Showing papers in "Medical & Biological Engineering & Computing in 1998"
TL;DR: In this paper, a microstamping technique was developed for high-resolution patterning of proteins on glass substrates for the localisation of neurons and their axons and dendrites.
Abstract: A microstamping technique has been developed for high-resolution patterning of proteins on glass substrates for the localisation of neurons and their axons and dendrites. The patterning process uses a microfabricated polydimethylsiloxane stamp with micrometer length features to transfer multiple types of biomolecules to silanederivatised substrates, using glutaraldehyde as a homobifunctional linker. To test the efficacy of the procedure, substrates are compared in which poly-d-lysine (PDL) was physisorbed and patterned by photoresist with those stamped with PDL. Fluorescein isothiocyanate labelled poly-I-lysine was used to verify the presence and uniformity of the patterns on the glass substrates. As a biological assay, B104 neuroblastoma cells were plated on stamped and physisorbed glass coverslips. Pattern compliance was determined as the percentage of cells on the pattern 8h after plating. Results indicate that the stamping and photoresist patterning procedure are equivalent. Substrates stamped with PDL had an average pattern compliance of 52.6±4.4%, compared to 54.6±8.1% for physisorbed substrates. Measures of background avoidance were also equivalent. As the procedure permits successive stamping of multiple proteins, each with its own micropattern, it should be very useful for defining complex substrates to assist in cell patterning and other cell guidance studies.
197 citations
TL;DR: The results suggest that transfer function analysis may be able to identify different components of cerebral autoregulation and also provide a deeper understanding of recent findings by other investigators.
Abstract: The dynamic relationship between spontaneous fluctuations of arterial blood pressure (ABP) and corresponding changes in cerebral blood flow velocity (CBFV) is studied in a population of 83 neonates. Static and dynamic methods are used to identify two subgroups showing either normal (group A, n = 23) or impaired (group B, n = 21) cerebral autoregulation. An FFT algorithm is used to estimate the coherence and transfer function between CBFV and ABP. The significance of the linear dependence between these two variables is demonstrated by mean values of squared coherence > 0.50 for both groups in the frequency range 0.02-0.50 Hz. However, group A has significantly smaller coherences than group B in the frequency ranges 0.02-0.10 Hz and 0.33-0.49 Hz. The phase response of group A is also significantly more positive than that of group B, with slopes of 9.3 +/- 1.05, and 1.80 +/- 1.2 rad Hz-1, respectively. The amplitude frequency response is also significantly smaller for group A in relation to group B for the frequency range 0.25-0.43 Hz. These results suggest that transfer function analysis may be able to identify different components of cerebral autoregulation and also provide a deeper understanding of recent findings by other investigators.
146 citations
TL;DR: It is found that between six and ten strides are needed to form a representative profile, and an envelope filter with a minimum cut-off frequency of approximately 9 Hz is necessary.
Abstract: The use of linear envelopes to represent the electromyographic (EMG) measurements obtained during locomotion has become common practice. Guidelines for designing envelope filters and specifying the minimum number of strides needed to produce valid EMG profiles have been developed. Electromyograms from eight major muscles of the lower leg are measured from five normal young adults during self-selected slow, free and fast walking speeds. 30 strides per task are measured. The 'ideal' EMG profile is defined from the ensemble average of the rectified EMG signal. An error measure is defined and used as a criterion to assess the appropriateness of various cut-off frequencies for envelope filters and the number of strides required for establishing a good EMG profile. It is found that between six and ten strides are needed to form a representative profile, and an envelope filter with a minimum cut-off frequency of approximately 9 Hz is necessary.
142 citations
TL;DR: A protocol for clinical gait analysis is described, and data from 30 normal adult female subjects are presented, showing 3D relative and absolute movements of pelvis and lower limbs to be consistent with functional anatomy.
Abstract: A protocol for clinical gait analysis is described, and data from 30 normal adult female subjects are presented. Extensive application to pathologic subjects has proven to be feasible and sufficiently accurate. The method is based on a particular location and attachment of retro-reflective markers on the body and on a particular arrangement of four TV cameras. A motion analyser measures the 3D coordinates of each marker. A modelling approach, based on individual anthropometric measurements, and a functional approach, based on kinematical considerations, are used to estimate the location of hip, knee, and ankle joint centers and the orientation of the flexion-extension axis of the knee. 3D relative and absolute movements of pelvis and lower limbs are obtained and shown to be consistent with functional anatomy.
141 citations
TL;DR: The paper reviews the development of collagen-populated hydrated gels for their eventual use as a therapeutic option for the treatment of burn patients or chronic wounds: tools for pharmacological and toxicological studies, and cutaneous models for in vitro studies.
