensitive diagnostic tool for identification of subjects with a latent TTP tendency.

Surface profiling by means of double spectral modulation.

Double modulation-in frequency and intensity-of the power spectral distribution of a light beam is proposed for interferometric profilometry. The procedure is based on two facts: (1) the continuous spectrum of a light source is frequency modulated by the path difference in an interferometric device, (2) the continuous spectrum of a light source is intensity modulated by the transparency of an object placed in the exit plane of a spectroscopic device. Both procedures can be used to measure the profile of a surface with high precision. Moreover, phase shifting is automatically performed by the continuous wavelength variation along the spectrum, so that no piezoelectric transducers are necessary. The method is adaptable for the analysis of remote surfaces through optical fibers.

The distribution of anterogradely labeled I--IV primary afferents in histochemically defined compartments of the rat's sternomastoid muscle.

The sternomastoid muscle of the rat is divided into a white (dominated by fast-glycolytic twitch fibers) and a red (dominated by fast oxidative-glycolytic twitch fibers, but also containing slow-oxidative twitch fibers) compartment. Previous reports on exclusive location of muscle spindles in the red portion were confirmed. On the basis of anterograde labeling with horseradish peroxidase-wheat germ agglutinine conjugate (WGA-HRP) it was shown in this study that, in addition to muscle spindle compartmentalisation, there was also an exclusive occurrence of tendon organs in the red part of the muscle; moreover, fine afferents (III- and IV-afferents) were mainly distributed to this portion as well. Radioimmunassay studies revealed that this part of the muscle contained twice as much substance P as the white part. It could be shown by acetylcholinesterase (AChE) histochemistry that the myelinated fibers of the white branch to the muscle exclusively displayed high enzyme activity which is characteristic for motor fibers; on the other hand, in the branch to the red portion two classes of AChE-positive fibers were found: a large one with a peak in the alpha-range, and a small one with a peak in the gamma-range. In addition, there was also a group of enzyme-negative (sensory) fibers. These results also indicate the red portion of the sternomastoid muscle to be its "sensory compartment".

Vagal primary afferent terminals in the dorsal motor nucleus of the rat: are they making monosynaptic contacts on preganglionic efferent neurons?

After horseradish peroxidase (HRP) application to the cut cervical vagus nerve in rats, labelled primary afferent terminals could be demonstrated in the dorsal motor nucleus at the ultrastructural level by a combined glucose oxidase-silver-gold intensification technique. Some labelled boutons contacted labelled dendrites of preganglionic neurons. Thus, the occurrence of a few monosynaptic primary afferent-preganglionic efferent contacts in the dorsal motor nucleus could be demonstrated.

Value of urinary sediment in the diagnosis of interstitial rejection in renal transplants.

The occurrence of lymphocyturia, or a sharp increase in preexisting lymphocyturia, has been found to correlate with immunological rejection. In most studies time-consuming staining techniques or counting chambers have been used. A new staining technique, with prestained slides, is investigated as a predictor of cellular rejection and to distinguish between cellular rejection and cyclosporine (CsA) toxicity, or other causes of renal function impairment. In 18 consecutive renal transplant recipients, treated with CsA, urinary sediments were analyzed almost daily for two months, and prediction of cellular rejection was related to renal biopsies and retrospective clinical evaluation. In addition 24 transplant biopsies were compared with urinary sediment prediction; in both parts of the study a lymphocyturia of more than 20% and polymorphs less than 55% (of 100 nucleated cells, excluding squamous epithelial cells) were considered to suggest interstitial rejection. Episodes of lymphocyturia (greater than 20%), with simultaneous increase of the number of epithelial cells, resulting in a relative decrease of polymorphs (less than 55%), were found 10 times. Of these, 9 corresponded well with biopsy or clinical evaluation and 1 was false-positive. Correlating urinary sediment analysis with biopsy histology (n = 24), 19 were accurate, 3 equivocal, and 2 false; this corresponds to a sensitivity of 77% and a specificity of 91%. In conclusion, the analysis of urinary sediments with prestained slides is a quick and simple method to diagnose cellular rejection and to distinguish it from toxic of ischemic renal damage. Results are comparable to those of the fine-needle aspiration technique without invasive insult to the patient.

The central projections of primary afferent neurons of greater splanchnic and intercostal nerves in the rat. A horseradish peroxidase study.

The central projections of primary afferent fibers of the greater splanchnic nerve of the rat were investigated using the transganglionic horseradish peroxidase transport technique. In addition, the corresponding spinal ganglion cells and the preganglionic sympathetic neurons were demonstrated. For comparing visceral and somatic afferents, intercostal nerve afferents were labelled by the same technique. Splanchnic afferent dorsal root ganglion cells were found at segments T3 to T13 ipsilaterally, with the greatest density at T8 to T12. Labelled cells represented about 10%-15% of all neurons in the ganglia at maximal projection levels. They were randomly distributed within individual ganglia. The great majority were medium to small sized and round to slightly oval in shape. In the spinal cord, labelled visceral afferent axons were found maximally at T8 to T11, but could be detected in decreasing density up to T1 and down to L1. They were distributed over Lissauer's tract and the dorsal funiculus to a medial and lateral collateral pathway (MCP and LCP, respectively). The MCP, somewhat more prominent than the LCP, was destined primarily to clustered presumptive terminal fields in medial lamina I and outermost lamina IIa. Only a few axons continued further to laminae V and X. Splanchnic afferent axons, most likely derived from the MCP, formed a longitudinal bundle ventral to the central canal. The LCP consisted of more or less well-defined axon bundles emanating from the lateral Lissauer's tract and curving round the lateral edge of the dorsal horn and through the dorsolateral funiculus. Presumptive terminal sites of LCP axons are the lateral laminae I and IIa, the nucleus of the dorsolateral funiculus and the dorsal part of lamina V. A few LCP axons were seen in the vicinity of lateral dendrites of preganglionic sympathetic axons. Visceroafferent terminals were absent from laminae IIb-IV and VII. The possible consequences of the MCP/LCP duality for the central connections of splanchnic afferents are discussed. Some splanchnic afferents ascended to the gracile and cuneate nuclei, and rarely to the spinal trigeminal nucleus. These results fit into the general concept of visceroafferent terminal organization that has emerged during the last few years. Differences to other reports in the detailed arrangement of fibers and terminals are discussed. Somatoafferent cell bodies represented the vast majority of neurons in the respective spinal ganglia. Cell sizes encompassed the whole range from very small to very large without a clear predominance of one particular size class.(ABSTRACT TRUNCATED AT 400 WORDS)