Extraction of traditional COP-based features from COM sway in postural stability evaluation.

Postural control during quiet standing is evaluated by analyzing CoP sway, easily measured using a force platform. However, recent proliferation of motion tracking systems made easily available an estimate of the CoM location. Traditional CoP-based measures presented in literature provide information about age-related changes in postural stability and fall risk. We investigated, on an age-matched group of subjects, the relationship between classical CoP-based measures computed on sway path and statistical mechanics parameters on diffusion plot, with those extracted from CoM time-series. Our purpose is to understand which of these parameters, computed on CoM sway, can discriminate postural abnormalities, in order to use a video tracking system to evaluate balance in addition to motor capabilities.

Affordable, automatic quantitative fall risk assessment based on clinical balance scales and Kinect data.

The problem of a correct fall risk assessment is becoming more and more critical with the ageing of the population. In spite of the available approaches allowing a quantitative analysis of the human movement control system's performance, the clinical assessment and diagnostic approach to fall risk assessment still relies mostly on non-quantitative exams, such as clinical scales. This work documents our current effort to develop a novel method to assess balance control abilities through a system implementing an automatic evaluation of exercises drawn from balance assessment scales. Our aim is to overcome the classical limits characterizing these scales i.e. limited granularity and inter-/intra-examiner reliability, to obtain objective scores and more detailed information allowing to predict fall risk. We used Microsoft Kinect to record subjects' movements while performing challenging exercises drawn from clinical balance scales. We then computed a set of parameters quantifying the execution of the exercises and fed them to a supervised classifier to perform a classification based on the clinical score. We obtained a good accuracy (~82%) and especially a high sensitivity (~83%).

Measurement on Tinetti test: instrumentation and procedures.

A measurement system and associate signal processing procedures for quantifying subject's performance during the performance-oriented assessment of balance as defined in Tinetti test (TT) is described. It is based on two inclinometers measuring trunk inclination in two orthogonal planes. Signals from the transducers are acquired by a PC through A/DC board. Signal processing consists in computing morphological parameters describing the main features of subject movement during the different TT maneuvers. The system is simple, cheap, user friendly, causes no discomfort to the patient and can easily be modified to comply with either new requirements or the needs of other performance tests dealing with trunk movement. Preliminary results of measurements on both normals and patients suggest the viability of this approach and the possibility of discriminating normal from abnormal performance, based on the values of the morphological parameters.

Effects of caloric stimuli on frog ampullar receptors.

The observation that caloric nystagmus can be evoked even in microgravity conditions argues against Barany's convective theory. To justify this result, gravity-independent mechanisms (mainly endolymphatic volume changes and direct action of the temperature on vestibular sensors) are believed to contribute to caloric-induced activation of vestibular receptors. To define the importance of both gravity-dependent and gravity-independent mechanisms, the posterior semicircular canal of the frog was thermally stimulated by a microthermistor positioned close to the sensory organ. The stimulus produced a gravity-dependent transcupular pressure difference that, depending on the position of the heater, could result in either excitation or inhibition of ampullar receptor sensory discharge. When the heater was positioned on the ampulla, or when the canal rested on the horizontal plane, no responses could be evoked by thermal stimuli. These results suggest that, in our experimental conditions (DeltaT up to 1.5 degrees C), neither a thermally induced expansion of the endolymph nor a direct action of the temperature on vestibular sensors play any major role.

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.

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.

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.

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.

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.

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.

[Current computerized support for vestibular function tests. II. An expert system for the classification of vertigo]. / Nouveaux supports informatisés à l'exploration de la fonction vestibulaire. II. Un système expert pour la classification des vertiges.

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.

[Current computerized support for vestibular function tests.I. Expert systems and their clinical applications]. / Nouveaux supports informatisés à l'exploration de la fonction vestibulaire. I. Les systèmes experts et leurs applications cliniques.

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.

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.

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.

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.

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.

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.