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Biomedical subjects

F Honegger

Publications and source records attributed to F Honegger.

33 records · Page 2Linked to original sources
PubMed1993

Synergies and strategies underlying normal and vestibulary deficient control of balance: implication for neuroprosthetic control.

Future developments of neuroprosthetic control will probably permit locomotion and posture to be maintained without the aid of crutches and will therefore require some form of balance control. Three fundamental questions will arise. First, the question of the location of imbalance-sensing transducers must be assessed. Secondly, the synergy, which is the relative amplitude and timing of muscle activity, and/or the strategy of joint torques required to re-establish a stable posture for different types of balance disturbances must be addressed. Thirdly, the control laws that map either trunk muscle activity or imbalance-sensing transducer outputs into multi-joint postural control of standing by paraplegic individuals must be generated. The most appropriate means of gathering the relevant information applicable to neuroprosthetic control systems is through the detailed analysis of normal and non-normal human models. In order to gain such detailed insights into normal balance control and its dependence on head angular and linear accelerations, the synergy and strategy of balance corrections in normal subjects or patients with vestibular deficits were investigated for two types of support surface perturbation, a dorsiflexion rotation (ROT) and a rearward translation (TRANS). These experimentally induced perturbations to upright stance were adjusted to cause equal amplitudes of ankle dorsiflexion, thus providing additional information about the role of lower leg proprioception on balance control. Synergies defined on the basis of peak cross-correlations of each recorded muscle's EMG to that of the largest muscle response were significantly different for TRANS and ROT. Translation synergies consisted of a sequential coactivation at several levels (soleus and abdominals some 30 msec before hamstrings, and trapezius some 15 msec before paraspinals), whereas the sequential activation of paraspinals and tibialis anterior dominated the balance synergy to ROT. Likewise, response strategies, defined using cross-correlations of joint torques, differed. That for TRANS was organised as a multi-link strategy with neck torques leading those of all other joints by 40 msec or more; hip joint lead ankle torques by 30 msec. That for ROT was organised around hip and ankle torques without a major correlation to neck torques. Vestibulary deficient subjects developed weaker synergies with respect to subjects with normal balance systems under eyes-open conditions and there was no clear synergy with eyes closed. Consequently, hip torques were delayed some 180 msec with respect to ankle torques, and correlations to neck torques were completely out of phase under eyes-closed conditions. Fundamental changes in TRANS synergies and strategies also occurred in vestibulary deficient subjects for eyes-open and eyes-closed conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Ankle↗
PubMed1993

Vestibular and proprioceptive modulation of postural synergies in normal subjects.

One way of investigating different muscle synergies underlying human balance control is to assume that only 1 or 2 centrally preprogrammed synergies are available to reestablish upright stance when it is perturbed. According to this hypothesis, the many, apparently different, synergies elicited by rotation or translation of a support-surface on which test subjects stand, in fact, result from a modulation of muscle responses induced by different amplitudes of afferent inputs. To test this hypothesis, we probed the balance control of 16 normal subjects with 5 combinations of rotation and translation of the support surface. Each combination yielded a constant angle (3 or 4 degrees) and angular velocity (18 and 36 degrees/s, respectively) over the first 120 ms of ankle dorsiflexion but resulted in differing velocities of upper leg, trunk, and head movements. These first 120 ms of link movements and the resulting muscle responses were analysed for amplitude and timing modulation using 3 techniques. First, velocities of initial link movements and areas of muscle EMG activity were examined separately for the minimum number of descriptors, which would optimally describe the linear variation of the interlink amplitude synergy with respect to the amount of support-surface rotation or translation employed to perturb balance. Initial trunk angular velocity, which was highly correlated with head linear acceleration (r = 0.9), provided the first best descriptor of initial link movements. Ankle angular velocity provided the second descriptor because it was not correlated with trunk angular velocity. The amplitude modulation synergy of EMG responses could be characterised by the modulation of tibialis anterior and paraspinal muscles between 160 and 240 ms and by that of soleus between 80 and 120 ms after stimulus onset. The linear combination of these best descriptors of link movements and that for EMG response amplitudes changed continuously in an identical manner with changes in the stimulus combination. Second, multivariate linear correlations between the amplitudes of initial link velocities and muscle EMG response areas best describing the response amplitude synergy were examined. Several significant correlations (r > 0.6) were obtained between leg and trunk muscle activity 120 ms after stimulus onset and trunk, or upper leg angular velocity, or head linear velocity, prior to 120 ms. Finally, crosscorrelations between muscle responses were examined for consistent interlink timing synergies between muscle responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1993

Predictors of less stable postural responses to support surface rotations in healthy human elderly.

