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Biomedical subjects

A Buizza

Publications and source records attributed to A Buizza.

18 recordsLinked to original sources
PubMed1998

Ocular fixation index and mathematical models.

Ocular fixation test and ocular fixation index (OFI) never have been interpreted in terms of mathematical models, despite their widespread diffusion. However, ocular fixation is a typical case of visual-vestibular interaction, and mathematical models have proven very helpful in interpreting some mechanisms of this interaction, e.g. those of the optokinetic-vestibular interaction. In the present paper, a first attempt is proposed toward a model interpretation of OFI. By using very simple mathematical models, the hypothesis is tested that visual suppression of vestibular nystagmus results from direct action of smooth pursuit system (SPS). The aim is to draw consequences and recognize possible limits of this hypothesis. Dependence of OFI on SPS performance is examined. Although the available experimental data are insufficient for comprehensive validation of the model, the results agree with the current interpretations. In particular, quantitative support is given to the sensitivity of OFI to central vestibular diseases. Although the interpretation of visual suppression and OFI in terms of mathematical models is still at a very preliminary stage, models may provide a theoretical reference framework for the interpretation of new experimental results and/or suggest new test protocols.

Fixation, Ocular↗
PubMed1997

Manuo-ocular coordination in target tracking. I. A model simulating human performance.

During eye tracking of a self-moved target, human subjects' performance differs from eye-alone tracking of an external target. Typical latency between target and eye motion onsets is shorter, ocular smooth pursuit (SP) saturation velocity increases and the maximum target motion frequency at which the SP system functions correctly is higher. Based on a previous qualitative model, a quantitative model of the coordination control between the arm motor system and the SP system is presented and evaluated here. The model structure maintains a high level of parallelism with the physiological system. It contains three main parts: the eye motor control (containing a SP branch and a saccadic branch), the arm motor control and the coordination control. The coordination control is achieved via an exchange of information between the arm and the eye sensorimotor systems, mediated by sensory signals (vision, proprioception) and motor command copy. This cross-talk results in improved SP system performance. The model has been computer simulated and the results have been compared with human subjects' behavior observed during previous experiments. The model performance is seen to quantitatively fit data on human subjects.

Hand↗
PubMed1995

The performance of different pressure pulse generators for extracorporeal lithotripsy: a comparison based on commercial lithotripters for kidney stones.

By using needle hydrophones and a PC-controlled experimental set-up, the acoustic output of 10 commercial extracorporeal shock-wave lithotripters has been measured. The pressure field was measured in the focus, along the beam axis, in the focal plane and "at the skin level" (a plane orthogonal to the beam axis, 5 cm backward from the focus, assumed as the entrance site of the pressure pulse into the patient's body). The set of tested instruments included the three technologies nowadays in use to generate the pressure pulse, namely electrohydraulic, electromagnetic and piezoelectric. Notwithstanding large intratechnology variability, the results indicate that electrohydraulic and electromagnetic generators can provide comparable performances. Piezoelectric generators produced pressure pulses with less energy than the others. Possible implications of the experimental results on treatment safety and effectiveness of kidney stone destruction are discussed.

Acoustics↗
PubMed1991

Effects of hydrostatic pressure on sensory discharge in frog semicircular canals.

The effects of endolymphatic and perilymphatic pressure changes on resting and mechanically evoked responses were studied in isolated posterior semicircular canals of the frog. The results demonstrated that ampullar receptors are extremely sensitive to hydrostatic pressure changes (0.25 mm H2O were sufficient to produce distinct changes), being inhibited by endolymphatic pressure increases and facilitated by perilymphatic ones. Intracellular recordings from single afferent axons showed that the effects of hydrostatic pressure result from a modified transmitter release from the synaptic pole of the hair cells. Unlike resting activity, mechanically evoked activity was always depressed in the presence of a hydrostatic pressure. This indicates that the sensitivity of ampullar receptors to mechanical stimuli, i.e. the gain of the conversion process, is maximal when no pressure is present between the inner and the outer fluid. The possible action of hydrostatic pressure on vestibular receptors is discussed.

Afferent Pathways↗
PubMed1990

Expert systems as a diagnostic aid in otoneurology.

Expert systems (ES) are a new tool for information processing developed by the branch of computer science known as artificial intelligence. ES are capable of solving problems in a given domain by using the knowledge and emulating the behaviour of specialists in that field. ES can be used as powerful tools for education since they are able to justify their own conclusions and to make the underlying reasoning explicit. This paper presents 'Vertigo', an ES aimed at the classification and diagnosis of different forms of dizziness. It has been conceived mainly as a teaching tool in otoneurological departments. The rationale of this project, its development, the structure and the use of the system are described. So far, 'Vertigo' has been tested on more than 200 cases of dizziness and is presently being used by ENT residents during their otoneurology stage.

