PubMed Health⌕ Search

Biomedical subjects

G Ranacher

Publications and source records attributed to G Ranacher.

14 recordsLinked to original sources
PubMed1985

[Statistical study of gaze displacement calibration].

The value of quantitative nystagmus analyses depends strongly on the accuracy of the calibration of gaze displacements. Therefore, 120 nystagmograms with one or two controls of the first calibrations (total: 300 calibrations) were evaluated to get a view over the characteristic properties, mainly the variations, of the calibration factors. Systematic and stochastic deviations were taken into account as potential sources of errors. These are mainly ascribed to variations of the corneo-retinal potential and inaccurate visual angles, e.g. as a result of head movements. Statistic evaluation shows no time-dependent variations of the mean and of the standard deviation of the calibration factors. For successive calibrations, relative differences (e2-e1)/e1 were additionally computed. These too, proved to be time-independent, yielding a mean and standard deviation of 2,37 +/- 16,4 %. It can be shown that in 76% of the nystagmograms positive differences are followed by negative ones, and vice versa. In 19% only positive differences and merely in 5% only negative differences were found. It is concluded, therefore, that stochastic variations predominate over the systematic ones. This means that changes in potential are by far of less consequence than patient-induced errors.

Electronystagmography↗
PubMed1979

[Computation of vestibular gain from single fast nystagmus phases (sinusoidal rotatory test) (author's transl)].

A new method for computing vestibular gain for each fast phase of nystagmus is proposed. Dividing amplitude by intersaccadic interval yields an approximative value for slow phase velocity. The ratio of slow phase velocity and simultaneous head velocity gives an estimation of instantaneous vestibular gain. These values are computed for five periods (duration 20 s each) of the sinusoidal rotatory test and the medians (fi) for right and left beating nystagmus resp., are determined. The results of 103 tests are compared with vestibular gain (fk) computed from cumulograms of the slow phases. A linear relation (fi = 8,01 + 0,762.fk, standard deviation si = 4,11%) is found. From this values for vestibular gain determined by these two methods are considered to be well comparable and convertable. As reasons for the non-ideal result of linear regression (compared with fi = fk +/- si) physiological and methodic factors are discussed.

Biophysical Phenomena↗
PubMed1979

[The cumulogram for the sinusoidal rotatory test (author's transl)].

The cumulogram (graphic representation of the cumulative eye position) seems to be a reliable method for studying intensity, symmetry, and regularity of nystagmic responses. Applying sinusoidal rotatory stimulation, the vestibular output can be described in terms of gain and phase difference. The numerical evaluation of cumulograms is demonstrated for sinusoidal tests. The dependence of age is determined for gain and phase difference. While the phase difference appears to be practically independent, the gain of the vestibulo-oculomotor system is strongly correlated with age.

Age Factors↗
PubMed1979

[Nystagmometry and biocybernetics (author's transl)].

Nystagmus can be predicted or simulated by means of mathematical models. If the simulation seems to be successful the parameters of the model may be used for an adequate description of the nystagmic response. Considering the biocybernetics of the vestibulo-oculomotor system a minimal extent of computer-nystagmometry is determined. The efficient application of this method requires the knowledge of standard values for the involved parameters. These values have been determined for tests with sinusoidal rotatory stimulation. Age dependent nominal values can be computed and are compared with actual results. The differences are divided by the standard deviation; values less than 2 are supposed to be normal. Thus a first step of automatic assessment of the vestibular system's function becomes possible.

Adolescent↗
PubMed1979

[Computer analysis of electronystagmograms. First report: the normal pendular test ENG (author's transl)].

In an attempt to standardize the interpretation of electronystagmograms the results of computerized analysis of pendular test nystagmograms have been statistically evaluated. All the nystagmus components show marked dependance on age. The range of normal reactions is determined by means of double standard deviation. The cumulogram of the nystagmus slow phase demonstrates the smallest deviation of all the analysed parameters, and this makes it suitable in the pendular test for diagnostic estimation. The cumulogram provides information on nystagmus slow phase duration, amplitude, symmetry or irregularity.

