Alejo Suarez

Changes in Postural Control Parameters after Vestibular Rehabilitation in Patients with Central Vestibular Disorders

Objective—The aim of this study was to determine postural responses before and after a vestibular rehabilitation program (VRP) in 14 patients with central vestibular disorders (CVD). Material and Methods—The confidence ellipse (CE) of the center of pressure distribution area and the sway velocity (SV) were the parameters used for the quantitative assessment of postural control (PC). These two parameters were analyzed before and after a VRP for two visual conditions. Behavioral postural responses were studied by means of the time–frequency scalogram using wavelets and the sway frequency content was measured in arbitrary units of energy density. Results—Ten patients showed a significant decrease in the CE and SV after the rehabilitative treatment, thus improving their PC. Seven of these patients were assessed again after a period of 12±5 months, during which they had not received any physical training. All of them showed increases in the CE and SV, indicating an impairment of PC. Conclusions—Many CVD patients damage the neural mechanisms involved in retaining the plastic changes in the PC parameters after rehabilitative treatment. Continuation of training may be necessary in order to maintain the improvement in PC obtained with a VRP.

Postural control and sensory perception in patients with Parkinson's disease

Conclusions. This study suggests that patients with Parkinsons disease (PD), even in the early stages, have decreased body limits of stability (LOS) and changes in the visual input impair their postural control. Objective. To assess the LOS and the postural responses after changes in visual input in a group of PD patients in stage 1 of the Hoehn and Yahr classification. Subjects and methods. Twenty PD patients in stage 1 and a group of 24 normal subjects as control were assessed in two tests: (1) the LOS and (2) measurement of the body center of pressure area (COP) 10 s before and after sudden change in visual flow velocity. We also investigated labeling of the COP trajectory in these two periods. The stimulation paradigm was a horizontal optokinetic stimulation (60°/s and suddenly stopped) using a virtual reality system. Results. LOS showed significant decrease in PD patients as compared with the control group (p<0.001, Kruskal-Wallis and Wilcoxon ranked test). The COP values increased significantly (p<0.001, Wilcoxon signed rank test) after sudden changes in the visual flow velocity in relation to the control group. After the visual stop the PD patient showed a spatial ‘roaming’ approaching the limits of stability and therefore impairing the postural control.

Clinical characteristics of positional vertigo after mild head trauma

Abstract Conclusion: This study showed that a population with benign paroxysmal positional vertigo related to mild head trauma (BPPVAT) was younger and more frequently presented with bilateral canalithiasis than another population with idiopathic etiology (IBPPV). In both groups, females presented a higher risk of BPPV. Objective: To compare the clinical features of a population with BPPVAT and another with IBBPV. Methods: We carried out statistical analysis of a population of 51 subjects with BPPVAT and another of 325 subjects with IBPPV, comparing age, gender, recurrence of symptoms, associated chronic dizziness (CD), and clinical presentation. Kolmogorov Smirnov test, Students t test, Mann–Whitney test, 95% binomial confidence interval for proportions, chi-squared, and Fishers test were used as statistical tools. A significance level of p < 0.05 was considered in all cases. Results: The population affected with BPPVAT was younger and bilateral canalithiasis was also more frequent. No differences were found in gender distribution, semicircular canals involved in the symptoms, recurrence after repositioning maneuvers, or associated CD.

Postural Behaviour Responses to Visual Stimulation in Patients with Vestibular Disorders