Abstract: The field of tissue engineering has opened several avenues in biomedical sciences, through ongoing progress. Skin substitutes are currently optimised for clinical as well as fundamental applications. The paper reviews the development of collagen-populated hydrated gels for their eventual use as a therapeutic option for the treatment of burn patients or chronic wounds: tools for pharmacological and toxicological studies, and cutaneous models for in vitro studies. These skin substitutes are produced by culturing keratinocytes on a matured dermal equivalent composed of fibroblasts included in a collagen gel. New biotechnological approaches have been developed to prevent contraction (anchoring devices) and promote epithelial cell differentiation. The impact of dermo-epidermal interactions on the differentiation and organisation of bio-engineered skin tissues has been demonstrated with human skin cells. Human skin substitutes have been adapted for percutaneous absorption studies and toxicity assessment. The evolution of these human skin substitutes has been monitored in vivo in preclinical studies showing promising results. These substitutes could also serve as in vitro models for better understanding of the immunological response and healing mechanism in human skin. Thus, such human skin substitutes present various advantages and are leading to the development of other bio-engineered tissues, such as blood vessels, ligaments and bronchi.
133 citations
TL;DR: In this article, the impedance of interdigitated electrode structures (IDES) is measured over a period of four days, from inoculation of the cells to killing of cells at the end of the experiments.
Abstract: Critical parameters to be assessed in cell culture are the number of viable cells and cell viability. Growth, product formation, toxicity effects and the overall success of cell culture can depend largely on these. With interdigitated electrode structures (IDES) adherent cells are cultured directly on a pair of interdigitated electrodes, and the impedance of the system gives insight into the adhesive behaviour of the cells. The signal is influenced by the changes in number, growth and morphological behaviour of adherently growing cells, mainly owing to the insulating effects of the cell membranes. Five different cell lines are used, and their divergent behaviour is monitored over a period of four days, from inoculation of the cells to killing of the cells at the end of the experiments. Even when the cells form close monolayers, great fluctuations in the impedance signal can be observed. Nevertheless, for a more complete description of cellular systems, other parameters, such as acidification and respiration, have to be included in the measuring system.
132 citations
TL;DR: Computer-assisted multichannel stimulation of the cortex will enable several new studies, including quick determination of the cortical regions, the stimulation of which disrupts cortical processing required by a task.
Abstract: Neurones can be excited by an externally applied time-varying electromagnetic field. Focused magnetic brain stimulation is attained using multiple small coils instead of one large coil, the resultant induced electric field being a superposition of the fields from each coil. In multichannel magnetic brain stimulation, partial cancellation of fields from individual coils provides a significant improvement in the focusing of the stimulating field, and independent coil channels allow targeting of the stimuli on a given spot without moving the coils. The problem of shaping the stimulating field in multichannel stimulation is analysed, and a method is derived that yields the driving currents required to induce a field with a user-defined shape. The formulation makes use of lead fields and minimumnorm estimation from magneto-encephalography. Using these methods, some properties of multichannel coil arrays are examined. Computer-assisted multichannel stimulation of the cortex will enable several new studies, including quick determination of the cortical regions, the stimulation of which disrupts cortical processing required by a task.
116 citations
TL;DR: Multivariate spectral estimation based on parametric modelling has been applied to epileptic surface EEG in order to detect EEG changes that occur prior to the clinical outbreak of the seizure.
Abstract: Multivariate spectral estimation based on parametric modelling has been applied to epileptic surface EEG in order to detect EEG changes that occur prior to the clinical outbreak of the seizure. A better time/frequency resolution has been achieved using residual energy ratios (Dickinson’s method). Prediction of oncoming seizures was based on detection of increased preictal synchronisation by calculation of coherence and pole trajectories. The method has been tested on simulated EEG data and on real EEG data from patients with primary generalised epilepsy. Prediction times of 1–6 s have been found in several seizures from five patients.
115 citations
TL;DR: A mathematical model for coherence based on signal-to-noise ratios is introduced to explain the experimental findings: the model demonstrates that noisy reference signals lead to coherence increase, whereas a coherent amount in the reference signal leads to coherent decrease.
