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Biomedical subjects

M London

Publications and source records attributed to M London.

71 records · Page 4Linked to original sources
PubMedDate not supplied

MR angiography with an ultrasmall superparamagnetic iron oxide blood pool agent.

The purpose of the study was to investigate the use of a dextran-coated ultrasmall superparamagnetic iron oxide (USPIO) as a blood pool contrast agent for thoracic and abdominal MR angiography. Abdominal and thoracic MR angiography was performed in six healthy volunteers using two-dimensional and three-dimensional spoiled gradient echo (SPGR) sequences before and after intravenous administration of USPIO. Doses ranged from 1.1 to 2.6 mg Fe/kg. Flip angle was varied from 20 to 60 degrees. Subjective image quality, analysis of signal-to-noise ratio (SNR), and blood T1 relaxation times were measured. USPIO significantly lowered the T1 of blood (from 1,210 ms precontrast to 159 ms postcontrast at a dose of 2.6 mg Fe/kg) (P < .01). Image quality on coronal fast three-dimensional breath-hold SPGR images of the abdomen increased with increasing dose and was maximum at the highest dose, producing an aortic SNR of 9.6 compared to 1.8 precontrast. Axial two-dimensional time-of-flight (TOF) aortic SNR was reduced significantly from 13 on precontrast to 6 on the postcontrast images at the highest dose (P < .05) due to T2* shortening effects. There was little flip angle dependence on image quality. Due to the T1 shortening effect and long intravascular half-life, USPIO improved visualization of vascular anatomy using three-dimensional fast SPGR imaging. The echo time must be minimized to minimize signal loss from T2* shortening effects. The blood pool distribution of USPIO is useful for equilibrium-phase MR angiography.

Abdomen↗
PubMedDate not supplied

Subthreshold voltage noise due to channel fluctuations in active neuronal membranes.

Voltage-gated ion channels in neuronal membranes fluctuate randomly between different conformational states due to thermal agitation. Fluctuations between conducting and nonconducting states give rise to noisy membrane currents and subthreshold voltage fluctuations and may contribute to variability in spike timing. Here we study subthreshold voltage fluctuations due to active voltage-gated Na+ and K+ channels as predicted by two commonly used kinetic schemes: the Mainen et al. (1995) (MJHS) kinetic scheme, which has been used to model dendritic channels in cortical neurons, and the classical Hodgkin-Huxley (1952) (HH) kinetic scheme for the squid giant axon. We compute the magnitudes, amplitude distributions, and power spectral densities of the voltage noise in isopotential membrane patches predicted by these kinetic schemes. For both schemes, noise magnitudes increase rapidly with depolarization from rest. Noise is larger for smaller patch areas but is smaller for increased model temperatures. We contrast the results from Monte Carlo simulations of the stochastic nonlinear kinetic schemes with analytical, closed-form expressions derived using passive and quasi-active linear approximations to the kinetic schemes. For all subthreshold voltage ranges, the quasi-active linearized approximation is accurate within 8% and may thus be used in large-scale simulations of realistic neuronal geometries.

Animals↗
PubMedDate not supplied

Enhancing the identification of excessive drinkers on medical wards: a 1-year follow-up study.

This paper describes a 1-year follow-up study examining whether hospital ward doctors and nurses continue to take quantitative alcohol histories and provide brief intervention to problem drinkers on general medical wards after the introduction of a simple protocol. Regular training in the use of this protocol was stipulated in the annual service contract between the Health Authority and the Hospital Trusts. Improvements in staff practice persisted at 1-year follow-up, although it fell from a peak at an earlier phase of the study. The positive role of state purchasers of health services in sustaining improvements in clinical practice is discussed.

Alcoholism↗
PubMedDate not supplied

Control of tuberculosis in the workplace: engineering controls.

In this review of engineering controls that can be used to check the spread of tuberculosis in health care settings, the authors address types of ventilation and supplements to ventilation such as HEPA filtration and ultraviolet germicidal irradiation. They also specifically cover engineering controls for use during medical procedures that pose an increased risk for transmission of TB.

Environment, Controlled↗
PubMedDate not supplied

The role of blood rheology in regulating blood pressure.

Review of the role of blood rheology in regulating blood pressure discloses that macromolecular binding to the erythrocyte membrane is a significant factor. Evidence is summarized supporting the thesis that blood viscosity is a prime regulator of blood pressure. Macromolecules may bind to erythrocytes and other macromolecules forming structures that increase blood viscosity when the blood stream flow rate is decreased. Review of the nature and extent of RBC membrane binding and a model for relating these bonds to blood pressure are presented.

Aged↗