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Evaluation of biomechanical models in posturography.
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An application of mathematical models in posturography.
The measurement of the horizontal displacements (HD) of the centre of mass of the human body when standing still, is often performed by means of a platform. The resulting measured HD as a function of time, both in the left-right or sinister-dexter and the posterior-anterior direction, are known as stabilograms. Such stabilograms are being more widely used to obtain the so called measured statokinesigram, similar to a Lissajous-figure, by eliminating time from the sinister-dexter stabilogram and the posterior-anterior stabilogram. It is shown that in using mathematical models of the standing person to obtained the stabilograms, the resulting statokinesigram is very different from the measured statokinesigram. It is also shown that the quantity line-integral calculated from a statokinesigram is much smaller when determined from a statokinesigram corrected by means of the mathematical models.
Influence of visual and somatosensory input on leg EMG responses in dynamic posturography in normals.
The contribution of visual and somatosensory input to stabilization after sudden postural disturbances was investigated. Fast transient platform movements (50 degrees/sec, 4 degrees), rotating toe-up around the ankle-joint, evoke EMG responses in the triceps surae (TS) and anterior tibial (TA) muscles. The short and medium latency responses (SL, ML) in the TS destabilize, the long latency responses (LL) in the TA stabilize the upright posture. The influence of vision was tested in normals comparing the conditions eyes open with eyes closed. The influence of additional somatosensory input was tested with the operator's index finger touching the back of the subject with eyes closed. Absent visual input (eyes closed) resulted in a decrease in latency of the stabilizing LL response and an increase in the integrated EMG (iEMG). With eyes closed the latency of the LL response decreased by 4 msec on average (mean eyes open: 111.6 msec (S.D. = 17.3), eyes closed: 107.6 msec (S.D. = 17.5); P < 0.001 (Wilcoxon test)), the iEMG increased by 10% (mean eyes open: 13.9 microV.sec (S.D. = 7.6), eyes closed: 15.5 microV.sec (S.D. = 8.6); P < 0.001). Additional somatosensory input as an external reference for body orientation in space resulted in an increase in latency and decrease in iEMG: the latency increased by 7 msec on average (mean eyes closed: 107.6 msec (S.D. = 17.5), index finger and eyes closed: 114.7 msec (S.D. = 19.9); P < 0.001), the iEMG decreased by 20% (mean eyes closed 15.5 microV.sec (S.D. = 8.6), index finger and eyes closed: 12.3 microV.sec (S.D. = 7.5); P < 0.001). There was no significant change in latency of SL and ML. We conclude that postural EMG responses in leg muscles after fast transient platform movements change according to different functional demands, modulated via visual and somatosensory input.
Quantitative posturography in altered sensory conditions: a way to assess balance instability in patients with chronic whiplash injury.
OBJECTIVES: To quantify neck mobility and posture with and without various postural perturbations. DESIGN: A multivariable 2-group study with repeated measures and treatments. SETTING: A human performance laboratory. PARTICIPANTS: Eleven patients with chronic whiplash injury (mean age, 33.3+/-6.7 y; weight, 73.4+/-11.4 kg; height, 173.3+/-7.2 cm) with a sex- and age-matched control group (mean age, 33.1+/-6.8 y; weight, 68+/-12.5 kg; height, 171.5+/-6.3 cm). INTERVENTIONS: Neck mobility and the effects of postural perturbations affecting the visual, vestibular, cutaneous, proprioceptive, and nociceptive systems were measured. MAIN OUTCOME MEASURES: Active range of motion, neck position sense, and postural activity. RESULTS: We found significantly reduced neck mobility and increased postural activity in the patient group compared with the control group. In patients, there was significantly greater postural activity with eyes closed, eyes open and speaking, and eyes closed with Achilles' tendons vibrations compared with eyes open with no vibrations. In the controls, there was no significant effect of experimental muscle pain on postural activity. CONCLUSIONS: Patients with chronic whiplash injury had a protective response to neck movement and different tuning, sequencing, and execution of the postural synergies probably because of excessive reliance on visual input despite a possible deficit and altered vestibular and/or proprioceptive activity. In healthy volunteers, the pain induced by a single bolus injection of hypertonic saline was probably too limited in intensity and spreading to decrease postural stability.