Abstract: Coherence has become an essential tool in the description of functional relationships between EEG signals generated within various brain areas. In EEG coherence analysis, the reference signal has an important influence, as an improper reference can distort the results and make them impossible to interpret. In the study, EEG are recorded from one volunteer in 11 sessions, with electrodes selected according to the international 10–20 system against FCz. Additional electrodes are placed on the nose, chin and left and right ear lobes, and recordings are made also against FCz. This enables re-referencing of the stored EEG signals for different reference sites, averaged reference signals, common average reference, Laplacian and bipolar. Coherence values using single reference electrodes depend on the reference site to a large extent. Reliable results are obtained using averaged non-cephalic signals as reference ([A1+A2]/2). Coherence based on FCz yields slightly lower or higher values than that based on non-cephalic reference sites. Completely different results yield common average reference recordings, Laplacian and bipolar recordings, probably owing to the cancellation effect of essential signal portions using these techniques. A mathematical model for coherence based on signal-to-noise ratios is introduced to explain the experimental findings: the model demonstrates that noisy reference signals lead to coherence increase, whereas a coherent amount in the reference signal leads to coherence decrease.
114 citations
TL;DR: The study shows that osteoblasts are both proliferate and differentiate in 3D structures, and the bioreactor may be a suitable tissue culture model for investigation of growth and differentiation processes in tissue engineering.
Abstract: Osteoblastic cells cultured on microcarriers in bioreactors are a potentially useful tool to reproduce the in vivo three-dimensional (3D) bone network. The aim is to compare different types of 3D and two-dimensional (2D) osteoblastic culture. ROS17/2.8 cells are cultured in a bioreactor (rotating-wall vessel) or in two kinds of control (3D petri dish, 3D Percoll) and on two types of microcarrier (Cytodex 3 and Biosilon). Growth and morphology are determined by cell count and SEM, and differentiation is determined by dosage of alkaline phosphatase (ALP) activity and northern blots (ALP and osteocalcin (OC)). SEM shows that Biosilon microcarriers are the best substrate. Proliferation in the RWV and 3D petri dish is still in the exponential phase, whereas growth in the 2D culture reaches a plateau after eight days of culture. ALP activity and the ALP and OC mRNA levels are similar at day 8 for both the RWV and 3D petri dish. However, at day 10, cells are more differentiated in the RWV. The study shows that osteoblasts are both proliferate and differentiate in 3D structures. A BrDU immunocytochemical approach shows that only the cells in the periphery of the aggregates proliferate. Therefore the bioreactor may be a suitable tissue culture model for investigation of growth and differentiation processes in tissue engineering.
105 citations
TL;DR: In this article, the authors discuss the biological and surgical issues which play a key role in the clinical outcome of cultured epidermal autografts used for the treatment of massive full-thickness burns.
Abstract: Cultured human keratinocytes have a wide spectrum of clinical applications. Clinical results reported by several investigators are, however, contradictory. In this review, the authors discuss the biological and surgical issues which play a key role in the clinical outcome of cultured epidermal autografts used for the treatment of massive full-thickness burns. The importance of cultivation of epidermal stem cells and of their transplantation onto a wound bed prepared with donor dermis is emphasised. The paper also reviews recent data showing that: (i) cultured epidermal autografts bearing melanocytes can be used for the treatment of stable vitiligo; (ii) keratinocytes isolated from other lining epithelia, such as oral, urethral and corneal epithelia, can be cultivated and grafted onto patients suffering from disabling epithelial defects; (iii) keratinocyte stem cells can be stably transduced with retroviral vectors and are therefore attractive targets for the gene therapy of genodermatoses.
TL;DR: Three automatic approaches to ventricular repolarisation duration measurement are compared on computer-generated and real ECG signals, in relation to their reliability in the presence of the most common electrocardiographic artefacts, to assess the amount of real and artefactual variability.
Abstract: Three automatic approaches to ventricular repolarisation duration measurement (R-Tapex, R-T(end threshold) and R-T(end fitting) methods) are compared on computer-generated and real ECG signals, in relation to their reliability in the presence of the most common electrocardiographic artefacts (i.e. additive broadband noise and additive and multiplicative periodical disturbances). Simulations permit the evaluation of the amount of R-T beat-to-beat variability induced by the artefacts. The R-T(end threshold) method performs better than the R-T(end fitting) one, and, hence, the latter should be used with caution when R-T(end) variability is addressed. Whereas the R-Tapex method is more robust with regard to broadband noise than the R-T(end threshold) one, the reverse situation is observed in the presence of periodical amplitude modulations. A high level of broadband noise dose not prevent the detection of the central frequency of underlying R-T periodical changes. Comparison between the power spectra of the beat-to-beat R-T variability series obtained from three orthogonal ECG leads (X,Y,Z) is used to assess the amount of real and artefactual variability in 13 normal subjects at rest. The R-Tapex series displays rhythms at high frequency (HF) with a percentage power on the Z lead (57.1 +/- 4.9) greater than that on the X and Y leads (41.9 +/- 4.6 and 46.1 +/- 4.9, respectively), probably because of respiratory-related artefacts affecting the Z lead more remarkably. More uniform HF power distributions over X,Y,Z leads are observed in the R-T(end threshold) series (31.8 +/- 3.8, 39.2 +/- 4.1 and 35.1 +/- 4.2, respectively), thus suggesting minor sensitivity of the R-T(end threshold) measure to respiratory-related artefacts.
