Noninvasive detection of ischemic bowel.
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PURPOSE: Acute mesenteric arterial occlusion is an abdominal catastrophe that carries high morbidity and mortality rates. Current diagnostic methods, however, lack sensitivity and specificity and do not provide information about the viability of the affected bowel. Early diagnosis and intervention would improve patient outcomes and survival rates. The basic electrical rhythm (BER) is the omnipresent electrical slow wave of the gastrointestinal tract that characterizes the underlying electrical activity of the bowel. BER frequency is known to fall with ischemia. Superconducting quantum interference devices (SQUIDs) can detect BER by measuring the magnetic fields generated by the electrical activity of the smooth muscle of the small bowel. The purpose of this study was to determine the ability of a SQUID to detect mesenteric ischemia in a free-lying section of small bowel in an animal model of acute superior mesenteric artery occlusion. METHODS: Seven adult male rabbits (six experimental and one control) were studied with transabdominal SQUID and electrode recordings during baseline and after the induction of mesenteric ischemia with balloon occlusion of the superior mesenteric artery. Continuous recordings were taken for 120 minutes of ischemia and analyzed with autoregressive spectral analysis to determine the BER frequency during specific time points of the study. Two independent investigators blinded to the experimental preparation examined the results to determine whether there was decreased BER frequency and thus ischemia. The results are expressed as mean +/- SEM, and paired t tests were used to determine statistical significance. RESULTS: BER was detected in all seven animals and fell from 10.7 +/- 0.5 cpm to 7.0 +/- 1.8 cpm after 30 minutes of ischemia in the magnetic channels (P <.05, with t test). The fall in BER was detected by the SQUID in all six experimental animals. The blinded observers correctly identified healthy and ischemic magnetic data recording, with a sensitivity of 94% and specificity of 100%. CONCLUSION: SQUIDs can noninvasively detect bowel ischemia early in a free-lying segment of small bowel in this animal model with a high degree of sensitivity and specificity. (+info)
Linearly and circularly polarized, 50 Hz magnetic fields did not alter intracellular calcium in rat immune cells.
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This study was conducted to determine if exposure to 50 Hz magnetic field (MF) affects intracellular calcium ([Ca2+]i). We employed flow cytometry for real-time detection of possible changes in [Ca2+]i in a large number of cells. A solenoid coil for vertical MF exposure and a multiple-loop square-coil for horizontal MF were utilized. In the laboratory, background 50 Hz MF was less than 0.08 microT when all necessary equipment was powered. Rat thymocytes were exposed to 0.1 mT horizontal or vertical field, or to 0.14 mT circularly polarized field for 30 min; the effects of consecutive exposures to vertical and horizontal MFs, or vice versa, for 20 min each also were examined. In addition, intact thymocytes or lectin-activated thymocytes, splenocytes and peripheral blood lymphocytes were exposed to the 5 mT vertical field for 30 min. In all these experiments, no alteration in [Ca2+]i was evident. As a positive control, a calcium ionophore always was added to the medium following MF exposure to verify that the cells were capable of increasing [Ca2+]i and the system would record the response. The data indicate that MF exposure had no effect on [Ca2+]i under any of the conditions examined. (+info)
Exposure of Sprague-Dawley rats to a 50-Hertz, 100-microTesla magnetic field for 27 weeks facilitates mammary tumorigenesis in the 7,12-dimethylbenz[a]-anthracene model of breast cancer.
