Cédrick T. Bonnet

Peripheral neuropathy may not be the only fundamental reason explaining increased sway in diabetic individuals

BACKGROUND Individuals with diabetic neuropathy sway more than control individuals while standing. This review specifically evaluated whether peripheral sensory neuropathy can be the only fundamental reason accounting for significant increased sway within this population. METHODS Twenty-six experimental articles were selected using MEDLINE and reference lists of relevant articles. The articles chosen investigated kinematic data of postural behaviour in controls and individuals with diabetic neuropathy during stance. Results of literature were compared with four expectations related to the peripheral sensory neuropathy fundamental hypothesis. FINDINGS Consistent with the peripheral sensory neuropathy hypothesis, the literature showed that individuals with diabetic neuropathy sway more than controls in quiet stance and even more so if their visual or vestibular systems were perturbed. Inconsistent with the hypothesis, individuals with diabetic neuropathy are more destabilised than controls in conditions altering sensation of the feet and legs (standing on a sway-referenced surface). INTERPRETATION The review showed that the peripheral sensory neuropathy hypothesis may not be the only fundamental cause accounting for significant increased postural sway in individuals with diabetic neuropathy. Visual impairments and changes in postural coordination may explain the divergence between expectations and results. In order to develop interventions aimed at improving postural control in individuals with diabetic neuropathy, scientific exploration of these new expectations should be detailed. Also at the practical level, the review discussed which additional sensory information - at the level of the hands and feet - may be more beneficial in individuals with diabetic neuropathy to reduce their postural sway.

Trends in perinatal health in metropolitan France from 1995 to 2016: Results from the French National Perinatal Surveys

OBJECTIVE To study trends in the main indicators of perinatal health, medical practices and risk factors in France since 1995. POPULATION AND METHOD All live births during one week in 1995 (n=13,318), 2003 (n=14,737), 2010 (n=14,903) and 2016 (n=13,384). Data were from interviews of women in postpartum wards and from medical records and were compared between years. RESULTS Between 1995 and 2016, maternal age and body mass index increased steadily. Pregnancies that occurred with use of contraception increased from 7.4% in 2010 to 9.3% in 2016. Smoking during pregnancy (16.6%) did not decrease since 2010. The frequency of more than three ultrasounds during pregnancy was 48.5% in 1995 and 74.7% in 2016. Deliveries in large public hospitals increased steadily. The caesarean section rate has been relatively stable since 2003 (20.4% in 2003, 21.1% in 2010 and 20.4% in 2016). The rate of induction of labour was 22% in 2010 and 2016. Overall, 83.8% of women had epidural analgesia/anaesthesia in 2016. Rates of pre-term birth in 2016 ranged from 7.5% among all live births to 6.0% among live born singletons; for singletons, this rate increased steadily from 1995 to 2016, whereas there was no clear trend for low birth weight. Exclusive breastfeeding decreased from 60.3% in 2010 to 52.2% in 2016. CONCLUSION Routine national perinatal surveys highlight successful policies and recommendations but also point out some health indicators, practices, preventive behaviours and risk factors that need special attention.

The contribution of body weight distribution and center of pressure location in the control of mediolateral stance

The study investigated the mediolateral control of upright stance in 16 healthy, young adults. The model analyzed the body weight distribution and center of pressure location mechanisms under three stance width conditions (feet close, under standard condition, and apart). Our first objective was to discuss some methodological requirements to investigate the contribution of both mechanisms by means of two platforms. It is proposed that both the amplitude contribution (in variability analyses) and active contribution (in cross-correlation analyses) need to be studied distinctively. These analyses may be concerned with the strength and the degree of active contributions, respectively. Based on this theoretical proposition, we expected and found that the amplitude contribution of both mechanisms was higher and lower in wide and narrow stances compared with that in the standard stance, respectively. Indeed, the closer the two reaction forces, the lower their mechanical contribution. As expected, the active contribution of both mechanisms was significantly lower and higher in wide and narrow stances, respectively. Indeed, the further the feet apart, the less active both mechanisms needed to be to control mediolateral stance. Overall, only the center of pressure location mechanism really changed its significant contribution to control mediolateral stance under the three conditions. The result is important because this mechanism is known to be secondary, weaker than the body weight distribution mechanism to control mediolateral stance. In practical terms, these findings may explain why the mediolateral variability of center of pressure displacement was significantly higher in narrow stance but not lower in wide stance.