TL;DR: A dynamic linear parametric model is designed to quantify the dependence of ventricular repolarisation duration variability on heart period changes and other immeasurable factors and may help to describe the regulation of the ventricularRepolarisation process.
Abstract: A dynamic linear parametric model is designed to quantify the dependence of ventricular repolarisation duration variability on heart period changes and other immeasurable factors. The model analyses the beat-to-beat series of the RR duration and of the interval between R- and T-wave apexes (RT period). Directly from these two signals, a parametric identification procedure and spectral decomposition techniques allow RT variability to be divided into RR-related and RR-unrelated parts and allow the RT-RR transfer function to be calculated. RT variability is driven by RR changes at low frequency (LF, around 0.1 Hz) and high frequency (HF, at the respiratory rate), whereas, at very low frequencies, the RR-unrelated contribution to the total RT variability is remarkable. During tilt at LF the RR-related RT percentage power increases (p<0.02), the RR-unrelated RT percentage power remains unchanged, the gain of the RT-RR relationship largely increases (p<0.001), and the phase is not significantly modified. Both the RR-related and the RR-unrelated RT percentage powers at LF are not affected by controlled respiration, and an increase in the RT-RR gain at HF is observed (p<0.02). The proposed analysis may help to describe the regulation of the ventricular repolarisation process and to extract indexes quantifying the coupling between heart period and ventricular repolarisation interval changes.
TL;DR: The influence of the volume conductor on the EEG, MEG, fetal ECG and fetal MCG is studied by means of simulations and it is found that displacement currents have a substantial effect on the fetalECG and to a lesser degree on the Fetal MCG.
Abstract: The influence of the volume conductor on the EEG, MEG, fetal ECG and fetal MCG is studied by means of simulations. The assumption that the Maxwell equations can be used in a quasi-static approximation is reconsidered and the fact that the conductivity of human tissue is frequency dependent is taken into account. It is found that displacement currents have a substantial effect on the fetal ECG and to a lesser degree on the fetal MCG. Moreover, the frequency dependence of the conductivity of the tissues within the head may have a considerable effect on the EEG.
TL;DR: Endothelial cells can be expected to recognise the flow direction, and change their shape and F-actin structure, and they did not elongate so strongly as in the case of one-way flow.
Abstract: The effect of flow direction on the morphology of cultured bovine aortic endothelial cells is studied. Fully confluent endothelial cells cultured on glass were subjected to a fluid-imposed shear stress of 2 Pa for 20 min and 24 h using a parallel plate flow chamber. Experiments on shear flow exposure were performed for (i) one-way flow, (ii) reciprocating flow with a 30 min interval and (iii) alternating orthogonal flows with a 30 min interval. After flow exposure, the endothelial cells were fixed and F-actin filaments were stained with rhodamine phalloidin. Endothelial cells were observed and photographed by means of a microscope equipped with epifluorescence optics. The shape index (SI) and angle of cell orientation were measured, and F-actin distributions in the cells were statistically studied. Endothelial cells under the one-way flow condition showed marked elongation (SI=0.39±0.16, mean±S.D.) and aligned with the flow direction. In the case of the reciprocating (SI=0.63±0.14) and the alternating orthogonal flows (0.64±0.14), cells did not elongate so strongly as in the case of one-way flow. Although most cells in the reciprocating flow aligned with the flow direction, the cell axes in the alternate orthogonal flow distributed around a mean value of −45.1° with a large S.D. value. Endothelial cells can be expected to recognise the flow direction, and change their shape and F-actin structure.
