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Biomedical subjects

E L de Beer

Publications and source records attributed to E L de Beer.

23 records · Page 2Linked to original sources
PubMed1977

The combined influence of the stimulus frequency of the vagal nerves and the atrial stimulus interval on the atrioventricular conduction time.

The way in which the A-V node adapts its conduction time to stepwise alterations of atrial stimulation rates was studied under different conditions of vagal nerve activity (open chest, anaesthetised rabbit). Increase of stimulation rate induced oscillatory adaptation to a longer conduction time. Decrease caused shorter conduction times without oscillation. The time constant did not differ. Oscillation amplitude and time constants were markedly influenced by vagal activity. The observed phenomena can be explained on the basis of a time and voltage dependent K+ conductance.

Animals↗
PubMed1976

A note on the phase-plane technique representation of cardiac action potentials.

In this study the applicability of the phase-plane technique for interpreting membrane properties of cardiac cells in a two-dimensional structure is discussed. The conditions are derived for which the effects of two-dimensionality of a sheet can be neglected and for which the one-dimensional phase-plane technique for estimation of the membrane current densities remains valid. The usual phase-plane technique appears to be applicable to nodal and atrial tissue.

Action Potentials↗
PubMedDate not supplied

The effect of controlled changes in volume on the active state of the rabbit isolated left ventricle.

The contractile properties of isovolumically contracting isolated rabbit left ventricles are studied under the influence of controlled rapid volume changes during systole and diastole. The time integral of the pressure curve (TTI), representing the active state, is used to quantify the energy consumption of the ventricle. Steady state conditions resulting from an introduced volume change show a TTI/EDV relation which represents the Starling curve. However, immediately after a quick volume increase (decrease) introduced in diastole, the TTI/EDV ratio has a higher (lower) value than indicated by the Starling relation. This shows a volume dependent activation (deactivation), related to changes in the inotropic state of the heart muscle cells within the ventricular wall. A volume increase at a later moment (in systole) always produces a lower rate of activation. Indeed, if the rapid volume change is introduced at moments later than 70% of time to peak pressure, TTI is less than observed from the Starling mechanism, indicating a deactivation. When comparing the decreasing effect on the active state introduced by volume decrease during systole, it is shown that this effect is not only a function of the amplitude of the decrease itself but is highly dependent upon the way EDV is reached.

Animals↗
PubMedDate not supplied

Effect of sarcomere length and filament lattice spacing on force development in skinned cardiac and skeletal muscle preparations from the rabbit.

Skinned cardiac and skeletal muscle freeze-dried preparations were activated in solutions strongly buffered for Ca2+. The response of single skeletal muscle fibres or thin strips of papillary muscle was investigated in relation to changes in Ca content of the perfusate. Sarcomere length was set and controlled during the experiments. The relation between the negative logarithm of the Ca concentration, the pCa, and the normalized developed force proved to be sigmoidal. The exact position of these curves proved to be dependent upon both sarcomere length and the distance between the filaments. The latter was shown by means of osmotic compression of the fibres using dextran. As a consequence of these observations, it was concluded that the length-tension relation is dependent upon the actual Ca concentration. The results are discussed in terms of cross-bridge interaction.

Animals↗