Title : Dynamic modulation of postural stability in polyneuropathy: Insights from IMU-based analysis
Abstract:
Introduction: Postural stability is maintained through a complex interplay of long-loop reflexes and higher brain centers. Long-loop reflexes, involving transcortical pathways, provide rapid, context-dependent responses to perturbations. Higher centers, including the cerebellum, basal ganglia, and cortex, modulate these reflexes and contribute to anticipatory postural adjustments. Various neurotransmitter systems, such as serotonergic, dopaminergic, and noradrenergic pathways, are implicated in this modulation, affecting the gain and timing of postural responses.
Methodology: We employed a novel approach to assess postural stability using an Inertial Measurement Unit (IMU) sensor attached at the C7 vertebral level. Data were collected from 71 healthy controls and 14 patients with polyneuropathy. The IMU recorded accelerometer data at 50 Hz for one minute during quiet standing. We calculated the magnitude of acceleration and applied an envelope curve to this time series, reflecting the modulation of postural control by higher brain centers.
Results: Comparison of envelope curve characteristics revealed significantly greater fluctuations in amplitude among patients with axonal sensorimotor or sensory polyneuropathy compared to healthy controls. This finding suggests a reduced efficiency in the dynamic modulation of reflex responses in polyneuropathy patients.
Discussion: Two primary mechanisms may explain the observed differences in postural stability modulation: Reduced proprioceptive input: Polyneuropathy leads to a decrease in sensory axons of peripheral nerves, diminishing proprioceptive information. Additionally, a potential reduction in vestibulocochlear nerve axons may result in decreased input from the semicircular canals, utricle, and saccule. Decreased muscle strength: The loss of motor axons in peripheral nerves results in reduced strength of anti-postural muscles. These mechanisms likely contribute to the fluctuations in reflex response modulation observed in polyneuropathy patients. The reduced proprioceptive input may lead to less accurate internal models of body position, necessitating more frequent and larger corrections. The decreased muscle strength could result in less precise and more variable motor outputs, further contributing to instability. The increased variability in postural control modulation may represent a compensatory mechanism, where the central nervous system attempts to adapt to unreliable sensory inputs and inconsistent motor outputs. This adaptation, while potentially beneficial for maintaining balance, may come at the cost of increased energy expenditure and cognitive load.
Conclusion: Our IMU-based analysis provides new insights into the dynamic nature of postural control deficits in polyneuropathy. These findings have implications for both the assessment and rehabilitation of balance disorders in neurological conditions.
Audience Takeaway Notes:
- Many workplaces are experimenting with MUs, this will help them see what other professionals are doing and what results are they getting
- IMUs can be used in both diagnostics and treatment of balance disorders
- They may consider acquiring Inertial Measurement Unit (IMU) themselves to use in their own practice