TL;DR: In this paper, the influence of potential crosslinking agents on the tensile properties of acellular collagen gels has been investigated, including the glycosaminoglycan, chondroitin-6-sulphate (Ch6SO4), the water-soluble carbodiimide cross-link agents 1-ethyl-3-(3-diaminopropyl) carbodiIMide (EDAC), and 1,1-carbonyldiimidazole (CDI), and the polyamines, putrescine
Abstract: Artificial skin substitutes based on autologous keratinocytes are being developed for grafting onto burns patients. In order to be used successfully in the clinic, these skin substitutes need to have sufficient strength to allow ease of handling. This may be achieved by crosslinking the collagen substratum on which the cells are cultured. The influence of potential crosslinking agents on the tensile properties of acellular collagen gels has been investigated, including the glycosaminoglycan, chondroitin-6-sulphate (Ch6SO4), the water-soluble carbodiimide crosslinking agents 1-ethyl-3-(3-diaminopropyl) carbodiimide (EDAC), and 1,1-carbonyldiimidazole (CDI), and the polyamines, putrescine and diaminohexane. Values for Young's modulus, maximum load, stress, displacement and percentage strain at maximum load were generated by subjecting the samples to a tear propagation test. Incorporation of 20% Ch6SO4 into collagen gels caused a significant increase in the Young's modulus, maximum load and stress at maximum load. Crosslinking treatment with EDAC, CDI or polyamines had little further benefit, and in many cases resulted in a decrease in particular parameters. In terms of mechanical strength, the best crosslinking combination proved to be the combination of CDI and diaminohexane, with results either improved or maintained when compared with the control no treatment variants. However, previous experience suggests that the use of CDI as a crosslinking reagent may inhibit infiltration and proliferation of fibroblasts in the substratum and it may be necessary to reach a compromise to obtain the best combination of biological and mechanical properties for artificial skin substitutes.
TL;DR: It is found that the transverse tripole is the only configuration giving convex recruitment contours and therefore maximises activation selectivity for a small (cylindrical) bundle of fibres in the periphery of a monofascicular nerve trunk.
Abstract: Various anode-cathode configurations in a nerve cuff are modelled to predict their spatial selectivity characteristics for functional nerve stimulation. A 3D volume conductor model of a monofascicular nerve is used for the computation of stimulation-induced field potentials, whereas a cable model of myelinated nerve fibre is used for the calculation of the excitation thresholds of fibres. As well as the usual configurations (monopole, bipole, longitudinal tripole, ‘steering’ anode), a transverse tripolar configuration (central cathode) is examined. It is found that the transverse tripole is the only configuration giving convex recruitment contours and therefore maximises activation selectivity for a small (cylindrical) bundle of fibres in the periphery of a monofascicular nerve trunk. As the electrode configuration is changed to achieve greater selectivity, the threshold current increases. Therefore threshold currents for fibre excitation with a transverse tripole are relatively high. Inverse recruitment is less extreme than for the other configurations. The influences of several geometrical parameters and model conductivities of the transverse tripole on selectivity and threshold current are analysed. In chronic implantation, when electrodes are encapsulated by a layer of fibrous tissue, threshold currents are low, whereas the shape of the recruitment contours in transverse tripolar stimulation does not change.
TL;DR: The therapeutic benefits of cultured skin substitutes prepared with skin cells from the patient or from cadaver donors are defined and future directions include genetic modification of transplanted cells to improve wound healing transiently or to deliver gene products systemically.
Abstract: Engineering skin substitutes provides a potential source of advanced therapies for the treatment of acute and chronic wounds. Cultured skin substitutes (CSS) consisting of human keratinocytes and fibroblasts attached to collagen-glycosaminoglycan substrates have been designed and tested in preclinical and clinical studies. Cell culture techniques follow general principles of primary culture and cryopreservation in liquid nitrogen for long-term storage. Biopolymer substrates are fabricated from xenogeneic (bovine) collagen and glycosaminoglycan that are lyophilised for storage until use. At maturity in air-exposed culture, CSS develop an epidermal barrier that is not statistically different from native human skin, as measured by surface electrical capacitance. Preclinical studies in athymic mice show rapid healing, expression of cytokines and regulation of pigmentation. Clinical studies in burn patients demonstrate a qualitative outcome with autologous skin that is not different from 1:4 meshed, split-thickness autograft skin, and with a quantitative advantage over autograft skin in the ratio of healed skin to biopsy areas. Chronic wounds resulting from diabetes or venous stasis have been closed successfully with allogeneic CSS prepared from cryopreserved skin cells. These results define the therapeutic benefits of cultured skin substitutes prepared with skin cells from the patient or from cadaver donors. Future directions include genetic modification of transplanted cells to improve wound healing transiently or to deliver gene products systemically.
TL;DR: Sealing resistance is highly significant with respect to the electrical neuronelectrode contact because it decreases the stimulation threshold of neurons cultured on a planar micro-electrode array using impedance spectroscopy.
