Postural disorders induced by cochlear implantation in normo-reflexic patients: A potential origin of a transient geocentric perception disorder.

BACKGROUND: Profound hearing loss is a public health problem with serious consequences for patient's quality of life. Some of them, submitted to cochlear implantation, revealed various postural disorders such as balance and spatial perception disorders without detail on their vestibular status. RESEARCH QUESTION: The purpose of this preliminary study was to analyze the evolution of the balance control and geocentric perception after cochlear implantation procedure in normo-reflexic patients before the implant activation. METHODS: We assessed balance control of five patients with profound hearing loss and five healthy participants by means of computerized dynamic posturography and their geocentric perception by the subjective visual vertical test before surgery, three days and forty-five days after surgery (prior to implant activation). RESULTS: Before surgery, the patients showed some difficulties to control their balance in challenged postural context without geocentric perception disorder. Patients presented an improvement in their postural accuracy, but their balance control remained inappropriate in challenging environment. Moreover, their geocentric perception was deviated towards their healthy ear immediately after cochlear implantation. This misperception naturally fades before the implant activation. SIGNIFICANCE: This transient spatial perception alteration might probably cause the perceived postural discomforts and the daily difficulties often reported by these patients in their clinical records early after cochlear implantation. This preliminary study allows for the first time the distinction between the both components of posture: balance control and geocentric perception. Therefore, a specific therapeutic care targeting the rehabilitation of spatial cognition could be proposed to these patients in order to reduce their transient postural disorders.

Does the postural variable affect the determination of balance compensation level in vestibular schwannoma patients?

Previous sensory organization test (SOT) outcomes provided evidences that the vestibular schwannoma (VS) removal led to acute and slow changes in the ability to use vestibular cues for balance control. However, the assumptions behind the equilibrium score (ES) are somewhat controversial within the literature. Therefore, we compared the time-course of balance control in eighteen VS patients across different postural variables. Analyses of variance and unsupervised clustering (k-means) were used to compare the whole dataset of four postural variables: ES, a modified ES which factored in the time before a fall (cES), the mean amplitude (MA) and the mean velocity (MV) of center of pressure displacements. Early after surgery, postural performances significantly decreased (p < 0.01), especially when vestibular cues are predominant, with lower ES (12.5 ± 22.8%) and cES (26.6 ± 16.7%) and higher MA (27.7 ± 7.1 mm) and MV (95.2 ± 53.2 mm.s-1) than before or three months after surgery. For each postural variable, the k-means clustering divided the whole dataset into two clusters: cluster #1 corresponded to a SOT with low sway amplitude and cluster #2 with high sway amplitude and falls. Overall, whatever the selected postural variable, the main recovery profile of VS patients was highlighted, thus surpassing the ambiguities inherent of the ES calculation.

Dynamical analysis of balance in vestibular schwannoma patients.

The analysis of the complexity of postural fluctuations is a recent method for assessing postural control. Complexity relates to the irregularity of the center of pressure time series and characterizes the ability of postural control to meet a changing environment. In our study, we used the sample entropy (SampEn) parameter to evaluate the complexity of postural sway velocity time series in patients with vestibular schwannoma (n=19) compared to healthy controls (n=20), using the sensory organization test. Patients performed postural assessments three days before surgical ablation of the tumor, then three times after surgery, at eight, thirty, and ninety days. The control group underwent posturographic tests only once. Our results demonstrated that SampEn values distinguished both groups before surgery only in postural tasks where vestibular afferences significantly contribute to maintaining balance. We also found an immediate decrease of complexity after the surgical resection of the tumor. Our results are in line with the theory of complexity loss of physiological systems stating that reducing the number of their structural components or altering their coupling leads to a decrease in complexity. Finally, our findings showed that progressive restoration of complexity over time was such that no difference was found between the two groups ninety days after surgery, due to the implementation of central adaptive mechanisms and the substitution by other sensory afferences. Thus, the SampEn parameter can highlight the postural effects of vestibular pathology, and complexity analysis appears to be a valuable tool for investigating the temporal structure of CoP time series.

Can the Risks of Cerebrospinal Fluid Leak After Vestibular Schwannoma Surgery Be Predicted?