The usefulness of computerized dynamic posturography for the study of equilibrium in patients with Meniere's disease: correlation with clinical and audiologic data.
The use of computerized dynamic posturogaphy (CDP) in the evaluation of patients with balance alterations not only allows quantification of the subject's capacity to maintain a stable centre of gravity, but also analysis of the degree to which the subject is able to use different types of sensory information. The present study investigated the possible use of CDP for clinical staging of vestibular diseases, specifically Meniere's disease (MD). We applied CDP sensory organization tests to 75 patients with definitive MD (AAO-HNS 1995 criteria). A total of 98 CDP sessions were included in the analysis, which focused on four CDP parameters specifically related to vestibular function (condition-5 score, condition-6 score, overall balance score, and VEST, a measure of the relative importance of vestibular information for maintenance of balance). We found a statistically significant relationship between audiometric hearing threshold and CDP scores, especially in patients with audiometrically advanced disease. In addition, CDP scores showed statistically significant variation with time elapsed since the last typical vertigo attack, suggesting that patients can be usefully grouped into three MD activity-level categories: recent post-attack (less than 1 week since last vertigo attack), late post-attack (1 week - 60 days since last attack), and inactive MD (more than 60 days since last attack). On the basis of these results, we propose expected ranges for each of the four CDP parameters in each of the three MD activity-level categories, allowing staging in terms of balance and posture. This staging system complements existing staging systems (based on audiometric criteria, and on subjective assessment of the severity of vertigo attacks and their implications for quality of life).
Multi-stimulus multi-response posturography.
In this study a method for the analysis of simultaneous multiple measurements of kinematics and stabilizing forces related to human postural dynamics is proposed. Each subject in a group of normal subjects (n=10) was tested with eyes-open and eyes-closed with simultaneous but uncorrelated vestibular and proprioceptive stimuli in order to investigate the contributions of individual sensory feedback loops. Statistical analysis was made by means of multi-input multi-output identification of a transfer function from stimuli to stabilizing forces of the feet and the resulting body position, the transfer function being compatible with a biomechanical model formulated as a stabilized segmented inverted pendulum subject to feedback of body sway and position. Each individual model estimated is effective in predicting a subject's response to new stimuli and in describing the interacting effects of stimuli on body kinetics. The proposed methodology responds to the current needs of data analysis of multi-stimulus multi-response experiments.
Motor control alteration in posturography in learning-disabled children.
BACKGROUND: Some authors have mentioned that intersensory integration is damaged in children with learning disabilities (LDs), and other investigators point to motor control alterations in the same patients. Thus, we decided to study these hypotheses by means of posturographic recordings. METHODS: A highly selected group of 27 children with LDs was compared with 27 children of control group without LDs. Patients and controls were placed on the Equitest equipment platform. Sensory organization tests evaluated different test conditions that systematically vary visual, vestibular, and foot somatosensory cues available to subjects while they attempt to maintain a stable, quiet stance. Movement coordination test involved sudden posterior and anterior translations of the patient support surface. RESULTS: No significant correlations between scholastics and posturographic performance were observed. No difference in the six conditions and in sensory organization ratios or in visual preference between both groups was disclosed. Motor control test on children with LDs showed significant higher values in latencies in averages of large translations. CONCLUSIONS: Our data suggest that vestibular-visual-somatosensory organization for posture control are not abnormal in children with LDs; instead, motor controls show higher latencies with large translation movements, which suggest abnormal rate and timing precision motor coordination.
Postural stability by computerized posturography in minor head trauma.
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Benign paroxysmal positional vertigo. Clinical observations by vestibular habituation training and by posturography.
