Centre of pressure displacements in trans-femoral amputees during gait

The aim of this study was to describe and quantify centre of pressure (CoP) displacement during walking in 12 unilateral trans-femoral amputees who had worn a prosthesis for at least 10 years. All subjects wore the same type of prosthesis and seven healthy subjects acted as controls. The CoP was acquired by an F-scan system and the displacements along the longitudinal axis of the foot versus time were quantified. An asymmetry of both temporal and spatial parameters of CoP patterns occurred between the sound and the prosthetic foot. The double support time and the time during which the CoP remained in the heel and mid-foot region were longer for the prosthetic limb. Conversely, the stance phase was longer for the sound limb, as was the time spent by the CoP in the forefoot. There was a redistribution of the time during which the CoP remained within the different zones of the sound foot with respect to the normal feet of the control subjects. The asymmetry seen in trans-femoral amputee stance is due not only to an abnormal spatio-temporal distribution of the CoP under the prosthetic leg, but also to a modification of the spatio-temporal distribution of the CoP under the sound foot compared to the normal foot. We conclude that an adaptation occurs in the control of the stance phase on the sound side during amputee gait.

Hemoglobin near-infrared spectroscopy and surface EMG study in muscle ischaemia and fatiguing isometric contraction

BACKGROUND

To assess how muscle ischaemia and isometric fatiguing contraction influence oxygen content in striated muscle.

METHODS

We simultaneously measured changes in hemoglobin near-infrared (NIR) spectroscopy and in surface EMG before, during, and after muscle ischaemia and ischaemia plus muscle isometric fatiguing contraction. Seventeen healthy male subjects (age range: 19-40 yrs) were examined in our Clinical Neurophysiology Unit. Test I (9 subjects): hemoglobin NIR spectroscopy and stimulated surface EMG were measured for 2 minutes at rest, for 4 minutes during complete ischaemia of tibialis anterior muscle, and for twelve minutes during recovery. Test II (all subjects): hemoglobin NIR spectroscopy and surface EMG were measured for 2 minutes with the subjects performing brief non-fatiguing contractions, for 4 minutes with the subject performing maximal isometric contraction in complete ischaemia, and for twelve minutes during recovery. EMG parameters measured: median density frequency (MDF); muscle fiber conduction velocity (MFCV). NIR spectroscopy parameters measured: percentage of amplitude decrement (% AD) and nadir time (NT) during ischaemia and ischaemic effort; half-recovery time (1/2 RT) from ischaemia effort.

RESULTS

At EMG, we observed a significant shift towards lower values of both MFCV and MDF during fatiguing isometric contraction. MDF recovery was faster then MFCV recovery. At NIR spectroscopy, the 1/2 RT slowed a fast pattern in twelve subjects and a slow pattern in five. A significant relationship was found between AD% and 1/2 RT values of test I and AD% and 1/2 values of test II. We found a positive relationship between NT and 1/2 RT in test II.

CONCLUSIONS

Surface EMG and hemoglobin NIR spectroscopy can be applied simultaneously to evaluate both fatigue intensity and blood flow changes in striated muscle.

Trigeminal evoked potentials in man: a new olfactory stimulation device

The recording of olfactory evoked potentials in healthy humans, using a continuous flow olfactory stimulator, is described. A stimulator pushed inert gas (N2) in a continuous flow through the nose at a rate of 4 l/min. At fixed 30-second intervals, (32 times) the flow was replaced by an equal amount of CO2, a trigeminal stimulant. Each pulse lasted 200 ms. An electronic timing circuit triggered both the stimulator and the recorder. Signal acquisition was performed using an Evoked Potential Recorder (Nicolet Compact Four by Nicolet Biomedical Instruments), triggered by the stimulator. Using this stimulator device reliable olfactory evoked potentials can be recorded in a clinical setting. Since this is a non invasive technique which can be used to test olfactory function whether or not the patient cooperates, it is expected to become widely used, particularly in non collaborating patients and in those suspected of malingering.