Diagnosis, Computer-Assisted↗
PubMed1988

Cross-coupled effects of repeated vestibular and optokinetic stimulations on the dynamics of the vestibulo-ocular and optokinetic reflexes in the cat.

Cats were submitted to repeated step stimulations either vestibular or optokinetic. Regardless of which of the two stimuli was used, dynamic modifications were observed in both vestibulo-ocular response and optokinetic after-nystagmus (OKAN). The progressive changes in post-rotational nystagmus and OKAN were quantified by measuring the duration of their primary phase. A parallel evolution of these two parameters was found. When repeated unidirectional vestibular stimulations were used, the same asymmetry was induced in both vestibuloocular responses and OKAN. These results support the hypothesis that the vestibulo-ocular and the optokinetic reflex share a common velocity storage mechanism, although alternative hypotheses cannot be excluded.

Animals↗
PubMed1987

[Current computerized support for vestibular function tests. II. An expert system for the classification of vertigo].

A computerized system (VERTIGO) aimed to the classification and diagnosis of different types of vertigo has been developed. It is based on the shell EXPERT (Weiss and Kulikowski, 1979). At present only the findings arising from patient history are considered as input data and the diagnostic possibilities of the system have been limited to the differential diagnosis of vertigo due to peripheral vestibular disorders. About thirty different forms of vertigo are taken into account. They are clustered in two groups, true vertigo and dizziness. Data are collected through a computer controlled questionnaire. Using the facilities offered by EXPERT, the sequence of the questions can be modified according to the flow of information in order to reproduce different diagnostic strategies. After history taking, the system presents a summary of the available findings followed by its diagnostic conclusions. Different conclusions can be proposed with different degrees of certainty. Conclusions can be justified by the system when required.

Adult↗
PubMed1987

[Current computerized support for vestibular function tests.I. Expert systems and their clinical applications].

Expert Systems are a new method developed by the branch of Computer Science known as Artificial Intelligence in order to make available the knowledge and the expertise of the specialists in a certain domain of the science to other operators in the same field. Most of their applications belong to the medical domain. In this paper the main features of the expert systems are briefly described. As an example the structure and the characteristics of the shell EXPERT (Weiss and Kulikowski, 1979) are presented in detail. This shell has already been used to develop several expert systems. It is the tool by which we constructed a consultation system (VERTIGO) aimed to classify different types of vertigo.

Expert Systems↗
PubMed1986

Velocity characteristics of smooth pursuit eye movements to different patterns of target motion.

Horizontal smooth pursuit eye movements were recorded in normal subjects in response to different patterns of target motion that was either periodic or not. Periodic patterns were triangular and sinusoidal waves. Non-periodic patterns were ramps with either constant or sinusoidally varying velocity. In both cases, several different amplitudes and peak velocities were considered. The experimental results indicate that (a) the performance of the smooth pursuit system depends on the spatio-temporal characteristics of target motion, (b) the relationship between smooth pursuit eye velocity and target velocity during the tracking of constant velocity ramps is strongly nonlinear with a saturation depending on the amplitude of target excursion, (c) in the remaining experimental conditions, there is a linear behaviour up to target velocities of 75 deg/s with a gain of about 0.9.

Adult↗
PubMed1985

New experimental data on cat's optokinetic responses. Is there need to revise previous models of the optokinetic reflex?

New data on cat's optokinetic reflex (OKR) provided by Godaux and Vanderkelen (1984) have been interpreted by using a nonlinear model of OKR previously proposed by the authors. A general agreement between experimental data and theoretical predictions was obtained. In particular, the steep decrease of OKR gain observed experimentally at high frequencies appeared as a straightforward consequence of the intrinsic nonlinearity of OKR. In contrast with a recent statement by Gillis et al. (1984), it was concluded that the new data seem to confirm, rather than disprove, previous models of cat's OKR.

Animals↗
PubMed1983

Model interpretation of visual-vestibular interaction in patients with labyrinthine and cerebellar pathologies.

Oculomotor responses to combined optokinetic and vestibular stimulations in labyrinthine and cerebellar defective patients are discussed in terms of parametric changes in a model describing the interaction between the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR). By making a few reasonable hypotheses about model parameter variations in relation to the type of pathology, the experimental results obtained by several authors can correctly be predicted and explained by the model. The model can therefore be used to define a set of parameters giving an estimate of the state of the system subserving VOR-OKR interaction in the examined patients. The model is also shown to be a powerful tool to assess the validity and the diagnostic significance of the procedures used to test VOR-OKR interaction.

Cerebellum↗
PubMed1982

Visual-vestibular interaction in the control of eye movement: mathematical modelling and computer simulation.