Balance corrections elicited in response to a rotation of the support-surface were compared between healthy elderly and young normal subjects using surface EMG records from the soleus, tibialis anterior, and neck extensor muscles, and measurements of trunk angular acceleration and ankle torque. Three differences were observed. First, EMG response latencies were significantly longer in the elderly. Second, the normal linear correlation between stabilizing ankle muscle activity and ankle torque was disturbed. These two differences were presumably responsible for the diminished ankle torque exerted on the support surface by the elderly subjects. Third, the magnitude of neck muscle activation was increased in elderly subjects, indicating an increased compensation at the head for trunk angular acceleration. The findings suggest that there are both neural and mechanical changes that may impact on postural corrections in elderly subjects, and that more than one factor needs to be identified when predicting an individual's risk for falling.

Adolescent↗
PubMed1992

A postural model of balance-correcting movement strategies.

The patterns of joint torques and movement strategies underlying human balance corrections were examined using a postural model. Two types of support-surface perturbation, dorsiflexion rotation (ROT) and rearward translation (TRANS), were employed. These two perturbations were adjusted to produce similar profiles of ankle dorsiflexion in order to obtain information on the role of lower leg proprioceptive inputs on triggering balance corrections. In addition, the dependence of balance control on head angular and linear accelerations was investigated by comparing the responses of normal and vestibularly deficient subjects under eyes-closed and eyes-open conditions. Differences in ROT and TRANS movement strategies were examined in three ways First, the amplitude and polarity of active joint torques were analysed. These were obtained by altering joint torques applied to a postural model until movements of the model accurately duplicated those of measured responses. Second, the pattern of body-segment angular movements depicted by stick figures moving in response to the computed joint torques was investigated. Third, the peak amplitude and patterns of crosscorrelations between joint torques were measured. Active ankle, knee, and hip joint torques computed for normal subjects rotated the body forward for ROT. In the case of TRANS, computed active torques in normals were of opposite polarity to those of ROT and reversed the forward motion of the body. Subjects with vestibular deficits had lower amplitude torques for ROT and failed to counter the platform rotation. Hip torques for TRANS in vestibular deficient subjects were of opposite polarity to those of normal subjects and resulted in excessive forward trunk rotation. Normally, neck torques acted to stabilize the head in space when trunk angular velocity peaked. Vestibular deficient subjects displayed head movements in response to ROT similar to those generated when neck torques were absent. For TRANS, these same subjects exhibited overcompensatory neck torques. Stick figures of normal responses indicated a stiffening of the body into a leg and a trunk-head link for ROT and a flexible multilink motion for TRANS. Likewise, normal response strategies, defined by using crosscorrelations of joint torques, differed for ROT and TRANS. All joint torque crosscorrelations were significant for TRANS. Neck torques led those of all other joint torques by 40 ms or more, and hip joint led ankle torques by 30 ms. Joint torque correlations for ROT were organised around hip and ankle torques without a major correlation to neck torques. Fundamental changes in all torque crosscorrelations occurred for vestibularly deficient subjects under both eyes-open and eyes-closed conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Biomechanical Phenomena↗
PubMed1992

[New indications for the rotating chair test for side localization and determination of central compensation in vestibular function disorder].