OBJECTIVE: Identifying predictive factors of cerebrospinal fluid (CSF) leak after translabyrinthine approach (TLA) for vestibular schwannoma. DESIGN: Retrospective study. SETTING: Tertiary care center. PATIENTS: All patients (n = 275) operated for a vestibular schwannoma by TLA between 2004 and 2013 were included. INTERVENTION: Vestibular schwannoma surgery by TLA. MAIN OUTCOMES AND MEASURES: The rate of postoperative CSF leak considering the age, sex, body mass index (BMI), tumor staging, and duration of surgical procedure. A logistic regression model was used to identify the predictors and compute a biometric predictive model of CSF leak. RESULTS: Thirty-three patients (12.0%) developed a CSF leak after surgery. In a multivariable model, an increased risk of CSF leak was found for younger patients (OR 0.95, 95% CI 0.92-0.98), longer duration of surgery (OR 1.85, 95% CI 1.12-3.05), and the male sex (0 = male; 1 = female; OR 0.22, 95% CI 0.09-0.54), while also adjusting for BMI. The probability of developing a CSF leak after vestibular schwannoma surgery was calculated using a statistical prediction model, with a percentage of false negative of 7.0% and an overall correct prediction of 88.4%. CONCLUSION: The predictors of CSF leak after TLA for vestibular schwannoma are young age, male sex, longer duration of surgery, which adjusting for BMI. In this regard, the surgical team should adapt its management during pre- and postoperative period to decrease the likelihood of a leak.

Dynamics of the locomotor-respiratory coupling at different frequencies.

The locomotor-respiratory coupling (LRC) is a universal phenomenon reported for various forms of rhythmic exercise. In this study, we investigated the effect of movement and respiratory frequencies on LRC. Participants were instructed to cycle or breath in synchrony with a periodic auditory stimulation at preferred and non-preferred frequencies. LRC stability was assessed by frequency and phase coupling indexes using the theory of nonlinear coupled oscillators through the sine circle map model, and the Farey tree. Results showed a stabilizing effect of sound on LRC for all frequencies and for the two systems paced. The sound-induced effect was more prominent when the rhythm of the stimulation corresponded to the preferred frequencies. The adoption of cycling or respiratory frequencies far off preferential ones led to a loss of stability in LRC. Contrary to previous findings, our results suggest that LRC is not unidirectional-from locomotion onto respiration-but bidirectional between the two systems. They also suggest that auditory information plays an important role in the modulation of LRC.

Sound-induced stabilization of breathing and moving.

In humans and other animals, the locomotor and respiratory systems are coupled together through mechanical, neurophysiological, and informational interactions. At a macroscopic observer-environment level, these three types of interactions produce locomotor-respiratory coupling (LRC), whose dynamics are evaluated in this paper. A formal analysis of LRC is presented, exploiting tools from synchronization theories and nonlinear dynamics. The results of two recent studies, in which participants were instructed to cycle or exhale at a natural frequency or in synchrony with an external rhythmic sound, are discussed. The metronome was either absent or present (study 1) and close to or far from the natural frequency of the cycling and breathing systems (study 2). The results evidenced a stabilization of cycling, breathing, and LRC when sound was present compared to when it was absent. A decrease in oxygen consumption was also observed, accompanying the increase in sound-induced LRC stabilization. These results obtained with a simple rhythmic metronome beat have consequences for exercising while listening to music; the consequences are further explored here.

Energy management using virtual reality improves 2000-m rowing performance.

Elite-standard rowers tend to use a fast-start strategy followed by an inverted parabolic-shaped speed profile in 2000-m races. This strategy is probably the best to manage energy resources during the race and maximise performance. This study investigated the use of virtual reality (VR) with novice rowers as a means to learn about energy management. Participants from an avatar group (n = 7) were instructed to track a virtual boat on a screen, whose speed was set individually to follow the appropriate to-be-learned speed profile. A control group (n = 8) followed an indoor training programme. In spite of similar physiological characteristics in the groups, the avatar group learned and maintained the required profile, resulting in an improved performance (i.e. a decrease in race duration), whereas the control group did not. These results suggest that VR is a means to learn an energy-related skill and improve performance.

Sound stabilizes locomotor-respiratory coupling and reduces energy cost.

A natural synchronization between locomotor and respiratory systems is known to exist for various species and various forms of locomotion. This Locomotor-Respiratory Coupling (LRC) is fundamental for the energy transfer between the two subsystems during long duration exercise and originates from mechanical and neurological interactions. Different methodologies have been used to compute LRC, giving rise to various and often diverging results in terms of synchronization, (de-)stabilization via information, and associated energy cost. In this article, the theory of nonlinear-coupled oscillators was adopted to characterize LRC, through the model of the sine circle map, and tested it in the context of cycling. Our specific focus was the sound-induced stabilization of LRC and its associated change in energy consumption. In our experimental study, participants were instructed during a cycling exercise to synchronize either their respiration or their pedaling rate with an external auditory stimulus whose rhythm corresponded to their individual preferential breathing or cycling frequencies. Results showed a significant reduction in energy expenditure with auditory stimulation, accompanied by a stabilization of LRC. The sound-induced effect was asymmetrical, with a better stabilizing influence of the metronome on the locomotor system than on the respiratory system. A modification of the respiratory frequency was indeed observed when participants cycled in synchrony with the tone, leading to a transition toward more stable frequency ratios as predicted by the sine circle map. In addition to the classical mechanical and neurological origins of LRC, here we demonstrated using the sine circle map model that information plays an important modulatory role of the synchronization, and has global energetic consequences.