After a brief description of the main anatomical structures subserving the oculomotor responses during combined vestibular and optokinetic stimulations, a mathematical model is presented. With respect to a previous model by Schmid et al. (1980), a more accurate definition of the roles of the neural mechanisms involved in oculomotor control in different conditions of visual-vestibular interaction is given. The model is proved to be able to predict not only oculomotor responses, but also single unit average responses in the vestibular nuclei and in the vestibulo-cerebellum. Experimental data available in the literature on monkeys and cats are used for model validation.

Animals↗
PubMed1980

Influence of otolithic stimulation by horizontal linear acceleration on optokinetic nystagmus and visual motion perception.

Several studies in the past have demonstrated the existence of an Otolith-Ocular Reflex (OOR) in man, although much less sensitive than canal ocular reflex. The present paper 1 confirms these previous results. Nystagmic eye movements (L-nystagmus) appear in the seated subject during horizontal acceleration along the interaural axis in the dark for an acceleration level (1 m/s2) about ten times the perception threshold with a sensitivity of about 0.035 rad/m. When sinusoidal linear acceleration is combined with optokinetic stimulation, the recorded nystagmus slow phase velocity exhibits strong periodic modulation related to subject motion. This marked effect of linear acceleration on the optokinetic nystagmus (OKN) appears at a level (0.1 m/s2) close to the acceleration perception threshold and has a 4-fold higher sensitivity than L-nystagmus. Modulation of OKN can reach a peak-to-peak amplitude as great as 20 degrees/s for a given optokinetic field size it increases with the velocity of the optokinetic stimulus, i.e. with the slow phase eye velocity. In parallel with changes in OKN slow phase velocity, linear acceleration induces a motion related decrease in the perceived velocity of the visual scene and modifications in self-motion perception. The results are interpreted in terms of a mathematical model of visual-vestibular interaction. They show that sensory interaction processes can magnify the contribution given to the control of eye movements by the otolithic system and provide a way of exploring its function at low levels of acceleration.

Acceleration↗
PubMed1980

A non-linear model for visual-vestibular interaction during body rotation in man.

A mathematical model for visual-vestibular interaction during body rotation in an illuminated visual surround is obtained by combining a previous model of the optokinetic reflex (OKR) with a simplified model of the vestibulo-ocular reflex (VOR). OKR is activated by the slip of the image of the external world on the retina, and represents a negative feedback loop around VOR. For large retinal slip velocities OKR behaves as a basically non-linear system. The validity of the model is proved via computer simulation by comparing predicted responses with the experimental results obtained in man by Koenig et al. (1978) in different situations of visual-vestibular interaction.

Eye Movements↗
PubMed1979

Otolithic-acoustic interaction in the control of eye movement.

In order to examine otolithic contribution to eye movements ten subjects were asked to track either a moving acoustic target or a stationary target during subject linear motion on a cart. The relative displacement between the subject and the target was the same in the two situations. Recordings of eye movements during subject lateral acceleration in the dark without any task, or with the task of tracking an imagined stationary target were made as a control. The frequencies ranged between 0.15 and 0.3 Hz and peak acceleration between 0.55 and 1.2 m/s2. No lateral eye movements (L-nystagmus) were recorded in the dark. Only saccadic eye movements were recorded during the tracking of a moving acoustic target. Slow eye movements interspersed by saccades were observed when the moving subject tracked an imagined or an acoustic stationary target. Contribution of the slow phase to tracking was more important in the presence of an acoustic target than in the presence of imagined target. The results are interpreted in terms of an otolithic contribution to the central reconstruction of the acoustic target velocity, or in terms of an adaptive control of the otolithic-ocular reflex gain. A conceptual model accounting for these interpretations is proposed.

Acoustic Maculae↗
PubMed1978

Quantification of vestibular nystagmus by an interactive computer program.

An interactive program for the analysis of nystagmus is presented, and some results obtained by processing postrotational responses are reported. The program is provided with a special subroutine which gives a quantification of the rhythm and regularity of the response through the histograms of the ratios between the duration of successive intersaccadic intervals and between the amplitudes of successive fast components. The consideration of these histograms has been proved to be highly significant in discriminating between normal and pathological responses.

Analog-Digital Conversion↗
PubMedDate not supplied

Harmonic versus impulsive acceleration testing of the vestibulo-ocular reflex in normal humans.

Vestibulo-ocular reflex (VOR) was tested in 9 normal humans by using both harmonic (sinusoidal) and impulsive (post-rotatory) angular accelerations. VOR gain and main time constant were 0.49 +/- 0.20 and 15.48 +/- 2.26 s, respectively, when computed from sinusoidal responses, 0.45 +/- 0.17 and 14.28 +/- 3.07 s when computed from impulse responses. Paired comparison could not prove statistically significant differences between the two sets of data. The conclusion is drawn that, in normals, equivalent information about VOR static and dynamic characteristics can be derived from either harmonic acceleration or post-rotatory tests.

Acceleration↗