Large lateral head movements and postural control.

Riccio and Stoffregen (1988) have suggested that task performance is the predominant constraint of change in postural control. To test this hypothesis, 12 healthy, young adults performed large lateral gaze shifts (left/right gaze shifts with a visual angle of 150° and at a frequency of 0.5 Hz or 1 Hz) and a control condition (looking at a stationary dot). Performance in the visual task was expected to be good under all conditions. In accordance with Riccio and Stoffregens hypothesis, the center of pressure sway variability (range or standard deviation) was expected to be similar in the three visual tasks when a destabilizing, narrow stance was adopted. Indeed, body sway had to be restrained in narrow stance to adequately perform the task. In standard and wide stance conditions, the center of pressure sway variability was expected to be larger when gaze shifts were performed. Indeed, in these more stable stance conditions, the task could be performed successfully in minimizing energy expenditure, that is, in letting body sway increase naturally. The results were consistent with these expectations. On a practical level, intentional, large gaze shifts may not cause postural instability per se, even though postural sway may increase significantly.

Broad Stance Conditions Change Postural Control and Postural Sway

ABSTRACT Intuitively, a broad stance (i.e., standing with the feet farther apart than usual) should significantly improve postural stability. However, this intuition was not confirmed in quiet stance. Hence, a motion analysis system (markers attached to the trunk and head) and a force platform were used to investigate 13 healthy, young adults who performed 8 trials in standard and broad stances. In broad stance, the medialateral center of pressure (COP) sway mean power frequency was expected to be greater, whereas the variability (standard deviation) of COP, head, and trunk sway and the mean velocity of head and trunk sway was expected to be significantly lower. Accordingly, adoption of a broad stance significantly increased the medialateral mean power frequency of COP sway; decreased the standard deviation of medialateral COP, trunk, and head sway; and decreased the medialateral mean velocity of head sway. A broad stance was also associated with lower variability for head and COP sways in the anteroposterior axis. Unexpectedly, an effect of trial repetition was found for the variability of medialateral trunk sway. This was probably due to the break halfway through the study. In practical terms, broad stance conditions can improve postural control in the medialateral and anteroposterior axes.

Impaired mediolateral postural control at the ankle in healthy, middle-aged adults.

ABSTRACT Elderly adults sway more than young adults. Based on the literature, the authors expected the mediolateral ankle postural control mechanism to be affected before age 60 years. Twelve healthy young adults (24.21 ± 2.50 years) and 12 middle-aged adults (51.13 ± 6.09 years) participated in the study. To challenge mediolateral stance, the conditions modified the mediolateral distance among the feet (narrow and standard distances), mandibular position (rest position, left and right laterality occlusion positions), and the occlusion with clenching (intercuspal occlusion, left and right maximal voluntary clenches). As we expected, middle-aged adults exhibited significantly reduced contribution of the ankle mechanism. It was so both in narrow and standard stances. A second objective was to show a greater contribution of the 2 mechanisms in narrow than in standard stances. The results confirmed our hypothesis. As we expected, mandibular conditions only had a significant effect on center of pressure sway. Unexpectedly, middle-aged adults did not increase their range of center of pressure sway in narrow stance. They may have overconstrained their center of pressure sway because of their ankle impairments. On the practical level, our results suggest that older adults should increase their stance width to relieve their hip and ankle control mechanisms and to stabilize their mediolateral posture.

Proximal Postural Control Mechanisms May Be Exaggeratedly Adopted by Individuals With Peripheral Deficiencies: A Review

ABSTRACT In quiet stance, it is understood that healthy individuals control their posture primarily by a peripheral mechanism for anteroposterior sway and by a proximal mechanism for medialateral sway. The authors proposed the hypothesis that patients suffering from disease-related deficiencies, at their feet and legs, may exaggeratedly adopt proximal control mechanisms at their hip in the anteroposterior and medialateral axes. They critically reviewed the literature to test the proximal control hypothesis against published findings. The selected articles analyzed postural control mechanisms in individuals with diabetic peripheral neuropathy and in healthy controls. The data selected were kinematic and electromyographic. In the anteroposterior axis, 4 authors had previously tested the proposed hypothesis, but the findings are contrasted. In the medialateral axis, one study failed to validate the tested hypothesis. Overall, the published studies did not conform with the proximal control hypothesis. However, these studies did not specifically or deeply test such a hypothesis. The lack of results is critical because individuals suffering from peripheral disease-related deficiencies may be unstable, in part, because of a change in postural control mechanisms. For improvement of their stability and appropriate interventions, scientific explorations of the proximal control hypothesis should be investigated. Two proposals are made to move forward.