The horizontal vestibulo-ocular reflex was studied in normals and 35 patients with an acute or compensated unilateral peripheral vestibular deficit (PVD) in order to determine the efficacy of different response measures obtained from a rotating chair test in localizing the deficit side and defining its central compensation. The profiles of chair velocity and the visual fixation period were chosen in such a way that the slow phase velocity profiles were comparable to those obtained during caloric tests. Mean slow phase eye velocity measured during the culmination period elicited by constant chair acceleration of 5 degrees/s2 over 40 s was significantly reduced for rotations towards the side of an acute or compensated PVD. Per-rotatory gain asymmetry (after correcting for spontaneous nystagmus) was not always specific for the side of the deficit and often not significantly different from normal values in the compensated stage of the deficit. In combination both parameters (SPV and gain asymmetry) were reliable indicators (sensitivity 88%) of the underlying pathology and correctly localized the deficit side during the compensated state. The decay of post rotatory SPV followed a more rapid time course than normal during acute and compensated stages of the deficit. It may be concluded from those results that the rotating chair test is a valuable indicator of the presence and side of a peripheral vestibular deficit even when it has been centrally compensated.

Caloric Tests↗
PubMed1991

Documentation of the recovery course and deficit side localization of an acute unilateral vestibular deficit using four-quadrant diagrams of slow phase velocity.

The horizontal vestibulo-ocular reflex was studied in normals and in patients with an acute or compensated unilateral peripheral vestibular deficit (PVD) in order to determine the efficacy of various response measures of deficit side and central compensation for high rotation velocities. The profiles of whole body rotation and the visual fixation period was chosen to yield slow phase velocity (SPV) profiles comparable with those obtained with caloric irrigation. The chair rotation direction producing the smaller amplitude of slow phase velocity measured over culmination period obtained with 40 s of 5 degrees/s2 constant acceleration to 200 degrees/s represented a lateralizing sign of all acute, and 85% of all compensated PVD cases.

Acute Disease↗
PubMed1991

Classification of peripheral and central (pontine infarction) vestibular deficits. Selection of a neuro-otological test battery using discriminant analysis.

The results obtained from a complete neuro-otological test battery were examined statistically in order to select measurement variables which would optimally indicate significant differences between four groups: normal patients, patients with partially compensated unilateral peripheral vestibular deficit, patients with an acoustic neurinoma and patients with central (brainstem) vestibular deficit. A stepwise-discriminant analysis was performed on measurements of slow-phase velocity obtained from each test. The primary measurements selected to assign a subject optimally to one population were the canal paresis (CP) of the caloric test, the eye-tracking gain contralateral to the deficit for a 15 deg/s stimulus, the gain asymmetry for optokinetic nystagmus with a 30 deg/s stimulus, and the level of spontaneous nystagmus. The resulting classifications were 100% correct for normal and central deficit patients. However, the division between peripheral deficit and acoustic neurinoma patients overlapped causing about 30% false classifications of neurinoma patients: some 20% of the peripheral deficit patients were classified as normal. If the CP was not available the discriminant analysis substituted the rotating chair response for 5 deg/s2, in place of CP. This substitution caused a 10 to 20% decrease in classification accuracy.

Diagnosis, Differential↗
PubMed1990

[Medical informatics systems exemplified by the diagnosis of equilibrium disorders].

An interdisciplinary field, namely the differential diagnosis of balance disorders and vertigo, is used to describe how a medical expert system can be developed using modern computer analysis, medical expertise, and human pattern recognition techniques. The advantages, results, and unresolved issues of close cooperation between biomedical engineers and physicians are described. The aim of this cooperation was to ensure that complicated data were presented in simple graphic form and that large amounts of diagnostic data were optimally linked together for the generation of a recommended diagnosis. Similar techniques may usefully be employed in other areas of medicine.

Caloric Tests↗
PubMed1989

The role of stretch and vestibulo-spinal reflexes in the generation of human equilibrating reactions.

Equilibrating reactions in standing humans were examined for evidence that either vestibulo-spinal or proprioceptive long loop stretch reflexes from ankle muscles, or both, are responsible for the control and organization of rapid postural responses. Specifically, the hypothesis was tested that the same postural response could be evoked by rotation of the support surface that mimics the ankle rotation occurring during support surface translations. Rotation perturbations evoked postural responses in leg and trunk muscles that were different in strategy, synergy and coactivation from translation responses, even though the short-latency response in the stretched triceps surae muscles was equal in latency and size. Movement patterns consisted of a stiffening strategy and hardly any compensating ankle rotation for rotation stimuli, and a multi-link strategy with motion focused about the neck, hip and ankle joints for translation stimuli. Dorsiflexion rotations caused earlier and stronger responses in tibialis anterior and quadriceps muscles just post to the onset of paraspinal muscles, whereas rearward translation activated soleus and abdominals strongest, both just prior to hamstring muscles. Correlated activation strengths of agonist and antagonist activity was a common feature for both types of perturbation, albeit, only in the ankle muscles for rotations and only in the trunk muscles for translations. These data suggest that sensory inputs, other than those generated in the lower leg predominate, in the triggering and modulation of equilibrating reactions. Possible candidates are those of the vestibular system or proprioceptive inputs from the trunk.