Patients with different vestibular disorders exhibit changes in postural behaviour when they receive visual stimuli, reproducing environmental stimulation. Postural control was studied using an AMTI Accusway platform, measuring the confidential ellipse (CE) and sway velocity (SV). Postural responses were recorded according to the following stimulation paradigm: i) without specific stimuli; ii) smooth pursuit with pure sinusoids of 0.2 Hz (foveal stimulation); and iii) optokinetic stimulation (retinal stimuli). Patients with central vestibular disorders (CVD), cerebellar damage and unilateral peripheral vestibular lesions (UPVL) in asymptomatic periods were studied. A group of normal subjects was studied as control. Signal processing was done with a scalogram by wavelets in order to observe the relation between time and frequency in postural control. While patients with CVD and cerebellar disease showed a significant increase in CE and SV in the three conditions of the paradigm compared to the normal group, the patients with UPVL showed no change. Wavelets processing showed that the main sway occurs in the Y axis (antero-posterior) and below at 0.4 Hz in normal subjects, while the CVD and cerebellar patients showed sway frequencies in both the X and Y axes. The clinical implications of these findings are discussed.Patients with different vestibular disorders exhibit changes in postural behaviour when they receive visual stimuli, reproducing environmental stimulation. Postural control was studied using an AMTI Accusway platform, measuring the confidential ellipse (CE) and sway velocity (SV). Postural responses were recorded according to the following stimulation paradigm: i) without specific stimuli; ii) smooth pursuit with pure sinusoids of 0.2 Hz (foveal stimulation); and iii) optokinetic stimulation (retinal stimuli). Patients with central vestibular disorders (CVD), cerebellar damage and unilateral peripheral vestibular lesions (UPVL) in asymptomatic periods were studied. A group of normal subjects was studied as control. Signal processing was done with a scalogram by wavelets in order to observe the relation between time and frequency in postural control. While patients with CVD and cerebellar disease showed a significant increase in CE and SV in the three conditions of the paradigm compared to the normal group, the patients with UPVL showed no change. Wavelets processing showed that the main sway occurs in the Y axis (antero-posterior) and below at 0.4 Hz in normal subjects, while the CVD and cerebellar patients showed sway frequencies in both the X and Y axes. The clinical implications of these findings are discussed.

Postural strategies in normal subjects and in patients with instability due to central nervous system diseases after sudden changes in the visual flow

Conclusion. The results suggest that after a sudden change in the visual input, postural adaptation is impaired in patients with instability and central nervous system disorders (CNSD). Objective. The aim of this study was the assessment of postural adaptation, as a transient phenomenon, when sudden changes in visual perception occur in normal subjects and in patients with instability due to different CNSD. Subjects and methods. Horizontal optokinetic stimulation (40 s and suddenly stopped) was performed in 16 patients with CNSD, and also in 22 normal subjects. Measurements were made of the body center of pressure area (COP) and the body sway velocity (SV) during 10 s before and after the stop and labeling the COP trajectory. Results. Values of COP and SV (Wilcoxon signed rank test, p=0.979 and 0.496, respectively) in normal subjects did not show any significant change before and after the stop. In 15 of the 16 assessed patients with instability associated with CNSD an increase of the COP and SV values (Wilcoxon signed test, p=0.001 and 0.004, respectively) was observed in the 10 s after the visual stop. COP labeling showed ‘roaming’ of the COP spatial evolution approaching the limits of stability.

Head tilt response: A complementary test to the Subjective Visual Vertical.

This paper studies the phenomenon of the perceived vertical by means of a novel dynamic experiment. This task is inspired in the Subjective Visual Vertical test and can be regarded as complementary in terms of how the information involved varies (visual, otolithic and neck proprioception). The experiment consists in presenting a white stripe in a pair of virtual reality goggles and adjusting the roll angle of the head until the stripe is aligned with the gravitational vertical. The roll angle of the head is measured and recorded along each trial where the white stripe changes position four times, after a specific amount of time. The task was run on a group of 28 normal subjects and a small sample of 5 patients with vestibular hypofunction. Six parameters derived from Control Theory were extracted from the data to characterize the subject transient response. All parameters for normal subjects were found to be normally distributed. Experimental results show that discrimination is possible between normal subjects and patients using just one or two of the parameters studied.

