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51.
Ostlund N Yu J Roeleveld K Karlsson JS 《Medical & biological engineering & computing》2004,42(6):825-831
Spatial filtering of surface electromyography (EMG) signal can be used to enhance single motor unit action potentials (MUAPs).
Traditional spatial filters for surface EMG do not take into consideration that some electrodes could have poor skin contact.
In contrast to the traditional a priori defined filters, this study introduces an adaptive spatial filtering method that adapts
to the signal characteristics. The adaptive filter, the maximum kurtosis filter (MKF), was obtained by using the linear combination
of surrounding channels that maximises kurtosis. The MKF and conventional filters were applied to simulated EMG signals and
to real EMG signals recorded with an electrode grid to evaluate their performance in detecting single motor units. The MKF
was compared with conventional spatial filtering methods. Simulated signals, with different levels of spatially correlated
noise, were used for comparison. The influence of one electrode with poor skin contact was also investigated. The MKF was
found to be considerably better at enhancing a single MUAP than conventional methods for all levels of spatial correlation
of the noise. For a spatial correlation of 0.97 of the noise, the improvement in the signal-to-noise ratio, where a MUAP could
be detected, was at least 6 dB. With a simulated poor skin contact for one electrode, the improvement over the other methods
was at least 19 dB. 相似文献
52.
In order to evaluate the risks and benefits of continuing established therapy with beta-adrenergic receptor blocking drugs during acute myocardial infarction (AMI), 183 consecutive patients, 63 with (beta-blocker group) and 120 without (control group) this therapy, were studied. Detailed information on previous diseases, present symptoms, established medication, clinical and laboratory findings on admission and during the first 12 hours in the CCU was collected. The incidences of congestive heart failure, hypotension, AV blocks and ventricular arrhythmias were not significantly more common in the control group (8 vs. 28%, p less than 0.01). Thus, continuation of established therapy with beta-adrenergic receptor blocking drugs does not seem to increase the risk of complications after hospital admission for AMI. The reason for the low incidence of inferior wall infarction in the beta-blocker group is not clear but it cannot be excluded that when patients on beta-adrenergic receptor blocking therapy develop an inferior AMI, they may run a greater risk of sudden death. 相似文献
53.
A new method is proposed, based on the pole phase angle (PPA) of a second-order autoregressive (AR) model, to track spectral
alteration during localised muscle fatigue when analysing surface myo-electric (ME) signals. Both stationary and non-stationary,
simulated and real ME signals are used to investigate different methods to track spectral changes. The real ME signals are
obtained from three muscles (the right vastus lateralis, rectus femoris and vastus medialis) of six healthy male volunteers,
and the simulated signals are generated by passing Gaussian white-noise sequences through digital filters with spectral properties
that mimic the real ME signals. The PPA method is compared, not only with spectra-based methods, such as Fourier and AR, but
also with zero crossings (ZCs) and the first AR coefficient that have been proposed in the literature as computer efficient
methods. By comparing the deviation (dev), in percent, between the linear regression of the theoretical and estimated mean
frequencies of the power spectra for simulated stationary (s) and non-stationary (ns) signals, in general, it is found that
the PPA method (devs=4.29; devns=1.94) gives a superior performance to ZCs (dvs=8.25) and the first AR coefficient (4.18<devs<21.8; 0.98<devns<4.36) but performs slightly worse than spectra-based methods (0.33<devs<0.79; 0.41<devns<1.07). However, the PPA method has the advantage that it estimates spectral alteration without calculating the spectra and
therefore allows very efficient computation. 相似文献
54.
Karlsson MR Kahu H Hanson LA Telemo E Dahlgren UI 《Scandinavian journal of immunology》2002,55(5):470-477
We have previously demonstrated that rats fed ovalbumin (OVA) develop a tolerogenic activity in serum, which upon transfer induces tolerance to OVA and suppression of the immune response to a bystander antigen. Here, we have extended these studies and analysed if the tolerogenic activity in serum could suppress an established immune response in the recipients. Rats were immunized with OVA, 4 and 1 week prior to the transfer of serum from either OVA-fed or control animals. Rats that received serum from OVA-fed donors had significantly lower delayed-type hypersensitivity (DTH) reaction against OVA 1 week after the serum transfer compared with the controls, and the levels of immunoglobulin (IgG) anti-OVA antibodies were significantly lower 2 and 4 weeks after serum transfer. Monomeric OVA in amounts corresponding to the OVA transferred with serum did not induce the reduction of DTH response or IgG anti-OVA antibody levels. In vitro, the proliferation of OVA-stimulated spleen cells, taken from recipients of tolerogenic serum, was significantly lower compared with spleen cells from the controls. The in vitro suppression seemed to be mediated by a population of CD25+ cells, because the removal of such cells from OVA-stimulated spleen cell suspensions resulted in increased proliferation in cultures from rats receiving tolerogenic serum. Our results showed that the tolerogenic serum factor can suppress an established immune response in recipient animals, possibly through induction of regulatory CD25+ cells. Whether this capacity might be used to influence chronic inflammatory conditions needs to be investigated. 相似文献
55.