Eye-head coordination toward auditory and visual targets in humans

Eye-head coordination during gaze orientation toward auditory targets in total darkness has been examined in human subjects. The findings have been compared, for the same subjects, with those obtained by using visual targets. The use of auditory targets when investigating eye-head coordination has some advantages with respect to the more common use of visual targets: (i) more eccentric target positions can be presented to the subject; (ii) visual feedback is excluded during the execution of gaze displacement; (iii) complex patterns of saccadic responses can be elicited. This last aspect is particularly interesting for examining the coupling between the eyes and the head displacements. The experimental findings indicate that during gaze orientation toward a visual or an auditory target the central nervous system adopts the same strategy of using both the saccadic mechanism and the head motor plant. In spite of a common strategy, qualitative and quantitative parameters of the resulting eye-head coordination are slightly different, depending on the nature of the target. The findings relating to patterns of eye-head coordination seem to indicate a dissociation between the eyes and the head, which receive different motor commands independently generated from the gaze error signal. The experimental findings reported in this paper have been summarized in a model of the gaze control system that makes use of a gaze feedback hypothesis through the central reconstruction of the eye and head positions.

Saccade latency toward auditory targets depends on the relative position of the sound source with respect to the eyes

The latency of saccadic eye movements evoked by the presentation of auditory and visual targets was studied while starting eye position was either 0 or 20 deg right, or 20 deg left. The results show that for any starting position the latency of visually elicited saccades increases with target eccentricity with respect to the eyes. For auditory elicited saccades and for any starting position the latency decreases with target eccentricity with respect to the eyes. Therefore auditory latency depends on a retinotopic motor error, as in the case of visual target presentation.

A clinically oriented approach to smooth pursuit eye movement quantitative evaluation

The electrooculographic technique was used to record smooth pursuit eye movements in 71 healthy subjects homogeneously distributed within an age range between the 2nd and the 6th decades. The target moved at constant velocity (triangular ramps) and 9 different target velocities (V), from 10 deg/s to 50 deg/s were considered and presented according to pseudorandom sequence. Ad hoc software suppressed catch-up saccades so that a pursuit index (PI) value was computed for each ramp taking into account only the smooth pursuit tracking modality. It was demonstrated that the relationship between V and PI could be described by the linear model PI = a + b * V. Pursuit index was proved to be influenced by the age of subject (decade factor in the analysis of variance), since an almost linear increase in b values yields a reduction of pursuit index values. The method was tested in 22 multiple sclerosis patients and an association was found between the occurrence of cerebellar signs and the reduction of a value.

Quantitative evaluation of saccadic and smooth pursuit eye movements. Is it reliable?

PURPOSE

The authors evaluated the reliability of the coefficients of the (1) amplitude/duration and (2) amplitude/peak velocity relationships of the mean precision values and the mean latency values (saccadic eye movements) and the coefficients of the target velocity/gain relationship (smooth pursuit eye movements). They computed test-retest maximum variability limits for these parameters.

METHODS

After a 1-week interval, saccadic and smooth pursuit eye movements were recorded twice from 20 healthy subjects; 12 of these subjects underwent a third recording session. The estimate of the intraclass coefficient of reliability, R, was adopted to evaluate the reliability of eye movement quantitative analysis.

RESULTS

The data demonstrated that the reliability was fairly good for the amplitude/peak velocity relationship, was good for the precision, and was excellent for the amplitude/duration, the target velocity/gain relationships, and the latency.

CONCLUSIONS

Quantitative analysis of both saccadic and smooth pursuit eye movements is reliable. One statistic used to estimate reliability, ie, the within-subjects mean square value, also enables the determination of test-retest normal variability values for both the variances and the differences of measurements.

Saccadic responses evoked by presentation of visual and auditory targets

Saccadic eye movements evoked by the presentation of visual and auditory targets were examined and compared. Differences were found either in the pattern of the saccadic response and in the characteristics of single saccades of the same amplitude. The longer latency and the higher percentage of multiple saccade responses in the auditory case were attributed to a more complex central processing, whereas the longer duration and the lower peak velocity of the saccades to auditory targets were attributed to reduced performances of the execution mechanism in the absence of vision.

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.