Postural response characterization in elderly patients with bilateral vestibular hypofunction

Abstract Conclusions: The measurement of the energy consumption (EC) of the bodys center of pressure (COP) to maintain the upright stance position was higher in elderly patients with bilateral vestibular hypofunction (BVH) compared with a control group and may be a valid parameter in the assessment of balance disorders. Objective: The aim of the study was to evaluate the energy consumption of the COP in elderly patients with BVH. Methods: The COP was recorded on a force platform (FP) for eight elderly patients with BVH related to aging and eight normal control group subjects. The EC of the COP was calculated using the discrete wavelet transform. The two groups were tested in standing position on the FP in three sensory conditions:1, eyes open; 2, eyes closed; and 3, standing on a foam pad placed on the force platform. Wilcoxons rank test and multi-factor analysis of variance were used, with the level of significance set at 0.05. Results: BVH patients showed higher values of EC of the COP signal measured in arbitrary units compared with the control group (conditions 1 and 2). None of the BVH patients could perform the test in condition 3. BVH patients had increased EC in the frequency band between 0.1 and 0.78 Hz when the visual information was canceled (condition 2).

Dynamic modeling and experimental results for a head tilt response

The estimation of the vertical in humans is important in everyday life although the mechanisms involved are not completely understood yet. This paper presents two sets of experiments with normal subjects, using the same virtual reality setup, aiming to help in this understanding. First, a steady state experiment is presented, which is used to determine the gravitational vertical precision while the second, a dynamical transient response experiment, is used to find dynamic models of each subject response. Results show that the dynamic models are able to reproduce the results of the steady state experiment while having the benefits that a dynamic model brings to evaluate subjects performance.

Sensorimotor interaction in deaf children. Relationship between gait performance and hearing input during childhood assessed in pre-lingual cochlear implant users

Abstract Conclusions: The results suggest that auditory input is not neutral in motor skills and the complex interaction between them is generated in the earlier stages of childhood development. Objective The assessment of gait performance in pre-lingual deaf children with cochlear implant (CI). Methods: Gait velocity (GV), using a 10-meter test, was measured by means of three inertial sensors in 10 pre-lingual cochlear implant users (CIU) (10–16 years old) in three sensory conditions: (1) cochlear implant turned on with environmental noise (EN), (2) cochlear implant turned on with EN and with cognitive dual task (DT), and (3) CI turned off (CI-OFF). GV with EN and DT was assessed in a normal hearing control group (CG) (n = 14). Mann-Whitney and Wilcoxon Signed ranked test were used for significance validation. Results: (1) GV in CG was lower in DT than with EN (p = .019). (2) GV was faster in CG with EN compared with the three conditions in CIU (EN, p = .006; DT, p = .0001; CI-OFF, p = .03). (3) CIU had slower GV walking with EN (p = .037) and with DT (p = .022). (4) Dividing the CIU sample by age, the acoustic information generates a slower gait for those implanted after 3 years old.

Chronic balance disorders after acoustic neuroma surgery: assessment of gravitational vertical perception

Abstract Conclusion: The head tilt response (HTR) test performed in a group of patients with chronic dizziness after acoustic neuroma surgery showed alterations in the gravitational vertical perception (GV). Objective: The assessment of the accuracy in the GV through the HTR test in patients with long-term balance disorders after acoustic neuroma surgery. Methods: The HTR was performed in two groups of patients that had undergone acoustic neuroma surgery: six uncompensated patients (UPs) who maintained vestibular symptoms 1 year after surgery and two compensated patients (CPs) without vestibular symptoms. Twelve healthy control adults were also tested (control group, CG). Three parameters were measured in the HTR test: steady-state error (SSE), rise time (TRS), and mean energy of the error signal per step (MEE). Results: The UP group showed higher values for the TRS and MEE parameters compared with the CG (p < 0.05) when performing the HTR test to the side of the lesion and to the contralateral side, while the SSE only showed significant higher values when the patient estimated the GV towards the side of the lesion. The two patients in the CP group did not have differences in the three parameters assessed when compared with the CG.