Computers↗
PubMed1979

[Cumulometry with fast components of nystagmus (author's transl)].

The cumulogram of slow nystagmus phases has proved as a useful method for the analysis of vestibular nystagmus. However, its computation depends on the availability of special apparatuses. Therefore, the relations are studied between the cumulogram of slow phases and the cumulogram of fast phases that can be determined more easily. The analysis of 57 pendular tests shows the close correlation (r = 0,98) of the respective values for vestibular gain. Considering the statistical connection the comparison of these two methods and their results, resp., is well practicable.

Adolescent↗
PubMed1977

[Nystagmus analysis by computer (author's transl)].

Automatic quantitative nystagmus analysis by means of a digital computer primarily gives a lot of data. Analysis then means reducing this amount of numerical data to a few relevant results. Because the diagnostic importance is not known yet for all available nystagmus parameters, this implies the risk of losing essential informations. Therefore, limitations of the number of parameters as well as of the duration of the investigated intervals by the method of analysis have to be avoided. This then allows studying the diagnostic value of new parameters (e.g. of the fast components) or the time course of reaction intensity. From this point of view a method of quantitative nystagmus analysis is described.

Computers↗
PubMed1977

[Duration of postacceleratory nystagmus in theory and experiment (author's transl)].

For special questions the validity of models has to be verified in each case. One possibility for controlling the model of the vestibulo-oculomotor system (completed with a neuronal integrator) which is used for automatic quantitative nystagmus analysis is the duration of the postacceleratory nystagmus. Theoretically for this parameter an upper limit exists which is independent of stimulus strength and influenced only by the system parameters and stimulus duration. Several experimental studies are compared with the theoretical calculations. As a result, the conception of the model is confirmed; however, nystagmus duration appears to be a valuable characteristic only under certain experimental conditions. For this reason, nystagmus duration is not considered as a parameter of the quantitative analysis.

Acceleration↗
PubMed1977

[Comparison of nystagmus responses after thermic stimulation (author's transl)].

A model of the vestibulo-oculomotor system allows theoretical considerations concerning unsymmetrical nystagmus responses. For thermic stimulation unsymmetrics are estimated by means of a commonly used formula for relative differences of reactions. It is shown that the relation between these unsymmetrics and the real change of nystagmus intensity is nonlinear and also different for abnormal decrease and increase of intensity, respectively. Possible misinterpretations are avoided, e.g., by analysis of absolute parameters of nystagmus.

Caloric Tests↗
PubMed1977

[The application of the digital computer in vestibulometry (author's transl)].

All the interesting parameters of nystagmus-reactions during routine vestibular examination are calculated by a digital computer. The new parameters are plotted in a numerical and graphical way. This histogram figure their temporal distribution comparing reactions of both sides and give information about quantitative and qualitative criterions of the ENG. By correlation of parameters with each other and with further clinical findings their diagnostical value is investigated.

Computers↗
PubMed1976

[The velocity of the fast phase of nystagmus].

For the development of a computer program for nystagmus analysis the characteristics of the parameters duration, amplitude and velocity of the fast nystagmus phase were studied as well as their dependence on stimulus intensity. The results show that the duration is constant and not dependent on strength of stimulus. The amplitude was found to be approximately proportional to the velocity in the range of applied intensities but generally an exponential relation is suggested. Examples for evaluations of nystagmograms by means of a computer are shown. The analysis of these parameters is assumed to be of diagnostic importance.

Diagnosis, Computer-Assisted↗
PubMed1975

[Data processing in electronystagmography (author's transl)].

As a method for objective registration of nystagmic responses electronystagmography gives a lot of information about the state of the vestibulo-oculomotor system. Concerning accuracy, reproducibilityand objectivity the commonly used methods for diagnostic interpretation of this material are not quite satisfying. By means of a data acquistion system it is possible to utilize the advantages of the techniques of data processing. In common with fundamental considerations regarding to the choice of the parameters to evaluate the essential parts of the computer-program (calibrations, elimination of interferences, analysis of the fast and slow nystagmic components) are described and examples for the results are shown.

Computers↗