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Biomedical subjects

L H van der Tweel

Publications and source records attributed to L H van der Tweel.

At least 19 recordsLinked to original sources
PubMed1999

ECG of the "newborn" mouse (Mus domesticus) with specific reference to comparative AV transmission.

INTRODUCTION: The objective of this study was to record the ECG of the smallest living mammal to extend the domain of data for comparative AV nodal electrophysiologic purposes. These data are needed to establish the relationship between the PR interval and heart size in mammalian species of all sizes. METHODS AND RESULTS: In recently born mice (age 1.5 to 8 weeks) weighing between 2.5 and 10 g and with estimated heart weights between 15 and 60 mg, ECGs, using bipolar limb leads, were recorded during general anesthesia. The PR interval, representing AV transmission time was about 40 msec, which is quite long for hearts of this size. On the basis of detailed analysis of the data, we postulate the presence of a fixed delay or discontinuous propagation in the AV node not only in newborn mice, but in mammals of all sizes. CONCLUSION: AV transmission times obtained in mammals (including humans) cannot be explained on the basis of generally accepted, classic AV conduction theories. The acceptance of the presence of a fixed delay in the AV node may ultimately be of value to better understand AV node function during sinus rhythm and supraventricular arrhythmias.

Animals↗
PubMed1992

Counterphase dichoptic flicker is seen as its own second harmonic.

If a patternless field is modulated sinusoidally in time so that the luminance change in one eye is in counterphase to that in the other, the resulting flicker appears faster than if the modulation to both eyes has the same phase. If observers set the frequency and the amplitude of a comparison in-phase field so that it matches a neighbouring counterphase field, modulated at, say, 2.5 x its threshold, they set the frequency to twice the counterphase frequency, and the amplitude to a value that is, for a given frequency, a constant ratio of the modulation of the counterphase field. Counterphase stimulation thus appears to cause an internal second-harmonic signal. However, it is not possible to cancel this by adding a second harmonic component to the stimulus.

Flicker Fusion↗
PubMed1985

Evoked potential latencies as a function of contrast: a system analytical approach.

That the latency of the pattern evoked potential (EP) increases as the stimulus contrast decreases can be understood as the result of, first, a low-pass filtering process of the (contrast) signal followed by, second, and nonlinear 'threshold' stage. We show here that by using this simple concept it is possible to estimate the shape of the 'unit step' response of the low-pass filter with the latency vs. contrast data. We show also that the step responses calculated from several subjects are in reasonable agreement if they are normalized with using the subjects' own contrast thresholds. Within experimental error, the response of a filter consisting of four low-pass first-order stages with a 10.5 Hz cut-off frequency gives a reasonable fit to our own data and to that of one other study (Musselwhite and Jeffreys, 1982).

Differential Threshold↗
PubMed1982

A displacement servosystem for muscle research permitting 50 micrometers length changes within 40 microseconds.

In order to determine the tension response of a stimulated intact muscle fibre to a very fast length change a servo system has been developed capable of imposing a displacement of 50 micrometers i.e. about 1% of the fibre length, within 40 microseconds. The system is designed so as to limit the displacement overshoot to less then 1%. This paper presents the performance of the system: both unloaded and loaded with a muscle fibre.

Animals↗