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At least 289 records · Page 16Linked to original sources
PubMed1989

Transfer functions and correction factors used in hearing aid evaluation and research.

In hearing aid research and application it is often necessary to transform the sound pressure level or acoustic gain measured at one physical point (e.g., 2 cc coupler) to an equivalent value at another physical point (e.g., tympanic membrane). Results of currently available studies on various transformations are summarized in this report. When no data were available, the desired transfer function was calculated as a linear combination of known contributing transfer functions. Values are given for the center frequencies of 1/3 octaves and critical bands.

Electronics, Medical↗
PubMed2001

Correction factors in the EPR dose reconstruction for residents of the Middle and Lower Techa riverside.

During 1949-1956, the first Soviet nuclear weapons plant, Mayak, released about 7.6 x 10(7) m(-3) of liquid radioactive waste with a total activity of 10(17) Bq into the Techa River (Southern Urals, Russia). 90Sr contributed 11.6% to the total waste radioactivity. As a result of these radioactive discharges, about 28,000 local residents were exposed to ionizing radiation, and some of them received relatively high doses. Internal exposure of the population residing at the Middle and Lower Techa riverside was mostly from 90Sr deposited in bone and tooth tissues. In order to reconstruct radiation doses to this population group, a study of 35 teeth extracted from local residents was carried out using electron paramagnetic resonance measurements. A total of 73 samples from these 35 teeth (tooth enamel, 33; crown dentin, 20; and root dentin, 20) were prepared and measured with electron paramagnetic resonance. The study revealed high doses (up to 15 Gy) absorbed in tooth enamel of the individuals born during 1945-1949, which was attributed to very high local 90Sr concentration in tooth enamel of this particular age group in the population. The analysis presented here takes into account (a) the time courses both of the release/intake of 90Sr and of the tooth formation, and (b) expected variations in measured absorbed doses due to differing geometric sizes of tooth structures. This methodology enables a more consistent picture to be developed of the 90Sr intake by the Middle and Lower Techa riverside population, based on electron paramagnetic resonance tooth dosimetry.

Age Factors↗
PubMed2005

Hemolytic uremic syndrome: a fatal outcome after kidney and liver transplantation performed to correct factor h gene mutation.

Factor H-associated hemolytic uremic syndrome (HUS) is a genetic form of thrombotic microangiopathy characterized by deficient factor H (HF-1) levels/activity and uncontrolled complement activation. The disorder mostly leads to end-stage renal disease and often recurs after kidney transplantation. We previously demonstrated that in a child with HF-1-associated HUS a simultaneous kidney and liver transplantation restored the defective HF-1 with no recurrence of the disease in the transplanted kidney. Here we describe a second childhood case of HF-1-associated HUS treated by combined kidney and liver transplant and complicated by a fatal, primary non-function of the liver graft. Graft hypoperfusion during surgery triggered ischemia/reperfusion changes and complement activation. Conceivably, as a result of defective complement regulatory potential, massive shedding of vascular heparan sulfates was documented in the transplanted liver. This might have impaired the physiological thromboresistance of vascular endothelium ending with widespread microvascular thrombosis and infarction. This case indicates that more fundamental research is needed before combined liver and kidney transplant is considered an option for children with HF-1-associated HUS.

Complement Activation↗
PubMedDate not supplied

Finite element model determination of correction factors used for measurement of aortic diameter via conductance.

Traditional methods for estimating the slope alpha and offset volume Vp for determining real-time chamber volume by the conductance catheter technique are not suited to measurements made in the aorta due to the relatively low resistivity of the aortic wall. We developed three distinct three-dimensional finite element models of the conductance catheter and surrounding tissues in order to predict alpha and Vp and to examine the nature of the electric field near the aortic wall. A heterogeneous isotropic model of the catheter, aorta and surrounding tissues accurately predicted the values of alpha and Vp. A homogeneous anisotropic model was developed to examine the effects of anisotropy of blood and the layers of the aortic wall on measured values of resistance, alpha and Vp. This model demonstrated that anisotropy of blood and aortic wall tissue can increase the values of both alpha and Vp. Finally, a three-dimensional homogeneous isotropic rectangular model allowed examination of the effects of catheter position. This model showed small effects of catheter position on measured resistance (9.7% increase) and larger effects on alpha (21.2% decrease) and Vp (41.9% increase). We conclude the following: the FEA models may lead to accurate estimate values of alpha and Vp in vivo. The unique anisotropic conductive properties of the layers of the aortic wall contribute to the high observed values of alpha and Vp in the aorta. Finally, catheter position has a proportionately greater effect on alpha and Vp than on measured resistance. The results of this study should assist in the determination of aortic mechanical properties using conductance catheter measurements of vessel dimension.

Animals↗