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Y Mahler

Publications and source records attributed to Y Mahler.

At least 37 records · Page 2Linked to original sources
PubMed1987

A three-level amplitude discriminator for the separation of multi-unit electrophysiological information.

A device is described that consists of two parallel, three-level differential amplitude discriminators suitable for the selection of electrophysiological data. The present device has been designed for simplicity of construction and operation. The unit allows for a visualisation of the selected levels in precise relationship to the input signal oscilloscope channel. The design eliminates the possibility that a lower level will exceed a higher level. The resulting ease with which complex multi-unit electrophysiological data may be discriminated for analysis using the three digital reference level outputs, makes this instrument suitable for a wide range of electrophysiological experiments.

Electrophysiology↗
PubMed1985

Model of mechanical alternans in the mammalian myocardium.

A model is proposed to elucidate the cause and mechanism of mechanical alternans in cardiac muscle in terms of discrete calcium movements. Mechanical alternans, the cause of which lies within the borders of excitation-contraction-coupling (ECC), is analyzed. In this case, the "input" of the ECC system (the action potentials and intervals) is constant while the "output" (contractile force) oscillates between two constant values, indicating that the system has a "memory" with two "internal states". It is proposed that these two "states" are associated with a part of the sarcoplasmic reticulum ("releasable terminal") containing the readily releasable calcium. A mechanism of "calcium-concentration-dependent threshold" is suggested to govern the "release function", i.e. the release of calcium from the "releasable terminal" to the myofilaments. The "release function" is analyzed in both the linear and the non-linear cases and its implication on the initiation of sustained and transient mechanical alternans are described. The dependence of mechanical alternans on a disturbance is also explained. The model response resembles the experimental observations of mechanical alternans in mammalian myocardium in the following manners: abrupt transition from low to high heart rates, slow progressive acceleration of rate, variations in persistence at subthreshold rates, effect of premature and delayed beat following the small and large beats, restitution curves, and transient mechanical alternans initiated by a delayed beat.

Animals↗
PubMed1985

Model of calcium movements in the mammalian myocardium: interval-strength relationship.

A model is proposed to describe the interval-strength relationship in mammalian cardiac muscle in terms of "discrete" calcium movements associated with each cycle. The sarcoplasmic reticulum is assumed to be comprised of three functional sub-compartments: (1) The "main calcium store" which contains most of the calcium (predominantly bound) and is considered, due to its large buffering capacity, to account for the "long-term memory" lasting 7-10 beats. (2) The "releasable terminal" which contains the calcium readily available for release (all or most of it free) and accounts for the "short-term memory" which affects the subsequent beat. (3) The longitudinal network of the SR recirculating the myofibrillar calcium to the "main calcium store". The total content of calcium in the main store is determined by the transsarcolemmal influx and efflux. While influx occurs only during depolarization, efflux occurs during the whole cardiac cycle. The amount of free calcium in the main store is determined by an equilibrium equation. The release of calcium from the "releasable terminal" is governed by a "concentration-dependent" mechanism. This implies that when the concentration in the "releasable terminal" increases, the fraction released increases and the residual calcium left for the subsequent contraction decreases. The model predicts the following interval-strength relationships: steady state peak tension; changes from one steady rate to another; restitution curves; post-stimulation potentiation; paired stimulation; premature beats; post-extrasystolic potentiation following interpolated, basal or complimentary interval.

Animals↗
PubMed1985

Transient heat clearance method for regional blood flow measurements.

A method for assessing regional blood flow by transient heat clearance is described. A probe at room temperature is attached to the tissue which is to be investigated and the temperature of the probe is thereby decreased. The time constants which describe the increases in tissue temperature as the temperature approaches equilibrium temperature are related to blood flow. Regional blood flow can be determined by the method of transient heat clearance without calibration.

Body Temperature Regulation↗
PubMed1984

Flow-pressure relationship in perfusion studies of the living primate eye.

Anterior chamber constant rate perfusion studies were performed in normal living monkey eyes. On careful inspection, the IOP-flow relation was seen to consist of a three stage curve. In the low range of infusions (0-6 microliters/min) IOP raised linearly. In the middle range (6-12 microliters/min) it remained almost constant and raised, again with high infusion rates (12-25 microliters/min). Calculating outflow facility from this pressure-flow relationship, it was shown that C value was constant in the low infusion range, increased in the middle range and decreased slowly over the high infusion rate range. A comparison was made with a similar curve derived from flow of fluids through non completely collapsible tubes. The change of IOP following high infusion rates consisted of a decrease in the steady-state pressures achieved. Comparison with formerly observed close phenomena was made and some thoughts about possible causes were brought.

Animals↗
PubMed1983

Electroconductivity of bone in vitro and in vivo.

In view of conflicting data in the literature regarding the electroconductivity of bone, measurements were performed both in vivo and in vitro by using alternating current of 100.0 mA and 1.0 mA at a frequency of 1000 cycles/second and the four-electrode method. Electrodes were inserted through all of the bone layers into the bone marrow space of the femora of seven rabbits. Bone electric resistance was measured also in situ 30 minutes after the death of the animals. A threefold increase in resistance of bone, from about 600 to about 1700 ohm, occurred in situ 30 minutes after the death of the animals, and an enormous resistance, about 10(10) ohm, was measured in vitro. It was also apparent that femora from the different rabbits had different values of electric resistance both in vivo and in vitro. If electroconductivity of bone is determined by body fluids rather than by the bone tissue per se, measuring the "specific resistance" of bone in vivo is meaningless.

Animals↗
PubMed1980

Electroconductivity of collagen in vitro and in vivo.

Electrical conductivity was measured on thermally reconstituted collagen fibers in vitro and on isolated rat tail tendon collagen fiber bundles in vivo. The results obtained indicated that collagen per se is not an electroconductor under physiological conditions, but rather a biological insulator.

Animals↗
PubMed1980

Automated processing of dynamic properties of intraventricular pressure by computer program and electronic circuit.

A procedure for automatic detection and digital processing of the maximum first derivative of the intraventricular pressure (dp/dtmax), time to dp/dtmax(t - dp/dt) and beat-to-beat intervals have been developed. The procedure integrates simple electronic circuits with a short program using a simple algorithm for the detection of the points of interest. The tasks of differentiating the pressure signal and detecting the onset of contraction were done by electronics, while the tasks of finding the values of dp/dtmax, t - dp/dt, beat-to-beat intervals and all computations needed were done by software. Software/hardware 'trade off' considerations and the accuracy and reliability of the system are discussed.

Analog-Digital Conversion↗