Active vision task and postural control in healthy, young adults: Synergy and probably not duality.

In upright stance, individuals sway continuously and the sway pattern in dual tasks (e.g., a cognitive task performed in upright stance) differs significantly from that observed during the control quiet stance task. The cognitive approach has generated models (limited attentional resources, U-shaped nonlinear interaction) to explain such patterns based on competitive sharing of attentional resources. The objective of the current manuscript was to review these cognitive models in the specific context of visual tasks involving gaze shifts toward precise targets (here called active vision tasks). The selection excluded the effects of early and late stages of life or disease, external perturbations, active vision tasks requiring head and body motions and the combination of two tasks performed together (e.g., a visual task in addition to a computation in ones head). The selection included studies performed by healthy, young adults with control and active - difficult - vision tasks. Over 174 studies found in Pubmed and Mendeley databases, nine were selected. In these studies, young adults exhibited significantly lower amplitude of body displacement (center of pressure and/or body marker) under active vision tasks than under the control task. Furthermore, the more difficult the active vision tasks were, the better the postural control was. This underscores that postural control during active vision tasks may rely on synergistic relations between the postural and visual systems rather than on competitive or dual relations. In contrast, in the control task, there would not be any synergistic or competitive relations.

Postural mechanisms to control body displacements in the performance of lateral gaze shifts.

ABSTRACT Medialateral postural control mechanisms (bodyweight distribution and center of pressure location) have been studied in static conditions. Our objective was to determine how these mechanisms are adjusted to perform voluntary movements, in our case 80° lateral gaze shifts at 0.125 Hz and 0.25 Hz. In healthy, young adults, we expected body marker (neck, lower back) and center of pressure displacements to be significantly greater in gaze shift conditions than in the stationary gaze condition. To explain these changes in center of pressure displacement, the amplitude contribution of both mechanisms was expected to increase significantly. All these results were found accordingly. Unexpectedly, the active contribution of the bodyweight distribution mechanism was negatively related to body marker displacements in the gaze shift conditions (ns in stationary condition). Moreover, changes in the contribution of the mechanisms were statistically weaker in effect size than changes in body displacement. However, the participants were not unstable because they performed the visual tasks as requested. We propose that the strength of medialateral postural control mechanisms may not only be strengthened to control challenging ML stance conditions but also slightly weakened to allow the performance of adequate body motions in ongoing tasks.

Interest of active posturography to detect age-related and early Parkinson's disease-related impairments in mediolateral postural control

Patients with Parkinsons disease display impairments of postural control most particularly in active, challenging conditions. The objective of the present study was to analyze early signs of disease-related and also age-related impairments in mediolateral body extension and postural control. Fifty-five participants (18 Hoehn and Yahr stage 2 patients in the off-drug condition, 18 healthy elderly control subjects, and 19 young adults) were included in the study. The participants performed a quiet stance task and two active tasks that analyzed the performance in mediolateral body motion: a limit of stability and a rhythmic weight shift task. As expected, the patients displayed significantly lower and slower body displacement (head, neck, lower back, center of pressure) than elderly control subjects when performing the two body excursion tasks. However, the behavioral variability in both tasks was similar between the groups. Under these active conditions, the patients showed significantly lower contribution of the hip postural control mechanisms compared with the elderly control subjects. Overall, the patients seemed to lower their performance in order to prevent a mediolateral postural instability. However, these patients, at an early stage of their disease, were not unstable in quiet stance. Complementarily, elderly control subjects displayed slower body performance than young adults, which therefore showed an additional age-related impairment in mediolateral postural control. Overall, the study illustrated markers of age-related and Parkinsons disease impairments in mediolateral postural control that may constrain everyday activities in elderly adults and even more in patients with Parkinsons disease.