Abstract: Sealing resistance is highly significant with respect to the electrical neuronelectrode contact because it decreases the stimulation threshold of neurons cultured on a planar micro-electrode array. A method is proposed for measurement of the sealing resistance using impedance spectroscopy. The effect of the sealing resistance on the total impedance spectrum of a cell-electrode interface is modelled for complete coverage of the electrode by the cell. Sensitivity analysis demonstrates that the impedance spectrum is determined by four parameters: two electrode parameters, the sealing resistance and the shunt capacitance between the lead of the electrode and the culture medium. Experimental verification of the model is performed by simultaneous measurement of the impedance spectrum and electrode coverage. A good and unique fit between the simulated and measured impedance spectra was obtained by varying the two electrode parameters and the sealing resistance.
TL;DR: Encouraging results suggest that PDGF-BB may be a potential growth factor to enhance the quality of the healing ligament.
Abstract: A biological approach to improve healing of the medical collateral ligament (MCL) was investigated by exploring the use of therapeutic growth factors based on in vitro and in vivo experiments. The in vitro cell culture studies involved screening a variety of growth factors to select those that exhibit the most positive effects on cell proliferation and extracellular matrix synthesis. The selected growth factors were applied in vivo to a rabbit model where the MCL was ruptured. Biomechanical and histological evaluations are performed to determine whether the selected growth factors can enhance the properties of the healed MCL, whether these improvements are dose dependent, and whether combinations of growth factors can enhance MCL healing to a greater extent than individual growth factors. In vitro studies showed that epidermal growth factor (EGF) and platelet derived growth factor-BB (PDGF-BB) have the greatest effect on ligament fibroblast proliferation, whereas transforming growth factor-β1 (TGF-β1) superiorly promotes extracellular matrix synthesis. These growth factors were then applied in vivo at different dosages, in isolation and in combination, and the ligaments were evaluated six weeks post-operatively. Tensile testing of the femur-MCL-tibia complexes (FMTCs) revealed that the specimens treated with a high dose of PDGF-BB have ultimate load, ultimate elongation and energy absorbed to failure values that are significantly greater than those from the other groups. The high dose of PDGF-BB was more effective than the low dose, indicating a dose dependency. The addition ofTGF-β1 to PDGF-BB did not lead to any further increases in the structural properties of the FMTC. These encouraging results suggest that PDGF-BB may be a potential growth factor to enhance the quality of the healing ligament.
TL;DR: The results favour the hypothesis of a mechanism of neurofilament crossbridging through the variable antiparallel overlapping of the phosphorylable Lys-Ser-Pro domains of Neurofilament sidearm sidearms from adjacent filaments, following an equilibrium regulated by neurofilaments-associated proteins, bivalent cations and theosphorylation level of Lys- Ser-Pro motifs from both neuro Filament sidarms and neuroFilament- associated proteins.
Abstract: Neurofilaments are organised into parallel bundles in axons through cross-bridges formed by lateral projections of neurofilament subunits. Pure neurofilaments form gels in vitro, consisting of interconnected parallel arrays of filaments regulated by the phosphorylation level of neurofilament subunits. Neurofilament-associated polypeptides sharing phosphorylated epitopes with the repetitive lysine-serine-proline (Lys-Ser-Pro) motifs of the neurofilament heavy subunit sidearm are characterised: they regulate in vitro the neurofilament gelation kenetics in a concentration-and phosphorylation-dependent manner. Studies with synthetic peptides show that interactions between neurofilaments involve both acid and base amino acid residues of neurofilament sidearms and demonstrate the opposite effects of peptides containing either one (inhibition) or two (activation) Lys-Ser-Pro motifs. Electron microscopy reveals an organised network of native neurofilament sidearms, regulated by the phosphorylation level of neurofilament subunits, suggesting a structural transition between intra- and inter-neurofilament sidearm interactions. These results favour the hypothesis of a mechanism of neurofilament crossbridging through the variable antiparallel overlapping of the phosphorylable Lys-Ser-Pro domains of neurofilament sidearms from adjacent filaments, following an equilibrium regulated by neurofilament-associated proteins, bivalent cations and the phosphorylation level of Lys-Ser-Pro motifs from both neurofilament sidearms and neurofilament-associated proteins.
TL;DR: The electrically induced differentiation was completely inhibited by a blockade of calcium influx using LaCl3, indicating that repeated potential shift in the vicinity of a cellular membrane may stimulate morphological response, probably through calcium ion channels.
Abstract: Morphological differentiation of PC12 cells cultured on an indium-tin oxide (ITO) electrode has been induced to grow neurites in the absence of nerve growth factor (NGF) by electrical stimulation. Rectangular pulse wave potentials were applied to the electrode at amplitudes of 200 mV and 400 mV with frequencies of 50 Hz, 500 Hz, and 1 kHz. The PC12 cells differentiated most prominently at 200 mV with 100 Hz. No statistically significant differences were observed among the electrically induced neurite lengths. The electrically induced differentiation was completely inhibited by a blockade of calcium influx using LaCl3. This indicates that repeated potential shift in the vicinity of a cellular membrane may stimulate morphological response, probably through calcium ion channels.