Vestibular Habituation Training (VHT) is the treatment of choice for paroxysmal positional vertigo (ppv). The origin of the disturbance is peripheral and the data observed in the cases treated confirm that it is not located in horizontal canal function. However, canal dysfunction can be present together with ppv. Usually a separate course is observed for the phenomena attributed to horizontal dysfunction and those to the ppv lesion. The specificity of the Dix-Hallpike manoeuvres linked to the typical ppv is also confirmed by the data obtained by testing for VHT (VHT-test-battery). Ppv can have a repercussion upon the vestibulospinal reflex. That the same ppv disturbance can coincide with normal as well as with abnormal posturographic data, pleads for the intervention of central adaptive mechanisms. The effect of VHT is due to stimulation of these central adaptive mechanisms and not to any impact upon the peripheral lesion.
Posturography measuring instability in vestibular dysfunction in the elderly.
Balance dysfunction may be a cause of falling in the elderly. Disturbance of the vestibular system may have a repercussion upon balance performance, causing instability. Unilateral vestibular hypofunction (UVH) and its disturbing influence upon the vestibulospinal reflex (VSR), measured by the postural sway, has been studied. This influence is dependent on the interfering action of central adaptive and compensatory mechanisms. This central compensation may be different for vestibulo-ocular reflex (VOR) and the VSR. This comparative study shows that the elaboration of compensation in elderly people is less efficacious at the VSR level than at the VOR level. The influence of visual fixation is also stressed by comparing the posturographic recordings made with eyes open and eyes closed.
Gender differences in the balance of healthy elderly as demonstrated by dynamic posturography.
BACKGROUND: Prior studies indicate that older women fall more often than men although there is no evidence of gender-based balance differences. Using a force platform, we measured the effects of restricted sensory input and support surface movement to detect gender differences in balance. METHODS: Healthy, elderly community dwellers (N = 234, mean age = 76 +/- 5 years, 52% female) were administered the following perturbations on the balance platform: The platform and/or visual surround were fixed or tilted proportionally to the subject's sway with the eyes open or closed, forward or backward horizontal translations, and toes-up and toes-down rotations. RESULTS: Gender-based balance differences were not present during quiet standing, or when the support surface or visual input were manipulated separately. Women swayed and lost their balance more than men when the surface was sway-referenced while vision was compromised, but by the third trial their sway control was comparable to the men. Women also initially lost their balance more frequently than men during toes-up and -down rotations, and compared to men continued to lose their balance more often during repeated toes-up rotations. Finally, women developed less angular momentum than men in response to forward platform rotations. DISCUSSION: Elderly women show impairments of balance when simultaneously deprived of visual and somatosensory inputs or during a backwards destabilization. Since there is little evidence for a CNS source for such gender differences, biomechanical origins (e.g., dorsiflexion strength and range of motion) are a more likely cause. Limited postural control of women under conditions stressing balance may explain their greater frequency of falling.
On the role of dynamic models in quantitative posturography.
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Quantitative posturography: use in multiple sclerosis.
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Posturography--applications and limitations in the management of the dizzy patient.
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Comparative study of posturography and electrooculography in at-risk subjects for Huntington's disease.
A simultaneous blind study of posture and eye movements was undertaken in 9 subjects at risk for Huntington's disease. After quantitative evaluation of the postural and electrooculographic abnormalities, the subjects were subdivided into subgroups, and the results were compared to test the relationship between the two methods. There was a significant correlation between the two evaluations. 5 of the 9 patients had evaluation scores which reflected abnormalities similar to those observed in patients suffering from Huntington's disease. These preliminary results suggest that posture and eye movement recordings could be tested for their predictive value in Huntington's disease.
Vestibular habituation training and posturography in benign paroxysmal positioning vertigo.
A number of cases with typical positioning vertigo (BPPV) show a unilateral vestibular hypofunction (UVH) by caloric testing. However, treatment by habituation exercises (VHT) improves vertigo independently of the presence of UVH. Moreover, VHT has no influence upon the results of caloric and rotation tests. These findings prove the independence of the pathogenetic mechanisms of the peripheral vestibular disturbances UVH and BPPV.