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We have shown previously (W. Loscher et al., Cancer Lett., 71: 75-81, 1993; M. Mevissen et al., Carcinogenesis (Lond.), 17: 903-910, 1996) that 50-Hz magnetic fields (MFs) of low [50 or 100 microTesla (T)] flux density enhance mammary gland tumor development and growth in the 7,12-dimethylbenz[a]anthracene (DMBA) model of breast cancer in female Sprague Dawley rats. In these previous experiments, groups of rats were given 20 mg of DMBA (four weekly gavage doses of 5 mg each) and were MF- or sham-exposed for 13 weeks. The objective of the present study was to examine whether the use of a lower dose of DMBA (10 instead of 20 mg per rat), MF exposure of the rats before DMBA injection, and the increase of the MF exposure period after DMBA application to 26 weeks enhance the effect of MF on tumor development and growth. A group 99 rats was exposed to a homogeneous, horizontally polarized 100-microT MF of 50-Hz for 24 h/day for 7 days/week; another group of 99 rats was sham-exposed under the same environmental conditions as the MF-exposed rats. The exposure chambers were identical for MF-exposed and sham-exposed animals. The age of the rats was 45-49 days at the onset of exposure; duration of MF or sham exposure was 27 weeks. DMBA was administered p.o. at a dose of 10 mg/rat after 1 week of MF or sham exposure. The animals were palpated once weekly from week 6 onwards to assess the development of mammary tumors. At the end of the exposure period, the animals were killed for the determination of number and volume and histological verification of mammary tumors. All of the recordings were done in a blinded fashion; i.e., the investigators were not aware which animals were MF- or sham-exposed. Mammary tumor development and growth was significantly enhanced by MF exposure, the most marked effect on tumor incidence (190% above sham control) being observed 13 weeks after DMBA administration. At the time of necropsy, i.e., 26 weeks after DMBA administration, the incidence of histologically verified mammary tumors was 50.5% in controls and 64.7% in MF-exposed rats, the difference being statistically significant. More marked intergroup differences were recorded when tumor incidence was separately evaluated for each of the six mammary complexes, the most pronounced MF effect on tumor incidence being seen in the cranial thoracic complex. The data substantiate that, at least under the experimental conditions used in our laboratory, 50-Hz, 100-microT MF exposure significantly facilitates the development and growth of mammary tumors in the DMBA rat model of breast cancer. (+info)
Extremely low frequency magnetic fields and fertility: a follow up study of couples planning first pregnancies. The Danish First Pregnancy Planner Study Team.
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OBJECTIVES: To evaluate the impact of extremely low frequency (ELF) magnetic fields on markers of human fertility. METHODS: A follow up study of time to pregnancy, semen quality, and reproductive hormones was conducted among couples planning first pregnancies (36 males were welders and 21 were non-welders). The male and the female partner were monitored for exposure to ELF magnetic field by personal exposure meters. As summary measures of exposure the median value was calculated together with the 75 percentile value and the proportion of measurements exceeding 0.2 and 1.0 microT, respectively. Each summary measure was divided in three categories: low, medium, and high. RESULTS: Couples in which the man had a medium or a high proportion of measurements > 1.0 microT had a reduced probability of conception per menstrual cycle compared with the men with low exposure, but the result was only significant for the men with medium exposure. This finding was partly attributable to a high probability of conception per menstrual cycle among the men with low exposure compared with non-welders in the original cohort of 430 couples. Other summary measures were not related to probability of conception or other markers of fertility. A possible negative association was found between high probability of conception and female exposure measures based on the median, the 75 percentile, and the proportion of measurements > 0.2 microT, but no association was found with the proportion of measurements > 1.0 microT. CONCLUSIONS: The findings provide no consistent support for a hypothesis of a deleterious effect of low level ELF magnetic fields on markers of human fertility. However, due to the relatively small size of the studied population only large associations would be detected. (+info)
Functional mapping in the human brain using high magnetic fields.
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An avidly pursued new dimension in magnetic resonance imaging (MRI) research is the acquisition of physiological and biochemical information non-invasively using the nuclear spins of the water molecules in the human body. In this trial, a recent and unique accomplishment was the introduction of the ability to map human brain function non-invasively. Today, functional images with subcentimetre resolution of the entire human brain can be generated in single subjects and in data acquisition times of several minutes using 1.5 tesla (T) MRI scanners that are often used in hospitals for clinical purposes. However, there have been accomplishments beyond this type of imaging using significantly higher magnetic fields such as 4 T. Efforts for developing high magnetic field human brain imaging and functional mapping using MRI (fMRI) were undertaken at about the same time. It has been demonstrated that high magnetic fields result in improved contrast and, more importantly, in elevated sensitivity to capillary level changes coupled to neuronal activity in the blood oxygenation level dependent (BOLD) contrast mechanism used in fMRI. These advantages have been used to generate, for example, high resolution functional maps of ocular dominance columns, retinotopy within the small lateral geniculate nucleus, true single-trial fMRI and early negative signal changes in the temporal evolution of the BOLD signal. So far these have not been duplicated or have been observed as significantly weaker effects at much lower field strengths. Some of these high-field advantages and accomplishments are reviewed in this paper. (+info)
Single-shot diffusion measurement in laser-polarized Gas.
