ABSTRACT
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.
Subject(s)
Animals, Newborn/physiology , Atrioventricular Node/physiology , Electrocardiography , Heart/physiology , Animals , Mice , Organ Size , Reproducibility of Results , Signal Transduction/physiologyABSTRACT
The body proportions in 191 individuals with Turner syndrome (TS) were investigated. At 3 years of age the mean sitting height in TS was normal, thereafter trunk growth was impaired, resulting in a standard deviation score (SDS) of -2.4 in the adult. From 3 to 12 years of age the mean SDS of leg length increased from -2.7 to -3.6; and then fell to -2.5. At 3 years of age the ratio of sitting height to leg length was 3.2 standard deviations (SD) above the normal mean. Thereafter the ratio slowly approached the normal percentiles. It was +0.6 SD in 15- to 18-year-old women. Thereafter it increased to 1.7 for adults with TS. Knemometric measurements in 32 individuals with TS and 32 controls revealed that in TS the upper legs were relatively shorter than the lower legs. We conclude that children with TS, and to a lesser extent adults, have a disproportionately short stature with relatively short legs whereas body proportions are almost normal in adolescents.
Subject(s)
Somatotypes , Turner Syndrome/pathology , Adolescent , Adult , Anthropometry , Child , Child, Preschool , Female , Growth , Humans , Karyotyping , Turner Syndrome/genetics , Turner Syndrome/physiopathologyABSTRACT
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.
Subject(s)
Flicker Fusion/physiology , Humans , Photic Stimulation , Psychophysics , Sensory ThresholdsABSTRACT
In the museum world, designers in general hardly take into account the legitimate wishes of elderly visitors, whose visual acuity is often less than optimal, with regard to the legibility of the captions by paintings or in show-cases. The conditions necessary for letter and word recognition, the influence of illumination, contrast and colour are discussed. Test-cards for use in musea, and the recruiting of a representative test-group of senior citizens, are recommended.
Subject(s)
Museums , Reading , Age Factors , Lighting , Sensory AidsABSTRACT
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).
Subject(s)
Evoked Potentials, Visual , Models, Biological , Differential Threshold , Humans , Photic Stimulation , Reaction TimeABSTRACT
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.