TL;DR: The results suggest that Cindex may be a useful noninvasive indicator of peripheral vascular compliance in humans.
Abstract: A non-invasive technique is implemented to measure a peripheral vascular compliance index Cindex, using an infrared photoplethysmographic waveform as an indicator of intravascular volume change and a continuous blood pressure monitor to measure the blood pressure during each heart-beat. The non-linear behaviour of Cindex with pressure and the effect of age on Cindex are studied in 62 males (15–73 years). Repeatability tests and the effect of ice-water exposure of a portion of a limb are studied in 10 and 14 subjects, respectively. For each individual, Cindex measurements are taken at discrete values of local mean arterial pressure (Pmean), and a Cindex against Pmean plot is obtained. There is a statistically significant difference (p<0.05) in Cindex for the lower values of Pmean (60–100 mmHg) between two age groups formed (15–52 and 58–73 years). The cold-pressor test (CPT) shows a 68% median decrease in Cindex, with an inter-quartile range of 60–77%, in a matter of seconds. The results suggest that Cindex may be a useful noninvasive indicator of peripheral vascular compliance in humans.
TL;DR: The wavelet adaptive filter for the removal of baseline wandering in ECG signals is described and shows a lower ST-segment distortion than the standard filter and the adaptive filter.
Abstract: A wavelet adaptive filter (WAF) for the removal of baseline wandering in ECG signals is described. The WAF consists of two parts. The first part is a wavelet transform that decomposes the ECG signal into seven frequency bands using Vaidyanathan-Hoang wavelets. The second part is an adaptive filter that uses the signal of the seventh lowest-frequency band among the wavelet transformed signals as primary input and a constant as reference input. To evaluate the performance of the WAF, two baseline wandering elimination filters are used, a commercial standard filter with a cutoff frequency of 0.5 Hz and a general adaptive filter. The MIT/BIH database and the European ST-T database are used for the evaluation. The WAF performs better in the average power of eliminated noise than the standard filter and adaptive filter. Furthermore, it shows a lower ST-segment distortion than the standard filter and the adaptive filter.
TL;DR: In this article, a system based on cardiac myocytes cultured over microfabricated metal microelectrode arrays, from which potentials with a mean amplitude of 16.9 μV can be reliably recorded, which can be reversibly blocked with μmoll−1 concentrations of the sodium ion channel blocker lidocaine.
Abstract: There are a range of techniques that can be used to assay bioactive compound. One potentially promising technique is a system consisting of microfabricated extracellular recording devices over which electrogenic cells can be grown. To date, research in this area has concentrated on the use of neurons as an electrogenic cell type. However, these cells have limitations. Only small extracellular potentials have been recorded from mammalian neurons cultured over microfabricated electrode arrays. Although such potentials may be of use in assays examining the effects of bio-active compound analogues on firing frequency, they are of little use for more detailed pharmacological studies involving analyses of signal shape. What is required is a system from which much larger extracellular potentials can be recorded. This preliminary study reports on a system based on cardiac myocytes cultured over microfabricated metal microelectrode arrays, from which potentials with a mean amplitude of 16.9 μV can be reliably recorded, which can be reversibly blocked with μmoll−1 concentrations of the sodium ion channel blocker lidocaine. Less common potentials with amplitudes of up to 3.5 mV were also recorded. It is demonstrated that cardiac myocytes cultured over microfabricated micro-electrode arrays can be used in assays of cardioactive compound analogues.
TL;DR: The authors show that cord blood derived and CD34+ progenitors isolated from the peripheral blood give rise to residential Langerhans cells when co-seeded with normal human keratinocytes.
Abstract: In addition to their basic biological interest, models of reconstructed epidermis provide useful tools for in vitro assessment of the toxicology and efficacy of new chemicals and drugs. The fact that the majority of these in vitro models are composed only of keratinocytes has excluded their use in the fields of skin pigmentation and immunology. After the successful introduction of functional melanocytes into the epidermal reconstruct, the integration of Langerhans cells remains an important challenge, particularly since after isolation of Langerhans cells from human epidermis, these cells cannot be subcultured and do not integrate into the reconstructing epidermis. The authors show that cord blood derived and CD34+ progenitors isolated from the peripheral blood give rise to residential Langerhans cells when co-seeded with normal human keratinocytes.
TL;DR: The Certainty algorithm is relatively insensitive to the certainty threshold used, can consistently differentiate between similarly shaped MUAPs from different MUAPTs, and can make correct classifications despite biological shape variability, background noise and signal shape non-stationarity.