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A single-shot pulsed gradient stimulated echo sequence is introduced to address the challenges of diffusion measurements of laser polarized 3He and 129Xe gas. Laser polarization enhances the NMR sensitivity of these noble gases by >10(3), but creates an unstable, nonthermal polarization that is not readily renewable. A new method is presented which permits parallel acquisition of the several measurements required to determine a diffusive attenuation curve. The NMR characterization of a sample's diffusion behavior can be accomplished in a single measurement, using only a single polarization step. As a demonstration, the diffusion coefficient of a sample of laser-polarized 129Xe gas is measured via this method. (+info)
Correlation between functional and electrophysiological recovery in acute ischemic stroke.
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BACKGROUND AND PURPOSE: There is still controversy about the prognostic value of motor evoked potentials (MEPs) in the assessment of hemiplegia. The aims of this study are to determine the relationship between functional and electrophysiological recovery and thus the value of MEP as a prognostic indicator of clinical outcome in acute ischemic stroke. METHODS: Seventeen healthy subjects and 38 stroke patients were included in this study. Functional recovery was assessed with the Modified Canadian Neurological Scale (MCNS), the Barthel Activities of Daily Living Index (BI), and the Rankin scale. Transcranial magnetic stimulation was used to determine the change in central motor conduction time (CMCT). Stroke outcome was assessed at the end of 2 weeks. One-way ANOVA with post hoc comparisons using the Scheffe procedure as well as t tests were used to assess the significance of the results in this study. RESULTS: Unpaired t test showed significantly higher mean scores of the MCNS (2P=0.001), BI (2P=0.002), and Rankin scale (P<0.001) at day 14 in the group of patients with recordable MEP at day 1. A better clinical improvement with a higher mean score of the MCNS (2P<0.001), BI (2P<0.001), and the Rankin scale (2P<0.001) was also observed in the patients in whom the CMCT improved. CONCLUSIONS: These data show that there is a close relationship between clinical and electrophysiological improvement and that MEP is a useful prognostic indicator of clinical outcome. (+info)
Spectroscopic and kinetic studies on the oxygen-centered radical formed during the four-electron reduction process of dioxygen by Rhus vernicifera laccase.
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The oxygen-centered radical bound to the trinuclear copper center was detected as an intermediate during the reoxidation process of the reduced Rhus vernicifera laccase with dioxygen and characterized by using absorption, stopped-flow, and electron paramagnetic resonance (EPR) spectroscopies and by super conducting quantum interface devices measurement. The intermediate bands appeared at 370 nm (epsilon approximately 1000), 420 nm (sh), and 670 nm (weak) within 15 ms, and were observable for approximately 2 min at pH 7.4 but for less than 5 s at pH 4.2. The first-order rate constant for the decay of the intermediate has been determined by stopped-flow spectroscopy, showing the isotope effect, k(H)/k(D) of 1.4 in D(2)O. The intermediate was found to decay mainly from the protonated form by analyzing pH dependences. The enthalpy and entropy of activation suggested that a considerable structure change takes place around the active site during the decay of the intermediate. The EPR spectra at cryogenic temperatures (<27 K) showed two broad signals with g approximately 1.8 and 1.6 depending on pH. We propose an oxygen-centered radical in magnetic interaction with the oxidized type III copper ions as the structure of the three-electron reduced form of dioxygen. (+info)