Biomedical subjects

J H Allum

Publications and source records attributed to J H Allum.

At least 19 recordsLinked to original sources

PubMed1998

Interactions between vestibular and proprioceptive inputs triggering and modulating human balance-correcting responses differ across muscles.

Interactions between proprioceptive and vestibular inputs contributing to the generation of balance corrections may vary across muscles depending on the availability of sensory information at centres initiating and modulating muscle synergies, and the efficacy with which the muscle action can prevent a fall. Information which is not available from one sensory system may be obtained by switching to another. Alternatively, interactions between sensory systems and the muscle to which this interaction is targeted may be fixed during neural development and not switchable. To investigate these different concepts, balance corrections with three different sets of proprioceptive trigger signals were examined under eyes-open and eyes-closed conditions in the muscles of normal subjects and compared with those of subjects with bilateral peripheral vestibular loss. The different sets of early proprioceptive inputs were obtained by employing three combinations of support surface rotation and translation, for which ankle inputs were nulled, normal or enhanced, the knees were either locked or in flexion, and the trunk was either in flexion or extension. Three types of proprioceptive and vestibulospinal interactions were identified in muscles responses. These interactions were typified by the responses of triceps surae, quadriceps, and paraspinal muscles. The amplitudes of stretch responses at 50 ms after the onset of ankle flexion in triceps surae muscles were related to the velocity of ankle stretch. The amplitude of balance-correcting responses at 100 ms corresponded more with stretch of the biarticular gastrocnemius when the knee was re-extended at 60 ms. Absent stretch reflexes at 50 ms in triceps surae with nulled ankle inputs caused a minor, 12-ms delay in the onset of balance-correcting responses in triceps surae muscles. Vestibular loss caused no change in the amplitude of balance-correcting responses, but a negligible decrease in onset latency in triceps surae even with nulled ankle inputs. Stretch responses in quadriceps at 80 ms increased with the velocity of knee flexion but were overall lower in amplitude in vestibular loss subjects. Balance-correcting responses in quadriceps had amplitudes which were related to the directions of initial trunk movements, were still present when knee inputs were negligible and were also altered after vestibular loss. Stretch and unloading responses in paraspinals at 80 ms were consistent with the direction of initial trunk flexion and extension. Subsequent balance-correcting responses in paraspinals were delayed 20 ms in onset and altered in amplitude by vestibular loss. The changes in the amplitudes of ankle (tibialis anterior), knee (quadriceps) and trunk (paraspinal) muscle responses with vestibular loss affected the amplitudes and timing of trunk angular velocities, requiring increased stabilizing tibialis anterior, paraspinal and trapezius responses post 240 ms as these subjects attempted to remain upright. The results suggest that trunk inputs provide an ideal candidate for triggering balance corrections as these would still be present when vestibular, ankle and knee inputs are absent. The disparity between the amplitudes of stretch reflex and automatic balance-correcting responses in triceps surae and the insignificant alteration in the timing of balance-correcting responses in these muscles with nulled ankle inputs indicates that ankle inputs do not trigger balance corrections. Furthermore, modulation of balance corrections normally performed by vestibular inputs in some but not all muscles is not achieved by switching to another sensory system on vestibular loss. We postulate that a confluence of trunk and upper-leg proprioceptive input establishes the basic timing of automatic, triggered balance corrections which is then preferentially weighted by vestibular modulation in muscles that prevent falling. (ABSTRACT TRUNCATED)

Adult↗

PubMed1997

[Follow-up of caloric test response after acute peripheral vestibular dysfunction].

This study examined retrospectively the spontaneous recovery of patients with an acute peripheral vestibular deficit in order to determine whether the caloric test response and with it vestibular function improves over time. The caloric bithermal was tested three times on 79 patients who were hospitalised with an acute deficit. The first test was recorded on emergency admission by observing nystagmus beats under the Frenzel glasses. Two to five days later a complete electronystagmus (ENG) examination was performed. A second ENG was performed, on average, 4 months later. 46% of the patients recovered a normal caloric canal paresis value (less than 32%). By comparing the canal paresis values in the first and second ENG an improvement exceeding 30% was demonstrated in 50% of the patients and there was no correlation between the extent of the canal paresis deficit and the amount of recovery. A simultaneous cochlear deficit had no influence on the recovery of vestibular function.