Abstract: A certainty-based classification algorithm is described, which comprises part of a clinically used EMG signal decomposition system. This algorithm classifies a candidate motor unit action potential (MUAP) to the motor unit action potential train (MUAPT) that produces the greatest estimated certainty, provided this maximal certainty is above a given threshold. The algorithm is iterative, such that the certainty with which assignments are made increases with each pass through the data, and it has specific stopping criteria. The performance and sensitivity (to the assignment threshold) of the Certainty algorithm and an iterative minimum Euclidean distance (MED) algorithm are compared by classifying sets of MUAPs detected in real concentric needle-detected EMG signals, using a range of assignment thresholds for each algorithm. With regard to MUAP assignment and error rates, the Certainty algorithm consistently provides better mean results and, more importantly, less variable results than the MED algorithm. The Certainty algorithm can provide mean assignment and error rates of 80.8 and 1.5%, respectively, with a maximum error rate of 3.2%; the MED algorithm can provide mean assignment and error rates of 80.3 and 3.3%, respectively, with a maximum error rate of 6.5%. The Certainty algorithm is relatively insensitive to the certainty threshold used, can consistently differentiate between similarly shaped MUAPs from different MUAPTs, and can make correct classifications despite biological shape variability, background noise and signal shape non-stationarity.
TL;DR: The results suggest that the PEC transducer acts as a displacement meter of muscle vibration when investigating the mechanical activity of muscle.
Abstract: The piezoelectric contact sensor has been widely utilised in mechanomyography (MMG). The authors aim to clarify the mechanical variables (i.e. acceleration, velocity or displacement) reflected by the MMG signal detected with a piezoelectric contact sensor (PEC), and compare the results with those obtained simultaneously by an accelerometer (ACC). To measure the acceleration-frequency response, a mechanical sinusoidal excitation of 5 to 300 Hz at a constant magnitude of 0.01 G was applied to the two transducers. The acceleration-frequency response of the ACC transducer was confirmed to be almost flat. The PEC without any restriction of the transducer housing (including the combined seismic mass) demonstrated a similar response to the ACC transducer. The PEC transducer output with restricted housing decreased with increasing sinusoidal frequency and an attenuation slope of −40 dB/decade and phase angle of −180 degrees. The voluntary MMG signal during isometric knee extension was recorded simultaneously with the two transducers. The amplitude spectral density distribution of the MMG from the PEC transducer was narrow and the mean frequency was approximately one-half that obtained from the ACC tranducer. The amplitude spectral density distribution with the PEC transducer resembled that of the double integral over time of the ACC transducer signal. The phase angle of the PEC transducer signal was different from that of the ACC transducer signal by approximately −180°. These results suggest that the PEC transducer acts as a displacement meter of muscle vibration. In addition, differences in the MMG frequency components relating to the transducer type must be taken into consideration when investigating the mechanical activity of muscle.
TL;DR: A pattern classification system, designed to separate myoelectric signal records based on contraction tasks, is described and an evaluation of the system, in terms of system performance and the complexity of the ANNs, is presented.
Abstract: A pattern classification system, designed to separate myoelectric signal records based on contraction tasks, is described The amplitude of the myoelectric signal during the first 200 ms following the onset of a contraction has a non-random structure that is specific to the task performed This permits the application of advanced pattern recognition techniques to separate these signals The pattern classification system described consists of a spectrographic preprocessor, a feature extraction stage and a classifier stage The preprocessor creates a spectrogram by generating a series of power spectral densities over adjacent time segments of the input signal The feature extraction stage reduces the dimensionality of the spectrogram by identifying features that correspond to subtle underlying structures in the input signal data This is realised by a self-organising artificial neural network (ANN) that performs an advanced statistical analysis procedure known as exploratory projection pursuit The extracted features are then classified by a supervised-learning ANN An evaluation of the system, in terms of system performance and the complexity of the ANNs, is presented
TL;DR: The software enables the combination of different segmentation techniques to improve its efficiency and can be utilised in numerous applications, including pre-processing for three-dimensional presentations, volumetric analysis and construction of volume conductor models.
Abstract: Segmentation software is described, developed for medical image processing and run on Windows. The software applies basic image processing techniques through a graphical user interface. For particular applications, such as brain lesion segmentation, the software enables the combination of different segmentation techniques to improve its efficiency. The program is applied for magnetic resonance imaging, computed tomography and optical images of cryosections. The software can be utilised in numerous applications, including pre-processing for three-dimensional presentations, volumetric analysis and construction of volume conductor models.