Humans↗
PubMed1989

Automatic electronystagmus analysis and documentation: recent advances in the study of vestibular, optokinetic and pursuit tracking function.

A normal or pathologically altered peripheral vestibular system and associated brainstem structures can be diagnosed from the pattern of eye movement responses elicited by appropriate stimuli. Recent advances in two stages crucial to an accurate assessment of pathological or normal responses are described in this article. The first stage involves the automatic analysis of electronystagmus signals to yield the main parameters of clinical and scientific interest, slow phase eye velocity and fast phase frequency. Since four algorithms based on the first derivative of eye position perform this task remarkably well on-line, it is not necessary to employ features of the stimulus to separate the slow and fast phases of nystagmus. Examples are used liberally to illustrate the accuracy, advantages and limitations of the algorithms. The second stage involves a numerical and graphical comparison of measurements from a patient's analyzed responses with normal responses. This documentation phase permits immediate recognition of normal, borderline, or pathological optokinetic, eye tracking, caloric and rotating chair test results. Selected examples of pathological responses illustrate the documentation technique.

Algorithms↗
PubMedDate not supplied

Indicators of the influence a peripheral vestibular deficit has on vestibulo-spinal reflex responses controlling postural stability.

For a controlled sway stabilization task, the areas underlying EMG responses in ankle and neck muscles, as well as amplitudes of ankle torque responses, were shown to be significantly correlated with the clinically defined extent of a patient's peripheral vestibular deficit. The responses, elicited by ankle dorsiflexion of the support surface on which the subject stood, were statistically examined in order to select those measurements which would best indicate differences between a normal, a patient with a unilateral deficit, or one with a bilateral deficit. For this purpose, a stepwise discriminant analysis was performed on measurements of head and trunk angular accelerations in addition to muscle EMG and ankle torque signals. The primary measurements selected to optimally assign a subject to a population were the periods of ankle torque and neck extensor activity associated with correcting for the imposed body displacement backwards and maintaining upright head position respectively. The resulting division into populations was 100% correct. However, within the population of unilateral deficit patients, the technique failed to correctly identify those with acute from those with compensated deficit. This technique of investigating vestibulo-spinal reflex responses is more specific and sensitive than Romberg tests, because it will quantify and specify the underlying cause of the patient's balance and ambulatory disorder.

Adult↗
PubMedDate not supplied

Principles underlying real-time nystagmus analysis of horizontal and vertical eye movements recorded with electro-, infra-red-, or video-oculographic techniques.

New methods for separating fast and slow phases of human nystagmus in real time are presented that are adaptive to the time-dependent noise properties of the input eye movement signal and therefore applicable to different recording techniques and directions. The methods employ a statistical filter technique to track slow-phase eye movements, uninfluenced by fast phases and blink artifacts, and fuzzy-logic techniques to identify fast-phase eye movements. Because these two techniques are decoupled from one another, highly accurate phase separation and slow-phase velocity profiles are achieved. In addition, the tracking of the variance of slow-phase and fast-phase eye movement recording permits a quality control of the analysis for different recording techniques and a variety of ocular nystagmus responses. Because blinks impose different eye velocity profiles on the recordings, depending on the type of recording technique and direction (horizontal, vertical), blink detection and its effect on fast-phase amplitude must be individually adjusted to each recording technique. Results are illustrated in the context of simultaneously recorded video-oculographic, infra-red, and electro-oculographic recordings of vestibulo-ocular reflex and optokinetic reflex responses causing horizontal or vertical eye movements.

Algorithms↗