Adult↗

PubMed1997

Evaluation of electrically elicited stapedius reflex threshold measured through three different cochlear implant systems.

OBJECTIVE: To evaluate intraoperative electrically elicited stapedius reflex thresholds (ESRTs) measured through three different cochlear implant systems: the Nucleus Mini 22, the Clarion Enhanced Bipolar, and the Med-El Combi-40. SUBJECTS AND METHODS: Relations between intraoperative ESRT and postoperative maximum comfort level (MCL) were examined in seven children (4 Nucleus, 2 Clarion, and 1 Med-El) and one adult (Clarion). RESULTS: Preliminary results indicated most ESRTs were either higher or both higher and lower (across the electrode array within a subject) than MCLs. All systems provided satisfactory means for measuring ERSTs. CONCLUSION: It is recommended that hand-held systems have a direct readout to the programming station and that audio and visual feedback be improved for all units.

Adolescent↗

PubMed1995

Estimating net joint torques from kinesiological data using optimal linear system theory.

Net joint torques (NJT) are frequently computed to provide insights into the motor control of dynamic biomechanical systems. An inverse dynamics approach is almost always used, whereby the NJT are computed from 1) kinematic measurements (e.g., position of the segments), 2) kinetic measurements (e.g., ground reaction forces) that are, in effect, constraints defining unmeasured kinematic quantities based on a dynamic segmental model, and 3) numerical differentiation of the measured kinematics to estimate velocities and accelerations that are, in effect, additional constraints. Due to errors in the measurements, the segmental model, and the differentiation process, estimated NJT rarely produce the observed movement in a forward simulation when the dynamics of the segmental system are inherently unstable (e.g., human walking). Forward dynamic simulations are, however, essential to studies of muscle coordination. We have developed an alternative approach, using the linear quadratic follower (LQF) algorithm, which computes the NJT such that a stable simulation of the observed movement is produced and the measurements are replicated as well as possible. The LQF algorithm does not employ constraints depending on explicit differentiation of the kinematic data, but rather employs those depending on specification of a cost function, based on quantitative assumptions about data confidence. We illustrate the usefulness of the LQF approach by using it to estimate NJT exerted by standing humans perturbed by support-surface movements. We show that unless the number of kinematic and force variables recorded is sufficiently high, the confidence that can be placed in the estimates of the NJT, obtained by any method (e.g., LQF, or the inverse dynamics approach), may be unsatisfactorily low.

Algorithms↗

PubMed1995

Differential control of leg and trunk muscle activity by vestibulo-spinal and proprioceptive signals during human balance corrections.

Knowledge about how proprioceptive signals trigger and modulate human balance corrections has important implications for the rehabilitation of postural and gait disorders, and increases our understanding of normal interactions between these sensory systems. We used combinations of support-surface rotation and rearward translation to examine the triggering effects of ankle and knee movements on balance corrections. By comparing the responses in normal subjects to those in persons with a bilateral peripheral vestibular deficit, we determined the modulating influence of vestibular inputs on balance responses. Differences in normal and vestibular-loss responses under the different proprioceptive conditions revealed four general findings. First, ventral leg muscle responses are strongly modulated by vestibulo-spinal inputs and by proprioceptive inputs from the ankle and knee. Second, triceps surae muscle responses are initially dependent on ankle inputs, and after 100 ms are modulated by knee inputs; they are not altered by vestibular loss. Third, paraspinal responses in vestibular-loss subjects are enhanced because of unstable trunk sway induced by the lack of ventral leg-muscle activity. Fourth, the earliest possible triggering signal for establishing the timing of interlink muscle activity appears to be knee flexion and/or trunk rotation on the pelvis. These results indicate that a confluence of knee and trunk proprioceptive and vestibulo-spinal inputs, rather than either input alone, is involved in establishing the muscle synergy underlying normal balance corrections.

Electromyography↗

PubMed1994

The influence of a bilateral peripheral vestibular deficit on postural synergies.

