Search PubMed⌕ Search

Biomedical subjects

M L McNeel

Publications and source records attributed to M L McNeel.

8 recordsLinked to original sources
PubMed1982

Life expectancy and causes of death in a group of head-injured veterans of World War I.

The life spans and causes of death were examined for a group of Bavarian veterans of World War I who had suffered head injuries and for comparable control subjects who had not. The occurrence of posttraumatic fits was a significant prognostic factor for a higher death rate after the age of 50 years. Other indicators of the severity of injury did not lead to differences in the death rates. There were significantly more deaths due to cerebrovascular causes in the head-injured group than in the control group, but no subgroup was found to have significantly more cerebrovascular deaths than any other.

Adult↗
PubMed1973

Determinants of time-dependent membrane conductance. The nonrole of classical ion-membrane molecule interactions.

We have examined the steady-state and time-dependent electrical properties of a model membrane system. The model assumes that the directed velocity and energy of ions moving through the membrane are determined by the applied electric field, ionic diffusion forces, and central elastic collisions between ions and membrane molecules. A simple analysis of the steady-state electrical properties of the model yields results identical with ones obtained previously using a more complex analysis procedure. The time-dependent conductance changes of the model in response to a step change in electric field strength when there is solution symmetry display three qualitative patterns dependent on the nature of the ion-membrane molecule interaction. One of the patterns of conductance change is quite similar to that observed in the sodium conductance system of a number of excitable tissues: an initial conductance rise to a maximum (activation) followed by a decay to a final steady-state value (inactivation). However, the correspondence between the time-dependent model behavior and known experimental behavior of excitable systems is only qualitative. We conclude that the classical ion-membrane molecule interactions we consider are not involved in determining time-dependent conductance processes in the excitable systems for which comparison is possible.

Biological Transport↗
PubMed1971

Kinetic theory model for ion movement through biological membranes. 3. Steady-state electrical properties with solution asymmetry.

An electrodiffusion model for plasma membrane ion transport, which takes into account the influence of high electric field strengths and ion-membrane molecule interactions, is presented and analyzed. A generalized Nernst-Planck equation for steady-state situations is derived which has electric field-dependent mobility and diffusion coefficients. Under the assumption of a constant electric field within the membrane, this equation is integrated to give a more general form of the Goldman equation. Based on this equation numerical computations of ionic chord conductance as a function of applied electric field strength were carried out for several permeant ion concentration ratios. The model is capable of yielding significantly larger rectification ratios than is the Goldman equation. Further, high field asymptotes to the current vs. electric field strength curve do not generally intersect at the origin.

Biological Transport↗
PubMed1971

The independence principle. A reconsideration.

The electrodiffusion model presented in the previous paper, which specifically excludes ion-ion interactions, is analyzed for the ratio of one-way fluxes (flux ratio) as a function of the ionic driving force across the membrane. Significant deviations from the behavior expected on the basis of the Ussing relation are found. These are sufficient to explain the "nonindependent" ion movement noted in some biological flux ratio data. One-way fluxes are dependent on the ionic concentration on both sides of the membrane. The coupling of these fluxes to ionic concentrations comes from the dependence of ionic mobility and the diffusion coefficient on the equilibrium potential. It is concluded that nonindependent behavior in experimental data is not sufficient to implicate ion-ion interaction as the source of the discrepancy.

Biological Transport↗