Ghazzawi IM; Sarraf MG; Taher MR; Khalifa FA 《Human reproduction (Oxford, England)》1998,13(2):348-352
A prospective study was carried out to compare the fertilizing capability
and pregnancy outcome following intracytoplasmic sperm injection (ICSI)
using spermatozoa obtained from ejaculates, or surgically from epididymis
or seminiferous tubules. A total of 77 ICSI cycles (one per patient) was
included. In all, 28 patients had severe oligoasthenoteratozoospermia, 19
patients had obstructive azoospermia and 30 patients had non-obstructive
azoospermia. The main outcome measures were fertilization rate per injected
metaphase II oocyte and the clinical pregnancy rate per embryo transferred
back to the female recipients. In patients with severe
oligoasthenoteratozoospermia, the fertilization and pregnancy rates were 79
and 25 %. In patients with obstructive azoospermia, for whom epididymal
spermatozoa were used, these were 75 and 28%, and in the non-obstructive
group for which testicular spermatozoa were used for injection, they were
69 and 21% respectively. These rates were not significantly different in
the three groups (P = 0.85 and P = 0.14 respectively), suggesting that
spermatozoa from the ejaculates and epididymal or testicular biopsies are
able to fertilize equally by using ICSI. Live birth per embryo transfer was
significantly reduced in patients with non-obstructive azoospermia compared
to the other two groups. The high abortion rate (50%) in the group in which
testicular spermatozoa were used raises doubts about the developmental
competence of such embryos.
相似文献
56.
57.
Prediction of AVM obliteration after stereotactic radiotherapy using radiobiological modelling 总被引:1,自引:0,他引:1
Mavroidis P Theodorou K Lefkopoulos D Nataf F Schlienger M Karlsson B Lax I Kappas C Lind BK Brahme A 《Physics in medicine and biology》2002,47(14):2471-2494
This study was carried out in order to derive the radiobiological parameters of the dose-response relation for the obliteration of arteriovenous malformation (AVM) following single fraction stereotactic radiotherapy. Furthermore, the accuracy by which the linear Poisson model predicts the probability of obliteration and how the haemorrhage history, location and volume of the AVM influence its radiosensitivity are investigated. The study patient material consists of 85 patients who received radiation for AVM therapy. Radiation-induced AVM obliterations were assessed on the basis of post-irradiation angiographies and other radiological findings. For each patient the dose delivered to the clinical target volume and the clinical treatment outcome were available. These data were used in a maximum likelihood analysis to calculate the best estimates of the parameters of the linear Poisson model. The uncertainties of these parameters were also calculated and their individual influence on the dose-response curve was studied. AVM radiosensitivity was assumed to be the same for all the patients. The radiobiological model used was proved suitable for predicting the treatment outcome pattern of the studied patient material. The radiobiological parameters of the model were calculated for different AVM locations, bleeding histories and AVM sizes. The range of parameter variability had considerable effect on the dose-response curve of AVM. The correlation between the dosimetric data and their corresponding clinical effect could be accurately modelled using the linear Poisson model. The derived response parameters can be introduced into the clinical routine with the calculated accuracy assuming the same methodology in target definition and delineation. The known volume dependence of AVM radiosensitivity was confirmed. Moreover, a trend relating AVM location with its radiosensitivity was observed. 相似文献
58.
59.
Björn Jonson Rolf Nilsén Hans-Göran Karlsson 《Medical & biological engineering & computing》1975,13(2):209-213
The relationship between the arterial blood pressure and the volume of the arteries within a segment of an extremity is nonlinear. The present paper shows how the flow and volume pulsations of the arteries within a limb segment can be simulated taking this property into account. An electrical model was constructed comprising one resistor and two voltage dependent ‘capacitors’, the latter corresponding to the pressure dependent elasticity, or compliance, of the arteries. Adequate simulations were obtained over a wide pressure range, which is impossible with linear models. The nonlinear, i.e. pressure dependent, relationship between the volume and pressure of arteries, observed under static conditions, must also be taken into consideration when studying pulsatile events with models whether mathematical or physical. 相似文献
60.
Berge-Lefranc JL; Jay P; Massacrier A; Cau P; Mattei MG; Bauer S; Marsollier C; Berta P; Fontes M 《Human molecular genetics》1996,5(10):1637-1641
While constructing a cDNA library of human embryos, we have isolated a
clone homologous to jumonji, a mouse gene required for neural tube
formation. We have determined the complete coding sequence of the human
homologue (JMJ) and deduced the amino acid sequence of the putative
protein. We show here that human and mouse jumonji putative proteins are
homologous and present 90% identity. During human embryogenesis, JMJ mRNAs
are predominantly expressed in neurons and particularly in dorsal root
ganglion cells. They are also expressed in neurons of human adult cerebral
cortex. In view of these observations, we propose JMJ as a candidate gene
for developmental defects of the central nervous system in the human. The
human JMJ gene maps at position 6p24-6p23.
相似文献