The role of vestibular sensory information in the triggering, selection and modulation of postural response synergies was evaluated by comparing the EMG responses of normal subjects to balance perturbations with those of subjects with a bilateral peripheral vestibular deficit. The balance perturbations were a rotation and/or a translation of a support surface on which the test subjects stood with eyes open. Onset latencies and most timing patterns of muscle responses were not altered in vestibular-loss subjects. Major changes were observed, however, in the muscle amplitude synergy. Responses between 120 and 240 ms in tibialis anterior, soleus, and quadriceps muscles were reduced more than 50% with respect to normal amplitudes. In contrast, responses in paraspinal muscles were enhanced nearly 100% with respect to normal values. These changes in muscle amplitudes with accompanying vestibular loss were highest for rotation and lowest for translation perturbations. The identification of a bilateral vestibular loss using EMG amplitudes was always 100% correct for rotation perturbations and between 75 to 85% correct for translation perturbations. Multivariate linear correlations between muscle EMG response areas, and the amplitudes of initial link velocities revealed an increased contribution of afferent signals from the upper leg and a decreased dependence on signals from the trunk and head to postural synergies in vestibular-loss subjects. The afferent modulation of the muscle amplitude synergy correcting a balance disturbance to the stance of normal subjects is, on the basis of these findings, highly dependent on vestibular afferent signals. Our results indicate that vestibular afferent signals are used to enhance the amplitude of responses in tibialis anterior, quadriceps, and soleus muscles; and inhibit the responses of paraspinal muscles, once the response timing has been triggered and selected by proprioceptive signals. Lacking this modulation, bilateral vestibular deficit subjects respond to balance perturbations under eyes-open conditions as if the perturbation were 50% slower. Clinically, our results document that the perturbation of choice, when testing vestibular deficit patients, is a rotation (greater than 3 degrees in amplitude and 15 degrees/s in velocity) and not a translation of the support surface.

Adult↗

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

Human auditory-evoked potentials before and after magnetic resonance imaging.

The effect of magnetic fields on auditory brainstem responses (ABRs) was examined under two conditions. The first involved recording ABRs before and immediately after magnetic resonance imaging (MRI). ABRs were then recorded as the static magnetic field was increased stepwise to 2T. No significant changes in ABR latencies were noted under either condition. These results indicate that MRI has no measurable effect on the transmission latencies of auditory brainstem neural pathways.

Adult↗

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

Diagnosis and surgery of cerebellopontine-angle tumors.

The present report is based on the analysis of clinical data collected from 80 patients with cerebellopontine-angle tumors. Special reference is made to the history of the patient, the neurootologic test battery, particularly to the sensitivity and specificity of audiological and vestibular diagnostic procedures. The postoperative findings are evaluated especially with respect to postoperative morbidity and the preservation of facial nerve and auditory functions.

Audiometry↗

PubMed1991

The effect of age on the visuo- and vestibulo-ocular reflexes of elderly patients with vertigo.

To evaluate the effect of age and vestibular deficit on the vestibulo-ocular and associated visual reflexes, rotating chair (VOR), eye tracking test (ETT) and optokinetic (OKN) responses were investigated using comparisons between three populations: young normals, vertiginous elderly patients, and age-matched normal elderly subjects. The gain of ETT and OKN responses were reduced for both elderly populations as compared to young normals, but less so for the vertiginous elderly. VOR gain was more significantly reduced in the vertiginous elderly, though VOR time constant was as reduced as for the normal elderly. These results indicate that visual inputs, even in the elderly, are probably employed to compensate for a vestibular deficit.

Aged↗

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↗

PubMed1990

Shifts in auditory brainstem response latencies following plasma-level-controlled aminoglycoside therapy.

The ototoxic effect of plasma-level-controlled netilmicin and tobramycin was monitored in 20 intensive care patients, using auditory brainstem responses (ABRs). ABRs were recorded at the onset and after 6 days of treatment. Significant shifts in the ABR wave V latency were observed independent of the type of medication received or whether the patients were intubated or not. Shifts were also observed in wave I latencies. These latter changes were only significant for the complete population, probably because this potential is more difficult to elicit and measure than is wave V. The I-V interlatency time was greater for netilmicin than for tobramycin. These results indicate that the cumulative effects of aminoglycoside ototoxicity may be different for the central and peripheral nervous systems, and therefore ABR measurements may be the most accurate way of controlling ototoxicity in intensive care patients.

Adult↗